US2852604A - Sound reproduction apparatus - Google Patents

Description

Sept, 6, 1958 R. H. MaccuTcHEoN 2,852,604

' sounn REPRODUCTION APPARATUS Filed Aug. 5, 1954 OZ-Il m m L a mm i 3 mm mm 5 m mm 5 m $50 $5 mmlv $05 $96 alwm mu Nu om OI w? a W m I w W m. 2 w u m m J! t w 1. lu s 52E 99E. womaow m zoz United States Patent ()fiice 2,852,604 Patented Sept. 16, 1958 SOUND REPRODUCTION APPARATUS Richard H. MacCutcheon, Shaker Heights, Ohio Application August 5, 1954, Serial No. 447,983

6 Claims. (Cl. 179-1) The present invention relates to improvements in socalled electronic sound reproduction apparatus.

In recent years there has been increasing interest evidenced in binaural and stereophonic reproduction of both recorded and live sound. The advantages of providing separate sound reproducing channels for spaced points or for the separate ears of a listener are now well known and have been for many years-at least since the time of the Disney movie Fantasiabut widespread commercial and consumer acceptance has been limited because plural parts (from microphones on) have to be used throughout resulting in a high cost for satisfactory multichannel equipment. Further, for commercial, adminis trative law and labor relations reasons broadcast station operators do not often seem disposed to make several broadcast channels available for a single program, and as for recorded music the public does not seem willing to accept the bother and trouble of handling reels and threading binaural tape, while the idea of using twin needles and cartridges responsive to twin sets of phonograph record grooves has run into many mechanical problems associated with tracking.

It is an object of the present invention to provide simple and inexpensive means for at least partially overcoming the above mentioned difiiculties.

It is a further object of the invention to provide apparatus and methods for simulating a binaural efiect while using only a monaural source of electric energy in the audio frequency range, such as a single radio broadcast receiver, or a conventional all-electric phonograph, or single track sound film equipment.

Other objects and advantages will become apparent and the invention may be better understood from consideration of the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a diagrammatic and block diagram of a preferred embodiment of the invention; and

Fig. 2 is a one line diagram of a modification.

In accordance with the invention, a single channel (monaural) source of audio frequency is used. In Fig. 1 this takes the form of a conventional radio tuner and amplifier combination, 10, which may have usual accoutrements such as an antenna 11, ground 12, power plug 13, control knob 14 for tuning and control knob 15 for adjusting volume. The output of the receiver 10 is taken through Wires 16 so that a portion of this output leads to a circuit which includes a time delay means which, in Fig. 1, is a simple echo chamber comprising a substantially sound proofed box 17 containing a reproducer 18 and spaced therefrom a pick-up, e. g., microphone, 19. If desired the space between reproducer and pick-up may be variable (as indicated by the loop in the mike cord 20 and by the double headed arrow 21 adjacent the pick-up) but this is not essential and there has been some indication that the preferred efiective distance between these elements is exactly the same as the distance between ears on the average human head, although the spatial distance between elements may be less, for example where in a manner too well known to require illustration here the air space is eliminated and reproducer and pick-up are separated by a helically coiled hard metal wire embedded in a sound absorbing material such as sponge rubber.

As observed in Fig. 1, the output of the time delay means is taken through connections 20 to an amplifier 22 which preferably has its own gain control as indicated by a knob 23 and an associated double headed arrow. The amplifier output is taken through connections 24 to a high and low frequency separating means 25 assumed to be an ordinary crossover network, a standard item of commerce and therefore not described. Meanwhile a similar crossover 26 is fed from connections 27 from taps 28 on line 16, and thus in a branch circuit relation with respect to the time-delayamplifiercrossover-25 combination. There is thus provided a low frequency substantially undelayed signal and a low frequency time delayed signal and a high frequency substantially undelayed signal and a high frequency time delayed signal. In accordance with the invention these signals are half scrambled by taking undelayed low frequency (hereinafter abbreviated L. F., or bass) and delayed H. F. (treble) to sound reproducing means at one side, and delayed bass and undelayed treble to sound reproducing means at the other side. The sound reproducing means might be earphones located on either side of a human head, but as shown in Fig. 1 they comprise loud speakers 30, 31 located in corners of a room along a common wall 32, with speaker 30 fed L. F. through connections 33 from the undelayed crossover 26 and fed H. F. through connections 34 from-the delayed crossover 25, while speaker 31 is fed H. F. through connections 35 from the undelayed crossover 26 and fed L. F. through connections 36 from the delayed signal crossover 25.

