WO1998054926A1 - Enceinte acoustique permettant d'amplifier le point ideal - Google Patents

Enceinte acoustique permettant d'amplifier le point ideal Download PDF

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Publication number
WO1998054926A1
WO1998054926A1 PCT/US1998/010865 US9810865W WO9854926A1 WO 1998054926 A1 WO1998054926 A1 WO 1998054926A1 US 9810865 W US9810865 W US 9810865W WO 9854926 A1 WO9854926 A1 WO 9854926A1
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WIPO (PCT)
Prior art keywords
audio
frequency
loudspeaker
emitters
listener
Prior art date
Application number
PCT/US1998/010865
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English (en)
Inventor
Jerald L. Bauck
Original Assignee
Bauck Jerald L
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bauck Jerald L filed Critical Bauck Jerald L
Priority to EP98924945A priority Critical patent/EP0988773A4/fr
Priority to AU76999/98A priority patent/AU7699998A/en
Priority to JP50089599A priority patent/JP2002500844A/ja
Priority to CA002290518A priority patent/CA2290518C/fr
Publication of WO1998054926A1 publication Critical patent/WO1998054926A1/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
    • H04R5/00—Stereophonic arrangements
    • H04R5/02—Spatial or constructional arrangements of 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
    • H04R1/22—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
    • H04R2205/00—Details of stereophonic arrangements covered by H04R5/00 but not provided for in any of its subgroups
    • H04R2205/022—Plurality of transducers corresponding to a plurality of sound channels in each earpiece of headphones or in a single enclosure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2205/00—Details of stereophonic arrangements covered by H04R5/00 but not provided for in any of its subgroups
    • H04R2205/024—Positioning of loudspeaker enclosures for spatial sound reproduction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10—General applications
    • H04R2499/15—Transducers incorporated in visual displaying devices, e.g. televisions, computer displays, laptops
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
    • H04S2420/01—Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF's] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]
    • 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 the fields of audio signal reproduction and audio signal processing, and more particularly to a system for increasing the area over which a satisfactory audio illusion is created and maintained, relative to prior art audio reproduction systems.
  • the method may employ a multi-way loudspeaker pair with drivers operating over diverse frequency ranges arrayed generally in a horizontal dimension (for a normally-oriented head of a listener) and with higher-frequency drivers generally closer together and displaced more towards the center of the listening space than lower-frequency drivers, and specially-adapted signal processing components for audio imaging to create or maintain desirable audio imaging.
  • stereophony or, more commonly and colloquially, “stereo”
  • stereophony includes a number of methods of recording sounds and another number of methods for playing those recorded signals back to a listener or listeners. While it has always been an accepted idea that a listener should be "transported” to another acoustical space, such as the acoustic space occupied by an audience member at a live concert or a more synthetic, more conceptual, space for many modern popular recordings in which there was no actual performance in front of a live audience, the methods used for this "transporting" have largely failed in that goal .
  • 3D audio In keeping with current usage, we will use the current term, 3D audio, to refer to the latter-day systems. These systems typically employ some kind of circuitry or algorithm which compensates for the fact that sound emanating from each of two loudspeakers impinges on both ears of a listener, so that, for example, sound radiating from a left-placed loudspeaker of a pair of loudspeakers travels to the left ear of a listener, but also travels to the right ear of a listener, this latter sound being called crosstalk.
  • each loudspeaker to each ear can be anticipated by designing the circuitry or algorithm, from knowledge of so-called head-related transfer functions (HRTFs), so that when the circuit or algorithm, taken together with at least two loudspeakers, all as a unit, can separately and distinctly control the sounds at the ears of one or more listeners. It is also possible to correct for frequency response aberrations caused by the diffraction of the listener's head so that a natural timbre is perceived by the listener.
  • HRTFs head-related transfer functions
  • any crosstalk canceller with any of the several described modifications or other modifications may be used either explicitly or implicitly as the imaging component of the invention.
  • One application of crosstalk cancellation is in playing back recordings made with an acoustical mannequin, a dummy head with microphones placed in its ear canals or thereabouts . Such a recording-playback system results in the most realistic impression of being transported to another space .
  • crosstalk cancellers are as part of an imaging circuit or algorithm, a so-called speaker-spreader or layout reformatter such as described by Schroeder and Atal , and Cooper and Bauck.
