WO2006096801A2 - Colonne de haut-parleurs reflecteurs - Google Patents

Colonne de haut-parleurs reflecteurs Download PDF

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Publication number
WO2006096801A2
WO2006096801A2 PCT/US2006/008365 US2006008365W WO2006096801A2 WO 2006096801 A2 WO2006096801 A2 WO 2006096801A2 US 2006008365 W US2006008365 W US 2006008365W WO 2006096801 A2 WO2006096801 A2 WO 2006096801A2
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WO
WIPO (PCT)
Prior art keywords
loudspeakers
reflective
loudspeaker array
planar surface
frame
Prior art date
Application number
PCT/US2006/008365
Other languages
English (en)
Other versions
WO2006096801A3 (fr
Inventor
D. Broadus Keele, Jr.
Douglas J. Button
Original Assignee
Harman International Industries, Incorporated
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Filing date
Publication date
Application filed by Harman International Industries, Incorporated filed Critical Harman International Industries, Incorporated
Publication of WO2006096801A2 publication Critical patent/WO2006096801A2/fr
Publication of WO2006096801A3 publication Critical patent/WO2006096801A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/227—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  using transducers reproducing the same frequency band
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/26—Spatial arrangements of separate transducers responsive to two or more frequency ranges
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/323—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only for loudspeakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/40—Details of arrangements for obtaining desired directional characteristic by combining a number of identical transducers covered by H04R1/40 but not provided for in any of its subgroups
    • H04R2201/401—2D or 3D arrays of transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/40—Details of arrangements for obtaining desired directional characteristic by combining a number of identical transducers covered by H04R1/40 but not provided for in any of its subgroups
    • H04R2201/405—Non-uniform arrays of transducers or a plurality of uniform arrays with different transducer spacing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2430/00—Signal processing covered by H04R, not provided for in its groups
    • H04R2430/20—Processing of the output signals of the acoustic transducers of an array for obtaining a desired directivity characteristic
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R27/00—Public address systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/12—Circuits for transducers, loudspeakers or microphones for distributing signals to two or more loudspeakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
    • H04S3/002—Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution

Definitions

  • This invention relates generally to loudspeakers, and more particularly to a loudspeaker array configured to cooperatively operate with an acoustically reflective planar surface to provide a constant-beamwidth sound field.
  • a loudspeaker enclosure may be a source for a sound field.
  • a typical loudspeaker enclosure may be used to generate a sound field for "live" sound reinforcement, for home entertainment, for car audio, for a discotheque, or the like.
  • three-dimensional radiation patterns of sound fields generated by a loudspeaker vary with frequency.
  • Such a sound field also may not be focused at the intended listeners, and spectral content of the sound field may vary with direction.
  • an unfocused sound field may cause constructive and destructive wave interference patterns, which may further distort the sound field at different locations.
  • a theoretically ideal loudspeaker produces a sound field with a spectral content that does not vary with direction, and that has three-dimensional constant radiation patterns over a wide frequency range.
  • a loudspeaker with radiation patterns that do not differ significantly with respect to frequency is referred to herein as a constant-directivity or a constant-beamwidth loudspeaker.
  • the present invention includes a reflective loudspeaker array that is cooperatively operable with an acoustically reflective planar surface to optimize a frequency response and a radiation pattern of a sound field produced by the reflective loudspeaker array.
  • the frequency response and radiation pattern are optimized by advantageously combining sound waves that are produced directly by the reflective loudspeaker array with reflected sound waves produced when the directly produced sound waves "bounce" off the acoustically reflective planar surface.
  • the reflective loudspeaker array includes a frame and five or more loudspeakers coupled with the frame.
  • the frame may include a longitudinally extending frame surface having a radius of curvature of a predetermined angle in which the loudspeakers are disposed.
  • the frame includes a first end having a base with a substantially flat surface and a second end.
  • the loudspeakers may be positioned linearly along the surface of the frame so that one of the loudspeakers is positioned at the first end of the frame and one of the loudspeakers is positioned at the second end of the frame.
  • the base may be positioned next to, and substantially in parallel with, an acoustically reflective planar surface, such as a floor, a wall, a ceiling or any other acoustically reflective boundary or acoustically reflective barrier.
  • the loudspeaker positioned at the first end of the frame includes a frontal plane that may be positioned substantially perpendicular with the acoustically reflective planar surface.
  • the loudspeaker positioned at the second end of the frame also may include a frontal plane that forms an angle with the acoustically reflective planar surface that is less than ninety degrees.
  • the reflective loudspeaker array also may include multiple rows and/or columns of loudspeakers in the frame.
  • the frame may include a plurality of subframes that are moveable with respect to each other to adjust one or more radius of curvature of the frame, such as one or more vertical and/or horizontal radius of curvature.
  • the reflective loudspeaker array may provide audio signals to drive the loudspeakers and produce audible sounds in the form of a focused soundfield with a substantially constant beamwidth.
  • the magnitude of the provided audio signals and/or the output sound pressure levels may be selectively reduced depending on the location of the loudspeakers in the reflective loudspeaker array.
  • the loudspeaker at the first end of the frame may be provided an audio signal that is a maximum magnitude of any audio signal provided to the reflective loudspeaker array or maximum output sound pressure level.
  • the remaining loudspeakers may be provided signals with stepwise reduced magnitudes toward the second end of the reflective loudspeaker array and/or output corresponding stepwise reduced sound pressure levels.
  • the loudspeakers also may be grouped in sub arrays.
  • a sub array at the first end of the frame, nearest the acoustically reflective planar surface, may receive the maximum magnitude of audio signals and the remaining sub arrays may receive a step wise reduced magnitude of the audio signal depending on the location of the sub arrays.
  • the sub array at the second end of the reflective loudspeaker array may receive the audio signal with the lowest relative magnitude.
  • direct audible sound generated by the reflective loudspeaker array may produce a perceived mirror image reflective loudspeaker array that is axially aligned with the reflective loudspeaker array, and perceived to be positioned on the opposite side of the acoustically reflective planar surface that the reflective loudspeaker array is near.
  • the symmetric combination of the reflective loudspeaker array and the mirror image reflective loudspeaker array may form a virtual composite array.
  • the virtual composite array generates an acoustic image that is perceived acoustically and visually to increase the height of the reflective loudspeaker array.
  • the perceived number of loudspeakers, the sensitivity, and the sound pressure level capability of the reflective loudspeaker array may be increased.
  • the virtual composite array may extending the operating frequency bandwidth an octave lower and minimize perceived variations in a near field sound pressure level and a far field sound pressure level, as a listener moves from a position close to the reflective loudspeaker array to a position farther away.
  • the acoustic image is produced from audio signals provided to drive the loudspeakers to generate direct audio sound waves.
  • a portion of the direct audio sound waves reflect off the acoustically reflective planar surface as reflected audio sound waves.
  • the direct audio sound waves are generated to be constructively combinable with the reflected audio sound waves to produce the acoustic image that is perceived to be about double the height of the reflective loudspeaker array.
  • FIG. 1 is a perspective view of an example reflective loudspeaker array positioned adjacent an acoustically reflective planar surface.
  • FIG. 2 is another perspective view of the reflective loudspeaker array of FIG. 1 illustrating a mirror image reflective loudspeaker array.
  • FIG. 3 is a side view of an example reflective loudspeaker array.
  • FIG. 4 is a schematic diagram of a passive compensation network for the reflective loudspeaker array of FIG. 3.
  • FIG. 5 is an example of attenuation related shading versus height for a reflective loudspeaker array.
  • FIG. 6 is a front view of another example of a reflective loudspeaker array positioned adjacent an acoustically reflective planar surface.
  • FIG. 7 is a cross-sectional view of a portion of the reflective loudspeaker array illustrated in FIG. 6.
  • FIG. 8 is a side view of the reflective loudspeaker array illustrated in FIG. 6.
