EP1042866A1 - Procede et systeme de haut-parleur a decalage de phase de 90 degres - Google Patents

Procede et systeme de haut-parleur a decalage de phase de 90 degres

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Publication number
EP1042866A1
EP1042866A1 EP98966031A EP98966031A EP1042866A1 EP 1042866 A1 EP1042866 A1 EP 1042866A1 EP 98966031 A EP98966031 A EP 98966031A EP 98966031 A EP98966031 A EP 98966031A EP 1042866 A1 EP1042866 A1 EP 1042866A1
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EP
European Patent Office
Prior art keywords
phase
frequencies
signals
audio
low frequency
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Legal status (The legal status 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 status listed.)
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EP98966031A
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German (de)
English (en)
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EP1042866A4 (fr
Inventor
David Griesinger
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LEXICON
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LEXICON
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Publication of EP1042866A1 publication Critical patent/EP1042866A1/fr
Publication of EP1042866A4 publication Critical patent/EP1042866A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S1/00—Two-channel systems
    • H04S1/002—Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
    • H04S7/30—Control circuits for electronic adaptation of the sound field
    • H04S7/307—Frequency adjustment, e.g. tone control

Definitions

  • This application is based upon the U.S. Provisional Patent Application No. 60/068,716, entitled “Method and System for Driving Speakers With a 90 Degree Phase Shift,” filed December 23, 1997.
  • Field of the Invention This invention relates to a method and system of driving a pair of stereo loudspeakers, or a pair of loudspeakers that are part of a multiple loudspeaker array, with a non-zero optimal phase relationship in the low frequency region, approximating 90 degrees in the region where localization becomes impossible.
  • this method and system allows room modes to be excited independently by both loudspeakers thereby producing a full bass response which may be further modified by a shelf filter to equalize the sound pressure level in the bass frequency range.
  • Stereophonic pairs of loudspeakers are used for sound reproduction in a listening room, and are often called upon to reproduce sound in the low frequency region where localization becomes impossible.
  • Such loudspeakers are commonly used in pairs or multiples, and frequently are in combination with other loudspeakers intended to reproduce the higher audio frequencies.
  • the upper frequency range is reproduced by a pair of satellite loudspeakers with a limited response below about 200Hz, the low frequency signals being combined into a single monophonic subwoofer, often placed along the center line of the room.
  • this invention has no application.
  • the present invention as described in detail below, can provide better performance than the conventional usage wherein the loudspeakers are driven in phase at low frequencies.
  • the performance of full-range speakers or dual subwoofers can be inferior to that of the satellite-subwoofer system.
  • the satellite-subwoofer system will give identical results when the subwoofer is located along the center line of the room, but more bass (and a more spacious sound) can be obtained if the subwoofer is placed off axis and near a corner of the room. With two subwoofers driven in phase, the best placement is to put both together in the same corner of the room.
  • the present invention is concerned with a method and system for driving a pair of loudspeakers in an appropriate phase relationship in the low frequency region, by means of a phase shifting and equalizing circuit.
  • One embodiment includes a pair of all-pass phase difference networks optimally producing a quadrature relationship in the low frequency region below about 200Hz, while maintaining an in- phase relationship at higher frequencies, and additionally includes equalizing networks to introduce a small bass boost to compensate for the ⁇ 3dB reduction in bass energy along the center line of the room that the quadrature circuit often produces.
  • an electronic signal processing system for driving first and second power amplifiers and first and second loudspeaker systems in a listening room.
  • First and second input terminals are adapted to receive a stereophonic pair of audio input signals.
  • Corresponding first and second output terminals produce a stereophonic pair of output signals for driving the first and second power amplifiers and the first and second loudspeaker systems.
  • Circuitry is provided for varying the phase relationship between said first and second output signals such that their phase difference tends towards zero at high audio frequencies and increases to approximately quadrature or 90 degrees phase difference at low frequencies, the gain of the circuitry between each said input terminal and said corresponding output terminal being approximately constant at all audio frequencies, thereby providing increased apparent spaciousness of low frequency sounds reproduced by said loudspeakers in said listening room.