I have found that human ears place the source of sound by nothing except relative time delay between a particular sound reaching one ear and the same sound reaching the other, and as may be apparent as the description proceeds, I have taken advantage of this fact in a way that is greatly superior to anything known in the past (except true binaural or stereo-phonic sound reproduction having all the disadvantages already mentioned).

Since, according to the invention, one or more frequency separating means are being provided anyway, it may be found desirable to secure the well known advantages of so-called woofer-tweeter combinations by using co-axial or vertically aligned or side by side speaker units for separately handling low and high frequency reproduction at each general location. Thus, in Fig. 2 the side by side arrangement is shown, there being a left side L. F. woofer 40, a left side H. F. tweeter 41, a right side H. F. tweeter 42, and a right side L. F. woofer 43. Left woofer and right tweeter are fed from an undelayed circuit through a crossover 44 while right woofer and left tweeter are fed from a time delayed circuit which includes a crossover 45.

In crossover network terminology, crossover frequency is defined as the frequency at which units for which the network is designed will be driven with equal energy, and. for a woofer-tweeter assembly the optimum may be anywhere from 400 to 3000 cycles per second depending on the characteristics of the reproducers used and the discrimination and preference of the particular listener. In carrying out the present invention it may sometimes be preferable to use two crossover networks operating at the same crossover frequency, but for best all around results it may be desired to have the crossover frequencies of separate crossovers independently adjustable as by knobs (4647 in Fig. 2) which may be connected to standard parts connected in standard circuits for the purpose of 3 giving such adjustment (for example see Newitt High Fidelity Techniques, page 160, Rinehart & Co., Inc., 1953 In Fig. 2, the two crossovers are shown supplied by identical amplifiers 48-49, respectively, each having its gain adjustable by a knob shaft 50-51, respectively. Amplifier 48 is shown fed directly from an electric pickup type phonograph 52, and in a branch circuit amplifier 49 is fed from the phonograph through a variable speed drive time delay comprising, as illustrated, a continuous loop tape magnetic recorderreproducer which differs from many commercial tape recorders .in that it does not involve the nuisance of changing reels or repeatedly threading tape, and has no fixed speed, it being assumed that the speed of its drive motor (not shown) is substantially steplessly variable over a considerable range by mere adjustment of a rheostat knob 54. The VSDTD (variable speed drive time delay) device is assumed to have some (unillustrated) usual tape recorder-reproducer appurtenances such as power supply, preamplifier, means of producing bias, switches, etc., and its drive motor rotates a drive spool connected by a closed loop of magnetic recording tape 56 to an idler or driven spool 57. As shown the tape passes through four heads, a recording head 58, a pick-up head 59, another pick-up head 60 (so that by using one pick-up or the other a wider range of time delay may be gained than that permitted by drive motor speed variation alone), and an erase head 61 designed to clear the tape.

During operation, the tape speed through the pick-up heads will always be substantially the same as the tape speed through the recording head so that any phase change due to time delay adjustment will not be accompanied by change of output pitch or frequency for any given input signal. Still with the arrangement of Fig. 2 the time delay is very easily adjustable, as are also the relative amplification to the two networks and the frequency of the respective outputs from the respective networks.

If it be assumed that during operation a listeners head 62 is located as shown in Fig. 2, his left car will first hear any single bass note along line 63 from the nudelayed speaker 40. While it might be expected that his right ear would hear the same note travelling along line 64 from the same speaker a fraction of a second later, if the time delay between speakers is somewhat the same as the time delay between ears (or within 30 or 40% thereof because great accuracy is not here of importance), his mental reaction will be to discount this as his right ear picks up the same sound along line 65 from the right hand speaker 43. For one thing the listeners own face and forehead act as a shield preventing direct radiation from speaker 40 to right ear 62, and consequently he will place the sound according to the artificially introduced delay and also somewhat according to actual frequency because each crossover has a considerable overlap or range of frequencies at which both speakers which it feeds will audibly respond. At the end of the sequence, listener 62 will have the same assumed bass note reach his left ear along 66 from speaker 43 but here again the forehead interferes with direct radiation and furthermore the spatial relation will already have inscribed itself on his conscious mind and he will merely attribute this weak final effect to some kind of not unpleasing echo at the back of the hall. At any rate, if the listener is somewhat nearly centered, so that time relay and volume loss in travel from each speaker to him is about the same for either side, and if he faces the front, sound along 63 will seem to be loud because direct and first in time (for the particular note), sound along 65 will seem loud :because direct and reinforced by sound along 64, while sound along 66 will be neither early in time, nor direct, nor reinforced.