  • the listener can receive the impression that, for example, a pair of loudspeakers which is placed on the sides of a television receiver cabinet, much too close for perceiving any readily noticeable amount of stage width, appear to be farther apart, with well-defined sounds apparently emanating from points in space where there are no actual loudspeakers, a "virtual loudspeaker" impression.
  • the input signals it is most common for the input signals to be any kind of ordinary stereo; the input signals may also be provided by a home theater or multichannel television audio decoder, providing five or more channels of audio signals.
  • Still another application of the principle of crosstalk cancellation is in the creation of interactively-controlled sound sources (and their reflections in an acoustic environment, if desired) such as would exist in computer-based or game-console-based games, when the sounds for those games are presented to the player or players over loudspeakers .
  • a crosstalk canceller is a basic component of controlling signals at the ears of a listener, usable with either binaurally recorded programs or with any kind of traditional stereo programs, for the general enhancement thereof.
  • Playback systems which do not effectively use a crosstalk canceller are also sometimes known as 3D. Such systems can create the impression that sound is arriving from points in space where there are no actual loudspeakers, but rather than provide the impression that there are virtual loudspeakers or other spatially discrete or distinct sources, the impression is that of a wall of sound with little or no impression of spatially discrete sources. To the extent that these systems benefit from placing loudspeakers close together (as described below) , they may also benefit from the invention. And of course, enhancement of these "nondiscrete" systems is possible by the use of the virtual loudspeaker concept.
  • sweet spot wherever the favored region is, it is commonly called the "sweet spot, " and we will use that terminology here, even though “spot” may tend to imply “point” rather than “region.”
  • the sweet spot is restricted in its extent, frequently being so small that only one person can enjoy the best spatial impression at one time, whether for traditional or 3D stereo; the sweet spot size is sometimes so small that even a single listener may feel constrained as to where he or she should hold his or her head to fully enjoy the sweet spot.
  • the sweet spot is an elongated region, really rather prolate ellipsoidal in shape, allowing listeners to move in and out along the bisecting line, or up and down while remaining mostly in the bisecting plane, but being very unforgiving with respect to listener movement to the left and right, over wide variations in a standard two-loudspeaker setup. This is the most unfortunate direction in which to have a small extent of the sweet spot, since it is most commonly desired that multiple listeners be seated abreast of one another and not lined up nose-to-nape.
  • the signals at the listener's ears are formed by the interference ( summation) of acoustic waves emanating from the loudspeakers.
  • the field can be controlled precisely (assuming the absence of resonant structures) at only two points. Presumably, those points are to be at the listener's ears.
  • the ear signals are a result of a so-called 3D system or any other technique, if the listener moves his or her head so that the ears are no longer at the designated positions, image distortion will appear, caused by unintended ear signals created by unanticipated interference.
  • the primary causes of the changing interference are differing times-of-arrival due to differing loudspeaker-to-listener distances, followed in importance by amplitude variations of the impinging waves due to the same varying distances (aggravated by the listener sitting close to the loudspeakers), and reflections from any uncompensated reflections (improved by the listener sitting close to the loudspeakers) .
  • the perceived image distortion due to this effect is not, strictly speaking, a shift, but is accompanied by an increase in the spatial extent of the image, or, more oddly, a kind of ambiguity or uncertainty as to the actual location of the image.
  • One prior art method attempts to reduce the shifting of phantom images by the use of specially designed loudspeakers.
  • researchers investigating the precedence effect found that the shift of a previously centered phantom image could be partially compensated by increasing the level of the later-arriving sound, that is, by increasing the signal gain of the more distant loudspeaker of the pair.
  • Another prior art technique introduced by Cooper and Bauck, used a method (which is independent of the present invention) of alleviating the perceived sweet spot problem in 3D systems by modifying the responses of the acoustically-specified imaging filters at the higher frequencies, effectively allowing gradual transition to "default" imaging of the affected frequencies at the loudspeakers.
  • Listeners seem to prefer having the higher frequencies remain mostly stationary with head movements than to have them flitting around or be otherwise poorly imaged.
  • the sweet spot can in fact be enlarged by modifying the filters down to lower frequencies, but at the expense of more and more of the higher frequencies falling into the loudspeakers, a trade-off in sweet spot size for "sweetness.” It is an object of the invention that it may be combined with such prior art methods .
