STEREO ELECTROACOUSTICAL TRANSDUCING

Abstract: Stereo electroacoustical transducing apparatus is disclosed having left and right channels with woofer means (11a) for receiving left and right input audio electrical signals at first and second inputs (31L/R) and providing left and right output electrical signals. The woofer means (11a) has an acoustic response that falls off sharply above a predetermined upper cutoff frequency in the lower range of audio frequencies and including a woofer enclosure (11) for supporting woofer driver means (21-26L/R, 31L/R) for radiating in phase spectral components of the left and right input signals below the predetermined upper cutoff frequency. Left (13) and right (12) satellite radiating means radiate sound signals representative of the left and right output signals respectively, and the left and right output electrical signals are coupled to the left (13) and right (12) satellite means.

Description: The present invention relates in general to electroacoustical transducing and more particularly concerns novel apparatus and techniques for providing stereo reproduction with compact electroacoustical apparatus that is relatively inexpensive to fabricate, flexible in positioning and arrangeable to interfere only negligibly with room decor. EP-A-0015186 discloses a triphonic audio network in which signals output by a stereo amplifier are fed both to a pair of woofers and to a pair of speakers for the mid and upper frequencies. FR-A-2387562 discloses a stereo system in which a single bass speaker is mounted in a table and fed by summed left and right stereo signals, the stereo signals also being fed respectively to remote medium/high pitch speakers. It is an important object of this invention to provide improved stereo electroacoustical transducing apparatus. According to the present invention, there is provided stereo electroacoustical transducing apparatus comprising: a woofer enclosure having left and right inputs for receiving left and right input audio electrical signals respectively, and left and right outputs, the woofer enclosure supporting woofer driver means for radiating spectral components of the left and right input signals below a predetermined frequency; left and right satellite means for radiating sound signals substantially above the predetermined frequency, representative of the left and right output signals respectively; the left and right outputs of the woofer enclosure coupling left and right electrical signals output from the woofer enclosure to the left and right satellite means respectively; characterised in that: the woofer driver means is mounted on a baffle which divides the woofer enclosure into first and second subchambers tuned to different frequencies below the predetermined frequency, the woofer enclosure summing bass spectral components of the left and right input audio electrical signals in phase to provide a summed bass acoustical signal for radiation by port means as a listener non-localisable bass output signal, the port means providing the sole acoustic output from the woofer enclosure, the woofer enclosure having an acoustic response that falls off above the predetermined frequency so that sound radiated by the woofer enclosure is not usable by a listener for localising said sound in a listening environment. An embodiment of the present invention will now be described with reference to the accompanying drawing in which: FIG. 1 is a perspective view of an embodiment of the invention showing left and right pairs of satellite enclosures and a common woofer enclosure; and FIG. 2 is a combined schematic-diagrammatic representation of a preferred embodiment of the invention. With reference now to the drawings and more particularly FIG. 1 thereof, there is shown a perspective view of an embodiment of the invention comprising a dual-channel woofer enclosure 11, a right satellite pair 12 and a left satellite pair 13. Each satellite pair comprises an upper enclosure 12U, 13U, and lower enclosure 12L, 13L which may be supported on an arm, such as 14, to allow each enclosure to be oriented in a different direction to direct energy above 150 Hz toward the side predominantly for reflection into the listening area with some energy radiated directly into the listening area. Dual-channel woofer enclosure 11 contains left and right woofers preferably in an enclosure embodying the principles of U.S. Patent No. 4,549,631 granted to Amar G. Bose on October 29, 1985, for MULTIPLE PORTING LOUDSPEAKER SYSTEMS. Referring to FIG. 2, there is shown a combined schematic circuit-diagrammatic representation of a preferred embodiment of the invention showing the interconnecting relationship among dual-channel woofer enclosure 11 and right and left satellite pairs 12 and 13, respectively. Enclosure 11 includes left and right woofers 21L and 21R, respectively. The left and right channels