It is well known that concert (and even most jazz) orchestras have the bass instruments arranged at one end and the high pitched instruments, piccolos and the like, at the other. Furthermore, in dialog, or in a play or opera, one voice or some voices (for example, female voices) are not only pitched higher than others (for example, male) but almost always placed sidewise from them (rather than upstage or back), and in reproducing it doesnt matter much whether the sides are relatively the same as at the live show but it seems to matter greatly whether or not sides can be distinguished. In this respect the arrangement of the invention seems superior to the crude expedient of simply placing a single woofer at one side and a single tweeter at the other without having anything to which time delay could be relatively introduced at all so that the combination just sounds like a spaced woofer and tweeter (which it is) with the treble disassociated from the bass to produce an effect known to the art as disembodied top response without much effect of realism or presence. By contrast, the arrangements of the present invention places sides (and, as with true binaural, even intermediate mid points) bytime delay which is handled differently in the various circuits according to difference in frequency. This is, of course, far superior also to the simple expedient of putting the whole sound first to one side (as of a room) and then, after a time delay, to the other, for tests have indicated that the ear can tell the difference and realizes its just sound coming from one place and then from the other at least to the point where sounds of movement (Doppler effects and the like) can not be satisfactorily reproduced although they can be in a system like that of the invention at least if the relatively delayed and undelayed signals and the relatively different order of frequency signals are adjustable at least as to relative gain between them.

While I have illustrated and described particular embodiments, various modifications will obviously occur to those skilled in the art, and I desire it to be understood that the invention is not to be limited except by the scope of the appended claims .and reasonable equivalents thereof.

What is claimed is:

1. Simulated binaural sound reproduction apparatus comprising means for developing audio frequency electric energy signals, means for dividing said signals into first components of substantially undelayed relatively low frequency, second components of substantially delayed relatively low frequency, third components of substantially delayed relatively high frequency, and fourth components of substantially undelayed relatively high he queucy, and means including spaced sound reproducers and connections thereto for creating from said first and third components sound arranged to be directed at one side of a listener and for creating from said second and fourth components sound arranged to be directed at his other side.

2. A sound reproducing system comprising a source of audio frequency electrical output, means for breaking down said output into respective parts of relatively high and relatively low frequency, means for further breaking down the output to provide time delayed and substantially undelayed signals for each of said par-ts and means including a plurality of electro mechanical reproducers and connections from said source through both of said means to said reproducers to provide at a first side of a listener a low frequency undelayed signal and a high frequency delayed signal and at a second side a low frequency delayed signal and a high frequency undelayed signal.

3. A sound reproducing system as in claim 2 further characterized by at least one independently variable gain control arranged for relatively adjusting volume of delayed signals with respect to undelayed signals.

4. A sound reproducing system as in claim 2 further characterized by means for adjusting the time delay of the time delayed signals.

5. Sound reproduction apparatus comprising a monaural source of audio frequency signals. dual circuits fed from said source, a variable time delaydevice in one of said circuits and having its own variable gain amplifier, a first crossover network fed from said last mentioned amplifier, a second crossover network in the other circuit and fed from said source, left and right hand sound reproducers, and connections from said circuits to feed one reproducer with substantially undelayed relatively low frequency signals from said second crossover and to feed a reprcducer on the same side with time delayed relatively high frequency signals from the first crossover and to feed a reproducer on the opposite side with time delayed relatively low frequency signals from the first crossover and to feed a reproducer on said opposite side with substantially undelayed relatively high frequency signals from the second crossover.

References Cited in the file of this patent UNITED STATES PATENTS 2,137,932 Snow Nov. 15, 1938 2,327,956 Begun Aug. 24, 1943 2,714,633 Fine Aug. 2, 1955

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