  • a simple plot of time-of-arrival differences is shown in FIG. 1, for a single point in space.
  • the hyperbolic curves represent contours of equal time-of-arrival differences, in milliseconds.
  • the horizontal and vertical axes are positions of the point in space, in meters.
  • the small, heavy circles represent the locations of the two loudspeakers, modeled as point sources.
  • A is calculated for loudspeakers at a distance of 1.5 meters, while B is calculated for a loudspeaker distance of 0.5 meters.
  • the loudspeaker spacing and the line between loudspeakers will be referred to as the baseline distance, or simply the baseline.
  • the baseline distance or simply the baseline.
  • a short-baseline array may be dictated by other needs, such as the need to attach loudspeakers on the sides of a television or computer video monitor, or the practical difficulty of locating the several loudspeakers common in current home theaters in their optimum locations. It is nearly universal practice in loudspeaker design to configure the tweeters and woofers of a two-way loudspeaker, or more generally the various transducing drive units (acoustical emitters) covering different frequency bands in a multiway loudspeaker, in a primarily vertical direction.
  • a midrange driver may be located beside a tweeter, perhaps with one or both of them comprising a "line source" or ribbon-style driver, such side-by-side placement is usually accepted as a compromise in the pursuit of other design goals, and it is usually desired that those drivers should be as close together as possible, horizontally, to maintain signal integrity at the listeners' ears.
  • Electromagnetic versions of such arrays are also used from time to time in communications and radar antennas.
  • the intent is to control, at least partly, the radiation pattern at various frequencies, usually with the intent that it maintain a constant shape, or beamwidth, at all frequencies of the intended range of operation.
  • Such a goal can be attained, at least partially, by creating an array which is effectively the same length at all frequencies, as measured in number of wavelengths at each frequency. The normal procedure for doing this is to progressively low pass filter the feed signals to the elements of the array more severely for elements lying more towards the ends of the array.
  • a closely related scenario is that of a binaural recording being played over a crosstalk canceller.
  • the low-frequency problem at first appears to be even worse, since the filter specification is for even more bass signal for a virtual source towards the listener's left, as taught most clearly by Cooper and Bauck in their explanation of sum-and-difference style of signal processing.
  • the bass response of the left-minus-right (L - R) component that which is predominant in the placement of the left-oriented image, at first inspection seems to be such as to make the whole enterprise nearly impractical, showing a first-order increasing slope (20 dB per decade of frequency) with decreasing frequency, and with the onset of the slope occurring at a higher frequency with more closely-spaced loudspeakers.
  • L - R left-minus-right
  • the L - R signal is small, so the filtered signal might still be of a reasonable size, assuming that the loudspeakers are not too close together.
  • the only practical problem is maintaining a good signal to noise ratio, but this is generally not a problem with either analog or digital implementations.
  • the net result is that the extent of the problem is essentially the same as creating a virtual source as described in the preceding paragraph. More severe scenarios are easily imagined. It is quite easy to conceive or create a stereo signal which does not correspond to any natural sound image and which will wreak havoc when played through, for example a loudspeaker-spreader or other layout reformatter or crosstalk canceller, all examples of 3D audio systems.
  • a bass guitar in one originating channel of a conventional stereo formatted signal, with silence in the other channel, when played over a crosstalk canceller is highly unnatural; the playback system attempts to place the sound of a bass guitar in one ear of the listener and silence in the other ear, an extremely demanding task at any reasonable playback volume .
  • an audio reproduction system including means for providing any number of audio inputs, means for providing audio imaging using a crosstalk canceller, and a pair of two-way loudspeaker systems, each arrayed with woofer and tweeter substantially horizontally for normally-oriented heads of one or more listeners, such loudspeaker systems comprising frequency-selective crossover circuits to separate and route signals into a left woofer and tweeter pair and a right woofer and tweeter pair, the woofer and tweeter of each pair arranged so that the left and right tweeters are closer together than the left and right woofers, so that time-of-arrival differences from the tweeters vary less with off-center listeners than do time-of-arrival differences from the woofers, for similarly off-center listeners.
  • FIG. 1A is a plot of equal time-of-arrival contours for a simple model of a prior art loudspeaker array.
