US1978456A - Binaural address system - Google Patents

Description

Oct. 30, 1934. R, GosHAW BINAURAL ADDRESS SYSTEM Filed May 4, 1932 INVENTOR Irl R. EnShaW ,WBY

i ATTORNEY Patented ct. 30, i934 UNITED sTATss BINAURAL ADDRESS SYSTEM Irl R. Goshaw, Nutley, N. J., assigner to Wired Radio, Inc., New York, N. Y., a corporation of Delaware Application May 4, 1932, Serial No. 609,061

5 Claims.

This invention relates to electrical transmission and reproducing systems, and particularly to public -address and recording systems for large auditoriums and outdoor areas.

An object of the invention is to transmit to a group of listeners a source of sound in its natural aspect. l

Another object of the invention is to maintain directional effects in a sound source for a large audience when the sound is reproduced electrically at different points.

A still further object of the invention is to provide an amplification system having varying amounts of amplification in accordance with the amplitude or strength of the input signal.

Binaural' transmission systems for recording and reproducing in talking motion pictures and public address systems are well knownI in the 1 art. Such systems obtain binaural aspects by the phase and amplitude discrimination between a signal arriving at microphones or other pick-up devices positioned to correspond to the ears of a person. It has been found, however, in the practical use of such systems that it is diilicult to distinguish the direction of a source of sound solely by phase displacement, and that where a high percentage of successful tests were made, the sense of direction was obtained chiefly by amplitude variations arriving at the listener.

The present invention utilizes the fact that amplitude is the principal factor in direction determination. The invention contemplates means for emphasizing this effect to such an extent that an entire audience willbe aware of the binaural aspect regardless of the position of any one per- .son with respect to the sound'source or reproducers. The means to produce this differential in amplification is an amplifying circuit which varies its amplification constant with amplitude input, a preferable type of circuit being described hereinafter. Two such amplifying circuits are fed from two groups of pickup devices positioned at the sides or ends of th'e action space, and feed groups of reproducing devices such as loud speakers located in nearby positions, the binaural effect being so emphasized that each listener in a'large audience will not only be able to receive the signal at the proper volume but will also be definitely aware of its direction. Such a system is applicable to public address systems as stated above, and also to sound recording and reproduction for talking motion pictures.

The invention will be more fully understood by reference to the following specification read in conjunction with the accompanying drawing in which:

Fig. 1 is a.diagrammatic drawing of the position'ing of pick-up and sound reproducing devices in accordance with the invention; and

Fig. 2 is a schematic drawing of the amplifiers employed in the arrangement of Fig. 1.

Now referring particularly to Fig. 1 an action area 5 which may constitute a stage or platform in an auditorium or outdoors, has positioned at each end or corner thereof, a plurality of pickup devices 6 and 7. These pick-up devices may extend partially. along the front portion of the .area or in any suitable positions to intercept signals advantageously. Each group of devices or microphones are connected to the input of similar amplifiers 9 and l0 which feed a plurality of groups of loud speakers 11 and 12. These speakers may be .positioned behind .curtains orin the partitions of the auditorium, and for outdoor work may be mounted upon supporting structures in accordance with well known public address systemv practice.

Two sources of sound, S1 and S2 have been shown within the area 5, it being obvious that the source S1 will produce at the group of pick-up 6 a much higher volume level than at group 7, the amplitude of the signal varying in accordance with the.

square law minus a certain absorption constant depending upon `the medium through which the sound is projected. Similarly, the source S2 -will produce in the microphones 7 a volume level greater than that in the microphones 6 in accordance with the same law. Now, when each amplifier produces proportional amplitudes in the reproducing devices there will occur to those listeners seated near either group of loud speakers, no change whatever with respect to direction. These listeners will always receive sound from the same group of speakers regardless of amplitude variation in the pick-up devices because of theirproximity to the speakers. The present invention corrects this defect in present binaural systems by producing a differential amplification in the proper direction in accordance with the strength of the signal which emphasizes the desired effect 'and consequently produces the binaural aspects for the entire audience.

Now referring to Fig. 2 an amplifier system is shown having two stages, it being understood that more stages can be added in accordance with well known amplifier practice. A sound signal is translated into electrical currents by a pick-up device or microphone 15. The microphone is in a series circuit including the primaries of input transformers 16 and 17 and a source of energy 18. The output of the transformer 16 is impressed upon a vacuum tube 19 of the screen grid variavble mu type well known in the art in which the control grid bias varies the amplification factor of the tube without distortion. In the input circuit of the tube 19 is a biasing resistance 20 which controls the amount of operating bias potential on this tube, the fixed potential being determined speakers 12.

by a battery 21. The output circuit of tube 19 includes the primary of inter-stage transformer 22 and a source of polarizing potential 23 which also provides a polarizing potential for the screen grid or second anode 24. Of course the potential for the element 24 may also be furnished by -a separate energy supply.