include left and right satellite passive equalization networks 22L and 22R, respectively, capacitors 23L bind 23R, respectively, and input light bulbs 25L and 25R adjacent to right and left protective circuits 26R and 26L, respectively. The elements described and a common line intercouple left and right input terminal pairs 31L and 31R, respectively, with output terminal pairs 32L and 32R, respectively. Each output terminal pair 32L and 32R is connected to a respective input terminal pair 33L and 33R, respectively, of lower enclosures 13L and 12L, respectively. Each of these enclosures includes an upper frequency driver 34L and 34R, respectively, each of which has one terminal connected to one of the input terminals of input terminal pairs 33L and 33R, respectively, and the other terminal connected to one of the terminals of output jacks 37L and 37R, respectively. Each of the other terminals of output jacks 37L and 37R, respectively, is connected to the other terminal of input terminal pairs 33L and 33R, respectively. A capacitor 35L and 35R is connected in parallel with each driver 34L and 34R, respectively, when a switch 36L and 36R, respectively, is in the R position as shown. Left and right upper enclosures 13U and 12U, respectively, enclose left and right upper frequency drivers 41L and 41R, respectively, connected to left and right plugs 42L and 42R, respectively, which engage jacks 37L and 37R, respectively, to connect the left upper frequency drivers 34L and 41L and the right upper frequency drivers 34R and 41R, respectively, in series. Moving switches 36L and 36R to the D position disconnects capacitors 35L and 35R from shunting drivers 34L and 34R, respectively, so that both upper frequency drivers in that channel radiate spectral components substantially equally. Having briefly described the structural arrangement of the system principles of operation will be discussed. The system basically comprises a stereophonic electroacoustic transducing system having a woofer with dual satellite systems positioned to the left and right of the listener and oriented to radiate a portion of the upper frequency energy directly to the listener and a portion to the listener after reflection. Each satellite driver is a full-range driver, which may be of the type disclosed in U.S. Patent Nos. 4,061,890, 4,158,756 and 4,577,069. The woofer enclosure encloses both left and right bass transducers mounted internally on a baffle which divides the internal volume substantially in a 3:1 ratio, each volume ported such that the port tuned frequencies have substantially a 2:1 ratio, as described in the aforementioned U. S. Patent No. 4,549,631. The in phase left and right low frequency outputs are acoustically summed by this arrangement. This summing of bass outputs is effective because 1) program material generally has little phase differentiation of left and right input signals below 150 Hz and 2) the non-localization phenomenon referred to below means that virtually no stereo imaging information is lost. The performance advantages described in the aforementioned Bose Patent No. 4,549,631 are threefold: 1) Efficiency is above that of an optimized conventional ported system of the same size. 2) The natural low pass filtering of the woofer enclosure allows for a steep rolloff above 150Hz; because human auditory apparatus cannot easily localize on sound sources of frequencies band-limited below 150 Hz in a semi-reverberant environment (such as any real listening room), the woofer enclosure may be placed at or near a room corner, where bass efficiency is additionally increased by up to 6dB. This natural low pass filter characteristic is achieved without costly passive or active crossover networks and is thus less expensive than conventional embodiments of woofer/satellite systems. 3) The excursion requirements of the woofer cone for a given acoustic output are reduced from that of a conventional ported system with the same size woofer. This reduction produces less distortion at high output power. In addition, distortion is further reduced by the low pass filtering mechanism of 2) above. This reduction in distortion components above 150 Hz is an important factor in realizing a sound source which is not easily localized even at high bass output levels. The woofer is preferably designed for substantially flat power radiation into a typical room when 3 to 5 feet from a corner. A feature of the system is the interconnection in a manner that facilitates interconection by unskilled users to avoid confusion. The inputs are on a block of four connector terminals 31L and 31R on woofer enclosure 11. The woofer enclosure includes the crossovers and equalizing networks for the satellite enclosures, and has two sets of two-connector push terminals 32L and 32R for the satellite enclosures 13 and 12, respectively. The protection circuitry arrangement is another feature