  • FIG. IB is a plot of equal time-of-arrival contours for a simple model of another prior art loudspeaker array .
  • FIG. 2 is a generalized block diagram of a sound reproduction system under an illustrated embodiment of the invention.
  • FIG. 3A is a block diagram of an illustrated example of the imaging circuit component of an embodiment of the invention, shown in support of an analysis of the invention.
  • FIG. 3B is a block diagram of another illustrated example of the imaging circuit component of FIG. 2, shown in support of an analysis of the invention.
  • FIG. 4 is a plan view layout diagram showing examples of transfer functions of the system of FIG. 2 from a loudspeaker to a listener.
  • FIG. 5A is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3B, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 20° relative to a listener.
  • FIG. 5B is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3B, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 20° relative to a listener .
  • FIG. 5C is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3A, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 20° relative to a listener.
  • FIG. 5D is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3A, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 20° relative to a listener.
  • FIG. 6A is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3B, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 3° relative to a listener.
  • FIG. 6B is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3B, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 3° relative to a listener .
  • FIG. 6C is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3A, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 3° relative to a listener.
  • FIG. 6D is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3A, for a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 3° relative to a listener .
  • FIG. 7A is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3B, for an embodiment of the invention, a loudspeaker array comprising woofers at ⁇ 20° and tweeters at ⁇ 3°, both relative to a listener.
  • FIG. 7B is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3B, for an embodiment of the invention, a loudspeaker array comprising woofers at ⁇ 20° and tweeters at ⁇ 3°, both relative to a listener.
  • FIG. 7C is a plot of the magnitude of the transfer function of an imaging filter of the imaging component of FIG. 3A, for an embodiment of the invention, a loudspeaker array comprising woofers at ⁇ 20° and tweeters at ⁇ 3°, both relative to a listener.
  • FIG. 7D is a plot of the magnitude of the transfer function of another imaging filter of the imaging component of FIG. 3A, an embodiment of the invention, a loudspeaker array comprising woofers at ⁇ 20° and tweeters at ⁇ 3°, both relative to a listener.
  • FIG. 8 is a plot of an error measure of an analysis of a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 20°, relative to a listener, plotted versus listener displacement left and right, and forward and backward, of an optimum seating position.
  • FIG. 9 is a plot of an error measure of an analysis of a prior art loudspeaker array comprising full-range loudspeakers at ⁇ 3°, relative to a listener, plotted versus listener displacement left and right, and forward and backward, of an optimum seating position.
  • FIG. 10 is a plot of an error measure of an analysis of an embodiment of the invention, a loudspeaker array comprising woofers at ⁇ 20° and tweeters at ⁇ 3°, both relative to a listener, plotted versus listener displacement left and right, and forward and backward, of an optimum seating position.
  • FIG. 11 is a television monitor or computer video monitor, according to the invention.
  • FIG. 12 is a wide-format television receiver console, with a three-way loudspeaker array configured according to the invention for vertical dispersion control from the tweeters .
  • FIG. 2 is a generalized block diagram of a specific embodiment of an audio reproduction system 10 according to an illustrated embodiment of the invention.
  • the audio system 10 provides means 20 for coupling one or more audio signals into audio processing circuitry (e.g., computer algorithm) 30. Processed audio signals are then coupled into loudspeaker frequency selective crossover networks 40, including a separate crossover network 42 for the left loudspeaker and a separate crossover network 46 for the right loudspeaker.
  • the left crossover 42 may be comprised of a low pass filter 43 to separate and route low frequency signals to left woofer 53, and a high pass filter 45 to separate and route high frequency signals to left tweeter 55.
  • right crossover 46 may be comprised of a low pass filter 47 to separate and route low frequency signals to right woofer 57, and a high pass filter 49 to separate and route high frequency signals to right tweeter 59.
  • the collection of left loudspeaker 52 and right loudspeaker 56 are referred to as the loudspeaker array 50.
  • two-way left and right loudspeaker systems are described, being the simplest embodiment of the invention, but it will be understood that three-way, or generally, multiway, loudspeakers may be accommodated, and the loudspeaker systems may be arrayed in other ways and in other numbers than the usual symmetric left-right pair, according to the invention.
  • Left loudspeaker 52 is comprised of a left woofer 53 and a left tweeter 55
  • the right loudspeaker 56 is comprised of a right woofer 57 and a right tweeter 59.
