Near-field reproduction of binaurally encoded signals

Abstract: A transportable sound reproduction system for transducing binaurally encoded signals with near-field reproduction includes a support 10, a head locator 20 attached to the support for positioning a listener's head at a desired location in the near-field, and a pair of speakers 28,30 located close to and forward of the desired location of the listener's head. A carrying case 36 for transporting the system has protective packaging 40 with compartments 42 for detachably securing the components of the system.

Description: The present invention relates in general to sound reproduction systems for transducing binaurally encoded signals and more particular concerns novel apparatus for transducing binaurally encoded signals with near-field reproduction, including signals incorporating transaural crosstalk equalization, by means of which a binaural signal is processed for reproduction by loudspeakers so that the left ear hears only the left signal and the right ear hears only the right signal. It is the aim of such systems to reproduce for the listener a fully realistic, three dimensional auditory illusion that is indistinguishable from the listening experience received when the listener is present in the actual sound field that the system is emulating. For background reference is made to U.S. Patent No. 4,893,342 entitled HEAD DIFFRACTION COMPENSATED STEREO SYSTEM and a paper of David Griesinger entitled "Theory and Design of a Digital Audio Signal Processor for Home Use" in J. Audio Eng. Soc., Vol. 37, No. 1/2 1989 January/February p. 40, which refers to work of Schroeder using interaural crosstalk elimination to play binaural recordings made in actual concert halls. Reference is also made to papers of M.R. Schroeder et al. entitled "Comparative study of European concert halls: correlation of subjective preference with geometric and acoustic parameters" in J. Acoust. Soc. Am., Vol. 56, No. 4, October 1974 p. 1195, of Moller entitled "Reproduction of Artificial-Head Recordings through Loudspeakers" in J. Audio Eng. Soc., Vol. 37 No. 1/2 1989 January/February p. 30, of Cooper et al. entitled "Prospects for Transaural Recording" in J. Audio Eng. Soc. Vol. 37, No. 1/2, 1989 January/February p. 3, U.S. Patent No. 3,236,949 entitled APPARENT SOUND SOURCE TRANSLATOR, and the letter of Salara entitled "Transaural Stereo and Near-Field Listening" in J. Audio Eng. Soc., Vol. 38, No. 1/2 1990 January/February p. 40. EP-A-0 421 681 discloses an electro-acoustic transducer accommodated in a cabinet and a sound guide being of a lesser diameter than the external acoustic miatus to allow at least the sound radiating end of the sound guide tube to be introduced into the external acoustic miatus. DE 32 14 080 discloses a system with two spherical speakers positioned at either side of the head of the listener. US-A-4, 388, 492 discloses a miniature stereo device which provides a satisfactory stereo effect including a main body having an audio device which generates a stereo output, and a pair of speakers positioned at both sides of the main body for reproducing stereo output. According to the present invention there is provided a transportable sound reproduction system for transducing binaurally encoded signals to near-field reproduction comprising, a head locator furnishing tactile or optical feedback to indicate the correct listening position for positioning a listener's head at a desired location in said near-field, and a pair of speakers for establishing said near field in fixed relation to said head locator such that said speakers are located close to and forward of the desired location of said listener's head, and equalisation and power amplifying circuitry coupling said binaurally encoded signals to said pair of speakers. Preferably, the head locator comprises a chin rest. The system may further comprise a transportable support. The speakers may be detachably mounted by a pair of arms, each of said arms mounting one of said speakers to said support. The support may comprise a bass enclosure which may further comprise a pair of output connectors. Furthermore, each of the speakers may further include an input connector for detachably electrically connecting a respective speaker to a respective one of said output connectors. Preferably, the bass enclosure contains equalization circuitry, power amplifying circuitry, and at least a loudspeaker driver. The bass enclosure may have an output port located about 10cm (4 inches) in front of the location of the listener's head when his/her head is positioned by said head locator. Preferably, each of said arms is of the order of 20.5cm (8 inches) in length and said support is constructed and arranged to coact with said arms to mount said speakers at desired locations relative to a desired location of a listener's head and established by said head locator about 17.5cm (7 inches) to the front of and to the side of and about level with the listener's ears when his/her head is positioned by said head locator. The speakers may be located at desired locations about 17.5cm (7 inches) to the front of and to the side of and about level with a listener's ears when his/her head is positioned by said head locator. Furthermore, according to the present invention there is provided a kit comprising: a transportable sound reproduction system according to any of the preceding claims, and a carrying case including protective packaging with compartments for detachably securing the components of the transportable sound reproduction system