of the system. When two low frequency transducers are located in a common volume, aberrations in frequency response and high excursion operation occur when one woofer is driven with a significantly different amplitude low frequency signal than drives the other. This phenomenon would occur if the protection circuit in one channel trips, causing attenuation of the signal to the woofer in that channel. By placing the lamp of the protection circuit in the tripped channel adjacent to the PTC (positive temperature coefficient) device of the untripped channel, the untripped channel is thereby caused to trip, thereby bringing the signals fed to each woofer back into balance. The bottom satellite enclosures each have a set of two-connector input push terminals 33L and 33R, respectively, and a switch 36L and 36R, respectively, for selecting the R position shown attenuating the high-frequency output of the bottom enclosure while increasing the high-frequency output of the upper enclosure by 6 dB to provide predominantly reflected energy with the upper enclosure oriented to point away from the listener. In the D mode of switches 36L and 36R, both top and bottom enclosures have the same full spectrum output, although the high-frequency power response is reduced somewhat. By providing the top satellite enclosures 12U and 13U with phone plugs 42L and 42R for mating with jacks 37L and 37R, respectively, at the top of the bottom satellite enclosure, an easy, good connection is made for providing signal input to each upper enclosure while allowing rotation of the upper enclosure relative to the lower enclosure for selecting an appropriate radiation angle of each. In an exemplary embodiment of the invention the woofer enclosure 11 includes two 16.5 cm (6½ inch) woofers 21L and 21R mounted in an enclosure having internal dimensions of 29 cm. high X 15 cm. wide X 48 cm. long. Woofers 21L and 21R both load a system as described in the aforesaid Bose U.S. Patent No. 4,549,631 with a small chamber having a volume of 4.1 liters and a port measuring 6.4 cm. diameter by 13.0 cm. long with a port tuning frequency of 90 Hz. The larger chamber has a volume of 12.4 liters and a port measuring 6.4 cm. diameter by 26.0 cm. long with a port tuning frequency of 45 Hz. Each satellite assembly 12 and 13 consists of two enclosures each having a 60 mm driver with shielded magnet for lower flux leakage having internal dimensions of 7.4 cm. high X 7.4 cm. wide X 7.2 cm. deep forming a volume of 390 cc. The system is especially advantageous to use where space is restricted because the woofer enclosure 11 may be located anywhere in the listening area, even hidden behind or under funiture. Locating the woofer enclosure in a corner increases the bass efficiency of the system up to four times that of the same woofers in a conventionally placed enclosure. The satellite assemblies may be located on a bookshelf, suspended from the ceiling, supported by arms clamped to a desk, shelf or other piece of furniture or otherwise suitably located. Locating passive equalizing circuit components in the woofer enclosure helps keep the weight and volume of the satellite assemblies relatively low. While it is preferred that the system include two or more enclosures for each satellite assembly, a number of advantages of the invention may be attained by using only one driver for each satellite assembly. It is also within the principles of the invention to use any number of woofers in the woofer enclosure, including a single woofer fed by a suitable means for combining the left and right channels, such as a two-winding voice coil. It is within the principles of the invention to include other components in the woofer enclosure. For example, the woofer enclosure might include a power amplifier, receiver, cassette player, compact disc player and/or other sources. Because the sound radiated by the woofer enclosure is largely unused by the listener for localizing in a listening room, the woofer enclosure may be located anywhere in the room near a convenient power outlet. It is also within the principles of the invention to locate a crossover/passive equalization network in a separate enclosure which could feed both the woofer enclosure and the satellite drivers. It is within the principles of the invention to include two separate left and right channel bass enclosures, each with separate woofer means mounted internally between two ported volumes as described previously. It is also within the principles of the invention to include mid-frequency and high frequency transducers, or a combination mid and high frequency transducers, on the outer surface of such a bass enclosure in order to provide for a complete left or right channel loudspeaker system. The woofer enclosure may include at least two left and the same number of right woofers energised by the left and right input signals respectively.

