Sound Reproducing Systems Utilizing Acoustic Processing Unit

Other objects, features and advantages of the invention will become apparent, and its construction and operation better understood, from the following detailed description of preferred embodiments, when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the present invention;

FIG. 2 is an elevation view partly cut away, of an acoustic processing unit according to the invention;

FIG. 2A is a fragmentary elevation view of a transducer useful for converting sound signals produced by the acoustic processing unit of FIG. 2 to electrical signals in combination with electro-acoustic reproduction systems; and

FIG. 3 is an exploded perspective view, partly cut away, of the acoustic processing unit of FIG. 2.

Referring now to the drawings, FIG. 1 illustrates the acoustic headphone embodiment of the invention in schematic form as consisting of a multi-channel signal source 10, such as a multi-channel electronic organ, which produces six separate electro-acoustic signals on six separate output lines 12. In the case of an electronic organ, the output signals would be derived from the output system of the respective channels, immediately ahead of the loudspeaker for the channel. The six electro-acoustic signals from source 10 are applied to an acoustic processing unit 14, wich comprises a substantially sealed enclosure in which a corresponding number of electro-acoustic transducers are mounted and connected to receive a respective electro-acoustic signal. Sound signals radiated from the individual transducers are acoustically mixed within the enclosure to produce composite sound signals which are acoustically coupled from the enclosure by acoustic transmission means 16 and 18 and are transmitted through a pair of acoustic paths 20 and 22 having earpieces 20a and 20b, respectively, to the right ear R and the left ear L of a listener P. Each of acoustic transmission means 16 and 18 includes a pair of acoustic pipes arranged to couple sound from two different spaced-apart portions of the enclosure volume, which are joined together and to the transmission paths 20 and 22, respectively, by a "T"-connection, so as to produce in the transmission paths 20 and 22 separate sound waves each containing a dominant sound wave corresponding to one or more selected different ones of the electro-acoustic signals applied to the processing unit and sub-dominant sounds corresponding to others of the applied electro-acoustic signals. Accordingly, the listener P hears in both ears some portion of the sound radiated from all of the transducers, some more predominantly than others.

As illustrated in FIGS. 2 and 3, which are elevation and perspective views, respectively, a preferred construction of acoustic processing unit 14 comprises a relatively small box-like enclosure 30 which may be formed of wood or a rigid plastics material; in a successfully operated embodiment the enclosure, made of wood, was approximately ten inches long, about four inches high and about three inches deep. The internal volume of the enclosure is divided into two approximately equal volume chambers A and B by a baffle 32 disposed parallel to the front wall 34 of the enclosure. The enclosure is sealed except for a single port 36 for porting chamber A, and chamber A is ported to chamber B by an opening 38 formed in baffle 32. The function of the ports will be evident as the description proceeds.

In the embodiment illustrated in FIGS. 2 and 3, seven conventional loudspeakers, each having a circular vibratile diaphragm approximately two inches in diameter, are mounted within the enclosure. Four of the loudspeakers 40, 42, 44 and 46 are supported on the inner surface of wall 34 and uniformly distributed along the length dimension thereof, and, as shown in FIG. 3, substantially equidistant from the side walls of the enclosure. Each of the loudspeakers has the usual driver and basket disposed behind the speaker cone. Loudspeakers 40, 42, 44 and 46 are mounted with the outer perimeter of their diaphragms in direct contact with the inner surface of wall 34, so as to trap a relatively small volume of air between the diaphragm and the wall, and are positioned concentrically with respect to relatively small circular openings 48, 50, 52 and 54 in wall 34, typically having a diameter of 1/4 inch. Each of these four loudspeakers is connected to receive an electro-acoustic signal from a different one of the channels of the electronic organ which, for example, may be those channels which respectively predominantly carry electro-acoustic signals representing diapason sounds, tibia sounds, string sounds, and string ensemble sounds; that is, the sounds prominently involved in the creation of animation in an electronic organ. When channel is connected to which of the four loudspeakers is a matter of choice of the designer, dependent on which two of the four channels are to be dominant in the two sound signals transmitted to the earphones, as will now be explained.