  • FIG. 9 is an example of a pair of reflective loudspeaker arrays in cooperative operation.
  • FIG. 10 is a schematic of a vertical plane sampling grid depicting a plurality of sample points over an acoustically reflective planar surface.
  • FIG. 11 is a plan view of the vertical plane sampling grid of FIG. 10 depicting a plurality of sampling points at various angles over an acoustically reflective planar surface.
  • FIG. 12 is an on-axis response for a compact monitor at a height of one meter above an acoustically reflective planar surface.
  • FIG. 13 is an on-axis response for a straight line array at a height of one meter above an acoustically reflective planar surface.
  • FIG. 14 is an on-axis response for a reflective loudspeaker array at a height of one meter above an acoustically reflective planar surface.
  • FIG. 15 is a plurality of responses of a compact monitor at the distances indicated by the sample points depicted in FIG. 10 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 16 is a plurality of responses of a compact monitor at the sampling point angles depicted in FIG. 11 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 17 is a plurality of responses of a straight line array at distances indicated with the sample points depicted in FIG. 10 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 18 is a plurality of responses of a straight line array at the sampling point angles depicted in FIG. 11 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 19 is a plurality of responses of a reflective loudspeaker array at distances indicated with the sample points depicted in FIG. 10 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 20 is a plurality of responses of a reflective loudspeaker array at the sampling point angles depicted in FIG. 11 at a height of one meter above an acoustically reflective planar surface.
  • FIG. 21 is a plurality of responses of a compact monitor at the sampling point angles depicted in FIG. 11 at a height of zero meters above an acoustically reflective planar surface.
  • FIG. 22 is a plurality of responses of a straight line array at the sampling point angles depicted in FIG. 11 at a height of zero meters above an acoustically reflective planar surface.
  • FIG. 23 is a plurality of responses of a reflective loudspeaker array at the sampling point angles depicted in FIG. 11 at a height of zero meters above an acoustically reflective planar surface.
  • FIG. 24 is a group of frequency response plots for an example configuration of the pair of reflective loudspeaker arrays illustrated in FIG. 9.
  • FIG. 25 is another group of frequency response plots for another example configuration of the pair of reflective loudspeaker arrays illustrated in FIG. 9. DETAmED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • the present invention includes a reflective loudspeaker array that can be operated when aligned with an acoustically reflective planar surface.
  • the reflective loudspeaker array includes an array of loudspeakers that are intended to operate to produce sound waves near or very close to a sound reflecting surface or boundary, such as a table, a stage, a floor, a wall, a ceiling, or any other form of surface defining a plane.
  • the reflective loudspeaker array may be operated as a Constant Beamwidth Transducer (CBT) loudspeaker line array that takes advantage of an acoustically reflective planar surface to increase the perceived acoustic size of the reflective loudspeaker array due to the acoustic reflection of the sound waves by the acoustically reflective planar surface.
  • CBT Constant Beamwidth Transducer
  • the reflective loudspeaker array may provide a number of strong performance and operational advantages.
  • the performance and operational advantages include: elimination of undesirable floor reflections; a perceived increase of the effective height of the reflective loudspeaker array; an increase of the sensitivity of the reflective loudspeaker array; an increase of the maximum sound pressure level (SPL) capability; a decrease of near-far variation of sound pressure level (SPL); and an operating bandwidth that may be extended down by at least about an octave.
  • the term "constant-beamwidth transducer” is used to describe how the loudspeakers in the reflective loudspeaker are disposed and driven.
  • the transducers are omnidirectional type loudspeakers that are organized and focused into a concentrated beam of soundwaves by the cooperative operation of the loudspeakers included in reflective loudspeaker array with the acoustically reflective planar surface.
  • a general discussion of a constant beamwidth transducer is provided.
  • An ideal transducer in the form of a rigid circular spherical cap of arbitrary half angle whose normal surface velocity (pressure) is attenuated according to a Legendre function may function as an ideal constant-beamwidth transducer.
  • the Legendre attenuation may be independent of frequency.
  • Such an ideal transducer may produce a broadband, symmetrical, directional acoustic field.
  • the acoustic field may have a beam pattern and a directivity that are essentially independent of frequency over all frequencies above a determined cut-off frequency and that change very little as a function of distance from the ideal transducer.
  • Such an ideal transducer may cover an arbitrary coverage angle with a constant-beamwidth that extends over a virtually unlimited operating bandwidth.
  • the Legendre function order (v) may be chosen so that the first zero of the Legendre function occurs at the half angle of the spherical cap.
  • the far-field sound pressure level pattern may be essentially equal to the sound pressure level on the surface of the spherical cap.
  • an ideal constant-beamwidth transducer would be in the form of an entire circular sphere, not merely a spherical cap.
  • the surface pressure and velocity would be nearly zero over a large inactive portion of the outer surface of such a sphere, however. Therefore, the part of the sphere outside of a spherical cap region can be removed without significantly changing acoustic radiation patterns.
  • a spherical cap may have a nearly ideal constant-beamwidth behavior even though the rest of the sphere is missing.
  • the advantages of a constant-beamwidth transducer above the cutoff frequency may include an essentially constant beam pattern, very low side lobes, and a pressure distribution at all distances out to the far-field that is approximately equal to the surface distribution. Because both the surface velocity and surface pressure have the same dependence on ⁇ , the local specific acoustic impedance may be independent of ⁇ . Thus, the entire transducer may be uniformly loaded.
  • Equation l A simplified four-term series approximation to the Legendre attenuation of Equation l is:
  • the first, second and third order terms may be derived as follows:
  • the terms "attenuation,” “attenuate,” and “attenuated” refer generally to a relative sound pressure levels, or relative electrical signal levels.
  • the speaker driver or drivers producing the highest sound pressure level are said to be “attenuated” to 0 dB, and sound pressure levels generated by the remaining speaker drivers are indicated relatively.
  • the electrical signal having the highest level is said to be “attenuated” to 0 dB, and the levels of the remaining electrical signals are indicated relatively.
  • an upper-operational frequency limitation exists that has a wave-length approximately equal to the center-to-center spacing of the speaker array. At frequencies above the upper-operational frequency, the constant-beamwidth behavior of the speaker array may deteriorate.
  • the speaker drivers of the speaker array are discrete, the development of off- axis lobes may cause a sonic beam radiated by the speaker array to become uncontrollably wide above the upper-operational frequency.
  • the response may drop abruptly above the upper-operational frequency, because the speaker array's energy is spread out over a much wider angle.
  • the attenuation above the upper-operational frequency may be essentially chaotic.
  • the individual speaker drivers of the speaker array may be selected to individually provide a measure of narrow coverage. This may allow the speaker array to approximate its lower-frequency behavior at higher frequencies.
  • the center-to-center spacing of the speaker array's speaker drivers may determine the upper-operational frequency.
  • the size of the speaker array and the speaker array's angular coverage may determine the lower-operational frequency for constant-beamwidth operation.
  • the relationship between the size of the speaker array, the angular coverage of the sonic beam produced by the array, and the lower-operational frequency is approximately similar to the corresponding relationships for constant directivity horns:
  • X horn mouth width (or height)
  • ⁇ coverage angle of horn (-6 dB point)
  • f i frequency down to which coverage angle is maintained
  • K constant (2.5 x 10 4 meters-degs-Hz, or 1 x 10 6 inches-degs-Hz) that may change in different loudspeaker designs.
  • a reflective loudspeaker array providing 65 degrees of constant-beamwidth coverage down to 1.15 kHz should be about 100 mm high.
  • K may be about 7.6 x 10 3 meters-degs-Hz, or 3.0 x 10 5 inches-degs-Hz.
  • the first example reflective loudspeaker array described with reference to FIG. 1 is designed to provide about 34 degrees of constant-beamwidth coverage down to approximately 225 Hz (lower-operational frequency), and is therefore about 1.0 m high.
  • FIG. 1 is a perspective view of one example of a reflective loudspeaker array 100.