Claims: Stereo electroacoustical transducing apparatus comprising: a woofer enclosure (11) having left and right inputs (31L,31R) for receiving left and right input audio electrical signals respectively, and left and right outputs (32L,32R), the woofer enclosure (11) supporting woofer driver means (21L/R) for radiating spectral components of the left and right input signals below a predetermined frequency; left (13) and right (12) satellite means for radiating sound signals substantially above the predetermined frequency, representative of the left and right output signals respectively; the left and right outputs (32L/R, 33L/R) of the woofer enclosure coupling left and right electrical signals output from the woofer enclosure to the left (13) and right (12) satellite means respectively; characterised in that: the woofer driver means (21L,21R) is mounted on a baffle which divides the woofer enclosure (11) into first and second subchambers tuned to different frequencies below the predetermined frequency, the woofer enclosure summing bass spectral components of the left and right input audio electrical signals in phase to provide a summed bass acoustical signal for radiation by port means (11A,11B) as a listener non-localisable bass output signal, the port means (11A,11B) providing the sole acoustic output from the woofer enclosure (11), the woofer enclosure having an acoustic response that falls off above the predetermined frequency so that sound radiated by the woofer enclosure is not usable by a listener for localising said sound in a listening environment. Apparatus according to claim 1, wherein the woofer driver means comprises left (21L) and right (21R) woofers energised by the left and right input signals respectively. Apparatus according to claim 1 or claim 2, wherein the woofer enclosure (11) is free of active crossover networks. Apparatus according to any of the preceding claims, wherein the predetermined frequency is substantially 150 Hz. Apparatus according to any of the preceding claims, wherein the satellite means (13,12) comprises a plurality of enclosures. Apparatus according to claim 5, wherein each of the satellite means (13,12) comprises upper (13U,12U) and lower (13L,12L) enclosures each having a respective driver (41L/R, 34L/R), and means for intercoupling the upper driver to the lower driver in each of the left and right satellite means. Apparatus according to claim 6, wherein the means for intercoupling the upper to the lower driver in each of the left and right satellite means comprises a plug (42L/R)-and-jack (37L/R) connector for electrically and mechanically connecting the upper (13U,12U) and lower (13L,12L) enclosures while allowing relative selectable angular displacement therebetween to control the relative direction of radiation from the satellite means drivers. Apparatus according to claim 6 or 7, wherein one (13L,12L) of the satellite means enclosures (13L/U,12L/U) includes means (35L/R,36L/R,34L/R,42L/R) for selectively bypassing a predetermined range of spectral components from one of the satellite means drivers (34L/R), while augmenting that same predetermined range of spectral components for the other satellite means driver (41L/R). Apparatus according to claim 8, wherein the means for selectively bypassing includes a switch (36L/R). Apparatus according to any of the preceding claims, wherein the woofer enclosure (11) includes electronic means for powering the woofer driver means and the satellite means. Apparatus according to any of the preceding claims, further comprising: protection circuit means (25L/R,26L/R) in each channel for attenuating signals in a respective channel in response to an overload condition, and means (26R/L) for intercoupling the protection circuit means (25L/R) in each channel with that of the other (25R/L) so that the occurrence of attenuation in one channel in response to an overload in that channel is accompanied by corresponding attenuation in the other channel so that the signals then fed through both channels are substantially in balance. Apparatus according to any of the preceding claims, wherein the left (13) and right (12) satellite means each comprises at least two drivers, each radiating different portions of the audio spectrum. Apparatus according to any of the preceding claims, wherein the woofer driver means comprises at least two left and the same number of right woofers energised by the left and right input signals respectively. Apparatus according to claim 1, wherein the woofer driver means comprises a single woofer driver having a voice coil component with two separate windings energised by the left and right input signals respectively. Apparatus according to claim 1, wherein the woofer enclosure (11) includes electronic means for powering the woofer driver means and the satellite means, which comprises an electronically summed left and right signal means to provide a monaural signal to drive the woofer driver means. Apparatus according to any of the preceding claims, wherein the woofer enclosure comprises separate left and right enclosures. Apparatus according to any of the preceding claims, wherein the satellite means (13,12) is physically attached to the woofer enclosure (11).

Inventors: SCHREIBER, WILLIAM P.
Applicants: BOSE CORPORATION
Application year: 1988
Main classification: H04R5
IPC codes: H04R5, H04S5, H04S3