FR2690806A1 - Method and apparatus for mitigating the disadvantages of the feedback or echo effect and improving the sound definition of acoustic transducers. - Google Patents

Abstract

A method wherein an audiofrequency signal of a sound reproduction system is chopped by inserting a plurality of contactors (C2, C3). Cut-off frequencies create active periods (PA) in which the audiofrequency signal is transmitted, and inactive periods (PP) in which said audiofrequency signal is not transmitted. The cut-off frequencies of a switch (CH2) controlling the contactors (C2, C3) enable phase-shifted contactor activity. Acoustic feedback is greatly attenuated due to the alternating electrical nature of the audiofrequencies to the microphone (SM1) from the transducer (HP2). Continuous electrical overloads on the transducers are avoided, enabling them to return to a stable position during each inactive period of the contactors.

Description

Method and apparatus for mitigating the disadvantages of the effect
Feedback or echo and improve the sound definition of trans
acoustic ductors.

The present invention relates to sound reproduction with the aim of improving listening comfort in any use of sound reproduction systems in reverberant medium or subject to the disadvantage of the effect.
Larsen. It is conventional to use special directional microphones with a small range to avoid the feedback effect. On the other hand, the use of a mixer to attenuate certain frequencies of echo reasoning in the rooms is necessary.

 In each case, one of the components of the message is reduced, thus distorting the initial message.

 The object of the present invention is to keep the signal intact, but not to distribute it in a continuous jet so as not to saturate the room with sound. It is still possible to mute the microphone information alternately with the speakers so that the two devices are not simultaneously in operation, thus avoiding the feedback effect. These cut-off frequencies can be effective from 14,000 Hz depending on the installations and beyond.

 According to the present invention, technical means such as electrical or mechanical contactor cut into successive zones and contiguous the audio-frequency signals of a sound reproduction system. We thus create, alternately, an active period P.A. figure 1 letting through the audio frequency signals and a passive period P.P. figure 1 not letting the audio frequency signals pass. The cut-off frequency is such that it does not disturb the audible spectrum from 14,000 Hz and can be adjusted on all higher frequencies by a switch.

 According to a second characteristic, the active period P.A. is fitted with a mechanical or electronic timer device regulating the percentage of the functional active period P.A.F. compared to the active period, Figure 2.

 According to a third version, a switch can control several contactors mounted on the same installation or electrically independent installations but having an acoustic connection. The contactor control can be synchronous, that is to say that the active periods of the contactors are done together as well as the passive periods. They can be asynchronous, the active periods of the contactors are shifted in time, up to the limit case where the active periods of the contactors occur during the passive period of the other contactors.

 FIG. 3 shows a case in point where the role of the pilot switch two contactors in an asynchronous manner causing a phase shift in the activities of the contactors at the same time. The active periods are shifted in time by T1.

 To better understand the present invention, we propose a device, non-limiting example of the invention, FIG. 4. The contactor C1 inserted in the sound reproduction chain, in this case between amplifier A and HP transducer, but for others applications that can be placed on any section of the installation, will cut the audio frequency circuit of the HP transducers coming from the SS source according to a cut-off frequency outside the audible spectrum. A T.L. electronic timer device will regulate the active active period during the active period of the contactor decreasing the contactor closing time period. The switching device CH1 will control the cut-off frequencies necessary for the system. Thus, the amount of sound emitted in the room is adjusted by reducing the active time of the sound reproduction system, in a non-audible frequency zone.

Another non-limiting device mounting case according to the present invention FIG. 5: in a sound reproduction system with microphone
SM1, two contactors C2 and C3 are inserted, thus creating three zones Z1, Z2,
Z3 or Z1 and Z2 receive the audio information from the microphone while
Z3 is cut off from the audio frequencies preventing the HP2 transducers from working.

In the following time, C2 will be in passive contact open period and C3 in active period which will allow the information to pass from zone 2 to 3. The switching device CH2 controls contactors C2 C3 in assynchronous mode. Thus the drawbacks of the Larsen effect are greatly reduced due to the alternating electrical operation of the audio frequencies of the microphone and the transducer, which is of considerable interest in reproducing direct sound. We show the advantage of avoiding continuous electrical overloads on the transducers, thus allowing them to return to their stable position at each passive period of the contactors, thus improving the definition of sound reproduction.

 The foregoing descriptions have been given purely by way of non-limiting illustration and variations may be made within the scope of the present invention.

 We show the interest of the invention for a listening comfort without saturation of sound for the listener which we noted during the tests.

Claims (9)

 1. Method for attenuating the drawbacks of the feedback or echo effect and improving the sound definition of the acoustic transducers in a sound reproduction system where the audio frequency signals are cut by alternating active period PA and passive period PP, the PA period can itself be set as a percentage in an active PAF active period and the cut-off frequencies are adjusted outside the audible spectrum from 14,000 Hz and beyond.  2. Method according to claim 1 or the cuts can be placed in any section or at several points of the sound reproduction system.  3. Method according to claims 1 and 2 or the cuts can be made on different electrically independent sound reproduction systems, having an acoustic connection.  4. Method according to claims 1, 2 and 3 or the periods of activity of PA cuts at different points can be synchronous, assynchronous or alternated.  5. Apparatus for attenuating the drawbacks of the feedback or echo effect and improving the sound definition of the acoustic transducers in a sound reproduction system comprising, a sound source SS, an amplifier A and transducers HP whose audio signal will be cut by a contactor C1 being controlled by a switch CH1 regulating the cut-off frequencies. The contactor creates active periods PA, contacts in the closed position through which the audio signal passes, passive periods open contacts interrupting the audio signal.  6. Apparatus according to claim 5 characterized in that several contactors C2, C3 can be installed on dif ferent sections of the same sound reproduction system.  7. Apparatus according to claims 5 and 6 characterized in that each contactor can be provided with a timer TL allowing the active PA period to be reduced to a PAF functional activity period.  8. According to claims 5, 6 and 7, switching device CH2 to control two or more electrically dependent or independent contactors simultaneously.  9. Apparatus according to claim 8 characterized in that  the switching device CH2 can adjust the phase shift of the acti  contactor times ranging from PA syn activity periods  chronicles and passive periods PP synchronized with res periods  assynchronous specters phase shifting the activities of active periods  Ves and passive of contactors C2, C3.