  • the loudspeaker array 100 includes a frame 102 having a first end 104 and a second end 106.
  • the frame 102 may be a housing, a strut, a track, a plate, or any other structure that maintains the position of a plurality of loudspeakers 108 with respect to each other.
  • the frame 102 of this example is formed with a curve of a constant radius of curvature and a predetermined length that results in an arc angle ( ⁇ 0 ) of about 45 degrees.
  • the frame 102 may be formed to include two or more curves, each with a constant radius of curvature that may or may not be the same.
  • the first end 104 may include a base 110.
  • the base 110 is configured to be positioned adjacent to, or contiguous with an acoustically reflective planar surface 112.
  • the base 110 may have a substantially flat surface that is contiguously alignable in parallel with the acoustically reflective planar surface 112.
  • the base 110 may provide a stand upon which the remainder of the reflective loudspeaker array 100 may be vertically and horizontally supported and maintained in position with respect to the acoustically reflective planar surface 112.
  • the second end 106 may be maintained in free air spaced away from the acoustically reflective planar surface 112.
  • the loudspeakers 108 may be any form of transducer or speaker driver capable of receiving an electrical signal and converting the electrical signal to a corresponding acoustical sound, hi one example, the loudspeakers 108 may be miniature wide-band speaker drivers, such as 32 mm full-range (200 Hz to 20 kHz) speaker drivers used in Harman Sound Sticks, or any of similar speaker drivers used in laptop computers, flat panel monitors, desktop speaker enclosures, and the like.
  • the loudspeakers 108 may each include a sound emitting surface that forms a frontal plane.
  • the sound emitting surface may include a movable surface having an area, and the areas of the movable surfaces of the loudspeakers 108 may be substantially equal in size.
  • the high-frequency beaming of such loudspeakers 108 may allow the reflective loudspeaker array 100 to maintain a nearly constant beam- width at frequencies up to a determined frequency, such as up to 16 kHz, even though according to a center-to-center high frequency operating limit that is discussed later, the upper-operational frequency should be approximately 8 kHz.
  • the acoustically reflective planar surface 112 may be in the shape of a square, a circle, a triangle, an ellipse, or any other shape having a substantially flat planar surface that the reflective loudspeaker array 100 may be aligned with.
  • the acoustically reflective planar surface 112 may create a plane that is almost infinite from the perspective of the reflective loudspeaker array 100, such as for example the floor, wall, or ceiling of a large room.
  • the acoustically reflective planar surface 112 may be smaller, such as, for example, a tabletop.
  • the loudspeaker array 100 may be concentrically aligned with a central axis of the acoustically reflective planar surface 112 that is perpendicular with the planar surface, so that the planar surface of the acoustically reflective planar surface 112 extends away from reflective loudspeaker array 100 about an equal distance in all directions.
  • the acoustically reflective planar surface 112 should be as large as possible.
  • the acoustically reflective planar surface 112 may have a diameter (D) 116 that is no smaller than a height (H) 118 of the reflective loudspeaker array 100.
  • the diameter (D) 116 is larger than the height (H) 118, the reflective loudspeaker array 100 may offset from the central axis of the acoustically reflective planar surface 112.
  • FIG. 1 there are 40 loudspeakers 108 linearly disposed in the frame 102 concentric with a common central axis of the frame 102 to form a single array.
  • any configuration of loudspeakers 108 that includes five or more loudspeakers 108 in one or more arrays may be used.
  • a sound pressure pattern distribution in a far sound field produced by the reflective loudspeaker array 100 is approximately equal to a sound pressure pattern distribution in a near sound field.
  • a far sound field is any distance from the reflective loudspeaker array 100 that is greater than the height (H) 118 of the reflective loudspeaker array 100
  • the near sound field is any distance from the reflective loudspeaker array 100 that is equal to or less than the height (H) 118 of the reflective loudspeaker array 100.
  • a vertical coverage area, or a vertical beamwidth of the reflective loudspeaker array 100 is defined as a portion of a sonic beam produced by a constant-beamwidth transducer where sound pressure levels are greater than -6 dB.
  • the angle of curvature of the frame 102 may dictate the vertical coverage over the operational frequency range.
  • a radius of curvature of the reflective loudspeaker array 100 may dictate the overall height (H) 118 of the reflective loudspeaker array 100.
  • FIG. 2 is another perspective view of an example reflective loudspeaker array 200 that includes a representation of a mirror image reflective loudspeaker array 202.
  • the mirror image reflective loudspeaker array 202 is a mirror image of the reflective loudspeaker array 200 and illustrates the effect of the sound waves reflected from the acoustically reflective planar surface 112.
  • the combination of the reflective loudspeaker array 200 and the corresponding mirror image reflective loudspeaker array 202 forms a perceived single composite virtual loudspeaker array that is about double the height of the reflective loudspeaker array 200 and has double the number of loudspeakers 108.
  • the first end 104 of the reflective loudspeaker array 200 and one end of the image reflective loudspeaker array 202 may be contiguously positioned to form a vertical stack that is the virtual composite loudspeaker array.
  • the virtual composite loudspeaker array is similar in overall appearance to the freestanding loudspeaker array included in the loudspeaker system described in U.S. Patent Application 10/701,256 filed on November 4, 2003, which is incorporated by reference. Accordingly, the reflective loudspeaker array 200 provides many similar characteristics to the freestanding loudspeaker array with significant additional benefits due to the advantageous use of the acoustically reflective planar surface 112. The benefits include both performance and operational advantages.
  • the reflective loudspeaker array 200 is designed to operate in conjunction with the acoustically reflective planar surface 112 (such as the floor, wall, or ceiling).
  • the acoustic reflections from the acoustically reflective planar surface 112 enhance the acoustic output of the reflective loudspeaker array 200 to generate an acoustic image.
  • the acoustic image is generated by the combination of the direct sound waves generated with the reflective loudspeaker array 200 and the reflected sound waves provided with the mirror image reflective loudspeaker array 202.
  • the reflected sound waves desirably enhance the direct sound waves and thus the operation of the reflective loudspeaker array 200.
  • the acoustically reflective planar surface 112 effectively doubles the height of the reflective loudspeaker array 200 because of the acoustic reflection provided by the acoustically reflective planar surface 112.
  • the acoustically reflective planar surface 112 may be thought of as affecting sound waves similarly to the way a mirror operates on light waves.
  • the reflected sound waves are a mirror image of the direct sound waves that, when constructively combined with the direct sound waves, produce the acoustic image.
  • the resulting virtual composite loudspeaker array also provides increases sensitivity.
  • the sensitivity of a loudspeaker is defined as the sound level the speaker generates at a given distance for a specific input power or applied voltage.
  • the rated sound pressure level (SPL) at one meter for an input power of one Watt or an applied voltage of 2.83 Vrms (one Watt in an eight-ohm load) are example sensitivity measurement parameters.
  • the sensitivity of reflective loudspeaker array 200 may be effectively doubled, as compared to a free-standing array of the same height, because the planar surface serves to effectively double the height of the reflective loudspeaker array 200 and effectively double the number of loudspeakers 108 disposed in the reflective loudspeaker array 200.
  • the height and number of loudspeakers 108 are effectively increased due to the combination of the reflected sound waves and the direct sound waves.
  • Cooperative operation of the acoustically reflective planar surface 112 provides a sound reflection that may raise the SPL and sensitivity of the reflective loudspeaker array 200 by about 6 dB.
  • the maximum Sound Pressure Level (SPL) capability of the reflective loudspeaker array 200 may be increased, hi other words, the reflective loudspeaker array 200 may be operated to play about 6-dB louder than a free-standing array of the same height because the reflections from the acoustically reflective planar surface 112 may essentially double the sound pressure level.
  • SPL Sound Pressure Level
  • the reflective loudspeaker array 200 in cooperative operation with the acoustically reflective planar surface 112 also may minimize near-far variation in SPL.
