US3816672A

US3816672A - Sound reproduction system

Info

Publication number: US3816672A
Application number: US00323574A
Authority: US
Inventors: H Gefvert; K Peter
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-07-06
Filing date: 1973-01-15
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11

Abstract

A sound system for reproducing the full frequency spectrum of recorded sound throughout a listening environment at its natural volume and in the same spatial relationships as the originally created sound includes a multidirectional main audio driver utilizing the convex area of a conical shell diaphragm integrated with an acoustically reflective throating inertial regulator disk to provide spatial acoustic coupling between the audio driver and the atmosphere that approximates a live performance. The regulator disk is a rigid reflective plate mounted in a plane which forms an interior angle between 45* and 75* with the axis of the conic diaphragm. The plate may be flat, or shaped hyperbolically or exponentially. It may be either integral with the conical diaphragm assembly or separate and attached by external means. A bass equalization device comprising a tube of controlled inertance having an acoustically resistive network inserted therein amplifies the output from the convex radiating surface of the audio driver and equalizes the bass and upper frequency audio power output. It also serves to cancel the outof-phase upper frequency sound waves generated by the concave radiating surface. The bass equalization device and the inertance regulator disk control the resonant frequency and inertance of the system. The bass frequency output faces a cabinet enclosure equalized without resonance so that 12 through 512 Hz. is generated without spurious harmonic partials or parasitic frequency components. Horizontal-radial and vertical dispersion speakers, comprising high frequency response speakers, are vertically oriented and face a conic, hyperbolic or exponential throating and inertance regulated dispersion surface for a full spatial distribution of the upper frequency audio output. The sound reproduction system may further be described as an inertially regulated sonic transducer. By controlling the diaphragm velocity and acoustic expansion rate audio reproduction can be recreated that approximates the spatial perspective of a live performance.

Description

United States Patent 91 Guefyert et al.

[45.] June 11, 1974 SOUND REPRODUCTION SYSTEM [22] Filed: Jan. 15, 1973 211 Appl. No.: 323,574

Related US. Application Data [63] Continuation of Ser. No. 52,590, July 6, 1970,

abandoned.

[52] US. Cl ..179/1l5.5 R, 179/1 E, 181/31 B [51] Int. Cl H04r 9/06 [58] Field of Search.....' l79/1l5.5 R, l E, 16 A,

179/1 D; 181/31 R, 31 A, 31 B I [56] References Cited UNITED STATES PATENTS 2,611,830 9/1952 Heineman 179/l15.5

2,615,995 10/1952 Voigt 81/31 B 3,424,873 l/l969 Walsh 179/1 15.5 R 3,512,606 5/1970 Anastin 181/31 B Primary Examinerl(athleen H. Claffy Assistant Examiner-Thomas L. Kundert Attorney, Agent, or Firm-Neuman, Williams, Anderson & Olson [57] ABSTRACT A sound system for reproducing the full frequency spectrum of recorded sound throughout a listening environment at its natural volume and in the same spatial relationships as the originally created sound includes a multidirectional main audio driver utilizing the convex area of a conical shell diaphragm integrated with an acoustically reflective throating inertial regulator disk to provide spatial acoustic coupling between the audio driver and the atmosphere that approximates a live performance. The regulator disk is a rigid reflective plate mounted in a plane which forms an interior angle between 45 and 75 with the axis of the conic diaphragm. The plate may be flat, or shaped hyperbolically or exponentially. It may be either integral with the conical diaphragm assembly or separate and attached by external means. A bass equalization device comprising a tube of controlled inertance having an acoustically resistive network inserted therein amplifies the output from the convex radiating surface of the audio driver and equalizes the bass and upper frequency audio power output. It also serves to cancel the out-of-phase upper frequency sound waves generated by the concave radiating surface. The bass equalization device and the inertance regulator disk control the resonant frequency and inertance of the system. The bass frequency output faces a cabinet enclosure equalized without resonance so that 12 through 512 Hz. is generated without spurious harmonic partials or parasitic frequency components. Horizontal-radial and vertical dispersion speakers, comprising high frequency response speakers, are vertically oriented and 99 assinietbrtzerbal 9 92152119 hr n a inertance regulated dispersion surface for a full spatial distribution of the upper frequency audio output. The sound reproduction system may further be described as an inertially regulated sonic transducer. By controlling the diaphragm velocity and acoustic expansion rate audio reproduction can be recreated that approximates the spatial perspective of a live performance.

20 Claims, 9 Drawing Figures DEC/EELS mmmmn m 3.816572 SHEET F 3 I I I I I I l I I I I 1 I I l O 20 3O 4O 5O 7O 8O 700 770 FRE UENCY I FIG. 5

PATENTEnJum m4 33163572 SHEET 30F 3 6 FIG. 7

Ill/I 1 SOUND REPRODUCTION SYSTEM This is a continuation, of application Ser. No. 52,590 filed July 6, 1970 and now abandoned.

