US3862366A - Sound radiation system - Google Patents

Sound radiation system Download PDF

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Publication number
US3862366A
US3862366A US279515A US27951572A US3862366A US 3862366 A US3862366 A US 3862366A US 279515 A US279515 A US 279515A US 27951572 A US27951572 A US 27951572A US 3862366 A US3862366 A US 3862366A
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United States
Prior art keywords
sound
loudspeaker
loudspeakers
frequency
high frequency
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Expired - Lifetime
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US279515A
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English (en)
Inventor
Denes Huszty
Andras Illenyi
Ilona Magos Nee Nemeth
Karoly Szabados
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Elektroakusztikai Gyar
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Elektroakusztikai Gyar
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/323—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only for loudspeakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—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

Definitions

  • ABSTRACT A sound radiator comprising at least four high frequency loudspeakers with their axes intersecting in zigzag relationship, and a single low frequency loudspeaker whose center is at a distance not more than 1.5 times the diameter of the low frequency loudspeaker from the center of that high frequency loudspeaker which is farthest from the low frequency loudspeaker.
  • the wave length of the crossover frequency of the low frequency and high frequency loudspeakers is not more than the smallest dimension of the housing for the unit measured in a plane perpendicular to the axis of the low frequency loudspeaker.
  • a perforated obstacle is disposed in front of part of the high frequency loudspeakers.
  • Subject matter of the invention is a sound radiation system built up of sound radiatingelements and elements modifying the radiation properties, further of active and passive electrical networks, constituting a functional unit whose transmission characteristics and radiated output are at the position of the listener in the room of a frequency-dependent uniformity better than that of sound radiators so far known and realized.
  • sound radiating elements preferably sound radiators (e.g., reflection box, horn loud-speaker, or any other arrangement) specially designed for each a low, medium, or high frequency transmission band should be understood.
  • active networks i.e., such as incorporate a loudspeaker
  • passive networks i.e., such as are void of a loudspeaker
  • the circuit controlling the output amplifier supplying the sound radiators is normally equipped with a circuit controlling the high and bass tones (Reference 3).
  • the problem of the quality of sound transmission confronts the designer of the transmission chain with difficulties hard to overcome.
  • the design of the transmission chain involves subjective and acoustic prob lems which in their interrelations are still subjects of research work.
  • the directional characteristics must be similar to one another and within a conic angle of radiation of 120 fluctuations must be kept at a minimum.
  • the unevenness of the characteristic manifesting itself between the critical bands of hearing i.e., making itself felt when measured with a noise voltage of a bandwidth of a third of an octave
  • the unevennesses of the directional characteristic and the axial sound pressure vs frequency characteristic i.e., the most characteristic, objectively measurable acoustic data of the sound radiation system are defined by a noise of a bandwidth of one third of an octave, then the task remains to design a sound radiator whose acoustic properties when measured with a signal of a bandwidth of one-third of an octave should remain as even and uniform as possible. This postulate has been ignored in all of the known solutions of the problem (Reference 1, 2, 3).
  • the level drop owing to the directional characteristics preferably departing from the inaudible properties of the electoacoustic transmission chain formed between the ear of the observer and the sound radiator, referred to the critical bandwidths of the sense of hearing, and from the spherical shape may be ignored.
  • a set of frequency-independent constant directional characteris tics has the welcome property that the directional factor, i.e., the quotient of the square of the sound pressure excited in the axis and the radiated output, of a sound radiator of such properties (Reference 10) may be produced in the manner specified in dependence on the frequency. So, e.g., the directional factor may be made constant irrespective of the frequency. All that has to be attended to is that the level of the signal supplying the sound radiator should as a function of the frequencyvary inversely to the variations of the axial characteristic in order just to compensate the unevenness of the axial characteristic (Reference 6). This problem may be tackled with the aid of known electrical metworks.
  • the same author has placed the high-tome loudspeaker over a deep-tone sound radiator.
  • the longitudinal axis of the high-tone sound radiator unit coincides with the longitudinal axis of the deep-tone sound radiator and at the same time the high-tone soud radiators are turned in respect-of one another roud their longitudinal axis.
  • this method does not guarantee an even approximate uniformity of the directional characteristics in the horizontal plane above 1 kHz.
  • the crossover frequency has to be selected low enough in order to prevent wideband, and consequently audible, unevennesses from arising in a manner essentially independent of the direction in the transmission characteristic.