  • listeners are typically positioned to listen above a main axis 204 of the reflective loudspeaker array 200.
  • the main axis 204 of the reflective loudspeaker array 200 is essentially at, or parallel with, the acoustically reflective planar surface 112.
  • listening above the mam axis 204 is not a detriment.
  • the SPL variations may be reduced because as the listener approaches the reflective loudspeaker array 200, he/she is farther off the main axis 204 of the reflective loudspeaker array 200. Conversely, as the listener retreats from the reflective loudspeaker array 200, he/she is closer to the main axis 204 of the reflective loudspeaker array 200. As proven through prototype testing described later, listening heights near the actual height of the reflective loudspeaker array 200 may greatly reduce or nearly nullify near-far variations of the SPL.
  • the cooperative operation of the reflective loudspeaker array 200 with the acoustically reflective planar surface 112 may also extend the operating bandwidth of the reflective loudspeaker array 200 downward by as much as an octave.
  • the vertical beamwidth of the reflective loudspeaker array 200 may be controlled down to a frequency that is determined by the size (height) and arc angle ( ⁇ 0 ) of the reflective loudspeaker array 200.
  • the size and angular coverage of the reflective loudspeaker array 200 may be in direct proportion.
  • the reflective loudspeaker array 200 may control its vertical coverage an octave lower (x 0.5) in frequency.
  • the reflective loudspeaker array 200 also may control vertical coverage an octave lower in frequency. Since the angular coverage of the reflective loudspeaker array 200 is defined as its coverage angle above the acoustical reflective planar surface 112, the operating frequency of the reflective loudspeaker array 200 effectively drops by about two octaves (x 0.25) as compared to a free-standing array. This is because the perceived height of the reflective loudspeaker array 200 has doubled and its coverage angle has halved, as compared to a free-standing array due to the combination of the direct sound waves and the reflected sound waves.
  • FIG. 3 is a side view of another example reflective loudspeaker array 300 that includes a frame 302 with a plurality of loudspeakers 108 (identified as loudspeakers 320-354) disposed on a surface 304.
  • loudspeakers 320-354 there are eighteen loudspeakers illustrated. In other examples, other quantities of loudspeakers, such as fifty one loudspeakers, or as few as five loudspeakers may be included in the reflective loudspeaker array 300.
  • the frame 302 longitudinally extends from a first end 306 to a second end 308.
  • a base 310 having a substantially flat surface may be included at the first end 306 so that the reflective loudspeaker array 300 may be positioned adjacent the acoustically reflective planar surface 112 with the surface of the base 310 disposed substantially parallel with the acoustically reflective planar surface 112.
  • the surface 304 of the frame 302 may have a constant curvature radius (R) of, for example, 1.0 m over an arc angle ( ⁇ 0 ), for example, of 60°.
  • the radius of curvature (R) may dictate the vertical height of the reflective loudspeaker array 300.
  • the arc angle ( ⁇ 9 ⁇ ) may dictate the vertical coverage angle of the acoustical image generated by the reflective loudspeaker array 300.
  • the vertical beamwidth of the sound field of the reflective loudspeaker array 300 may be about three-fourths of the arc angle ( ⁇ o).
  • the vertical coverage angle of the acoustical image produced by the combination of the direct and reflected sound waves is about 45°.
  • a centerline of each of the loudspeakers 320-354 may also form a loudspeaker angle ( ⁇ ) with respect to the acoustically reflective planar surface 112.
  • the loudspeaker 330 forms a loudspeaker angle ( ⁇ ) with the acoustically reflective planar surface 112.
  • Each of the other loudspeakers 320 - 354 may similarly form a loudspeaker angle ( ⁇ ) with the acoustically reflective planar surface.
  • Example loudspeaker angles are provided in TABLE 1, which is discussed later.
  • the center-to-center spacing (Q between the loudspeakers 108 may be a predetermined distance based on the size of the loudspeakers 108 and the highest frequency audio signals that will drive the reflective loudspeaker array 300. Accordingly, the high frequency operating limit of the reflective loudspeaker array 300 may be dictated by the spacing of the loudspeakers 108.
  • the center-to-center spacing may be uniform and/or non-uniform. In one example, the center-to-center spacing is uniform and is less than or equal to one half wavelength of the highest frequency signal that will drive the loudspeakers 320-354. For example, if the highest frequency the loudspeakers will be driven with is lOkHz, then the spacing may be 17.25 mm assuming a speed of sound of 345 m/s at 20 degrees Celsius and standard pressure.
  • Each of the loudspeakers 320-354 may be coupled to and/or mounted in the surface 304 of the frame 302.
  • a sound emitting surface of each of the loudspeakers 320-354 may form a frontal plane that is substantially parallel with the surface 304 in the vicinity where the respective loudspeaker 320-354 is positioned. Due to the relatively small diameter of the loudspeakers 320-354, although the surface 304 is curved, the frontal plane of the loudspeakers are substantially parallel with the surface 304 that is in the vicinity of each of the loudspeakers 320-354. In FIG. 3, the loudspeakers 320-354 that are disposed adjacently, such as 320 and 322, are substantially parallel.
  • the loudspeakers 320-354 that are separated on the surface 304, such as 320 and 334, are not substantially in parallel due to the constant angle of curvature of the surface 304 in which the loudspeakers 320-354 are disposed.
  • a first one of the loudspeakers 320 that is positioned proximate the first end 306 may have a frontal plane that is substantially perpendicular with the acoustically reflective planar surface 112.
  • a second of the loudspeakers 354 may be positioned proximate the second end 308 such that a frontal plane of the second loudspeaker 354 forms an angle (0) with respect to the acoustically reflective planar surface 112.
  • the angle (0) may be less than ninety degrees, such as in FIG. 3, where the angle (0) is about thirty-five degrees.
  • the first end 306 and the second end 308 both may be positioned contiguous with the acoustically reflective planar surface 112 such that the frame 302 of the reflective loudspeaker array 300 generally forms a semi-circle.
  • the angle (0) of the frontal plane of the second loudspeaker 354 proximate the second end 308 may be normal to the acoustically reflective planar surface 112 similar to the first loudspeaker 320 proximate the first end 306.
  • the reflective loudspeaker array 300 may be formed with a frame 302 that is normal with respect to the acoustically reflective planar surface 112.
  • the frame 302 may be formed linearly, or straight, so that the entire frame is perpendicular with respect to the acoustically reflective planar surface 112.
  • the surface 304 may also be normal with respect to the acoustically reflective surface 112.
  • delay may be introduced to the audio signals driving the loudspeakers 108 to simulate a radius of curvature (R).
  • the audio signal provided to the loudspeaker 306 nearest the acoustically reflective planar surface 112 may have no delay.
  • the audio signals provided to the remaining loudspeakers 308-354 may increase in a stepwise or continuously decreasing fashion toward the second end 308 so that the audio signal driving the loudspeaker 354 is subject to the maximum delay.
  • the delay may be stepwise or continuously increased uniformly or non-uniformly. It is to be noted that the constructive combination of the direct sound waves and the reflected sound waves to create an acoustical image is maximized when a radius of curvature is present. Thus, a frame that is normal to an acoustically reflective planar surface 112 will not produce the virtual composite array and corresponding desired acoustical image due to interference of the direct and reflected sound waves.
  • each of the loudspeakers 320-354 may be selectively attenuated with Legendre shading.
  • attenuation values for the loudspeakers 320-354 may be calculated.
  • Equation 1 or Equation 3 also may be used to calculate attenuation values for the loudspeakers 320-354.
  • stepped or quantized attenuation values may be used. For example, using Equation 4 as the basis for quantized attenuation values yields:
  • the numerical ranges may be the boundaries where values of x in Equation 4 transition from one quantization level to the next.
  • the attenuation level may transition from 0 dB to 3 dB.