FIELD OF THE INVENTION This invention is directed to a sound reproduction system and more particularly to a combination of unique electroacoustic transducers which cooperate to accurately reproduce sound throughout a listening environment in essentially the same geometric spatial profile as it is originally created.

BACKGROUND OF THE INVENTION The controlling and limiting factor in sound reproduction is an electroacoustic transducer, or loudspeaker, whose major element is a diaphragm which though limited in physical size, must transmit sound across an unlimited space within its environment. Sound is transmitted by the action of the vibrating diaphragm in setting air molecules in motion. The resulting motion of the air molecules is a function of the speed and distance of each excursion by the diaphragm of the transducer. The diaphragm moves back and forth under the control of electric signals received by the transducer. The diaphragm thus creates wave fronts of air particles, or sound waves, which travel through the atmosphere to the listener. The formula that expresses the relation between the inertance of the atmosphere and the diaphragm is:

Z F V, where Z is the inertance of the atmosphere;

V is the velocity of the vibrating diaphragm; and

F is the acoustic force impinged upon the atmosphere.

When the acoustic force is produced by a vibrating diaphragm, the inertance Z is defined by:

Z Z/S or P/V, where S is the area of the diaphragm, I

P is the pressure of the atmosphere on the diaphragm; and

V is the velocity of the vibrating conical diaphragm. To increase the output efficiency and the fidelity of sound reproduction, means must be employed to control and limit the amount of atmosphere (i.e., the number of air molecules) the diaphragm must face. If the diaphragm faces an atmosphere that is too limited, the molecular motion or wave front created by each excursion of the diphragm is limited and compressed, and the audio output fidelity is extremely poor, the sound being characterized by a megaphone or tunnel effect. If the radiating diaphragm faces an infinite atmosphere unlimited as to length, breadth and width, then the effect of the motion imparted by the diaphragm to the air molecules is quickly dispersed and the audio output is low, expecially in the high frequency ranges where the diaphragm movements are short and rapid.

The number and design of acoustic transducers necessary to create a sound system which is capable of accurately reproducing sound in any environment depends on two factors: (I) the spatial distribution of the acoustic output of each loudspeaker of the sound system, and (2) the efficiency and fidelity of sound reproduction of each speaker. Sound systems, as presently developed, ordinarily utilize at least two speakers to reproduce the full range of frequencies: a deep throated cone type speaker for low frequency sound reproduction and an almost straight-sided speaker for higher frequencies. A single speaker designed to reproduce a broad sound spectrum is capable of contributing little high frequency sound reproduction. This is due especially to the mass of the speaker cone which results in a relatively low resonant frequency and an inability of the speaker diaphragm to move quickly enough to reproduce high frequency sound. Further, the deep throat of the speaker cone attenuates the higher frequencies before they can project to the outer atmosphere.

A defect present in speakers designed specifically for high frequency reproduction is that they fail to compensate for the fact that high frequencies are more subject to obstructions than low frequencies. Most high frequency sound waves are created in a relatively limited area near the apex of the high frequency speaker cone; this is because at high frequencies the diaphragm must move in and out so quickly that in fact only the area of the cone near the apex or center moves a significant distance. Nor do high frequency sound waves disperse easily through a listening environment; the upper range frequencies have a tendency to propagate in concentration along the axis of the loud speaker cone, resulting in a narrow beam of generated sound. Thus most of the listening area of a given room is off the speaker axis and the sound reproduction as heard at these positions is limited.

Conventional low frequency speakers also have difficulty in accurately reproducing the frequencies for which they are designed. The speaker voice coil and diaphragm combination must be capableof reversing its direction of travel under the control of an input signal having considerable variation in amplitude and frequency. Most conventional low frequency speakers cannot fulfill this requirement because of the large mass of the diaphragm used to achieve a low resonant frequency. As a consequence, the output has a muddy or rounded effect at low frequencies due to the failure of the voice coil to instantaneously reverse its direction in response to changing input signals.

The sound system of this invention undertakes to present reproduced sound to the ear in the same geometric spatial profile as it was originally created without making compromises in tonal quality. It is known that sound is projected outwardly from various instruments and vocalists in classifiable patterns. These are broadly:

l. A hemisphere (e.g., stringed instruments and percussion instruments);

2. A narrow conical beam (e.g., brass instruments and voices);

3. A briad conical beam (e.g., Woodwinds); and

4. A radial pattern (e.g., guitars).

A properly designed sound system should incorporate a number of acoustic transducers such that the combination is capable of approximating the spatial distribution pattern of the recorded sound, the several transducers cooperating to make up for the deficiencies of the individual transducing elements.