  • the acoustically radiating elements, woofers 53 and 57 and tweeters 55 and 59, are arranged into a substantially horizontal array, for a normally-oriented listener's head. (If a listener's head 60 is not oriented in a normal, upright, position, then the array 50 may be reoriented so as to maintain the same approximate geometrical relationship to the head of the listener, or the imaging circuitry 30 may be adapted accordingly. However, an extremely precise upright alignment of the listener's head 60 is not normally required.
  • the left loudspeaker 52 and the right loudspeaker 56 may alternately or additionally comprise a so-called Walsh type driver, a roughly megaphone-shaped truncated cone from which the higher frequencies radiate preferentially from the larger-diameter regions; however, according to the invention, instead of the cones being oriented vertically with the small ends on top and the large ends on the bottom as in normal usage, they are instead oriented with the small end closer to the geometric center line and the large ends being relatively farther away from the centerline.
  • the tweeters 55 and 59 are to be substantially closer to the median line connecting the center of the head of the listener 60 and the midpoint of the loudspeaker array baseline than are the woofers 53 and 57.
  • the positions of the left tweeter 55 and the right tweeter 59 are interchanged, but not their electrical connections, so that, for example, as the listener moves to the right, off of the center line, he or she moves more directly in line with the left-channel tweeter, thereby providing a partial and automatic compensation of time-of-arrival error by amplitude adjustment means, according to the teachings of the precedence effect, and also providing additional image stability by geometrical means.
  • the imaging circuitry or algorithm 30 is adapted to account for the spatial layout of the various acoustical radiating elements.
  • FIG. 2 The operation of the embodiment of FIG. 2 will now be described. Assume as an example that a virtual image or virtual loudspeaker is to placed at 90°.
  • the tweeters 55, 59 are close together; with their high pass crossovers 45, 49, they receive little low frequency signal energy and thus are not subject to the large-excursion signals that would otherwise be required of loudspeakers at that close spacing operating in the bass region.
  • High frequency characteristics of head-related transfer functions from the tweeter angles are generally such as to provide enough transfer function differences between a particular tweeter and both ears (or both tweeters and one ear) as to provide an acceptable solution to the required equations.
  • the close tweeters provide an enlarged sweet spot.
  • the woofers spaced farther apart than the tweeters, receive little high frequency energy due to their low pass crossover filters. Thus, they do not impose the small sweet spot at high frequencies that they would if they received high frequency signals. On the other hand, being spaced farther apart than the tweeters, they do not have the large signal excursion requirements that they would if placed closer, say at the tweeter positions.
  • the 3D imaging system 30 is designed to account for the different spacings of the woofers and tweeters, and, just as importantly, to account for their crossover filters.
  • a crosstalk canceller the part of the 3D imaging system that needs to be designed specifically for the loudspeaker array-crossover combination is a crosstalk canceller, whether it appears as a separate component or sequence of software instructions, or whether is combined explicitly or implicitly with other 3D imaging components or software such as HRTF simulations in a complete virtual imaging system.
  • the crossover networks are designed so that, for example, in a two-way system, the woofer and tweeter operate over substantially different passbands.
  • a typical configuration is to operate a woofer up to around 2.5 KHz, where its operation is limited by a low pass filter at frequencies above 2.5 KHz, and to operate a tweeter at frequencies from 2.5 KHz upward, with its operation limited at frequencies below 2.5 KHz by a high pass filter.
  • the crossover filters do not have abrupt transition bands (it is physically impossible), there tends to be a small range of frequencies near the crossover frequency which are radiated by both woofer arid tweeter, even though the woofer and tweeter operate over substantially different passbands.
  • a typical example of this concept has two lower-frequency drivers, possibly of identical designs (diameter, electroacoustic parameters, etc.), but with one of them limited by filters to a rather narrower band of frequencies.
  • one driver commonly referred to as a woofer
  • the other driver perhaps referred to as a "mid-bass" driver
  • a crossover passes the higher frequencies to a tweeter.
  • Such a design allows for increased signal-handling capacity for the lowest frequencies where it is needed most, but does not impose undesirable directional effects at emitted frequencies from 100 Hz to 2.5 KHz caused by the dual drivers operating over somewhat shorter wavelengths where lobing could occur.