  • the crossover frequency has to be selected in a way that at the frequency where the sound radiation of the deep-tone and high-tone sound radiator units is overlapping, the deep-tone and high-tone sound radiator units have to present directional radiation properties already in the horizontal plane.
  • Directional radiation is strongly fluenced by sound deflection arising on the surface of the house.
  • every closed loudspeaker of necessity possesses a spherical directional characteristic
  • the cardinal idea was to design a sound radiation system built up of deep-tone and high-tone sound radiating elements which contrary to known methods would above 0.8 kHz guarantee frequencyindependent, reciprocally similar directional characteristics, and exploit the load carrying capacity of the deep-tone and high-tone radiating elements to the utmost possible.
  • the sound radiator should in dependence of the frequency and, by varying the transmission characteristic of the amplifier supplying the sound radiator system, be convertible to one of a directional factor variable by a definite method, all this inorder to approximate at the site of listening-in in the room a for the given task most appropriate transmission characteristic as good as this could be done.
  • the sound radiation system according to the invention provides a solution of the problem achieved by means of several measures applicable in'mutual independence of one another, yet in conjunction producing the best possible results.
  • the high-tone sound radiator incorporates four loudspeakers each of a diameter of 125 millimetres, whereas the deep-tone sound radiator consists of a loudspeaker of a diameter of 300 millimetre assembled in a completely sealed, cotton-damped house.
  • the crossover frequency of the two-way sound radiation system has been chosen so as to permit the maximum possible exploitation of the load carrying capacity of the loudspeakers constituting the sound radiation system and at the same time possibly in a way independent of the frequency to guarantee a similarity of the directional characteristics of the sound radiation system at the crossover frequency as well as in the neighbourhood of this frequency within a wide spatial angle.
  • the performance of the system may even be improved, when the sound radiator according to the patent referred to above is used as high-tone radiation feature.
  • this sound radiator a system of relatively moderate dimensions, a wide sound band, high output and constant directional characteristic may be built up, provided that by ch'bosing an appropriate position for the deep-tone sound radiation element care is taken that this latter feature should be sufficiently close to the high-tone sound radiators and that an adequate high crossover frequency should be selected.
  • the crossover frequency has been chosen so that its associated wavelength is below the lowest value of propagation measured on the surface of the house incorporating the loudspeaker features parallel to the plane of the aperture of the deep-tone radiating loudspeaker.
  • FIG. I presents an embodiment of the sound radiation system according to the invention, of lower volume.
  • FIG. 2 presents a sound radiation system being uniform with that of FIG. 1, still for a higher output.
  • FIG. 3 presents directional characteristics in the neighbourhood of a crossover frequency of f, 1.25 kHz for a design according to FIG. 1.
  • FIGS. 4 and 5 for the sake of comparison present directional characteristics with and without means of diffractions.
  • FIGS 6 and 7 present the applied means of diffraction, respectively viewed from above and perspectively.
  • FIG. 8 presents the design of a preferred means of diffraction.
  • FIGS 9 and 10 present examples of the modification of the transmission characteristics in the range of high tones in response to diffraction obstacles.
  • FIGS. 11, 12 and 13 present the modification of sections of a sound pressure versus frequency characteristic obtained indoor for different positions of the sound radiator as the result of the interaction of the sound radiator and the room.
  • FIG. 14 is a layout of the electroacoustic chain of a sound radiation system.
  • FIGS 15 and 16 are plots of the frequency characteristics of filters used in the system.
  • FIG. 17 presents the sound pressure versus frequency characteristics of the sound radiation system according to the invention plotted indoor.
  • FIGS. 18, 19 and 20 present the for practical purposes frequency-independent directional characteristics of the sound radiation system according to the invention.
  • the sound radiation system 1 incorporated the electronic system 2, the deep-tone radiating loudspeaker 4 encased in the deeptone radiator house 3, further four high-tone radiating loudspeakers 6 accommodated in a high-tone radiator house 5.
  • the loudspeakers 6 have been arranged horizontally in conformity with US. Pat. No. 3,648,801. For the measurements a reference system of coordinates has been used whose axes x, y and z are righthand twisted.
  • the distance of the critical section 8, i.e., the centre of the deep-sound radiating loudspeaker 4 from the centre of the extreme loudspeaker 6 of the hightone radiation system should not exceed 1.5 times the diameter of the loudspeaker 4 incorporated in the system.
  • FIG. 2 represents a design of the sound radiation system according to the invention of higher output where deep-tone radiating loudspeakers 4 accommodated in deep-tone sound radiating houses 3 and such radiating high-tones 5, ther high-tone radiating loudspeakers 6 according to the above patent arranged in two rows have been built in.
  • the references correspond to the code numbers used in FIG. 1.
  • the measuring results obtained for an embodiment of the layout according to FIG. 1 have been plotted.
  • a crossover frequency of f, 1.2 5 kHz has been specified and in the graph the semiplanar directional characteristics developing in the vicinity of this crossover frequency have been plotted.