True sound reproduction also requires that the volume of the reproduced sound be the same as that originally recorded. But speakers operate at varying levels of efficiency depending on the use for which they are designed, ranging from relatively efficient tweeters to inefficient midrange and low frequency reproducers. Further it is known that sound radiates from both the concave and convex surfaces of the speaker diaphragm; but the sound radiated from the rear or convex diaphragm surface must be attenuated in order not to cancel out the in-phase direct radiation. Prior attempts to utilize radiation from the rear of a diaphragm employ baffles in which the sound waves radiated from the rear are reflected to reinforce the bass frequencies transmitted from the front surface of the diaphragm. Such baffles require a diaphragm of considerable mass to provide the strength necessary to dampen out-ofphase sound waves reflected by the baffle directly back to the speaker. Such baffles are also ordinarily of great size and may introduce many out-ofphase components into the output, unless the range of reflected frequencies is limited by complex design.

In the sound system disclosed herein, which is capable of efficiently reproducing recorded sound at the same volume and in the same acoustic profile as it is recorded, each transducer is designed for a specific frequency range or purpose, resulting in a decrease in the number of design compromises in each transducer, and improved overall sound reproduction. Moreover, in the main audio driver of this invention, the acoustic radiation from both the front and rear surfaces of the speaker contributes to the total output of the sound system, resulting in improved efficiency of sound reproduction.

SUMMARY OF THE INVENTION The present invention provides means for reproducing recorded sound in the same spatial profile and volume level as it was originally created. Means are included to compensate for the varying reproduction characteristics of the electro-acoustic transducers in a multi-element sound system, thus recreating the full frequency spectrum as it was recorded.

The sound reproduction system of this invention includes a multidirectional main audio driver whose conic diaphragm is structurally supported so that the outer, convex surface of the cone is the electroacoustic coupling element between the electrical signals and the listening environment. Using the outside or convex area of the acoustic drivers cone provides equalized audio dispersion over a 360 sound projection pattern, as opposed to the 30 projection pattern from the concave area of a conventionally mounted speaker cone.

Prior to this time a major problem in using the convex or outside area of the cone has been the decreased audio power output therefrom. Although below 3,500 Hz, the audio output of the convex area of the conic diaphragm is equal in intensity to that from the inside or concave area, a loss in the higher frequencies occurs due to the lack of horn coupling or throating on-the outside area of the cone. To supply the acoustic throating ordinarily provided by the inside area of a conventionally mounted speaker cone, a reflective surface is mounted in or near the plane of the apex of the main driver and relative to the direction of oscillation of the main drivers diaphragm so that an acoustic throat is formed having the reflective surface as one side and the outside of the main driver conic diaphragm as the other side. This unique design restores the loss in high frequency output which ordinarily results from broadcasting from the concave surface of the main drivers conic diaphragm.

tion with the main audio driver of this invention to provide bass response equal in audio intensity to the response across the midrange and high frequency spectrum, as well as to acoustically cancel the out-of-phase components of the upper frequency spectrum. The equalization device is a tube whose resonant frequency and overall acoustic response characteristic are carefully controlled. The resonant frequency is a function of the length of the tube. The acoustic response of the tube throughout the frequency range of interest is controlled by inserting an acoustic network into the tube. The acoustic network controls the acoustic resistance and ultimately the acoustic response of the tube, expecially in the frequency spectrum including the resonant frequency of the equalization device. The result of using the network is to generate a more linear dynamic audio output as well as to extend the lower limit of audible frequency response. In a further refinement the walls of the tube may be lined with an acoustic damping material chosen for its absorbency of high frequency waves, providing damping of out-of-phase components of the high frequency audio output from the main drivers concave or inside surface. The audio output from the concave surface of the main driver is acoustically coupled to one end of the tube of the bass equalization device. The resonant frequency of the equalization device is so chosen that the device amplifies the low frequency components of this audio input, eliminating the need for a conventional cone-type woofer. Due to the low resonant frequency and the damping materials used in constructing the tube, the upper frequency components are sharply attenuated, eliminating the problem of out-of-phase components of high frequency sound output.

Four objectives are fullfilled by the base equalization device of this invention:

1. The bass output is linearized between 16 Hz. and

256 Hz., resonance peaks being eliminated; 2. The output is generated over a 360 radial pattern;

3. the acoustic power output is equal to that of the main driver generator of the system; and

4. the out-of-phase components of the upper frequency spectrum produced by the concave or inside area of the main generator diaphragm are effectively damped out.

To reproduce more accurately instruments which project their sound in a horizontal radial pattern in the upper frequency spectrum, a horizontal radial high frequency dispersion unit may be added to the system. The dispersion unit includes in combination a high frequency acoustic transducer and a hyperbolic dispersion surface. As used herein, a dispersion surface is a sub stantially conically'shaped surface having flared upper edges, the slope at which the cone flares being scientifically determined to distribute the acoustic output from the radiating surface of the associated transducer in a 360 degree radial pattern. hyperbolic or exporential surfaces of revolution may be employed instead of the conical surface. The axis of the dispersion surface is generally parallel to the axis of the high frequency transducer.