  • loudspeakers which have drivers operating over substantially overlapping frequency ranges, they are vertically-arrayed, do not use the overlapping passbands to affect desirable imaging effects, and do not operate with specially-designed imaging circuitry or algorithms.
  • horizontally-arrayed drivers according to the invention may have substantially overlapping passbands and such drivers are to be accompanied by suitably modified imaging circuits, as taught in the following discussion describing a simulation of an embodiment of the invention.
  • a simulation of a specific illustrated embodiment of FIG. 2 will help to described the invention and to clarify its teachings.
  • a spherical head model is used (i.e., the head 60 is assumed to be a rigid sphere 0.18 meters in diameter with "ears" 62 and 63 designated as points on a horizontal great circle displaced ⁇ 100° from the "nose" 61 which is defined to be the point at 0°) .
  • the sphere is assumed to be in a plane wave field when a single source is present. Positive angles are measured as counterclockwise rotations from the nose 61.
  • This model is used because it is convenient to acquire (compute) HRTFs from any angle and is more than adequate to describe and define the invention and its teachings .
  • the loudspeaker-listener layout example which is examined here is typical of that experienced by a personal computer user. In assumed free-field conditions, the relevant parameters are:
  • the loudspeaker array 50 has variously been described as being in a plane with the video monitor or on a horizontal line, it is to be understood that these geometries are required only as specifics to this simulation or as a particular embodiment, and in general may, for example, be arranged along an arc, or, as necessary, electrical delays may be added to the signal processing or in line with the crossovers so as to make the effective acoustic positions be along an arc, or any other geometric figure, as required. Alternatively, the designer of the crossover, if he or she does not place compensating delays in line with the various drivers, will find that the solution for the appropriate crosstalk canceller will dictate such delays. It is an object of the invention that various geometries can be accommodated, with the imaging circuitry 30 adapted accordingly.
  • the methodology of the simulation is, for each of three layouts described below, to first compute the imaging filters necessary to place an image at a near-worst case (for low-frequency signal capacity requirements) location of 90° for a centered listener (nominal position) .
  • the listener's head may then be moved over a grid of points around the nominal, or designed-for , head position, and an error value may be computed and plotted at each such location when using the filters designed for the nominal position.
  • the frequency response magnitudes of the required imaging filters may be plotted.
  • 3A may be used to implement the imaging circuit or algorithm 30 of FIG. 2, as long as there are no more than two inputs 20, as may the shuffler 80 of FIG. 3B, as is known in the art; other topologies are also possible, possibly employing additional lattices or shufflers.
  • the lattice 70 comprises the four filters of two unique transfer functions (assuming geometrical layout symmetry, as in the simulation) , S' and A' .
  • the shuffler 80 requires only two filters with transfer functions ⁇ and ⁇ .
  • the lattice requires summing junctions 75 and 76.
  • the shuffler requires summing junctions 81, 82, 85, 86, with signal sign inversions at two of the inputs of summing junctions 82 and 86, as indicated in FIG. 3B.
  • FIG. 4 serves to establish the naming convention for acoustic transfer functions, generically, S and A. Subscript indicates a transfer function associated with an "actual” loudspeaker, and subscript ⁇ indicates a transfer function of a "phantom, " in this case the desired image at 90°. With this notation, the imaging filter transfer functions when using symmetrically-placed full-range loudspeakers are
  • the grid over which the spherical-model head is moved for computing an error measure is a square of 0.322 meters per side centered on an x-y coordinate system which has as its origin the center of the nominally-placed spherical head.
  • frequency points f n , n ⁇ 1, 2, . . ., 50) evenly spaced between 20 Hz and 8000 Hz, frequency domain signals for the left ear E L (f n , x, y) and right ear E R (f n , x, y) , and nominal-position ear signals E L (f n , 0, 0) and E R (f n , 0, 0), an error measure
  • the choice of 8000 Hz as the highest frequency to include in the error is a compromise between including most of the significant audio range for localization and allowing too many sphere-model idiosyncracies to contribute. This is obviously a signal-based error function--its precise connection to perceived error is unknown.
  • the x-y grid spacing was 1/4 of the shortest wavelength included in the above sum, and there were 31 grid points in each direction, resulting in the square of 0.322 m. (A grid spacing of V- the shortest wavelength would be enough for adequate spatial sampling, but the finer grid gives a nicer surface plot . )
  • the ⁇ , ⁇ , S', and A' are shown in FIG. 5.