  • the quantized attenuation values used in this example are approximately to the nearest 3 dB level, so that attenuation approximations start at 0 dB (no attenuation), and drop by multiples of 3 dB. Other quantization resolutions or no quantization at all, may also be used.
  • TABLE 1 illustrates an example of an attenuation value U(x) calculated using Equation 3, a truncated attenuation value U tnmc (x) calculated using Equation 4, the truncated attenuation value in decibels, and a quantized attenuation value calculated using Equation 6 for each of the loudspeakers 320-354 in the reflective loudspeaker array 300.
  • the loudspeakers 320-354 may be divided into sub-arrays having equal quantized attenuation values. In one example, there are five sub-arrays.
  • a first sub-array may comprise loudspeakers 320- 330, each of which has a quantized attenuation value of 0 dB.
  • a second sub-array may comprise loudspeakers 332-342, each of which has a quantized attenuation value of -3 dB, and so on.
  • the loudspeakers near the transition points between the sub-arrays such as loudspeakers 332, 348 and 352, despite the quantized attenuation values, were moved to a different sub array to maintain an even number of loudspeakers in each sub arrays.
  • other configurations of sub-arrays such as sub arrays with odd numbers of loudspeakers are possible.
  • the twenty loudspeakers 320-354 may be driven by five passive attenuation circuits, and/or five amplifiers.
  • the amplifiers (not shown) for driving the five sub-arrays may be included in the reflective loudspeaker array 300, or may be positioned external to the reflective loudspeaker array 300.
  • each loudspeaker 320-354 or predetermined groups of the loudspeakers 320-354 may be driven by a respective audio amplifier.
  • fewer or greater numbers of sub-arrays and associated passive attenuation circuits may be employed in a reflective loudspeaker array 300.
  • FIG. 4 is a schematic diagram of an example loudspeaker driver circuit 400 included in a reflective loudspeaker array, such as the example reflective loudspeaker array 300 of FIG. 3.
  • the loudspeaker driver circuit 400 may be configured to include the approximate attenuation values shown in TABLE 1 with minimal use of electronic components.
  • the impedance of each of the loudspeakers 320-354 may be about 4.0 Ohms.
  • attenuation of each of the loudspeakers 320-354 is relevant.
  • attenuation for each of loudspeakers 320-354 may be increased or decreased by a constant, as long as each of the loudspeakers 320-354 has a nearly identical change.
  • the first sub-array comprising the loudspeakers 320-330 may be arranged in a series/parallel combination such that a combined impedance of the first sub-array is about 4.4 Ohms.
  • the second sub-array comprising the loudspeakers 332-342 may be arranged such that the combined impedance of the second sub-array is about 9.9 Ohms.
  • a third sub-array comprising loudspeakers 344-346, may be arranged in a series/parallel combination with a first resistor 402 having an resistance of about 2.5 Ohms and a second resistor 404 having a resistance of about 1.0 Ohms to yield an impedance of about 3.3 Ohms for the third sub-array.
  • a fourth sub array comprising the loudspeakers 348-350, may be arranged with third resistor 406 having a resistance of about 3.8 Ohms and a fourth resistor 408 having a resistance of about 1.0 Ohm to yield an impedance of about 4.6 Ohms for the fourth sub-array.
  • a fifth sub-array comprising the loudspeakers 352-354, may be arranged with fifth resistor 410 having a resistance of about 5.7 Ohms and a sixth resistor 412 having a resistance of about 1.0 Ohms to yield a total impedance of about 6.5 Ohms for the fifth sub-array
  • the impedance of the entire loudspeaker driver circuit 400 may be about 1.0 Ohm. Therefore, as illustrated in FIG. 3, the loudspeakers 320-330 may have no attenuation, the attenuation for the loudspeakers 332-342 may be about -3 dB, for the loudspeakers 344-346 may be about -6 dB, for the loudspeakers 348-350 may be about -9 dB, and for the loudspeakers 352-354 may be about -12 dB. As can be seen from TABLE 1, each of the loudspeakers 320-354 may have an attenuation that is roughly 6 dB below the quantized attenuation value.
  • the attenuation provided by the example impedance network shown in FIG. 4 conforms to the values shown in Table 1.
  • an impedance matching transformer (not shown) may be used. Such an impedance matching transformer may be included within the reflective loudspeaker array, or may be positioned between the reflective loudspeaker array and an audio amplifier (not shown) providing power to the reflective loudspeaker array.
  • the example schematic diagram shown in FIG. 4 allows the reflective loudspeaker array to be constructed with loudspeakers 320-354 with about equal impedances. For mass production, however, it may be desirable to fabricate the loudspeakers 320-354 with differing impedances by custom winding a coil included in each of the loudspeakers 320-354.
  • the reflective loudspeaker array 100 may be constructed for use with multiple amplifiers (not shown). For example, five amplifiers (not shown) may power the five sub-arrays of loudspeakers, so that one amplifier provides power to one sub-array. Such amplifiers may be either internal or external to the reflective loudspeaker array, and may provide desired attenuation without the use of passive components or custom-built speaker drivers.
  • FIG. 5 is an example of shading plot for a reflective loudspeaker array that is derivable from any one of Equations 1-4.
  • the attenuation applied to the loudspeakers is not quantized, thus, the loudspeakers are not divided into sub-arrays.
  • shading refers to frequency-independent magnitude-only changes in the level (attenuation) of signals that are applied to each of the loudspeakers in the reflective loudspeaker array to drive the respective loudspeakers. Shading may dramatically reduce side lobes of the reflective loudspeaker array, and may improve off-axis frequency responses.
  • the loudspeakers such as loudspeaker 320
  • the loudspeaker(s) such as loudspeaker 354, farthest from the acoustically reflective planar surface at the second end 308 (FIG. 3) may have maximum attenuation.
  • the remaining loudspeakers 322-352 may be uniformly increasingly attenuated based on distance from the first end 306.
  • the shading level is plotted against the normalized angle x (TABLE 1) of each of the reflective loudspeakers in the array.
  • Each loudspeaker in the array may be shaded with a value sampled from the curve at its normalized angle x in the array.
  • FIG. 6 is a front view of another example reflective loudspeaker array 600 that includes a frame 602 and a plurality of loudspeakers 108 disposed on a curved outer surface of the frame 602.
  • the frame 602 includes a first end 606 having a base 608 with a surface that can be positioned adjacently parallel with an acoustically reflective planar surface 112.
  • the frame also includes a second end 610 that is maintained in free air spaced away from the acoustically reflectively planar surface 112.
  • the frame 602 includes a plurality of subframes 614.
  • Each of the subframes 614 may be formed of plastic, wood, metal or any other rigid material, and are formed to accommodate being fixedly coupled with one or more of the loudspeakers 108.
  • the subframes 614 may each be formed to include at least one aperture that is formed to accommodate one or more of the loudspeakers 108.
  • the loudspeakers 108 may be coupled with the respective subframes 614 by fasteners, glue, friction fit, and/or any other coupling mechanism.
  • the subframes 614 may be coupled with each other to form the frame 602 and a surface to which the loudspeakers 108 may be coupled.
  • the subframes 614 may be moveably coupled with each to form the frame 602 by a plurality of linkages 616.
  • Each of the linkages 616 may be coupled between two adjacently positioned subframes 614 to allow movement in at least one direction and provide rigid support to movement in the remaining directions.
  • the subframes 614 are arranged in horizontal rows consisting of three subframes 614 and vertical columns consisting of ten subframes 614. In other examples, any number of subframes 614 may be included in the columns and/or rows.
  • Each row of subframes 614 includes linkages 616 that allow movement of each of the subframes 614 with respect to the adjacently positioned subframes 614.
  • the linkages 616 may be a flexible member coupled with adjacent subframes 614, such as a hinge, a flexible material or any other material capable of forming a flexible joint between the subframes 614.