  • the signal processing system further comprises a circuit between each input terminal and said corresponding output terminal wherein there is an equal bass boost applied to both said first and second output signals of approximately 3dB for those frequencies where the phase difference is approximately 90 degrees thereby maintaining approximately constant sound pressure at all frequencies along the lateral center line from front to back of said listening room.
  • phase difference of approximately 90 degrees at low frequencies is obtained without active electronics, by combining differences in the loudspeakers themselves, such as differences in enclosure volume, port area, cone mass, surround stiffness, and crossover components.
  • percussive sounds include higher frequency components that are easier to localize.
  • the ability to localize percussive sounds increases as the frequency rises.
  • the addition of a 90 degree phase shift as provided by this invention sometimes alters the localization of all sounds, and in particular percussive sounds.
  • the 90 degree phase shift results in a time delay in the lagging phase channel, which tends to produce localization shifting towards the leading phase channel.
  • the shift in localization will determine the highest frequency at which the 90 degree phase shift should be applied.
  • the leading phase shift should be applied to the right channel to minimize the perception of this effect.
  • an additional aspect of this invention is additional circuitry that detects rapidly rising (percussive) sound, and temporarily reduces the phase shift.
  • Another advantage of the invention is that it reduces unnatural in-head localization of certain low frequency sounds.
  • a further advantage of the invention is that it enhances the bass response perceived by the listener, and provides an optimal phase relationship between the loudspeakers in the low bass region.
  • An additional advantage of the invention is that it enhances the spaciousness perceived by the listener for low frequency sounds, while maintaining the sound pressure level the same as for two subwoofers in the same corner of the room.
  • FIG. 1 shows a representation of a typical stereophonic loudspeaker system in a listening room
  • FIG. 2 illustrates the perception of low frequency spaciousness caused after a direct sound decays in a large room, due to background spatial impression (BSI) created by reverberant sounds;
  • BSI background spatial impression
  • FIG. 3 show the effect of interfering delayed lateral sound reflections in a reverberant room causing localization fluctuations, as a function of angle from the front, which results in an impression of spaciousness;
  • FIG. 4 illustrates the variation in interaural time differences (ITDs) from interference between an asymmetric lateral mode and a medial mode with a 90 degree phase shift
  • FIG. 5 shows the absolute ITD and the net ITD for a typical listening room with a wall reflectivity of 0.9 as a function of lateral listener position, using a single loudspeaker;
  • FIG. 6 shows the absolute and net ITDs when the side wall reflectivity is reduced to 0.7, as a function of lateral listener position
  • FIG. 7 shows the absolute and net ITDs in the same room as for FIG. 5 when the front and back wall reflectivity is reduced to 0.6, keeping the side wall reflectivity at 0.9, as a function of lateral listener position;
  • FIG. 8 shows the absolute and net ITDs in a room as a function of its width, with a constant length and for a central listener position
  • FIG. 9 shows the absolute and net ITDs for a room with larger lateral dimensions as a function of room width
  • FIG. 10 shows the absolute and net ITDs in the same size room as in FIG. 5, produced by two spaced loudspeakers, as a function of lateral listener position, when the speakers are driven in phase;
  • FIG. 11 shows the absolute and net ITDs in the same room but with the two speakers driven in opposite polarity, as a function of lateral listener position, showing extreme phasyness
  • FIG. 12 illustrates a method for computing the impulse response of a room for each ear, as a function of listener and speaker positions, wall reflectivities, and image locations;
  • FIG. 13 shows a typical impulse response calculated for the left ear and the right ear
  • FIG. 15 shows a detailed schematic of a preferred embodiment of the present invention.
  • FIG. 16 shows the absolute gain (equal in both channels) and the phase difference between the left and right channel outputs of the circuit of FIG. 15 when the two inputs are driven in common, as a function of frequency.
  • the system and method of the present invention is the result of consideration of various acoustical phenomena which may be described in relation to the listening room and typical audio installation shown in FIG. 1.
  • the listening room 1 of FIG. 1 shows a listener 2 seated in a preferred listening position 3, often on the lateral center line of the room 4.
  • a left speaker 5 and a right speaker 6 are placed symmetrically in relation to the center line 4, so that the lines joining them to the listener 2 make equal angles ⁇ with the center line.