  • the ⁇ filter due to the factor of V. in its definition, levels off at low frequencies at -6 dB, while the ⁇ response is some 9.3 dB higher, at 3.3 dB, a quite tolerable level difference for most applications.
  • the responses corresponding to full-range loudspeakers at ⁇ 3° is shown in FIG. 6. Again, the ⁇ response at low frequencies is at -6 dB, but the ⁇ response has increased drastically to 25.6 dB above the ⁇ level .
  • the definition of the acoustic transfer functions need to be modified to account for the different locations of the drivers, as well as for the presence of their respective crossover filters.
  • the generic transfer functions S and A of FIG. 4 be specialized for the woofer and tweeter positions as S w , A w , S t , and A t .
  • the new, composite, "actual loudspeaker" acoustic transfer functions can be seen to become
  • the crossover filters are simply modeled as first-order low pass responses for C w 43 , 47 and first-order high pass responses for C t 45, 49, both having magnitude responses which are -3 dB from their asymptotic values at 1 KHz.
  • the main reason for picking 1 KHz for the crossover frequency is that the magnitudes of ⁇ , S', and A' in FIG. 6 become large at around that frequency. Also, practicalities such as driver characteristics played little role in crossover selection.
  • FIG. 7 The low frequency parts of these curves indeed resemble the low frequency parts of the curves for ⁇ 20° full-range loudspeakers in FIG. 5. Also, the high-frequency parts of the responses of FIG. 7 resemble the high-frequency parts of the responses in FIG. 6 for the very closely spaced full-range loudspeakers at ⁇ 3°.
  • FIG. 8 shows the error which results from full-range loudspeakers at ⁇ 20°
  • FIG. 9 shows the error from full-range loudspeakers at ⁇ 3°
  • the implications of these figures are clear.
  • ⁇ 20° full-range array has a small sweet spot which is longer in the y-direction than it is wide in the x- direction, a phenomenon readily noticed by listeners of both 3D and more standard stereo systems.
  • the sweet spot for ⁇ 3° full-range loudspeakers is much wider by comparison. It is lower than the error plot for ⁇ 20° loudspeakers at most points, with the exception at large positive values of y and Ixl.
  • the invention also has the advantage of having nearly zero incremental cost to implement, over conventional loudspeaker array-imaging circuit combinations, requiring only a new layout for the various drivers of the loudspeakers and a properly adapted imaging circuit. Neither of these changes comprises a significant recurring manufacturing cost; indeed, some expense may be saved if lower-power amplifiers or less expensive woofers can be used.
  • the applications for which the modified short-baseline array appears to be well-suited include that shown in FIG. 11, a computer or television video monitor which contains the modified array with woofers 103, 107 and tweeters 105, 109 and the associated imaging circuits (not displayed in the figure) such as required for virtual home theaters and game play.
  • FIG. 11 a computer or television video monitor which contains the modified array with woofers 103, 107 and tweeters 105, 109 and the associated imaging circuits (not displayed in the figure) such as required for virtual home theaters and game play.
  • FIG. 12 shows a three-way array (woofers 111, 112, midranges 113, 114, and tweeters 115, 116, 117, 118) as part of a television receiver. Also indicated in this figure is a variation on the tweeter configuration to control vertical dispersion in order to reduce reflections, a configuration sometimes used in home theater equipment. Of course, other vertical arraying methods may be used as well. FIGs .
  • 11 and 12 indicate that the placement of the various acoustical emitters may deviate from a straight line as seen by the listener; although not normally an optimal arrangement, since it imposes some path-length variations of its own as the listener adjusts his or her seating height, some amount of such variation is acceptable and may be an acceptable tradeoff in light of other design goals such as cabinet design or aesthetics.
  • the reason that some such variation is acceptable is that it is known that path length differences caused by vertical displacement of drivers (as well as vertical) reflections from the floor, ceiling or furniture) have a much smaller effect on horizontal imaging than do horizontal displacements (or reflections) of similar magnitudes.