  • FIG. 7 is a top cutaway view of the frame 602 of the reflective loudspeaker array 600 of FIG. 6 depicting a first subframe 702 and a corresponding first loudspeaker 704, a second subframe 706 and a corresponding second loudspeaker 708 and a third subframe 710 and a corresponding third loudspeaker 712.
  • a lateral edge of the first subframe 702 may be coupled with a first lateral edge of the second subframe 704 with a first linkage 714.
  • a second lateral edge of the second subframe 704 may be coupled with a lateral edge of the third subframe 706 with a second linkage 716.
  • each of the first, second and third subframes 702, 704 and 706 are moveable with respect to each other. More specifically, the first and third subframes 702 and 706 may pivot with respect to the second subframe 704. The first and third subframes 702 and 706 may bi-directionally pivot around the first linkage 710 and the second linkage 712. Thus, the first, second and third subframes 702, 706 and 710 are capable of articulating with respect to each other as indicated by arrows in FIG. 7.
  • each of the first, second and third loudspeakers 704, 708 and 712 include a respective sound emitting surface that forms a respective first, second and third frontal plane illustrated as dotted lines 720, 722 and 724, respectively in FIG. 7.
  • the first subframe 702 may be pivoted to create a determined row angle, between the first frontal plane 720 and the second frontal plane 722.
  • the third subframe 710 may be pivoted to create a determined row angle, between the third frontal plane 724 and the second frontal plane 722.
  • the row angles can be plus and minus 45 degrees, for example.
  • the movement of the first and third subframes 702 and 710 with respect to the second subframe 706 may adjust the sound coverage pattern of a row of loudspeakers 108, such as a horizontal coverage pattern. For example, if the row angles of the first, second and third subframes 702, 706, 710 were about plus 45 degrees, the pattern produced by operation of the respective loudspeakers would be wider than when the row angles of the first, second and third subframes 702, 706, 710 were about 0 degrees (i.e., the first, second, and third frontal planes 720, 722, and 724 were parallel and in the same linear plane).
  • FIG. 8 is a side view of the reflective loudspeaker array 600 of FIG. 6 with the subframes 614 pivoted with respect to each other to form an example frame configuration.
  • the frame 102 of a reflective loudspeaker array 100 may be formed with a continuous radius of curvature with a predetermined angle.
  • the reflective loudspeaker array 600 of FIG. 6 that includes the subframes 614 movably coupled by the linkages 616, configurations with other than a continuous radius of curvature are possible.
  • portions of the frame may be formed with different angles of curvature to provide upper and lower pattern control of the sound field produced by the loudspeakers 108 (not shown).
  • a loudspeaker in the reflective loudspeaker array 600 that is positioned nearest the acoustically reflective planar surface 112 may be substantially parallel with the acoustically reflective planar surface as evidenced by a dotted line 618 that is normal to the acoustically reflective planar surface 112.
  • the frame configuration includes a first portion of the frame 602 that is movably formed with a first radius of curvature (Rl) 806 at a first column angle 808.
  • the frame configuration includes a second portion of the frame 602 that is fashioned with a second radius of curvature (R2) 810 at a second column angle 812.
  • the first and second radius of curvatures 806 and 810 may be at different angles to adjust portions of the coverage area, such as vertical coverage by portions of the reflective loudspeaker array 600.
  • the first column angle 808 may be about 20 degrees
  • the second column angle 812 may be about 40 degrees to form a 2:1 ratio between the two column angles.
  • the angles of the radius of curvature of the portions of the reflective loudspeaker array 600 may be five degrees or greater. Since the reflective loudspeaker array 600 is operational adjacent to an acoustically reflective planar surface 112, a mirror image reflective loudspeaker array with the same radius(ii) of curvature may form the composite virtual array, as previously described. As also previously described, the direct sound waves and the reflected sound waves are positively combined to form an acoustic image with the previously described effects and advantages.
  • the horizontal and vertical coverage may adjusted to a desired configuration to best direct the coverage beam at the listeners in a given listening area configuration. For example, if the articulatable reflective loudspeaker array 600 is positioned above a first group of listeners, and also positioned beside a second group of listeners, such as positioned on a ceiling of a listening area having a lower floor and a balcony, the angles of curvature of each portion of the reflective loudspeaker array 600 may be adjusted accordingly to tailor the vertical height of the response provided to each of the two groups of listeners located at different vertical heights with respect to the reflective loudspeaker array 600. In addition, the previously discussed vertical shading may be employed to further focus the beam.
  • the horizontal coverage of the articulatable reflective loudspeaker array 600 may be adjusted to widen or narrow the horizontal coverage area being provided to the groups of listeners.
  • horizontal shading may be use similar to vertical shading.
  • the reflective loudspeaker array 600 may have a focused and yet vertically and horizontally adjustable coverage area that can be tailored to a particular listening room configuration and/or listener positioning to minimize reverberation and other undesirable reflection related effects.
  • FIG. 9 is an illustration of a pair of the reflective loudspeaker arrays 600 illustrated in FIG. 6 placed in an end-to-end configuration, such that the bases may be contiguously aligned and centrally positioned.
  • a first reflective loudspeaker array 902 and a second reflective loudspeaker array 904 may be positioned to form a curved loudspeaker array that is similar to the previously discussed free standing array.
  • the first reflective loudspeaker array 902 and the second reflective loudspeaker array 904 may be placed away from an acoustically reflective surface, since the combination may make generation of a mirror image (202 - FIG. 2) unnecessary.
  • each of the first and second articulatable loudspeaker arrays 902 and 904 may include one or more radius of curvature as previously discussed.
  • the rows of loudspeakers 108 may be articulated to develop a desired beam width as previously discussed.
  • horizontal and vertical shading may be employed. Accordingly, any asymmetrical array may be formed.
  • the response of the array may be tailored to the listening audience to have asymmetrical coverage patterns.
  • the asymmetrical coverage patterns may be individually focused on different listening spaces having different acoustical features.
  • the first reflective loudspeaker array 902 may be adjusted to a radius of curvature with a narrow vertical coverage area for a listening area of generally the same vertical height
  • the second reflective loudspeaker array 904 may be adjusted to a radius of curvature for a broad vertical coverage area for a listening space of a gradually increasing vertical height.
  • such coverage patterns may avoid arbitrarily reflected sound energy off surrounding structures, which can degrade speech intelligibility by increased reverberation and other interference.
  • the asymmetrical array with different angles of curvature that enable a focused beamwidth of sound field coverage that avoids arbitrary reflections.
  • Performance of a prototype of the reflective loudspeaker array was also compared with a conventional powered two-way compact monitor with dimensions of 173mm X 269mm X 241mm and a straight line array to demonstrate the significantly enhanced performance and unexpected results of the reflective loudspeaker array.
  • All systems were measured over the same acoustically reflective planar surface, which was a tile floor located in a large warehouse space. The center fronts of all three systems were located at the origin of the measurement region at a distance of 0.0 m. The above-ground-plane sound field of each of these systems was investigated by measuring a number of frequency responses in-front-of and to-the-side of the systems.
  • FIG. 10 depicts a vertical-plane sound field with twenty-five grid sample points 1002 positioned in front of each of a compact monitor system 1004, a straight line array system 1006 and a reflective loudspeaker array system 1008, and over an acoustically reflective planar surface 1010.
  • the sample points 1002 are positioned at distances of 0.1, 0.5, 1.0, 2.0, and 4.0 m from each of the systems, and at heights of 0.0, 0.5, 1.0, and 2.0 m above the acoustical reflective surface 1010.
  • the one meter high sample points were essentially on a horizontal axis of the compact monitor 1004 used for the comparison testing.
  • the sample points at a distance of 0.1 m are very close to the front of the systems.
  • FIG. 11 is a plan view of the vertical plane sound field of FIG. 10 depicting a plurality of off axis angles with respect to a central axis 1102 at which additional samples were taken for each of the systems 1004, 1006, and 1008 (FIG. 10) at a distance of two meters and a height of one meter above an acoustically reflective planar surface 1010 (FIG. 10).