A vertical radial dispersion unit may be added to the sound system of this invention to more completely reproduce the hemispherical outward sound patterns of certain other instruments. The dispersion unit consists of a high frequency responsive transducer having a dispersion surface cooperating therewith to disperse the high frequency waves in the hemispherical sound patterns creaded by certain instruments.

IN THE DRAWINGS FIG. 1 is a vertical section taken through a center line of a sound system embodying the present invention;

FIG. 2 is a perspective view of the sound system of FIG. I, mounted on a base containing the bass equal ization device, and illustrating a sound directing shield used in cooperation with the horizontal radial tweeter;

FIG. 3 is a perspective view of the sound system of FIG. 1 with the bass equalization device removed;

FIG. 4 is a graph depicting the acoustic output from the bass equalization device of the sound system of FIG. 1, over its effective operating range;

FIG. 5 is a schematic diagram of the main audio driver and its associated inertance regulator disk, illustrating their angular relationship and direction of their audio output;

FIG. 6 is a vertical section of the bass equalization device of the sound system of FIG. 1, illustrating the separation of the sound reproduction system into two sections, one including the main audio driver and the other including the high frequency dispersion speakers;

FIG. 7 is a section of a bass equalization device having two folds;

FIG. 8 is a horizontal section of the bass equalization device of FIG. 7, taken along the line 8-8; and

FIG. 9 is a horizontal section of the equalization device of FIG. 6, taken along the line 9-9, in which the device is folded in three planes to produce a more compact structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a view in vertical section of a preferred embodiment of the sound system of this invention.

The main multidirectional audio driver 2 of the sound system is shown having the axis of driver 2 mounted in the vertical plane, the driver being supported in this position by supporting frame structure 4.

Membranes

6 and 8 hold the diaphragm 9 of audio driver 2 centered in the supporting framework 4 but leave it free to move axially. The apex 10 of diaphragm 9 is flexibly connected by the membrane 6 to a supporting shoulder 11 of framework 4. The shoulder 11 supports a regulator disk 12 (shown more clearly in FIG. 3) which cooperates with diaphragm 9 to provide a throating effect and amplify the acoustic output of driver 2 as is clearly explained below. The outer end 14 of the diaphragm 9 of generator 2 is flexibly connected by membrane 8 tosupporting framework structure 4. The main driver generator 2 is otherwise of essentially conventional construction, and includes a magnetic core 16 which may be permanently magnetized to gen-. erate a constant magnetic field.

A voice coil 18 wound on a tubular member 20 extends into the air gap of the magnetic circuit formed by magnetic core 16. The voice coil 18 carries an exciting current which varies in amplitude and frequency to represent the volume and frequency of the sound to be reproduced. As a result of the flexible support provided by

membranes

6 and 8 the entire diaphragm 9 is free to move in response to the exciting current applied to the voice coil 18 and thus act as an electroacoustic coupling device between the electric circuit signals and the surrounding atmosphere of the listening environment. The diaphragm 9 thus radiates sound waves to the surrounding atmosphere in response to the exciting current in the voice coil.

Utilizing the convex cone area surface 2l of the diaphragm 9 to provide electroacoustic coupling results in a 360 sound radiation pattern surrounding the sound source and filling the listening environment, as opposed to the limited 30 sound pattern projected by the concave cone used in the prior art. The acoustic output of such prior art cone type loud speakers propagates through the listening area with decreasing intensity as the angle from the axis of the cone increases.

The acoustic energy from the outer or convex side 21 of the diaphragm 9 is the same as the energy from the inside surface 22, and below 3,500 Hz. There is however, a measurable loss in high frequency output from the convex surface 21 due to the elimination of horn coupling or throating on the outside or convex area 21 of the diaphragm 9. This throating effect is ordinarily provided by the two sides of the conventional horn megaphone type speaker; the outward projection of midrange and higher frequencies is a result primarily of a resulting horn coupling and outward emission, rather than the piston action of the cone itself. In the preferred embodiment disclosed herein, the throating action is provided by using the surface 21 of the moving diaphragm 9 as one side of the acoustic throat necessary to provide adequate audio coupling between generator and atmosphere, and reflecting regulator disk 12 as the other side of the throat.