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  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
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Abstract

L'invention concerne un procédé permettant de créer un point idéal d'écoute amplifié afin d'effectuer une reproduction sonore avec de multiples haut-parleurs. Ce procédé consiste à mettre en application une pluralité de circuits d'attaque (52, 56) audio déplacés généralement dans une dimension horizontale pour la tête orientée verticalement d'un auditeur (60), ces circuits d'attaque opérant sur une pluralité de bandes passantes (42, 46) différentes. Des circuits d'attaque de fréquence supérieure (55, 59) sont situés plus à proximité les uns des autres et déplacés davantage en direction d'une ligne médiane de l'espace d'écoute que les circuits d'attaque de fréquence inférieure (53, 57), ce qui provoque une modification plus limitée des signaux acoustiques pour des auditeurs (60) assis à distance de la position conçue pour l'écoute, mais ne provoque pas d'augmentation des besoins en capacité de signal basse fréquence pour les images fantômes généralement à l'extérieur de l'enceinte (50). On met en application un traitement de signaux spécial justifiant l'implantation des différents circuits d'attaque et de leurs réseaux (40) de croisement associés, afin de créer des images audio souhaitées.
PCT/US1998/010865 1997-05-28 1998-05-28 Enceinte acoustique permettant d'amplifier le point ideal WO1998054926A1 (fr)

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EP98924945A EP0988773A4 (fr) 1997-05-28 1998-05-28 Enceinte acoustique permettant d'amplifier le point ideal
AU76999/98A AU7699998A (en) 1997-05-28 1998-05-28 Loudspeaker array for enlarged sweet spot
JP50089599A JP2002500844A (ja) 1997-05-28 1998-05-28 拡大スイートスポット用ラウドスピーカアレイ
CA002290518A CA2290518C (fr) 1997-05-28 1998-05-28 Enceinte acoustique permettant d'amplifier le point ideal

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US4782497P 1997-05-28 1997-05-28
US60/047,824 1997-05-28

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EP1104221A2 (fr) * 1999-11-25 2001-05-30 Harman Audio Electronic Systems GmbH Dispositif de sonorisation
WO2002001916A2 (fr) * 2000-06-24 2002-01-03 Adaptive Audio Limited Systemes de reproduction sonore
WO2003030589A2 (fr) * 2001-09-28 2003-04-10 Adaptive Audio Limited Systemes de reproduction de son
US8345883B2 (en) 2003-08-08 2013-01-01 Yamaha Corporation Audio playback method and apparatus using line array speaker unit
CN111601219A (zh) * 2020-06-01 2020-08-28 峰米(北京)科技有限公司 一种自适应调整声场平衡的方法和设备
US11528554B2 (en) 2016-03-24 2022-12-13 Dolby Laboratories Licensing Corporation Near-field rendering of immersive audio content in portable computers and devices

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JP2007142856A (ja) * 2005-11-18 2007-06-07 Sharp Corp テレビジョン受信装置
JP5003003B2 (ja) * 2006-04-10 2012-08-15 パナソニック株式会社 スピーカ装置
KR100788702B1 (ko) 2006-11-01 2007-12-26 삼성전자주식회사 빔 형성 스피커 배열을 이용한 프론트 서라운드 시스템 및서라운드 재생 방법
JP4655098B2 (ja) * 2008-03-05 2011-03-23 ヤマハ株式会社 音声信号出力装置、音声信号出力方法およびプログラム
JP2010263295A (ja) * 2009-04-30 2010-11-18 Heiankaku:Kk スピーカ装置及び音の再生方法

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WO2003030589A2 (fr) * 2001-09-28 2003-04-10 Adaptive Audio Limited Systemes de reproduction de son
US8345883B2 (en) 2003-08-08 2013-01-01 Yamaha Corporation Audio playback method and apparatus using line array speaker unit
US11528554B2 (en) 2016-03-24 2022-12-13 Dolby Laboratories Licensing Corporation Near-field rendering of immersive audio content in portable computers and devices
CN111601219A (zh) * 2020-06-01 2020-08-28 峰米(北京)科技有限公司 一种自适应调整声场平衡的方法和设备

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JP2002500844A (ja) 2002-01-08
CA2290518C (fr) 2007-07-03
EP0988773A1 (fr) 2000-03-29
CA2290518A1 (fr) 1998-12-03
AU7699998A (en) 1998-12-30
EP0988773A4 (fr) 2006-01-11

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