  • the crossover filters have presented a characteristic of a slope of 12 dB/octave for a frequency sufficiently departing from the crossover frequency.
  • the directional characteristics have been measured in the plane xy in an open sound space at a distance ofZ metres from the sound radiator at the crossover frequency and in its environment.
  • FIG. 6 In the sound radiation system according to the layout shown in FIG. 1 the effects of various obstacles producing a diffraction have been subjected to an analysis. The results so obtained have been plotted in the graph in FIGS. 4 and 5.
  • the continuous line represents the semiplanar directional characteristics associated with the different frequencies of the sound radiation system without the use of a diffraction producing obstacles, whereas the dotted line has been drawn for results obtained for the use of diffraction bars according to the patent referred to above.
  • the generatrices represent the characteristics obtained with the use of a diffraction feature according to the invention.
  • FIGS. 4 and 5 clearly demonstrate that, e.g., at 5 kHz and at 6.3 kHz the diffraction bar produces no appreciable effect.
  • the loudspeakers 6 have been arranged on the sound wall 10.
  • the effect of the diffraction-producing lamellar obstacle ll manifests itself not only in the directional characteristic, but also in the sound pressure versus frequency characteristic measured in the axis of the sound radiator in a manner that where in response to the diffraction the directional characteristic tends to improve appreciably, the axial sound pressure curve will present a downwards trend, provided that the hightone sound radiation element is built up of the usual individual loudspeakers of a nearly straight-lined transmission characteristic.
  • the transmission characteristic conforms to'the relevant recommendations of sound film technics (Reference 14.). Still in order to guarantee the transmission characteristic normally obtained in radio and TV studios (Reference 15 however, in a manner that the directional characteristics of the sound radiation system should be similar for frequencies above 0.8 kHz, preferably care should be taken that in the given instance within a wide sound band the transmission characteristic of the sound radiation system measured at the position of thelistener should be a straight line.
  • the high-tone radiating feature should preferably be built up of individual loudspeakers whose axial transmission characteristic presents an expressly rising character at high tones. Loudspeakers of such a characteristic will by themselves create an expressly unpleasant acoustic effect, however, they will lend themselves readily for use in the sound radiation system arranged in the manner explained above.
  • the axial transmission characteristic of a sound radiation system built up of loudspeakers of a rising transmission characteristic is shown in FIG. 1, 7 and 8.
  • FIG. 10 presents in FIG. 10 by a continuous curve.
  • the dotted curve in FIG. 9 is the transmission characteristic of the high-tone radiating feature of a nearly straight-lined transmission characteristic. Obviously the change is considerable. According to experience the change occurring in response to the use of a diffraction sheet is for a given type of loudspeakers fairly independent of the scattering among the specimens of the loudspeak ers actually used, provided that the loudspeakers are well within the usual factory tolerances.
  • a solution producing yet further improvement has been achieved by an electrical correctional network executed in conformity with known designs, connected to the amplifiers or circuits of the sound radiation system, preferably before the output amplifiers and having transmission characteristics of a variable slope of i 6 dB/octave in the region above I kHz.
  • a frequencyindepende'nt sound radiator of a for practical purposes constant directional characteristic has been designed which in the room at the site of listening-in, dependent on the specification, presents a directional factor and transmission characteristic adjustable within extremes wide apart.
  • a network should be used the slope of whose characteristic should be continuously adjustable between slopes of at least :6 dB/octave at frequencies below 300 Hz.
  • the testing microphone has been installed at a distance of two metres, and the test has been carried out, first, with the sound radiator on the ground (full line), and then with it at a height of two metres from the ground (broken line).
  • the unevenness of the former transmission characteristic has been compensated by a passive electrical network inserted between the hot spot of a known, characteristic regulating electrical circuit and its cold spot earth point, and built up of a resistance, a condenser and an inductance in series.
  • the resonance frequency of the network and its Q-factor have preferably been made variable.
  • a circuit of this type is needed only when the sound radiation system has to satisfy extremely critical requirements. In this case, e.g., for studio operation, a permanent accommodation of the sound radiation system may be taken for guaranteed.
  • the network has preferably been installed inside the amplifier in a way that the unit will become accessible only after the bolts fixing the amplifier have been removed or loosened.
  • a network locally correcting the transmission characteristic has been in use in sound radiation systems operated in studios for a long time already (Reference 2).
  • the network had preferably to be a variable one and that the optimum adjustment had to be made dependent on the site of accommodation of the sound radiation system.
  • the resonance frequency of this network had to be selected somewhere in the neighborhood of 300 Hz, in the environment of the crossover frequency of the deep-tone and high-tone sound radiator units.