  • a first sample 1104 was taken at zero degrees from the central axis 1102
  • a second sample 1106 was taken at thirty degrees
  • a third sample 1108 was taken at sixty degrees
  • a fourth sample 1110 was taken at ninety degrees.
  • FIG. 12 is a frequency response illustrating two on-axis responses of the compact monitor 1004 of FIG. 10.
  • a first frequency response 1202 was taken at a distance of 0.5 meters from the compact monitor 1004 and at the sample point that is at a height of one meter above the acoustically reflective planar surface 1010.
  • a second frequency response 1204 was taken at the sample point that is at a distance of 2 meters from the compact monitor 1004 and at a height of one meter above the acoustically reflective planar surface 1010.
  • the first frequency response 1202 does not suffer from the effects of reflected sound waves (or bounce) from the acoustically reflective planar surface because the direct sound wave signal is much stronger than the reflected sound wave signal.
  • the second frequency response 1204 shows clear effects of reflected sound waves as illustrated by the undesirable comb effect.
  • FIG. 13 illustrates a frequency response 1302 for a normalized at IkHz on-axis response of the straight line array 1006 of FIG. 10.
  • the frequency response 1302 was taken from the sample point that is at a distance of 2 meters from the straight line array 1006 and at a height of one meter above the acoustically reflective planar surface 1010.
  • FIG. 14 illustrates a frequency response 1402 for a normalized at IkHz on-axis response of the reflective loudspeaker array 1008 of FIG. 10.
  • the frequency response 1402 was taken at the sample point that is at a distance of 2 meters from the reflective loudspeaker array 1008 and at a height of one meter above the acoustically reflective planar surface 1010.
  • FIGS. 15 and 16 illustrate the variation in frequency response of the compact monitor 1004 with distance (FIG. 15) and angle (FIG. 16).
  • samples were taken at the sample points 1002 of FIG. 10 at a height of one meter to generate a first frequency response curve 1502 at 0.1 meters, a second frequency response curve 1504 at 0.5m, a third frequency response curve 1506 at 2.0 meters, a fourth frequency response curve 1508 at 2.0 meters and a fifth frequency response curve 1510 at 4.0 meters.
  • FIG. 15 illustrates the variation in frequency response of the compact monitor 1004 with distance (FIG. 15) and angle (FIG. 16).
  • samples were taken at the first sample point 1104 to generate a first frequency response curve 1602, at the second sample point 1106 to generate a second frequency response curve 1604, at the third sample point 1108 to generate a third frequency response curve 1606, and at the fourth sample point 1110 to generate a fourth frequency response curve 1608.
  • FIGs. 17 and 18 similarly illustrate the variation in frequency response of the straight line array 1006 with distance (FIG. 17) and angle (FIG. 18).
  • samples were taken at the sample points 1002 of FIG. 10 at a height of one meter to generate a first frequency response curve 1702 at 0.1 meters, a second frequency response curve 1704 at 0.5m, a third frequency response curve 1706 at 2.0 meters, a fourth frequency response curve 1708 at 2.0 meters and a fifth frequency response curve 1710 at 4.0 meters.
  • FIG. 17 similarly illustrate the variation in frequency response of the straight line array 1006 with distance (FIG. 17) and angle (FIG. 18).
  • samples were taken at a height of one meter at the first sample point 1104 to generate a first frequency response curve 1802, at the second sample point 1106 to generate a second frequency response curve 1804, at the third sample point 1108 to generate a third frequency response curve 1806, and at the fourth sample point 1110 to generate a fourth frequency response curve 1808.
  • FIGs. 19 and 20 similarly illustrate the variation in frequency response of the reflective loudspeaker array 1008 with distance (FIG. 19) and angle (FIG. 20).
  • samples were taken at the sample points 1002 of FIG. 10 at a height of one meter to generate a first frequency response curve 1902 at 0.1 meters, a second frequency response curve 1904 at 0.5 meters, a third frequency response curve 1906 at 2.0 meters, a fourth frequency response curve 1908 at 2.0 meters and a fifth frequency response curve 1710 at 4.0 meters.
  • FIG. 19 similarly illustrate the variation in frequency response of the reflective loudspeaker array 1008 with distance (FIG. 19) and angle (FIG. 20).
  • samples were taken at the sample points 1002 of FIG. 10 at a height of one meter to generate a first frequency response curve 1902 at 0.1 meters, a second frequency response curve 1904 at 0.5 meters, a third frequency response curve 1906 at 2.0 meters, a fourth frequency response curve 1908 at 2.0 meters and a fifth frequency response curve 1710 at 4.0 meters.
  • samples were taken at a height of one meter at the first sample point 1104 to generate a first frequency response curve 2002, at the second sample point 1106 to generate a second frequency response curve 2004, at the third sample point 1108 to generate a third frequency response curve 2006, and at the fourth sample point 1110 to generate a fourth frequency response curve 2008.
  • FIGs. 21, 22 and 23 illustrate the variation in frequency response of the compact monitor 1004, the straight line array 1006 and the reflective loudspeaker array 1008, respectively based on samples that were taken at the angles of FIG. 11 at a height of zero meters above the acoustically reflective planar surface 1010. In this example, the samples were actually taken on the surface of the acoustically reflective planar surface 1010.
  • FIG. 21 with reference to FIG.
  • the frequency responses of the compact monitor 1004 include a first frequency response curve 2102 representing a sample taken at the first sample point 1104, a second frequency response curve 2104 representing a sample taken at the second sample point 1106, a third frequency response curve 2106 representing a sample taken at the third sample point 1108, and a fourth frequency response curve 2108 representing a sample taken at the fourth sample point 1110.
  • the sharp dip in frequency response at about 2.4 kHz is due to a woofer-tweeter interference effect due to the distance below the axis of the compact monitor 1004 at which the samples were taken.
  • the frequency responses of the straight line array 1006 include a first frequency response curve 2202 representing a sample taken at the first sample point 1104, a second frequency response curve 2204 representing a sample taken at the second sample point 1106, a third frequency response curve 2206 representing a sample taken at the third sample point 1108, and a fourth frequency response curve 2208 representing a sample taken at the fourth sample point 1110.
  • FIG. 23 with reference to FIG.
  • the frequency responses of the reflective loudspeaker array 1008 include a first frequency response curve 2302 representing a sample taken at the first sample point 1104, a second frequency response curve 2304 representing a sample taken at the second sample point 1106, a third frequency response curve 2306 representing a sample taken at the third sample point 1108, and a fourth frequency response curve 2308 representing a sample taken at the fourth sample point 1110.
  • the compact monitor 1004 was significantly detrimentally affected by the interaction with the acoustically reflective planar surface 1010 when compared to the performance of the straight line array 1006 and the reflective loudspeaker array 1008.
  • the detrimental effects, such as comb filtering, created with the acoustically reflective planar surface 1010 decreased as the sample point was moved close to the acoustically reflective planar surface 1010 (FIG. 16 (one meter above) versus FIG. 21 (zero meters above), however, the woofer-tweeter interference effect and a high frequency roll off is present in the responses of FIG. 21.
  • the reflective loudspeaker array 1008 suffers no similar detrimental effect from operating on the acoustically reflective planar surface 1010 since it is designed to cooperatively operate with the acoustically reflective planar surface 1010 as previously discussed.
  • the straight line array 1006 provided relatively flat and parallel frequency response curves at one meter above the acoustically reflective planar surface 1010 (FIG. 18)
  • the sampled responses at zero meters above the acoustically reflective planar surface 1010 depict an undesirable response when compared to the sampled responses of the reflective loudspeaker array 1008 at the zero meters height.