The openings 48 and 52 respectively confronting the diaphragms of loudspeakers 40 and 44 are acoustically coupled together by acoustic transmission paths 56 and 58 and to acoustic transmission path 22 by a "T"-junction 60, each of which transmission paths may be a length of quarter-inch flexible plastic tubing. Similarly, the openings 50 and 54 respectively confronting the speaker cones of loudspeakers 42 and 46 are coupled together by transmission paths 62 and 64 and through a "T"-junction 66 to tube 20, the transmission path going to the right earphone. The part of "T"-junctions 60 and 66 joined to tubes 22 and 20 constitute, in essence, a pair of acoustic output ports for the processing unit at which respective ones of a pair of composite sound signals are produced. Each of loudspeakers 40, 42, 44 and 46 and its associated acoustic transmission path functions similarly to a conventional stethescope; the cone of the loudspeaker is analogous to the diaphragm chest piece of a stethescope instrument and the tubing is not unlike the ear tubes of the stethescope. Sound waves generated by variations in the pressure of the air confined between the speaker diaphragm and the inner surface of wall 34 caused by vibrations of the diaphragm are transmitted by the sound conducting tube and earplugs to the ear of the user. The acoustic transmission paths 56, 58, 62 and 64 preferably are of equal length so as to introduce substantially the same transmission losses and thus provide a balance in the acoustic power supplied to sound conducting tubes 20 and 22. The efficiency of the transmission of sound from the enclosure is inversely proportional to the volume of air trapped between the speaker cone and the inner surface of wall 34; therefore, best results are obtained when loudspeakers having relatively shallow diaphragms are used.

The rationale of the described acoustic transmission means for coupling sound energy from chamber B of the enclosure will be understood if it be assumed that an electro-acoustic signal is applied to only loudspeaker 40. Vibration of the cone of the speaker 40 in response to energization of the driver thereof causes corresponding variations in the pressure of the air enclosed between the speaker cone and the wall 34, and these pressure variations are transmitted through tube 56, utilizing the principle of a stethescope, to "T"-junction 60 and to the left earphone. At the same time, the back side of the vibrating diaphragm of loudspeaker 40 causes variations in the pressure of the air enclosed in chamber B, which pressure changes are imposed on the back surface of the diaphragms of loudspeakers 42, 44 and 46, the effect decreasing with increasing distance from loudspeaker 40. The resulting pressure-induced vibrations of the diaphragms of speakers 42, 44 and 46 cause corresponding variations in pressure of the volume of air defined by the front surface of the cone and wall 34, thereby causing sound waves generally corresponding to the electro-acoustic signal applied to speaker 40 to emanate from openings 50, 52 and 54 as well. The mechanically-induced sound produced by loudspeaker 42, which is of greater amplitude than that produced by loudspeakers 44 and 46 by reason of its closer proximity to the electrically energized loudspeaker 40, is coupled via tube 62 and "T"-junction 66 to transmission path 20 and the right earphone, and opening 54 confronting loudspeaker 46 is also coupled to the right earphone. The sound signal parasitically produced by loudspeaker 44 in response to energization of speaker 40 is coupled via tube 58 to "T"-junction 60 and transmission path 22 to the left earphone. Thus, the sound signal generated by electrically-energized loudspeaker 40 is dominant in the left earphone, and a reduced amplitude proportion of a substantially corresponding sound signal appears at the right earphone, thereby to simulate to a significant degree what each ear would hear when a single tone is acoustically reproduced in a listening room environment.

It will now be evident that if any two of the four loudspeakers is simultaneously electrically energized, one of them will produce a dominant sound signal in one of the earphones and the other will produce a dominant sound signal in the other earphone, and the listener will also hear in both ears sub-dominant sound signals from each of the other three loudspeakers. This result obtains whether the two electrically energized speakers are adjacent or non-adjacent. It follows that if all four of loudspeakers 40, 42, 44 and 46 are energized simultaneously, a listener will hear in his right ear dominant sounds corresponding to the electro-acoustic signals applied to loudspeakers 42 and 46 and in his left ear will hear dominant sounds corresponding to the signals energizing loudspeakers 40 and 44, and in both ears will hear sub-dominant sounds corresponding to the electro-acoustic signals applied to the other loudspeakers.

The composition of the composite sound waves appearing at the left and right earphones is further affected by sound waves radiated directly into chamber B by additional loudspeakers, in the illustrated embodiment, three, supported within chamber A on baffle 38. A loudspeaker 70 connected to receive the electro-acoustic signals from the bass channel of the organ is preferably positioned equidistant from the ends of the baffle so as to straddle speakers 42 and 44, and two additional speakers 72 and 74 are positioned in alignment with speakers 40 and 46, respectively. The loudspeakers 70, 72 and 74 are concentrically placed over respective openings 76, 79 and 80 in baffle 32 having diameters substantially equal to the diameter of the speaker cones so as to radiate, when energized, sound waves directly into chamber B. Thus, the sound waves radiated by one or more of loudspeakers 70, 72 and 74 mechanically induce a corresponding signal onto the back sides of the diaphragms of loudspeakers 40, 42, 44 and 46 to a degree determined by the proximity of an energized speaker to the speakers from which sound is acoustically coupled to the headphones. Each of loudspeakers 70, 72 and 74, when energized, will also mechanically induce a corresponding lower amplitude signal onto the backside of the diaphragm of the other two loudspeakers to further affect the sound signals emanating from the front side of the diaphragm into chamber B. Because low frequency tones are essentially omni-directional in a listening room environment, the speaker 70 selected to reproduce the electro-acoustic signal from the bass channel is positioned as centrally as possible with respect to the other loudspeakers so as to have a substantially equal effect thereon and thus appear in substantially equal amplitude in both earphones of the headset to simulate the real live room environment, in which it is difficult to tell where the bass tones are coming from. Speakers 72 and 74 can be used for any other desired effect; for example, piano-like tones might be reproduced through loudspeaker 72, and loudspeaker 74 might be energized by an electro-acoustic signal having characteristics to simulate the effect of a Leslie rotating speaker.