  • this correctional network should preferably be positioned at a frequency lower than the crossover frequency, in order to obtain the best possible result in the given environment.
  • the network might as well be built up of a parallel oscillating circuit, or several of them, inserted in series in the regulating branch, and incorporating a resistance, condenser and inductance.
  • the diffraction causing element shown in FIG. 8 and accommodated on the front panel of the sound radiation system before the high-tone radiating feature has been designed so as to be at the same time part of the sheet covering the front surface of the sound radiation system.
  • the sheet itself is covered on its outer surface with a sound transmitting texture or loudspeaker silk.
  • FIG. 14 A block schematic of the circuitry used in the sound radiation system so designed is shown in FIG. 14.
  • a correctional network 16 is attached through the level control to the input unit 14.
  • the circuitry by means of appropriate crossover filters bifurcates to a deep-tone radiating channel branch 18 and to a high-tone radiating channel branch 19.
  • the deep-tone radiating loudspeakers 4 and the high-tone radiating loudspeakers 6 join the crossover filters 20 via level controls 21 and audio frequency output amplifiers 22.
  • a characteristic of one of the correctional networks has by way of example been plotted in the graph in FIG. 15.
  • the dotted area represents the range of regulation actually realized.
  • the curve A plotted in the graph in FIG. 17 is the uniform sound pressure versus frequency characteristic measured at a distance of 2 metres from the radiator in a room of a volume of V 120 metres cube, of a permanent reverberation of T 0.5 s, when all measures discussed above have been taken simultaneously.
  • the sound pressure versus frequency characteristic satisfies the conditions specified for the operation and monitoring of radio and TV studios.
  • Curve 8 which differs from the former in that with the high-tone controlling potentiometer appropriately adjusted the preamplifier will present a straightlined transmission characteristic, satisfies the postulate of pleasant-listening, whereas curve C satisfies the transmission characteristic recommended in sound film technics. All transmission characteristics have been obtained in a way that the potentiometer for high-tone control has been turned from its highest position to its lowest until the specified characteristic has appeared. The uniform transmission characteristic appearing in the low-frequency band has been obtained in the mid-position of the deep-tone controlling potentiometer, when also the correction plotted in the graph in FIG. 13 required for the compensation of the characteristic of a sound radiation sys tem positioned on the ground and at a distance of 1.5 metre from the wall has been applied.
  • FIGS. 1-9 and 20 plane xz.
  • the directional characteristics have been measured in an open sound space, at a distance of 2 metres from the sound radiator and then plotted for semiplanes.
  • a sound radiator comprising a low frequency and high frequency sound radiating unit housed in a common housing and an electronic circuit for said unit comprising an output amplifier and low-pass and highpass filters
  • said high frequency sound radiating unit comprising at least three loudspeakers excited by the same signal source and each having a flat front panel perpendicular to the radiating axis of the speaker, the panels being on a common level and meeting each other at angles substantially different from l80 along lines that are parallel to each other, said axes of adjacent speakers intersecting each other alternately before and behind saidspeakers;
  • said high frequency sound radiating unit contains at least four loudspeakers
  • said low frequency sound radiating unit comprising a single loudspeaker whose center is at a distance of not more than 1.5 times the diameter of the low frequency loudspeaker from the center of the high frequency loudspeaker which is farthest from the low frequency loudspeaker, the wave length of the crossover frequency of the low frequency and high frequency sound radiating units being not more than the smallest dimension of said
  • a sound radiator comprising a low frequency and high frequency sound radiating unit housed in a common housing and an electronic circuit for said unit comprising an output'amplifier and low-pass and highpass filters, said high frequency sound radiating unit comprising at least three loudspeakers excited by the same signal source and each having a flat front panel perpendicular to the radiating axis of the speaker, the
  • said high frequency sound radiating unit contains at least four loudspeakers, said low frequency sound radiating unit comprising a single loudspeaker whose center is at a distance of not more than 1.5 times the diameter of the low frequency loudspeaker from the center of the high frequency loudspeaker which is farthest from the low frequency loudspeaker, the wave length of the crossover frequency of the low frequency and high frequency sound radiating units being not more than the smallest dimension of said housing measured in a plane perpendicular to said axis of the low frequency loudspeaker, and a multiperforate barrier sheet disposed in front of at least a portion of said high frequency loudspeakers, said high frequency loudspeakers being disposed in a row, there being a said sheet disposed in front of only the end loudspeakers in said row.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Transducers For Ultrasonic Waves (AREA)
US279515A 1971-08-16 1972-08-10 Sound radiation system Expired - Lifetime US3862366A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
HUEE1935A HU163253B (xx) 1971-08-16 1971-08-16