  • the loudspeakers 5 and 6 are full-range loudspeakers, but in some systems, they only reproduce the higher audio frequencies, while the bass frequencies are either combined and fed to a single subwoofer 7 or else are fed separately to two subwoofers 8 and 9 at left and right of the center respectively.
  • the satellite-subwoofer system using a single subwoofer 7 is not the type of system to which this invention can be applied.
  • the subwoofer 7, shown dotted, is here placed on the center line, it may be advantageously placed off-center (and preferably towards the right) as will be shown later.
  • Both subwoofers 8 and 9 in FIG. 1 may alternatively be placed in the same corner of the room.
  • One of the purposes of this invention is to make such a placement disadvantageous.
  • FIG. 2 taken from reference [4], illustrates the phenomenon called background spatial impression, or BSI.
  • Sounds received at the left and right ear canals are detected and separated into multiple foreground streams and a background stream.
  • the foreground streams comprise sound events having a similar timbre, localization, or meaning, such as speech from a particular speaker, or sounds from a specific musical instrument. Sounds which do not have the coherence that identifies a foreground stream are perceived as a single background stream. It is the spatial properties of this background stream which primarily give rise to the perception of spaciousness and envelopment. Where it is not possible to separate a background stream, fluctuations in interaural time and intensity differences due to delayed lateral reflections create an impression of spaciousness.
  • ESI Reflected energy that arrives during a sound event, and within 50ms of the end of the sound event, is perceived as part of the sound event itself.
  • ESI spatial impression
  • ESI does not change as the strength of the source is varied.
  • ESI is usually not fully enveloping.
  • ESI is perceived as strongly occupying the same direction as the source sound.
  • ESI is the spatial impression of small rooms. We are not usually aware of ESI, but one can train oneself to hear it. When you listen to another person talk in a small room you can be very much aware that you are in a small room. However, the sound of the room is perceived as being in the same direction as the speaker. The room impression is bound to the sound of the voice itself. ESI is neither spacious nor enveloping.
  • background spatial impression arises from sound that arrives at least 50ms after the end of the direct sound. If this delayed energy is spatially diffuse (coming from all directions) then the fluctuations in the IID and the ITD are maximum, and a strong sense of envelopment results.
  • BSI is not bound to the direct sound that creates it.
  • BSI is perceived as separate from the direct sound, and as independent of the direct to reverberant ratio.
  • BSI depends strongly on the absolute strength of the source, as well as on the reverberant level and the profile of the decay.
  • To produce BSI it is essential to have a stream of direct sound events.
  • BSI does not occur during the decay of a single sound event (or during the decay at the end of a piece of music.)
  • the decay of a single sound event is itself an event - one can devote one's full perceptive powers to it.
  • BSI can only be heard in the gaps between foreground events, and has distinct properties different from foreground events. For example, if BSI has a pitch, it can have only one pitch.
  • a foreground event such as the decay of a chord, can be heard as a combination of pitches.
  • FIG. 2 shows how the detection process works.
  • the actual end of a sound, A is perceived typically by the listener when the sound has decayed to half power or about -3dB, at B in FIG. 2.
  • the sensitivity of the ear to reflections and reverberances from other directions enveloping the listener, the background sensitivity follows the line C, increasing to a maximum value D.
  • the perception of localization fluctuations which result in ESI and CSI effects is illustrated by the curves in FIG. 3, which were obtained from a computer simulation. Spaciousness in small rooms where there are no long-delayed reflections is mainly due to these ITD and IID fluctuations.
  • the localization fluctuations depend strongly on the angle of a single reflection from the front, as shown in curve A for a frequency of 1000Hz, reaching a maximum at about 45 degrees.
  • the dotted curve B shows the maxima at about 22 degrees and at 90 degrees. At low frequencies, the optimum angle for a single reflection is fully to the side of the listener, at 90 degrees.
  • This angular dependence of the interaural fluctuations is a key to understanding spatial impression in sound reproduction systems at high frequencies.
  • a continuous broadband stereo signal such as applause is played through a standard stereo speaker system outdoors or in an anechoic chamber, and we assume the listener is centered, and the speakers subtend +/-30 degrees, because the sound is continuous we expect that the spatial impression will be that of CSI.