therewithin. Preferably the kit further comprises compartments in said protective packaging for accommodating a pair of arms, each of said arms detachably securing a respective one of said speakers to said speaker support. Other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawings, in which: FIG. 1 is a perspective view of a transportable sound reproduction system according to the invention; FIG. 2 is an exploded side view showing the connection of an arm to the bass enclosure and a speaker; FIGS. 3A and 3B are end and side views of the connection of the chin support to the bass enclosure; FIG. 4 is a block diagram of some of the components housed within the bass enclosure; FIGS. 5A and 5B are diagrammatical representations of a carrying case shown open and closed; and FIGS. 6-8 are diagrammatical representations of alternate embodiments of the invention with different forms of head locators. 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 transportable sound reproduction system 10 for transducing binaurally encoded signals with near-field reproduction. System 10 includes a bass enclosure 12 having a carrying handle 14 and a pair of jacks 16, 18. A head locator, e.g., chin rest 20, is mounted to bass enclosure 12 and used for positioning listener's head 22 at a desired location in the near-field. Connectors 24, 26 run from jacks 16, 18 to speakers 28, 30. Speakers 28, 30 are detachably mounted to bass enclosure 12 by arms 32, 34 such that the speakers are located close to and forward of the desired location of listener's head 22. Arms 32,34 are constructed of a length, e.g. 20cm (8 inches) and are arranged with a position and angular orientation relative to bass enclosure 12 such as always to position speakers 28,30 at a desired location relative to the listener, e.g. about 17.5cm (7 inches) in front of and to the side of and about level with the listener's ears. Bass enclosure 12 is formed with a slotted port 80 and generally conforms to the commercially available Bose AM-3 woofer enclosure. Bass enclosure 12 has four rubber or plastic feet, such as 81, to help prevent it from vibrating. Referring to FIG. 2, there is shown an exploded view of the connection of arm 32 to bass enclosure 12 and speaker 28. Bass enclosure 12 includes an integral mounting bracket 44 having slot 46 for receiving arm 32. Speaker 28 has a similar integral mounting bracket 48 having slot 50 for receiving arm 32. Arm 32 is slid into slots 46,50 and held in place by tightening thumb knobs 52. Referring to FIGS. 3A and 3B, there is shown the attachment of chin rest 20 to bass enclosure 12. Chin rest 20 is attached to chin bracket 54 by screws 56. Chin bracket 54 is in turn attached to mounting plate 58 by screws 60. The whole assembly is then attached to bass enclosure 12 by screws 62. Referring to Fig. 4, bass enclosure 12 contains equalization circuitry 70 that energizes left, bass and right amplifiers 71, 72 and 73, respectively. Left and right amplifiers 71 and 73 have output jacks 16 and 18, respectively. The output of bass amplifier 72 energizes woofer driver 74. The port 80 (FIG. 1) of bass enclosure 12 is located about 10cm (4 inches) in front of the desired location of listener's head 22. Referring to FIGS. 5A and 5B, there is shown carrying case 36 for packaging transportable sound reproduction system 10 as a kit. Carrying case 36 includes handle 38 for ease of carrying and protective packaging 40 having compartments 42 for detachably securing bass enclosure 12, head locator 20, speakers 28, 30, and arms 32, 34. Referring to FIGS. 6-8, there are shown alternative embodiments of the invention with speakers 28 and 30 attached to a video monitor 91 showing different head locators. FIG. 6 shows a padded forehead rest 92 hingably supported from the top of monitor 91 so that it can swing up and back upon the top of the monitor when not listening. FIG. 7 shows a chin rest 20' mounted upon a hinged base plate bracket 93 and FIG. 8 shows a pair of angled sight tubes 94A and 94B oriented so that when the listener has a clear view through both tubes simultaneously, the head is correctly located. The head locators need not be attached to a monitor, but might alternatively attached to the bass enclosure, or other suitable transportable supporting structure. The invention has a number of advantages. It can be used virtually anywhere without the acoustics of the playback environment compromising the quality of the auditory illusion. It is transportable. It is relatively comfortable and hygienic. The listener may easily enter and exit the desired listening region. The head locator furnishes tactile or optical feedback to indicate the correct listening position. The invention may be rapidly and correctly assembled and disassembled. The speaker support arms may be keyed to assure proper location of the left and right speakers. The invention may reproduce sound at relatively high sound levels perceived by the listener at the desired location while perceived at significantly lower sound levels outside the desired location. When reproducing binaurally encoded signals, it creates a three dimensional auditory illusion that is more realistic than the illusions produced by headphones or by far-field loudspeakers. When binaurally encoded signals are also transaurally encoded before being reproduced by the invention, using encoding methods known in the art, the invention can create auditory illusions that are nearly indistinguishable from the listening experience the listener would receive in the actual sound field being simulated.