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US (1) US3862366A (xx)
AT (1) AT330869B (xx)
BG (1) BG20835A3 (xx)
CA (1) CA978093A (xx)
CS (1) CS171735B2 (xx)
DD (1) DD98415A5 (xx)
DE (1) DE2236306B2 (xx)
FR (1) FR2149449B1 (xx)
GB (1) GB1407243A (xx)
HU (1) HU163253B (xx)
PL (1) PL78133B1 (xx)
SE (1) SE386799B (xx)
SU (1) SU510171A3 (xx)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4322578A (en) * 1977-09-06 1982-03-30 Society Ap Selmin Sas Of Massimo Coltelli & Co. Method and devices for the omnidirectional radiation of sound waves
US4445227A (en) * 1981-12-28 1984-04-24 Magnavox Consumer Electronics Company Loudspeaker having improved directional characteristics
US5063869A (en) * 1988-09-16 1991-11-12 Deutsche Airbus Gmbh Wing type sailing yacht
US5250763A (en) * 1991-10-07 1993-10-05 Brown William G Acoustical equalization device system
US5278361A (en) * 1993-02-05 1994-01-11 Thomson Consumer Electronics, Inc. Loudspeaker system
US6201878B1 (en) * 1995-09-02 2001-03-13 New Transducers Limited Portable compact disc player
WO2001047320A1 (en) * 1999-12-21 2001-06-28 New Transducers Limited Loudspeakers
US6389935B1 (en) * 1996-09-02 2002-05-21 New Transducers Limited Acoustic display screen
US20030006092A1 (en) * 2001-06-27 2003-01-09 Rpg Diffusor Systems, Inc. Sound diffuser with low frequency sound absorption
US20040005069A1 (en) * 2002-04-02 2004-01-08 Buck Marshall D. Dual range horn with acoustic crossover
US20070263878A1 (en) * 2006-05-12 2007-11-15 Ensky Techonlogy (Shenzhen) Co., Ltd. Sound mask and sound box