  • CSI at high frequencies is usually fully enveloping c it sounds as if it is coming from all around the listener. However it can be weak if the reflected energy which creates it comes from the medial plane. In this example we are assuming we have very little reflected energy The fluctuations, if present at all, must be generated from the direct sound.
  • the speakers are at the optimum angle for producing interaural fluctuations.
  • the optimum frequencies will be about 1500Hz, which is just in the middle of our hearing system's maximum sensitivity for speech perception.
  • CSI in this band will be very strongly heard.
  • Passing the applause through a variable band pass filter confirms the result.
  • Applause limited to below 500Hz produces no surround from the stereo pair.
  • As the frequency is increased to the 1500Hz band a very strong surround is generated.
  • the surround impression decreases, only to rise again at about 3000Hz.
  • the theory of interaural fluctuations predicts this pattern.
  • a stereo pair can produce a strong sense of surround with no acoustic support from the room, at least at frequencies of about 1000 to 2000Hz.
  • Such a speaker pair is also capable of producing BSI, if the reverberant component of the recording is fully decorrelated in the left and right speakers.
  • the degree of correlation of the reverberation is important. If the reverberation is monaural the sound from the two loudspeakers will not cause the ITD and IID at the listener's ears to vary. No CSI or BSI will be produced regardless of frequency. In a real room there may well be some CSI or BSI, as lateral room reflections will contribute to the production of interaural fluctuations. This contribution from the room will be higher if the listener is not centered.
  • the frequency band for maximum spaciousness from a stereo loudspeaker pair depends on the angle between the loudspeakers. The wider the separation the lower the first spacious frequency, and the higher the perceived spaciousness.
  • the reverberant component of the recording should be reproduced by an array of decorrelated loudspeakers around the listener.
  • Room modes have interesting properties. Of primary interest to us here is that they have constant phase. For example, assume we can drive a room with a sinusoid from a loudspeaker, and tune the frequency to a single mode of the room c say the lowest fundamental length mode. This mode is characterized by a null at the center of the room. With pressure maxima of opposite sign at the two ends, if we measure the phase of the pressure in the room, we will find that the phase is constant (except for a change in sign) throughout the room. The amplitude will vary and the sign changes on opposite sides of the null in the center of the room, but there is no phase shift of any kind as we move the test microphone around.
  • the combination of a medial mode and a lateral mode can produce a very significant, and audible, ITD.
  • the medial mode should have a +/-90 degree phase shift with respect to the lateral mode. Since all room modes have constant phase, it is not obvious how such a phase shift can arise. However, musical sounds at low frequencies are almost never precisely adjusted to the exact center frequencies of the room modes. When the excitation and the room modes are not exactly at the same frequency a phase shift results which is constant throughout the room. This phase shift is close to +/-90 degrees about half the time.
  • FIG. 4 shows the results obtained from a Matlab program which investigates this interference between medial and lateral modes. The maximum ITD for a large space is shown as the broken line A.
  • the medial mode has a 90 degree phase shift relative to an asymmetric lateral mode.
  • the medial amplitude is high, at OdB relative to the lateral mode (solid curve B), the localization fluctuations produced are fairly small.
  • the medial mode is 6dB lower, shown by the dotted curve C, it is possible for the localization fluctuations to exceed the maximum for large rooms.
  • significantly larger fluctuations occur. This can be perceived as Aphasyness.g
  • the maximum shift in ITD results when the medial mode(s) and the lateral mode differ in phase by +/-90 degrees.
  • the maximum shift in ITD results when the medial mode(s) is weaker than the lateral mode.
  • the maximum shift in ITD occurs in a broad region around the null of the lateral mode. It is not confined to exactly the null point.
  • the maximum shift in the ITD can be quite large c larger in fact than the maximum shift of about +/-1 ms that is created by natural hearing in large spaces.
  • asymmetric lateral modes In a lateral standing wave there can be several null points. However, for a listener in the center of the lateral dimension of a room, only asymmetric lateral modes will have a null at the position of the listener. All asymmetric lateral modes will have a null along the center line of the room. Asymmetric lateral modes can be created only by the antiphase component of the loudspeaker signals. Medial modes can be created only by the in-phase component of the loudspeaker signals.