In the preferred embodiment disclosed herein, regulator disk 12 may properly be termed an inertial transducer in that it controls the inertance of the main audio driver system. It does this by controlling the amount of air which faces the conic diaphragm, thus limiting the number of free air molecules which must be set in motion to reproduce sound. In the preferred embodiment, the regulator 12 has a disk shape, the outer diameter of which is the same as the diameter of the large end of the conic diaphragm 9. It may, however, range from three-fifths to seven-fifths of the diameter of the large end of conic diaphragm 9. The regulator disk 12 is shown mounted on supporting shoulder 11 in a plane perpendicular to the generators axis and at or near the apex 10 of the generator 2, as shown in FIG. 1. As shown in FIG. 5, the angle between the diaphragm 9 and the regulator disk 12 in this exemplary embodiment is 60, with the sides of the diaphragm 9 being 30 off its central axis as shown by the angle (1). The angle 0 between disk 12 and diaphragm surface 21 may be as small as 45 or as great as the surface itself in a preferred embodiment is flat, but may be curved hyperbolically or exponentially in certain embodiments.

The combination of the inverted conic diaphragm 9 with the fixed regulator disk 12 provides many long sought advantages over the conventional cone speaker, without sacrificing the throating action necessary for full sound output. Since the fixed regulator disk 12 constitutes one side of the acoustic throat, a greater audio output results than with a cone diaphragm utilizing conventional horn coupling wherein both sides of the throat are in oscillation. Further, the loudspeaker baffle ordinarily used to capture and control emission from the outside or convex cone area is eliminated, together with the spurious resonances and wave fronts it creates, and with its customary loss of a portion of the output. In the multidirection audio driver 2 of this invention, the out-of-phase components of audio output are limited to the concave area 22 within the diaphragm 9, making them easier to control and eliminate.

It can also be seen in FIG. 5 that an angle 0 equal to 60 provides a favorable degree of angular force for restoring the diaphragm to its original position after each excursion. It is known that a 6 equals angle 1, the interior angle of the large end of the diaphragm; and that W, the outward component of energy from the cone is W X cosl'. Because the cosine of 60 equals 0.500, the forces in the oscillating conical diaphragm are equalized in the configuration, and a minimum of restoring force is required after each axial excursion.

A bass generation and equalization device 26 is used in combination with the multidirectional driver 2. The bass equalization device 26 is designed to equalize the bass energy from l6 to 256 Hz, to provide equal response over the full 360 listening area and to provide a power handling capacity equal to the output of the audio driver 2 disclosed above. The equalization device 26 also destroys the out-of-phase audio signals created by the concave surface 22 of diaphragm 9 of the audio driver 2.

The bass equalizer 26 includes a tube 27 having an entrance 28 for the acoustic output generated by the concave side 22 of diaphragm 9. The far end 30 of the tube is closed; the length and resistance to the passage of air of the tube are carefully controlled so that the high frequency sound waves are fully attenuated during their travel through the tube; the low frequency waves are delayed only long enough so that they are in phase with the sound generated by the convex surface of the main driver 2, thus reinforcing the low frequency sound output without adding any distortion to the audio output. The bass equalization device 26 to be used in cooperation with the main audio driver 2 allows the use of a diaphragm 9 of reduced mass for driver 2, because the desirability of a diaphragm with a low resonance point is reduced. Reduction in mass of the diaphragm 9 also allows a reduction in the flux density of the magnetic core 16, making the diaphragm 9 of the audio driver 2 more quickly responsive to changes in frequency and amplitude in the exciting input signal current.

The multidirectional audio driver 2 is positioned so that the audio output from the concave surface area 22 is directed into one end 28 of the tube 27 of bass equalizer 26. In the embodiment disclosed herein, audio driver 2 is directly coupled to one end 28 of bass equalizer 26. Accurate reproduction of the long wave lengths of low frequency sounds requires a physically large tone reproduction chamber. The longer the tube 27, the lower the minimum frequency of its acoustic output, because the resonant frequency of the tube is a function of tube length. Thus, the tube 27 of bass equalizer 26 provides the long air path required to amplify bass frequencies (below 200 Hz).

The resonant frequency of bass equalizer 26 is a function of the length of tube 27. For a resonant frequency of 55 Hz, which would provide a broad, fullrange response, the length of tube 27 is approximately one-quarter of the wavelength of a 55 Hz signal. When a conical shell diaphragm of 6 inches in axial depth is employed, the optimum tube length if about 4 feet. An ideal height to diameter ratio for equalization device 26 is 8 to 1; therefore, the diameter of tube 27 is 6 inches.

To reduce the space occupied by tube 27, it may be folded, for example, into two or three sections without loss of bass response, due to the long wavelengths in the frequency spectrum of interest. FIGS. 6 and 9 show a tube having a double fold; FIGS. 7 and 8 show a single folded tube. FIGS. 6 and 9 show a tube folded upon it self in two planes, resulting in an esthetically desirable configuration which occupies a minimum of space. In a further modification, if the size of the sound system itself is sought to be reduced, the length of the tube may be shortened (and thus the diameter as well), although with a consequent rise in resonant frequency, and thus a reduction in the range of linear bass response.