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9113257B2 (en) 2013-02-01 2015-08-18 William E. Collins Phase-unified loudspeakers: parallel crossovers
US20150312693A1 (en) * 2014-04-23 2015-10-29 William E. Collins Phase-unified loudspeakers: series crossovers

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2143175A (en) * 1937-10-23 1939-01-10 Samuel A Waite Sound reproducing system
US2802054A (en) * 1952-08-11 1957-08-06 Ferguson Radio Corp Sound reproducing apparatus
US3104730A (en) * 1963-09-24 Speaker enclosure
US3125181A (en) * 1961-06-21 1964-03-17 pawlowski
US3340956A (en) * 1965-11-01 1967-09-12 Motorola Inc Sound reproduction apparatus
US3648801A (en) * 1969-11-26 1972-03-14 Elektroakusztikai Gyar Sound radiator

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3104730A (en) * 1963-09-24 Speaker enclosure
US2143175A (en) * 1937-10-23 1939-01-10 Samuel A Waite Sound reproducing system
US2802054A (en) * 1952-08-11 1957-08-06 Ferguson Radio Corp Sound reproducing apparatus
US3125181A (en) * 1961-06-21 1964-03-17 pawlowski
US3340956A (en) * 1965-11-01 1967-09-12 Motorola Inc Sound reproduction apparatus
US3648801A (en) * 1969-11-26 1972-03-14 Elektroakusztikai Gyar Sound radiator

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4322578A (en) * 1977-09-06 1982-03-30 Society Ap Selmin Sas Of Massimo Coltelli & Co. Method and devices for the omnidirectional radiation of sound waves
US4445227A (en) * 1981-12-28 1984-04-24 Magnavox Consumer Electronics Company Loudspeaker having improved directional characteristics
US5063869A (en) * 1988-09-16 1991-11-12 Deutsche Airbus Gmbh Wing type sailing yacht
US5250763A (en) * 1991-10-07 1993-10-05 Brown William G Acoustical equalization device system
CN1046837C (zh) * 1993-02-05 1999-11-24 汤姆森消费电子有限公司 扬声器设备
WO1994018814A1 (en) * 1993-02-05 1994-08-18 Thomson Consumer Electronics, Inc. Loudspeaker system
US5278361A (en) * 1993-02-05 1994-01-11 Thomson Consumer Electronics, Inc. Loudspeaker system
US6201878B1 (en) * 1995-09-02 2001-03-13 New Transducers Limited Portable compact disc player
US6389935B1 (en) * 1996-09-02 2002-05-21 New Transducers Limited Acoustic display screen
WO2001047320A1 (en) * 1999-12-21 2001-06-28 New Transducers Limited Loudspeakers
GB2371941A (en) * 1999-12-21 2002-08-07 New Transducers Ltd Loudspeakers
US20030006092A1 (en) * 2001-06-27 2003-01-09 Rpg Diffusor Systems, Inc. Sound diffuser with low frequency sound absorption
US20040005069A1 (en) * 2002-04-02 2004-01-08 Buck Marshall D. Dual range horn with acoustic crossover
US7392880B2 (en) 2002-04-02 2008-07-01 Gibson Guitar Corp. Dual range horn with acoustic crossover
US20070263878A1 (en) * 2006-05-12 2007-11-15 Ensky Techonlogy (Shenzhen) Co., Ltd. Sound mask and sound box

Also Published As

Publication number Publication date
ATA627872A (de) 1975-10-15
FR2149449A1 (xx) 1973-03-30
CA978093A (en) 1975-11-18
DD98415A5 (xx) 1973-06-12
FR2149449B1 (xx) 1980-03-14
PL78133B1 (xx) 1975-04-30
SU510171A3 (ru) 1976-04-05
SE386799B (sv) 1976-08-16
CS171735B2 (en) 1976-10-31
DE2236306A1 (de) 1973-03-15
HU163253B (xx) 1973-07-28
GB1407243A (en) 1975-09-24
BG20835A3 (xx) 1975-12-20
AT330869B (de) 1976-07-26
DE2236306B2 (de) 1976-07-08

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