  • the straight line array 1006 Due to the detrimental effect of changes in height above the acoustically reflective planar surface 1010 of the on-axis and off axis responses of the straight line array 1006, the combination of the reflected and direct sound waves do not result in the performance and operation advantages achieved with the reflective loudspeaker array 1008. As a result, the capability of the straight line array 1006 to constructively combine the direct sound waves and the reflected sound waves to generate an acoustic image that is similar to the acoustic image generated by the reflective loudspeaker array 1008 is significantly less. Accordingly, the straight line array 1006 is unable to generate a mirror image and a resulting composite virtual array that is comparable in acoustic or operational performance to the mirror image reflective loudspeaker array (202 FIG.
  • the level change is only about 10 dB going from very close to the array at 0.1 m out to a distance of 4m.
  • the responses are quite well behaved, stay unifo ⁇ nly flat, and are fairly uniform with distance.
  • the reflective loudspeaker array 1008 has desirably increased uniformity and flatness throughout the frequency range.
  • the curves for the straight line array 1006 and the reflective loudspeaker array 1008 are both quite well behaved at one meter above the acoustically reflective planar surface 1010.
  • the response of the reflective loudspeaker array 1008 is significantly more desirable than the straight line array 1006 at zero meters above the acoustically reflective planar surface 1010.
  • the first reflective loudspeaker array 902 may be articulated to form a constant radius of curvature with an angle of about eight degrees
  • the second reflective loudspeaker array 904 may be articulated to form a constant radius of curvature with an angle of about thirty degrees.
  • FIG. 24 is a frequency response diagram representing frequency versus decibels with a 1 watt effective response at a determined distance from such a prototype configuration.
  • a first plot 2402 is indicative of a frequency response at a first sample point 906.
  • the first sample point is on a central axis 908 of the combination of the first reflective loudspeaker array 902 and the second reflective loudspeaker array 904.
  • the central axis 908 intersects the contiguously aligned bases of the pair of reflective loudspeaker arrays 902 and 904 at an intersection point 910.
  • a second plot 2404 is indicative of a frequency response measured at a second sample point 912.
  • the second sample point 912 is at an angle of five degrees above the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906.
  • a third plot 2406 is indicative of a frequency response measured at a third sample point 914.
  • the third sample point 914 is at an angle of twelve degrees below the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906.
  • a fourth plot 2408 is indicative of a frequency response measured at a fourth sample point 916.
  • the fourth sample point 916 is at an angle of twenty degrees below the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906.
  • each of the response curves are roughly flat and parallel.
  • the response curves illustrated in FIG. 24 depict a desirable response.
  • the first reflective loudspeaker array 902 may be articulated to form a constant radius of curvature with an angle of about nineteen degrees
  • the second reflective loudspeaker array 904 may be articulated to form a constant radius of curvature with an angle of about thirty-eight degrees.
  • FIG. 25 is a frequency response diagram representing frequency versus decibels with a 1 watt effective response at a determined distance from such a prototype configuration.
  • a first plot 2502 is indicative of a frequency response at the first sample point 906 on the central axis 908.
  • a second plot 2504 is indicative of a frequency response measured at a fifth sample point 918 that is at an angle of seven degrees below the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906.
  • a third plot 2506 is indicative of a frequency response measured at a sixth sample point 920 that is at an angle of fifteen degrees above the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906.
  • a fourth plot 2508 is indicative of a frequency response measured at a seventh sample point 922 that is at an angle of twenty-five degrees below the central axis 908 when measured from the intersection point 910, and is at the same distance from the array as the first sample point 906. Again, the response curves illustrated in FIG. 25 depict a desirable response.
  • a first constant radius of curvature in the first reflective loudspeaker array 902 and a second constant radius of curvature in the second reflective loudspeaker array 904 may be used to express the relationship between the respective angles. As evidenced by FIGs. 24 and 25, maintaining the ratio at or below a determined value may result in a desired frequency response. In one example, the desired ratio of the angle may be maintained at or below a 4:1 ratio. In another example, an angle of the radius of curvature of each of the first and second reflective loudspeaker arrays 902 and 904 is greater than or equal to five degrees.
  • the response of an asymmetrical loudspeaker array may be tailored to the listening audience to create asymmetrical coverage patterns. Listening spaces having different physical configurations may be accommodated by adjusting the asymmetrical coverage patterns of the asymmetrical loudspeaker array. Accordingly, by separately directing and focusing the coverage patterns of each of the first and second loudspeaker arrays 902 and 904, undesirable sound energy reflected by surrounding structures in a particular listening space may be minimized.
  • the reflective loudspeaker array provide significant advantages in performance due to cooperative operation with an acoustically reflective planar surface. Due to the cooperative operation, detrimental effects of acoustic reflections from an adjacently positioned acoustically reflective surface are minimized.
  • the acoustically reflective planar surface may provide the mirror image loudspeaker array resulting in a composite virtual array that is acoustically and visually perceived as twice the physical height of the reflective loudspeaker array.
  • the number of loudspeakers in the reflective loudspeaker array are also perceived to be doubled, thereby increasing the sensitivity and the maximum sound pressure level of the reflective loudspeaker array by 6 dB when compared to a free standing array.
  • the reflective loudspeaker array may also control vertical beamwidth operating frequency down an octave lower when cooperatively operated with an acoustically reflective planar surface due to the effective doubling of the height while the coverage area remains the same. Further, the reflective loudspeaker array may provide a more uniform SPL that minimizes near field and far field variations.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Abstract

Selon l'invention, une colonne de haut-parleurs réflecteurs peut être mise en oeuvre en coopération avec une surface planaire à réflexion acoustique pour fournir une combinaison constructive d'ondes sonores directes et réfléchies produisant un champ sonore uniforme. Le champ sonore uniforme produit un champ sonore contrôlé dans les sens vertical et horizontal, ainsi qu'une uniformité de distances proche de la colonne de haut-parleurs réflecteurs à des distances éloignées. Les ondes sonores directes et réfléchies peuvent être combinées de manière avantageuse et constructive pour générer une largeur de faisceau focalisée d'ondes sonores. La colonne de haut-parleurs réflecteurs comprend une pluralité de haut-parleurs couplés à une surface de la colonne de haut-parleurs réflecteurs. La surface peut être constituée de manière à comprendre au moins une courbe présentant un rayon de courbure. La colonne de haut-parleurs réflecteurs peut être placée à proximité d'une surface planaire à réflexion acoustique, de sorte qu'un plan frontal d'un haut-parleur adjacent situé le plus près de la surface planaire à réflexion acoustique soit aligné perpendiculairement, et qu'un plan frontal d'un haut-parleur éloigné de la surface planaire à réflexion acoustique ne soit pas aligné perpendiculairement.
PCT/US2006/008365 2005-03-08 2006-03-08 Colonne de haut-parleurs reflecteurs WO2006096801A2 (fr)

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WO2008142867A1 (fr) 2007-05-21 2008-11-27 Panasonic Corporation Dispositif de haut-parleur
CN103686522A (zh) * 2012-09-19 2014-03-26 淇誉电子科技股份有限公司 号角型扬声器
WO2014164234A1 (fr) * 2013-03-11 2014-10-09 Tiskerling Dynamics Llc Constance de timbre sur l'ensemble d'une plage de directivités pour un haut-parleur
WO2017112409A1 (fr) * 2015-12-22 2017-06-29 Bose Corporation Adaptateurs adaptables pour des fentes de diffraction dans des haut-parleurs
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WO2014164234A1 (fr) * 2013-03-11 2014-10-09 Tiskerling Dynamics Llc Constance de timbre sur l'ensemble d'une plage de directivités pour un haut-parleur
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WO2017112409A1 (fr) * 2015-12-22 2017-06-29 Bose Corporation Adaptateurs adaptables pour des fentes de diffraction dans des haut-parleurs
US9712911B2 (en) 2015-12-22 2017-07-18 Bose Corporation Conformable adaptors for diffraction slots in speakers
US9716942B2 (en) 2015-12-22 2017-07-25 Bose Corporation Mitigating effects of cavity resonance in speakers

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