The use of tube 27 alone for the bass generation and equalization results in undesirable peaks in the bass output signal, produced by the natural resonances of the system, i.e., the frequencies at which the system vibrates most freely and provides the greates reinforcement to the acoustic output of audio driver 2. A typical response curve 30 for the tube of equalization device 26, shown in FIG. 4, has a major peak 32 at about Hz., the resonant frequency of an exemplary tube 27 having dimensions as disclosed above and a less pronounced peak 34 at about Hz.

As described above, the length of the tube 27 provides. the desired extended and amplified bass frequency reproduction; thus the peaks cannot be reduced by adjusting the tube length without affecting the acoustic response of the equalization device. Rather in the sound system of this invention, the resonant peaks have been flattened" by introducing acoustic network 42 which reduces the Q of the bass equalization device 26. In an acoustic system Q is a figure of merit representing the ratio of the acoustic reactance to the acoustic resistance, the two components of the total acoustic impedance (or resistance to the propagation of sound) which determines the acoustic response of the system. The acoustic reactance is frequency dependent, and is at a minimum at the resonant frequency of a system. Because the operating frequencies of interest of bass equalization device 26 are at or near its resonant frequency, the acoustic response of the device is controlled to a great degree near this frequency by the acoustic resistance of the system. The formula for the inertance M of the circular tube of radius R is:

where P grams per cubic centimeter of atmosphere in tube; and

L length of tube in centimeters.

The acoustic reactance X 21rfM. Increasing the acoustic resistance or inertance by introducing network 42 lowers the Q of the acoustic system and maintains the peak output level at or near the normal output level of the system, as shown in curve (FIG. 4), which has reduced

resonant output peaks

38 and 40. A further benefit of increased acoustic resistance is that the frequency dependence of the total system acoustic response decreases as the acoustic resistance increases;

thus the change in audio output across the frequency spectrum of interest, i.e., the bass frequencies from 16-200 Hz, is reduced, as shown in curve 36.

In the bass equalization device 26, the acoustic resistance is increased and the peaks in frequency response greatly reduced as described above by the insertion of an acoustic network 42 in the tube 27 of equalization device 26. A typical acoustic network 42 includes materials of three different porosities arrayed in a sandwichlike combination. A typical sandwich network 42 includes a layer 44 of polyurethane 10, a layer 46 of polyurethane 30, and a layer 48 of polyurethane 100. The numeral following the term polyurethane indicates the porosity in pores per lineal inch of the materials of the network, which are commercially available under the same Scott Renticulated polyurethane. The network 42 is used to increase the acoustic resistance of tube 27 to the desired level, thereby reducing the frequency dependence of the audio output of equalization device 26. The polyurethane also absorbs the midrange to high frequency sound waves. It should be understood that as with all other materials and dimensions specifically stated herein, dimensions and materials for the construction of an exemplary acoustic network are stated for the purpose of example only and are not intended to be limiting or restrictive in any way.

The length of tube 27 and thus the resonant frequency of bass equalizer 26 being established, the acoustic network 42 is inserted therein to lower the Q and thus reduce the response peak at resonant frequency. A suitable network 42 for a tube 27 4 feet in length includes a first layer 4 approximately 1 inch in thickness of a material having a porosity of pores per lineal inch; a second layer 46 approximately three inches in thickness, having a porosity of pores per lineal inch; and a third layer 48 approximately 4 inches in thickness having a porosity of 100 pores per lineal inch. The exact composition of the inserted network 42 to produce the desired changes in acoustic output of the tube 27 of a specific embodiment of this invention are determined by linear extrapolation after the other parameters (length, diameter, and maximum acoustic power intended) of the tube 27 are determined.

Acoustic network 42 is positioned within tube 27 at a point where the sound wave encounters the maximum acoustical resistance. In a closed tube (the tube 27 of this system is effectively a closed tube because of the main drivers diaphragm coupled to one end) the points of maximum acoustical resistance occur at one-third and two-thirds of the effective tube length. The plug is ordinarily placed at the point of maximum acoustical resistance farther from the diaphragm 9 of main generator 2; the plug might otherwise have a greater effect than desired upon the tubes resonant frequency. It is known from experiment than an ideal placement is at a point between three-fifths and two-thirds of the way to the far, closed end 30 of the tube.

The sidewalls 50 of the tube 27 are lined with a layer 52 of acoustic damping material which attenuates the midrange and upper frequencies which are generated by the concave or inside area 22 of main generator 2.

A bass equalization device 26 provides an amplified audio output in the low frequency ranges of heretofore unatainable clarity, a result previously impeded by the large mass and low efficiency of low frequency electroacoustic transducers. Further, as a result of using the acoustic network 42 with the bass equalizer 26, a linear output without a peak at the resonant frequency is provided. The addition of network 42 to equalization device 26 also extends the lower limits of linear frequency response. The clearly appears in the acoustic response curves of FIG. 4, wherein curve 30 shows the frequency response of the bass equalization device 26 without the acoustic network and curve 36 shows the response with the network 42 inserted in tube 27 of equalization device 26.