  • % two modes is p, preset to pi/2. User must type in cm, or the
  • % are 1, 0.5, and 0.25.
  • % distance between the ears 17cm, and a base frequency of 62.5Hz
  • the ITD is determined by summing the medial and the lateral waves
  • % is determined by finding the angle where there is a positive
  • a single loudspeaker will excite most asymmetric modes, as well as most medial modes. There is a very good chance that an audible ITD will be produced, and the sound will appear to come from the correct side of the listener. However as can be seen in FIG. 4, if the listener is along the center line, and medial modes are suppressed by use of a dipole loudspeaker or acoustic treatment in the room, it is quite possible that the ITD will be larger than the maximum in natural hearing. The result is an unpleasant sensation of phasyness, even with a monaural source, namely a single loudspeaker.
  • the next group of figures illustrates a method for assessment of the low frequency spaciousness by means of a weighted sum of the ITD multiplied by the pressure, and divided by frequency.
  • Typical listening rooms have dimensions of about 10 to 25 feet, the walls, floor and ceiling being quite reflective at low frequencies, with absorption in the 10% range. This results in multiple reflections with little energy being absorbed, creating standing wave patterns which have pressure peaks and dips in various parts of the room.
  • Low frequency sound propagates from the speakers to the listener through these standing waves. While the pressure at the listener position is augmented by the standing waves, this augmentation is not uniform with frequency, in general having many peaks and dips in the frequency response.
  • FIG. 5 shows the results for a room with wall reflectivity of 0.9.
  • the solid curve A shows the absolute ITD as a function of listener position (at intervals of 1.5 " .)
  • the dotted curve B shows the net ITD for the same locations.
  • the absolute and net ITDs are defined by the following method:
  • Net_itd_sum sum( ITD * pressure / frequency)
  • Absolute_itd Absolute_itd_sum/reference where the measured or computed ITD at each frequency is combined and weighted as indicated.
  • the ITD can be computed from the long FFT of the impulse response at each ear, as will be described below.
  • the absolute and net ITDs are similarly shaped and are high.
  • the reflectivity of the side walls of the same room has been reduced to 0.7, with a dramatic effect on the absolute ITD curve A, which has been reduced substantially.
  • the reflectivity of the front and back walls of the same room has been reduced to 0.6, with side wall reflectivity of 0.9. This results in an increase of both the absolute and net ITDs (A and B respectively.)
  • FIG. 8 shows the ITDs for rooms with different widths, all 15' long.
  • the single speaker is 4' from the center line of the room (see 4 in FIG. 1.)
  • the listener is centered and is 6.9' from the speaker (about in the same position as in FIGs. 5-7.)
  • a large peak in the net ITD curve B coincides with the Agolden ratio @ of 1.6:1, at about 10' width, while the absolute ITD curve A ⁇ eaks at l l.5'-12'.
  • FIG. 9 shows the same length room, but with larger widths from 14' to 20'. There is a peak at 15' corresponding to a square room, but after this, both absolute ITD curve A and net ITD curve B fall off with increasing width.
  • a corollary is that spaciousness at low frequencies is reduced when the speakers are placed on the long wall of the room. If we excite the same room as used in FIG. 7 with two loudspeakers, one in each front corner, with the listener 6' from the front wall, with the signals in phase, it is not possible to excite odd order asymmetric lateral modes, including the lowest frequency lateral mode. Only the even order modes can be excited. When the speakers are driven in antiphase, the odd order modes can be excited, but not the even order modes.
  • FIG. 9 shows the same length room, but with larger widths from 14' to 20'. There is a peak at 15' corresponding to a square room, but after this, both absolute ITD curve A and net ITD curve B fall off with increasing width.
  • a corollary
  • FIG. 10 shows the ITDs for the in-phase case
  • FIG. 11 shows them for the antiphase case.
  • the absolute ITD becomes very high for a listener near the center line of the room, and the result is extreme phasyness, which is uncomfortable for most people.
  • the frequency response is more uneven than when all the room modes are driven, as if by a single loudspeaker. For these reasons, it has been recommended that when two subwoofers are used, they should be placed together in one corner of the room. This is not possible with full-range loudspeakers.
