US2263233A

US2263233A - Acoustic apparatus

Info

Publication number: US2263233A
Application number: US280941A
Authority: US
Inventors: Burck Werner
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1938-06-24
Filing date: 1939-06-24
Publication date: 1941-11-18
Anticipated expiration: 1958-11-18
Also published as: FR856727A

Description

Nov. 18, 1941. w, BURCK 2,263,233

V ACOUSTIC APPARATUS Filed June 24, 1939 RECTIFIER mo GAIN-INTENSIFYINC DEVICE GAlN-REGULATED AMPLIFIER 4 1 .5 6 AMPLIFIER I 2/ a )AMPLIFIERS I iNVENTOR. WERNER BKRCK 7k Mw L.

ATTORNEY.

Patented Nov. 18, 1941 ACOUSTIC APPARATUS Werner Biirck, Berlin, Germany, asslgnor to Telefunken Gesellschait fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application June 24, In

6Cialms.

This invention relates to an arrangement adapted to preclude acoustic feedbacks in acoustic apparatus- 1939, Serial No. 280,941

June 24, 1938 In a sound pick-up and acoustic studio, the

by providing a dynamic or sound-volume regulator means such that, when feedback occurs, the gain is cut down below the feedback level. However, this scheme has fallen short of giving full satisfaction. For, if the steady or normal amplification or gain of the installation, that is to say, the gain in the absence of voice action upon the microphone, is set to a level above the feedback limit, the amplification adjusts itself by the incipient feedback. The installation stays in a state of feedback with moderate volume. If. on the other hand, arrangements are made so that the gain is raised-only when there is acoustic action upon the microphone, then. to be sure, the installation will be free from feedback-in the absence of sound action on .the microphone: but, a feedback will arise upon the first loud action of sound on the microphone.

Now, the invention is concerned with an ar- I rangement comprising volume-range regulation circuits which is capable of operating with high amplification, while feedbacks are effectively precluded in spite of the use of circuits of the said kind.

The desired end is obtained according to the invention in the following way; the amplification of the equipment is no longer regulated only as a function of the sound intensity acting at the microphone, but in addition it is regulated in dependence upon the direction of incidence of the sound upon the microphone. This insures the important advantage that arrangement of the circuits may be so made that, for instance, waves reflected in the room, or standing waves which are primarily responsible for the initiation of acoustic feedback, will cause a reduction of the gain of the equipment, whereas the useful or signal sound which impinges upon the microphone mostly irom a definite direction or within a comparatively narrow solid angle, is utilized ior'an increase in the gain. In other words, the equipment operates in the following fashion: When the microphone is not acted upon by sigml sound, the amplification is low. There is no risk of any feedback being produced. As the microphon is acted upon by signal sound, the gain is raised as a function of the incident signal sound waves. As soon as the reflected sound occurring slightly later assumes such an intensity that there is a real risk of an acoustic feedback being produced, the gain is'immediately cut down so that the initiation of, a feedback is suppressed. The time-constants of regulation in this connection must be so chosen that the regulator action will set in within the transit time period of refiected waves in the room or space.

The appended drawing shows an exemplified embodiment of the basic idea of the invention as applied to an arrangement in which the danger of acoustic feedback in electro-acoustic transducers is largely diminished. The main microphone, say, for the speaker, indicated at l, is a directional microphone 2 with a highly concentrated characteristic which is also shown in the drawing at 1. The electrical oscillations corresponding to the sound waves which strike the microphone 2 are fed through the input amplifier l, the regulated amplifier 5 and the power amplifier t, and thence to the loudspeaker I. A rectifier and gain intensifying device 8 is subiect to control by output energy from the amplitier 4 and operates to increase the gain in the amplifier t in direct proportion to the amplitude of input energy applied thereto. Adjacent the main microphone or pick-up microphone 2 is mounted the regulator microphone 9. The characteristic I! of this microphone is reniform, as shown in the drawing. This microphone does not pick up in any appreciable degree the direct sound waves which issue from the original sound source to be amplified, such as a speaker positioned at I. In fact, it responds only to such stray sounds as are due to reverberation in the room. 'Ioprevent such stray sound waves from acting also upon the main or pickup microphone, a covering screen or bafile H is.mounted in the rear of the speaker I. Such sound waves as impinge upon the regulator microphone 9 are passed through the input amplifier I! to the rectifier and gain reducing device II and are thence passed to the joint regulating amplifier I in such a sense that the gain is cut down.