Claims: A transportable sound reproduction system for transducing binaurally encoded signals to near-field reproduction comprising, a head locator (20) furnishing tactile or optical feedback to indicate the correct listening position for positioning a listener's head (22) at a desired location in said near-field, and a pair of speakers (28, 30) for establishing said near field in fixed relation to said head locator such that said speakers are located close to and forward of the desired location of said listener's head (22), and equalisation (70) and power amplifying (71, 73) circuitry coupling said binaurally encoded signals to said pair of speakers (28, 30). A system in accordance with claim 1, wherein said head locator comprises a chin rest (20). A system in accordance with claim 1 or claim 2, further comprising a transportable support (10); and wherein said speakers (28, 30) are detachably mounted by a pair of arms (32, 34), each of said arms mounting one of said speakers to said support. A system in accordance with claim 3, wherein said support (10) comprise a bass enclosure (12). A system in accordance with claim 4, wherein said bass enclosure (12) has a pair of output connectors (16, 18) and each of said speakers (28, 30) further includes an input connector (24, 26) for detachably electrically connecting a respective speaker to a respective one of said output connectors. A system in accordance with claim 4 or claim 5, wherein said bass enclosure (12) contains equalization circuitry (70), power amplifying circuitry (71-73), and at least a loudspeaker driver (71,73). A system in accordance with any of claims 4 to 6, wherein said bass enclosure (12) has an output port (80) located about 10cm -4 inches- in front of the location of the listener's head when his/her head is positioned by said head locator (20). A transportable sound reproduction system according to claim 3, wherein each of said arms (32,34) is of the order of 20.5 cm -8 inches- in length and said support (10) is constructed and arranged to coact with said arms to mount said speakers (28,30) at desired locations relative to a desired location of a listener's head and established by said head locator (20) about 17.5cm (7 inches) to the front of and to the side of and about level with the listener's ears when his/her head is positioned by said head locator. A transportable sound reproduction system in accordance with claim 1 wherein said speakers are located at desired locations about 17.5cm -7 inches- to the front of and to the side of and about level with a listener's ears when his/her head is positioned by said head locator. A kit comprising: a transportable sound reproduction system according to any of the preceding claims, and a carrying case (36) including protective packaging (40) with compartments for detachably securing the speaker support (10), the head locator (20) for positioning a listener's at a desired location, and the pair of speakers (28, 30). A kit in accordance with claim 10, further comprising compartments (42) in said protective packaging (40) for accommodating a pair of arms (32,34), each of said arms detachably securing a respective one of said speakers (28,30) to said speaker support (10).

Inventors: JOHNSON EDWIN C JR, JOHNSON, EDWIN C., JR., JOHNSON, EDWIN C., JR., BOSE CORP.
Applicants: BOSE CORP, BOSE CORPORATION
Application year: 1995
Main classification: H04S1
IPC codes: H04R5, H04S1, H04R1, G10K15