  • FIG. 12 shows a listening room 1, with a listener 2 situated at distances P x from the left wall and P y from the front wall.
  • a single loudspeaker 10 is situated at S x from the left wall and S y from the front wall.
  • the walls are highly reflective, the side wall reflectivity being aw and the front and back walls having reflectivity al, there is a reflection in the left side wall that produces an apparent image 12 of the speaker (shown dotted.) Sounds reach the listener directly from the speaker via path 14 and from the image via path 16.
  • phase difference solid curve A
  • interaural time difference dotted curve B
  • FTL FFT(left impulse response)
  • FTR FFT(right impulse response)
  • phase left arctan(imag(FTL)/real(FTL))
  • phase_right arctan(imag(FTR)/real(FTR))
  • the object of this invention is to enable both loudspeakers in the room to excite all of the room modes.
  • the speakers cannot be driven in phase, as they will then fail to excite the odd lateral room modes, but neither can they be driven in antiphase, which would not allow the even modes to be excited.
  • the speakers are excited in a quadrature or 90 degree phase relationship, the sounds from each loudspeaker are orthogonal in the wave space and each speaker therefore excites all the room modes independently. Only when the symmetry is imperfect can some of the modes be canceled between the speakers, or if the phase difference is not exactly 90 degrees.
  • Constant phase differencing networks are well known in the art, and are usually designed to approximate a quadrature phase difference between the left and right output over a given range of frequencies. For a single decade of frequencies, in this case between 20Hz and 200Hz, the phase difference may be made nearly constant using only one pole in each of a pair of all-pass phase shifters. More complex arrangements can be made, using two or more poles per network. The advantage of additional poles would be to reduce the inevitable phase difference at frequencies outside the band of interest. Ideally, the phase difference should be essentially zero above about 400Hz.
  • the circuit 30 of FIG. 15 includes a phase shifter comprising op- amp UI, resistors R1-R3 and capacitor CI, this being driven from a first input terminal 32.
  • a second phase shifter comprising op-amp U3, resistors R6-R8 and capacitor C3, is driven from the second input terminal 34.
  • the amplitude response is exactly unity gain for all audio frequencies (subject to tolerances of the resistors.)
  • the phase shift becomes 90 degrees at a lower frequency than that in the first channel. Between these two frequencies, and for some little range outside them, the phase shift between the two outputs remains at or close to 90 degrees.
  • circuit of FIG. 15 provides two outputs from the op-amps UI and U3 that are in quadrature phase relationship over a significant range of frequencies.
  • the room modes are all being excited by both loudspeakers, there is a considerable increase in the bass energy in the room.
  • the loudspeakers are normally expected to be used in a phase-coherent relationship and are designed to give a flat bass response in this mode of operation, when their sound pressure levels sum in phase, the use of a quadrature phase between them at low frequencies will reduce the coherent bass output level by 3dB . Therefore, it is necessary to re- equalize the room response by performing a 3dB boost at the lower frequencies, in both channels.
  • the output signal from op-amp UI is passed to the boost stage comprising op-amp U2, resistors R4 and R5, and capacitor C2.
  • C2 has low impedance, and the gain through this stage is unity (OdB). At low frequencies, the gain is (R5 / R4 + 1), or 1.34, approximately 3dB.
  • the roll-off frequency is chosen to match the effect of the increasing phase difference between the two channels in the transition region between about 400Hz and 200Hz.
  • the output of this boost stage is applied to a first output terminal 36 of the circuit 30.
  • FIG. 16 shows the frequency response and the phase difference plotted against frequency, and also the amplitude produced when the channels are summed together.
  • Curve A shows the output amplitude, for IV AC input, which is 1.34V at low frequencies, and falls off to 1.09 at 2kHz (asymptotic to 1.0V at high frequencies. Both channels have identical frequency response, as the delay stage is all-pass and only the boost stage has additional low frequency gain.
  • Curve B shows the phase difference between the outputs, as simulated using PSPICE. Below 150Hz the phase remains within about " 12E of the desired 90E phase shift. Above 300Hz, where the phase difference is 45 E, the phase difference falls rapidly, and becomes about 30E at 500Hz and below 20E at 1000Hz.