The amplifier 5 will be understood from the above description to be subject to positive gain regulation by the device l and simultaneously subject to negative gain regulation by the device it. In the operation of my invention. one of its characteristics is that as soon as waves picked up by microphone 9 happen to surpass a certain limiting value, the gain of the equipment is reduced.

What is claimed is:

1. A system to prevent acoustic feedback of electro-acoustic transducers in studio output circuits comprising a studio, a first microphone having directional response characteristics, a second microphone having reniform response characteristics, and-a screen member, said first microphone located in said 'studio near the source where the sound orginates, said screen member located between the point where the sound originates and a wall of said studio, said second microphone located in said studio so that it will b acted upon by the stray sound waves and substantially unimpressed by the original sound, means to combine the outputs of said microphones so that the gain of the transducer is automatically controlled as a function of the drection of incidence of the sound originating in said studio.

2. A system to prevent acoustic feedback of electro-acoustic transducers in studio output circuits comprising a studio, a first microphone having directional response characteristics, a second microphone having reniform response characteristics, said first and second microphones being mounted within said studio so that the directions of maximum response are opposed, and means to combine the ouputs of said microphones so that the gain of the transducer is automatically controlled as a-function of the direction of the incidence of the sound originating in said sound studio.

3. A system to prevent acoustic feedback of electro-acoustic transducers in studio output circuits comprising a studio, a first microphone having directional respons characteristics, a second microphone having reniform response characteristics, said first microphone located in said studio near the source where said sound originates, said second microphone located in said studio so that it will be acted upon by stray sound waves and substantially unimpressed by the original sound, a controlled amplifier in the output circuit of said transducer, means connected to said first and secondrmicrophone circuits so that the sound oscillations picked up by the first microphone serve to raise the gain in said controlled amplifier while the stray sound waves picked up by the second microphone serve to cut down the gain of said controlled amplifier.

4. A system to prevent acoustic feedback of electro-acoustic transducers in studio output circuits comprising a studio, a first microphone having directional response characteristics, a second microphone having reniform response characteristics, said first microphone located in said studio near the source where the sound originates, said second microphone located in said studio so that it will be acted upon by stray sound waves and substantially unimpressed by the original sound, a first and a second rectifier, said first microphone connected to said first rectifier, said second microphone connected to said second rectifier, a controlled amplifier in the output circuit of said transducer, means connected to said first and second microphone circuits so that the sound oscillations picked up by the first microphone by means of said first rectifier serve to raise the gain in said controlled amplifier while the stray sound waves picked up by the second microphone by means of said second rectifier serve to cut down the gain of said controlled amplifier.

5. A system to prevent acoustic feedback of an -electro-acoustic transducer comprising a sharply directional microphone situated within the range of and facing a source of sound waves, a' broadly directional microphone positioned in a back-toback relation to the first said microphone, and means to opposingly combine the outputs of said microphones so that gain of the transducer is automatically reduced in proportion to the input energy derived from the second said microphone.

6. A system to prevent acoustic feedback of an electro-acoustic transducer comprising a sharply directional microphone situated within the range of and facing a source of sound waves, 'a broadly directional microphone positioned in a back-toback relation to the first said microphone, means to increase the gain of said transducer in direct proportion to the amplitude of energy delivered by the first said microphone, and means to reduce the gain in said transducer indirect proportion to the amplitude of energy derived from the second said microphone.

WERNER BiiRcK.