The port 36 in wall 30 allows maximum deflection of the low frequency speaker 70, and thus greater efficiency than if chamber A were sealed, and port 38 in the baffle allows porting of the sound in chamber B in the event that very low frequency sound signals should be produced therein. The basis function of earphones being to listen to the program one is playing without disturbing others, the port 36 is preferably stuffed with acoustic damping material 82 to minimize the escape of high frequency notes through port 36; the port is sufficiently small in diameter as to preclude any bass tones being heard. The damping material may be fiberglass acoustic insulation or other suitable acoustic damping material known to the art.

Although the described embodiment has four loudspeakers with alternate ones grouped in pairs to produce the dominant sound signals for the left and right earphones, it is to be understood that the principle can be extended to enclose a larger even number of loudspeakers in chamber B, and acoustically mixing the sound output from alternate ones of the speakers into the left earphone channel and acoustically mixing the outputs from the others and transmitting the composite sound signal to the right earphone channel. For example, should it be desired to reproduce as dominant signals the electro-acoustic signals from six separate channels, three acoustic paths would be utilized to mix and couple the signals from three of the loudspeakers to the left transmission path 22, and the signals from the other three loudspeakers would be similarly mixed and coupled to the right acoustic transmission path 20. If necessary or desired, the number of loudspeakers mounted on baffle 32 may be correspondingly increased. Thus, the inventive principle may be utilized to acoustically process as few as two electro-acoustic signals, or as many as there are likely to be in an electronic organ, even the most sophisticated. Should the processing unit be designed for exclusive use in the processing of stereophonic electro-acoustic signals, all that is required is an enclosure defining a single chamber in which only two transducers are supported, and a pair of acoustic transmission paths respectively coupled to the two transducers for coupling the two acoustic signals to the left and right ears of the listener. Each of the transducers will mechanically induce its vibrations in the other transducer, providing additional acoustic processing generally equivalent to that which would be provided if the stereophonic signals were reproduced by a pair of loudspeakers radiating into a listening room.

Also, although the disclosed embodiment of the acoustic processing unit employs but two chambers, the invention contemplates the provision of one or more additional chambers "stacked" above chamber A, each containing one or more loudspeakers supported to radiate sound energy into the adjacent chamber. For example, a third chamber, with wall 30 serving as a baffle, may be provided above chamber A, and one or more loudspeakers supported over openings therein substantially equal in diameter to the diameter of the speakers, so as to radiate sound energy into chamber A when energized by a respective electro-acoustic signal. The sound energy radiated into chamber A will mechanically induce corresponding vibrations in the diaphragms of the loudspeakers supported in chamber A which, in turn, will mechanically induce vibrations in the diaphragms of the loudspeakers supported in chamber B to be acoustically coupled from the unit to the earpieces of the acoustic transmission paths. It may be desirable in certain applications, for example, to place in the third chamber a bass speaker, of large diameter than the speakers employed in the other chambers, for supplying essentially omni-directional bass tones to both the left and right earpieces.

Although acoustic transmission means 16 and 18 have been described as comprising flexible plastic tubing of a particular diameter, it is contemplated that other sized tubing may be used and that the acoustic transmission paths may take other forms, as, for example, passageways of appropriate size molded or otherwise formed in the wall 34 and communicating with a pair of nipple connectors projecting from the wall to which the earphone transmission paths 20 and 22 can be connected. Further, although tests have shown that the smaller the loudspeakers (and consequently the smaller the enclosure) the better the described acoustic processing unit works, acceptable performance is possible with loudspeakers larger than those used in the described embodiment. Thus, it is preferred to utilize the smallest commercially available loudspeakers (which usually have relatively shallow diaphragms to thus enhance the stethescope effect) to gain the further advantages of reduction of the cost and weight of the acoustic processing unit and ease and convenience of mounting it in the organ cabinet.