  • the effect of the boost is shown in curve C, which is the sum of the voltages applied to the two loudspeakers, which approximately represents the low frequency sound pressure level in the room. This sum is 2.0V at all high frequencies, and varies from this value by " 0.34V in the low frequency region where the phase shift networks and the boost circuits are operational.
  • the bass is equalized to the same level as for coherent phase loudspeakers. Since more bass energy is coupled to the room modes, the actual bass level in the room may be higher, off the center line of the room.
  • the purpose of this invention is to produce the same increase in perceived spaciousness and externalization for a single channel source, or for a recording where the low frequency energy has been recorded in monaural in both stereo channels. These recordings are the rule for popular music. Adding the phase shift does not reduce the strength of the spaciousness for true stereo material, it only increases the effect for monaural material.
  • a method of predicting the increase in spaciousness based on the properties of the room modes is presented in the reference quoted below.
  • circuitry shown in FIG. 15 also lends itself to use within a pair of powered loudspeaker systems each having within the loudspeaker enclosure either the first or second channel circuitry of FIG. 15 and an audio power amplifier for driving the loudspeaker.
  • phase relationship may be varied to produce the desired phase degree differences mechanically.
  • phase relationship varying may be accomplished by mechanical manipulations of the loudspeaker enclosure volume, driver cone mass, port area and geometry, and crossover design, that combine to produce the desired 90 degree phase difference in the pressure output of the loudspeakers.

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Abstract

L'invention porte sur un procédé et un système favorisant le couplage d'une paire de haut-parleurs (5, 6) stéréophoniques pleine gamme ou de caissons d'extrêmes graves (8, 9) à tous les modes d'écoute d'une salle d'écoute latéralement symétrique, l'emplacement préféré d'un auditeur étant sur la ligne centrale latérale. Le procédé consiste à appliquer les signaux audio (30, 32) gauche et droit ou les composantes basse fréquence dans une paire de réseaux passe-tout à décalage de phase qui ont une relation en phase à de basses fréquences audio, là où la localisation n'est pas possible. Le procédé et le système de cette invention peuvent également être compensés par le renforcement des notes graves de 3dB dans chaque canal de façon à obtenir le même niveau de pression acoustique au niveau des basses fréquences comme cela se produirait avec une paire de caissons d'extrêmes graves (8, 9) placée dans un angle de la salle et commandés en phase, ce qui garantit un niveau de pression acoustique constant le long de la ligne centrale latérale de la salle d'écoute au niveau de toutes les fréquences audio.
EP98966031A 1997-12-23 1998-12-21 Procede et systeme de haut-parleur a decalage de phase de 90 degres Withdrawn EP1042866A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US6871697P 1997-12-23 1997-12-23
US68716P 1997-12-23
PCT/US1998/027174 WO1999033173A1 (fr) 1997-12-23 1998-12-21 Procede et systeme de haut-parleur a decalage de phase de 90 degres

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AU2013400A (en) 1999-11-25 2001-06-04 Embracing Sound Experience Ab A method of processing and reproducing an audio stereo signal, and an audio stereo signal reproduction system
US7382888B2 (en) * 2000-12-12 2008-06-03 Bose Corporation Phase shifting audio signal combining
SE527062C2 (sv) 2003-07-21 2005-12-13 Embracing Sound Experience Ab Stereoljudbehandlingsmetod, -anordning och -system
SE530180C2 (sv) 2006-04-19 2008-03-18 Embracing Sound Experience Ab Högtalaranordning
GB2591111B (en) * 2020-01-15 2023-08-09 Tgr1 618 Ltd Method for bi-phasic separation and re-integration on mobile media devices

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US4841572A (en) * 1988-03-14 1989-06-20 Hughes Aircraft Company Stereo synthesizer
US5172415A (en) * 1990-06-08 1992-12-15 Fosgate James W Surround processor

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US4841572A (en) * 1988-03-14 1989-06-20 Hughes Aircraft Company Stereo synthesizer
US5172415A (en) * 1990-06-08 1992-12-15 Fosgate James W Surround processor

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EP1042866A4 (fr) 2003-06-18
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