A preferred embodiment of the invention also includes a horizontal radial dispersion system 59, horizontal radial tweeter 60 in combination with a radial dispersion element 62. The horizontal radial tweeter 60 is of conventional design having a diaphragm 64 whose outer edges are permanently affixed by means of a con necting ring 66 to supporting framework 4. The voice coil and magnet structure 70 shown are of conventional design to accurately reproduce the applied high frequency signals.

A conventional electrical crossover network 72 supplies the frequencies of approximately 2,500 Hz. and above to the magnetic deflection system 70 of tweeter 60. The tweeter 60 faces hyperbolic dispersion surface 74 of dispersion element 62 to project in a 360 pattern the midrange and high frequencies and harmonics of instruments which project their sound to the listener in a horizontal radial pattern. An examplary dispersion surface 74 which testing has demonstrated provides full 360 radiation of the audio frequency output with minimum distortion, has a curvature such that a plane including the vertical axis of the dispersion element 62 forms an intersection with the dispersion surface 74 in the shape of an arc of a circle whose center lies on the outer edge 76 of connecting ring 66 (see FIG. 2) which holds in place the radial horizontal tweeter. In an alternative embodiment shown in FIG. 2, a shield of sound absorbing material covers one-third of the output area of horizontal radial dispersion system 59. The shield 75, shown in cross section in FIG. I is of polyurethane type material of highly absorbent quality, so that the resulting acoustic output of the horizontal dispersion system 59 more nearly approximates the conic dispersion pattern described above.

The vertical axis of the dispersion surface 62 is parallel to the axis of tweeter 60; in a preferred embodiment it is coaxial with that of the horizontal radial tweeter 60.

In a preferred embodiment, the radial dispersion element 62 is suspended in coaxial alignment with the horizontal radial tweeter 60 by means of adjustable bolts 77a, b, c, d. In an alternative embodiment (not shown) the apex 79 of the dispersion surface 74 may be attached to the permanent magnetic core 70 at the apex of the horizontal radial tweeter 60.

In a further alternative embodiment, a vertical radial dispersion system 81 is provided, including a second radial tweeter 80 mounted with its axis parallel to the axis of horizontal radial tweeter 60. It is ordinarily mounted above parabolic dispersion element 62 (see FIGS. 1 and 2) to project the vertical hemispherical sound patterns generated by certain instruments. The

tweeter 80 is of conventional design having a diaphragm 82 controlled by a magnetic deflection system 84 and being held in place by a supporting ring 86 within a framework 88 which may also include the dispersion element 62 as a part thereof. In this preferred embodiment the dispersion surface 74 is an integral part of framework 88. In a further addition to this preferred embodiment a dispersion element 92 is mounted directly on and supported by apex 94 of vertical tweeter 80 utilizing the center section 95 of magnetic deflection system 84 for support, to broadly disperse the vertical radial sound patterns. The curvature of the surface 96 of a preferred embodiment of this dispersion element 92 is such that a plane including the axis of dispersion element 92 forms a curve of a hyperbolic function at its intersection with dispersion surface 96. An alternative embodiment is illustrated in FIGS. 6 and 9 wherein the supporting structure 4 is divided into two sections, the first containing only main audio driver 2, the second containing the horizontal and vertical radial

dispersion speaker combinations

59 and 81. Both units are placed on and/or supported by the bass equalization system of the invention.

While a preferred embodiment of this invention is described above, and illustrated in the attached drawings, it will be understood that the invention is not limited thereto, since many modifications may be made. It is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A system for reproducing sound throughout a listening environment includingz a. a hollow flexible main audio driver including a conical radiating member having a small and a large end axially aligned with each other, and defining an inner concave sound radiating surface and an outer convex sound radiating surface;

b. driving means directly coupled to said small end for mechanically driving said radiating member;

0. a relatively rigid reflective member essentially the same diameter as the large end of the conical radi ating member disposed at an angle to the axis of said conical radiating member, adjacent said small end, the angle between the outer surface of said radiating member and the reflective member being betwe n 2 291 2 and 75;

d. tubular sound conducting conduit and bass equalizing means cooperatively mounted to receive sound energy from the concave inner surface of the large end of the conical driver so that the outer convex surface of said conical radiating member is freely exposed for direct electroacoustic coupling to the surrounding environment and the reflective member, the inner concave surface of said conical radiating, member being isolated from the surrounding environment by said conduit;

c. said outer surface and said reflective member cooperating to direct sound waves produced at the outer surface of said radiating member radially outwardly therefrom.

2. A sound reproducing system as claimed in claim 1 wherein said reflective member is a circular, plane disk.

3. A sound reproducing system as claimed in claim 2 wherein said reflective member has a diameter between three/fifths and seven/fifths of the diameter of said large end of said radiating member.