As an alternative to the described acoustic reproduction of the composite sound signals produced at the acoustic output ports of the acoustic processing unit, they may be converted to respective corresponding electrical signals for reproduction by electro-acoustic transducers, such as electric headphones or a pair of loudspeakers. To this end, the composite sound signals produced at the output ports of the processing unit, that is, at the outputs of "T"-junctions 60 and 66, are applied to respective acoustic-electric transducers, shown in FIG. 2A as a pair of loudspeakers 90 and 92 supported within respective cavities C and D defined by a box-like enclosure 94 having a baffle 96 which divides the internal volume of the enclosure into two substantially equal volume cavities. The enclosure may be formed of wood or a rigid plastics material, and each of cavities C and D is ported to the ambient by openings 98 and 100, respectively, formed in a wall of the enclosure. Loudspeakers 90 and 92, each of which has the usual driver and basket disposed behind the speaker cone, are mounted with the outer perimeter of their diaphragms in direct contact with the inner surface of wall 102 of the enclosure, concentrically with respect to circular openings in wall 102 in which short sections of hollow tubing 22 and 20 are inserted for coupling the composite sound signals from the acoustic output ports of the processing unit of FIG. 2 into the volumes defined by the wall 102 and the cones of speakers 90 and 92, respectively. Vibration of the speaker cones in response to the respective applied composite sound signals produce respective corresponding electrical signals having the same information content as the applied acoustic signals. The enclosure 94 is comparable in size to the enclosure of the acoustic processing unit, and if, as suggested earlier, the acoustic transmission paths take the form of passageways molded or otherwise formed in the wall 34 of the processing unit and communicating with a pair of nipple connectors, the upper wall 102 of enclosure 94 may be mounted immediately adjacent wall 34 of the acoustic processing unit enclosure for compactness and to shorten the acoustic transmission paths from the acoustic output ports to the acoustic-electric transducers. Loudspeakers 90 and 92 may be of the same size and type as those utilized in the processing unit and typically are inexpensive, readily available, one-inch or two-inch diameter speakers of the type employed in transistor radios.

Although the acoustic-electric transducers have been described as comprising loudspeakers, it is contemplated that alternatively microphones may be used to convert the composite sound signals to corresponding electrical signals.

The electric-acoustic signals from transducers 90 and 92 may be reproduced by any desired electro-acoustic transducers, the alternatives of loudspeaker reproduction and electric earphone reproduction being illustrated in FIG. 2A. The signals from transducers 90 and 92, representative of "left" (L) and "right" (R) composite sound signals, respectively, are applied to respective power amplifiers 104 and 106, and the amplified signals are alternatively applied, by actuation of a pair of ganged switches 108 and 110, to a pair of loudspeakers 112 and 114, or to the contacts 116 and 118 of the jack 120 of stereophonic electric headphones 122. As indicated by dotted line 124, the outputs of amplifiers 104 and 106 are normally applied to loudspeakers 112 and 114, and when the earphone jack is inserted the switches are activated to disconnect the loudspeakers and to apply the amplified signal to the headphones. Although not shown in FIG. 2A, it will be understood that because of the relatively high power capability of ampilfiers 104 and 106 required to drive the loudspeakers, it may be necessary to attenuate the amplified signals before application to the headphone.

It will now be evident that the use of the acoustic processing unit of FIG. 2 for acoustically processing and mixing signals from a plurality of independent channels, seven in the disclosed embodiment, to produce two composite sound signals, converting the two composite sound signals to corresponding electro-acoustic signals, and reproducing the two electrical signals with respective loudspeakers, greatly reduces the cost and space requirements of the sound reproduction system. Whereas a conventional organ system with the same number of channels requires seven reproduction channels each including a 30-watt amplifier and a relatively large and expensive loudspeaker, each of the order of six to ten inches in diameter, the present invention enables comparable reproduction of a like number of channels with nine small, inexpensive loudspeakers, seven low power amplifiers, one for each of the loudspeakers contained in the acoustic processing unit, each of which requires a power capability of no more than a few hundred milliwatts, only two high power amplifiers, of the order 30 to 35 watts each, and only two large loudspeakers, of the order of ten inches to twelve inches in diameter, for presentation of the multichannel signals to the outside world. Quite apart from the cost savings, the resulting saving in space enables the design and manufacture of organs with a large number of channels, desirably as many as eight or ten, which can be accommodated in a console of limited volume dictated by the length of the keyboard and tradition. Heretofore it has been totally unfeasible to accommodate more than about six conventional reproduction channels in a console of the size desired for intended home use. Moreover, when the electrical signals corresponding to the composite sound signals are reproduced by stereophonic electric headphones, the left ear hears the "left" channel and the right ear hears the "right" channel as determined by the characteristics of the acoustic processing unit; in other words, the headphone listener hears essentially the same presentation as would be heard from the pair of loudspeakers 112 and 114, and there is no cancellation or undesirable adding of signal components.

Although the invention has been described with reference to specific embodiments, variations within the spirit and scope of the invention will occur to those skilled in the art. For example, the acoustic processing unit may take physical forms other than those specifically described or suggested, and the acoustic-electric transducers may take forms other than the example shown and described.