The output of transformer 22 is impressed upon -the usual type of screen grid tube 26 this tube not having the variable mu characteristic. The tube 26 has thereon a iixed bias from a source 27 and an anode polarizing potential 28. The output of the tube 26 is through an output transformer 29, the output being impressed upon a reproducing device such as a loud speaker 30. In this stage, however, the screen grid element 31 of the tube 26 is connected so as to have thereon a variable voltage in accordance with the input of the amplifying system, but has its initial operating point fixed by a voltage source 32.

Now returning to the input circuit of the ampliier, the signal currents produced in the microphone 15 are transmitted 'through the output transformer 17 to a rectifying device 33 of any suitable type followed by a lter 34 which reduces the pulsating currents to a smooth direct current. The output of the filter is connected to the screen grid element 31 of tube 26 and also to one terminal of the resistance 20 of the tube 19. The voltage and current obtained from the lter 34 will be proportional to the level of the input signal. This energy impressed on the screen grid 31 will change the amplification factor of the tube 26 in accordance with the input signal, by shifting the operation of the tube from one characteristic to another having different slopes. That is, the stronger the signal the higher the amplification factor and since the tube is always operating on the straight portion of one of its characteristics, distortion will be eliminated.

This same result is accomplished by yimpressing energy from the filter 34 on the resistance 20 of the tube 19 which changes the amplification constant of the tube in the desired direction. For instance, the xed bias placed upon the tube 19 gives it a low mu which is increased as the bias is removed by the energy from the lter 19. That is, should the signal be of small amplitude on arriving at the microphone 15, the amplification system will provide a certain amount of overall gain which will be low compared with the gain in the system at a higher input level.

By the use, therefore, of two circuits of the above type at positions 9 Aand 10 in Fig. 1, a signal occurring at Si will produce in the loud speakers 11, a volume level much greater proportionally than that produced by the same signal in the loud In fact, the source Si depending upon its position, will practically be reproduced solely at the loud speakers 11 and not at the loud speakers 12, so that those listeners in the neighbourhood of speakers 12 will recognize the signal as originating at the point Si and not at the other end of the action area due to the proximity of the speakers 12.

By employing such a pick-up system for recording and by a similar arrangement of reproducing devices for the projection of talking pictures, the binaural aspects are obtainable. When the recording and reproducing ampliers are both of the type disclosed above, the binaural 'effect is doubly emphasized.

The differential amplifying system has been illustrated in one particular modification, but it is to b understood that other uses will suggest themselves to those skilled in the art, such equivalent systems being considered within the scope of the appended claims.

What is claimed is:

l. In a binaural public address system supplying a listening area, the combination of a plurality of sound pickup devices in the locality of a source of sound, a plurality of sound reproducers arranged on certain portions of the border of said area, and volume expanding means positioned intermediate said devices and said reproducers, said means having an amplifying factor which increases with an increase in signal input to render emphasis to amplitude discrepancies at said devices.

2. In a binaural system for a listening area, the combination of a plurality of microphones positioned at different points for detecting the same sound source. a plurality of speakers arranged outside said area and directing sound into said area, and a plurality of volume expanding amplifiers positioned intermediate said microphones and said speakers, said amplifiers having an amplifying factor which increases with increased volume level at the input of said microphones to provide a directional effect for listeners at substantially all positions within said area.

3. In a binaural reproducing system for a listening area, a microphone, a loud speaker positioned on the border of said area at a distance from said microphone, a volume expanding amplifier intermediate said microphone and said speaker, a second microphone, a second loud speaker positioned on another portion of the-border of said area at a distance from said second microphone, another volume expanding ampliiier intermediate said second microphone and said second speaker, said microphones being positioned to receive sound from a common source and said speakers directing sound into said area, and means for varying the amplication factor of said ampliflers in accordance with the volume of the sound reaching said microphones, the effective operating speakers being determined by the microphone receiving the larger amplitude of said sound.

4. In a binaural reproducing system for a denite listening area, a sound reproducer positioned at'one point of said area directing sound into said area, a second sound reproducer positioned at another point of said area directing sound into said area, a volume expanding ampliiier connected to each of said reproducers, and sound pick-up devices feeding said amplifiers, said de'- vices receiving varying amplitudes of sound from a sound source in the sound pick-up area, the gain of said amplifiers being arranged to effectively operate th'e sound reproducing device connected to the pick-up device receiving the larger amplitude.

5. In a binaural system for a listening area, a sound reproducer at a position in said area, a second reproducer at another position in said area, a microphone in a sound pick-up area connected to one of said reproducers, a second microphone in said pick-up area connected to the other of said reproducers, said microphones being positioned in a sound pick-up area, and volume expanding means intermediate said microphone and said reproducers for effectively reproducing the sound from said area at the respective reproducer in accordance with the microphone energized in said sound pick-up area.

IRL n. GosHAW.

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