4. A sound reproducing system as claimed in claim 3, in which said reflective member is formed with a surface of revolution coaxial with the axis of said radiating member.

5. A sound reproducing system as claimed in claim 4, wherein the intersection of said surface of revolution with a plane including said axis is a curve.

6. A sound reproducing system as claimed in claim 1, wherein said base equalization means comprises a closed tube having a length substantially greater than its width, such that the resonant frequency of said tube is a function of said tube length, and acoustic network means supported within said tube and dividing said tube into two separate lengths for controlling the acoustic response of said bass equalization device.

7. A sound reproducing system as claimed in claim 6 in which the acoustic distance from said radiating member to the end of said tube is approximately one/- quarter of the wavelength of the resonant frequency of said radiating member.

8. A sound reproducing system as claimed in claim 7 in which the inner surface of said tube is lined with an acoustically absorbent material adapted to attenuate high frequency sound waves generated by the inner surface of said radiating member.

9. A sound reproducing system as claimed in claim 8 in which said sound absorbent material is a porous polyurethane material.

10. A sound reproducing system as claimed in claim 6 in which said acoustic network means is positioned within said tube at a distance from the large end of said radiating member of between three/fifths and two/- thirds of the length of said tube.

11. A sound reproducing system as claimed in claim 6 in which said acoustic network means comprises a plurality of layers of microporous acoustic damping material in a sandwich array such that said network provides acoustic resistance to the passage of low frequency sound waves generated by the inner radiating surface response and extending the overall frequency response range of said bass equalization device.

12. A sound reproducing system as claimed in claim 1 including an electroacoustic transducer for reproducing high frequency sound waves of 2,500 Hz. and above, and a dispersion member facing said transducer, said transducer and dispersion member cooperating to disperse said high frequency sound waves radial outwardly therefrom.

13. A sound reproducing system as claimed in claim 12 wherein said dispersion member is formed with a surface of revolution coaxial with said electroacoustic transducer.

14. A sound reproducing system as claimed in claim 13, wherein the intersection of said surface of revolution with a plane including the axis of said dispersion member is a circular arc.

15. A sound reproducing system as claimed in claim 12 in which said electroacoustic transducer includes a permanent magnet and said dispersion surface has an apex, said apex being mechanically coupled to said magnet so that said magnet supports said dispersion surface in substantially coaxial relationship with said transducer.

16. A sound reproducing system as claimed in claim 12, including an absorbing member surrounding said dispersion member and absorbing a portion of said high frequency sound waves dispersed in a plane transverse to the axis of said transducer.

17. A system as claimed in claim 1 for reproducing sound throughout a listening environment comprising an audio driver and a bass equalization device, said equalization device comprising a tube having an open end juxtaposed with said driver and a length substantially greater than its width, such that the resonant frequency of said tube is a function of the tube length, and acoustic network means disposed within said tube and dividing said tube into two separate lengths for controlling the acoustic response of said bass equalization device.

18. A sound reproducing system as claimed in claim 17 in which the distance from said driver to the opposite end of said tube is approximately one/quarter of the wavelength of the resonant frequency of said driver.

19. A sound reproducing system as claimed in claim 17 in which said acoustic network means is positioned within said tube at a distance from said driver of between three/fifths and two/thirds of the length of said tube.

20. A sound reproducing system as claimed in claim 17 in which said acoustic network means comprises a plurality of layers of microporous acoustic damping material in a sandwich array such that said network provides acoustic resistance to the passage of low frequency sound waves generated by said driver and extending the overall frequency response range of said bass equalization device.

Claims

1. A system for reproducing sound throughout a listening environment including: a. a hollow flexible main audio driver including a conical radiating member having a small and a large end axially aligned with each other, and defining an inner concave sound radiating surface and an outer convex sound radiating surface; b. driving means directly coupled to said small end for mechanically driving said radiating member; c. a relatively rigid reflective member essentially the same diameter as the large end of the conical radiating member disposed at an angle to the axis of said conical radiating member, adjacent said small end, the angle between the outer surface of said radiating member and the reflective member being between about 45* and 75*; d. tubular sound conducting conduit and bass equalizing means cooperatively mounted to receive sound energy from the concave inner surface of the large end of the conical driver so that the outer convex surface of said conical radiating member is freely exposed for direct electroacoustic coupling to the surrounding environment and the reflective member, the inner concave surface of said conical radiating member being isolated from the surrounding environment by said conduit; e. said outer surface and said reflective member cooperating to direct sound waves produced at the outer surface of said radiating member radially outwardly thErefrom.

7. A sound reproducing system as claimed in claim 6 in which the acoustic distance from said radiating member to the end of said tube is approximately one/quarter of the wavelength of the resonant frequency of said radiating member.

10. A sound reproducing system as claimed in claim 6 in which said acoustic network means is positioned within said tube at a distance from the large end of said radiating member of between three/fifths and two/thirds of the length of said tube.