CA1041913A

CA1041913A - Loudspeaker compensation circuits

Info

Publication number: CA1041913A
Application number: CA221,685A
Authority: CA
Inventors: Saad Z.M. Gabr
Original assignee: A R D ANSTALT
Current assignee: A R D ANSTALT
Priority date: 1974-03-08
Filing date: 1975-03-10
Publication date: 1978-11-07
Also published as: BE874452Q; GB1502595A

Abstract

ABSTRACT OF DISCLOSURE

An audio amplification system comprises, between a preamplifier and a main amplifier, a circuit which may include an amplifier, adapted to compensate for non-linearity of the frequency response curve of the loudspeaker means. The main amplifier may include means for dividing the compensated signal into a plurality of signals each covering a respective part of the audio-frequency range.

Description

v ~ r ~ l .t ~ o a ~ m l- l i [ i ~ \ (1 S O ~
rcproduction sy~stem ~or compensation of loudspcaker charactcr-istics.
~ onvcntional electromagnctic loudspeakers arc typically ablc to reproduce signals at thc upper and lower ends of the audio frequency spcctrum, regardcd as extcnding from 20 H~
to 20 kll~., lcss well than signals over the central frequency range. ~ typical loudspeaker frequency response curve may be, and desirably is, smooth over the major central part of the spectrum but drops considerably towards both ends, perhaps showing an almost complete inability to reproduce signals at the extreme upper and lower ~requencies. The ob3ect of the invention is to provide a system for compensating for such loudspeaker characteristics.
In accordance with the invention, therefore, there is provided an amplifier and sound reproduction system for amplifying and reproducing an input signal covering at least a ma3Or part of the audio-frequency range, the system comprising a multi-section filter for receiving the input signal, the multi-section filter being arranged to divide the input signal into at least three signals each covering substantially only a respective part of the audio frequency range, at least three variable output amplifier means connected to the multi-section filter so that each amplifier means receives a respective one of the divided signals, loudspeacker means receiving the outputs of the amplifier means, and a compensation circuit arranged to boost the upper and lower frequency portions of the input signal in inverse relation to the frequency response characteristics of the loudspeaker means.

~g 1 ;3 rl.e system is perferably positioned between a pre-amplifier stage and the main ampliying stage of a high-fAidelity amplification system, which is desirably a modular system of the kind described in Application 205 694 filed July 26th 1974 and incorporates appropriate features of the system therein disclosed. The invention thus also provides an ampllrier sy.s~em in which the or each lnput sig-lal is tre~ted successlvely in preamplifier stage, an active or passive fllter stage, a multi-section filter and a plurality of parallel amplifier channels handling respective frequency ranges of the input. The outputs of the amplifier channels can be fed to respective loudspeakers or groups of loudspeakers or may be -2a-:; :` '' '' ' ' : ' `

1(1~1~13 combined and fed to a single loudspeaker or fewer loudspeakers than the number of channels. In accordance with the invention, the or each loudspeaker to which the compensated signal is fed may be provided with a suspension of compressed rubber or plastics foamed material.
By way of illustrative example only, an amplifier system embodying theinvention is described below with reference to the accompanying drawing, in which:
Fig. 1 shows the circuit of the amplifying system in block schematic form;
Fig. 2 shows the frequency response curve of a loudspeaker compensation circuit element included in the circuit of Fig. l;
and Fig. 3 shows the frequency response curve of a typical electromagnetic loudspeaker.
The circuit illustrated in Fig. 1 can be employed as a monophonic system but will more usually be one channel of a stereophonic or quadraphonic system. A signal to be amplified is derived from an input source for example a tuner or a record or tape player through appropriate selection means 10 and applied to a preamplifier 12. The preamplifier output is taken to an electronic loudspeaker compensation circuit 14 in accordance with the invention. The circuit 14 has a frequency responsive curve 15 generally as indicated in Fig. 2. The corrected signal is fed to a loudspeaker 18 after amplification in a main amplification stage 16. The loudspeaker response curve is indicated at 19 in Fig. 3 and it will be clear from comparison of Figs. 2 and 3 that in the absence of other factors the effective sound output of the loudspeaker will be approximately flat over the entire audio frequency range.

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The electronic compensation circuit can of course be arranged to produce an effective sound output which has another shape than generally level, if this is desired for example to deal with special acoustic conditions. The circuit 14 may also include means for selective adjustment of its characteristics in particular its frequency response curve, but it is preferred, as mentioned above, to divide the compensated signal provided at the circuit output in a multi-section filter 20 in the amplification stage 16. The filter 20 divides the compensated signal into two or more signals each covering a part only of the full frequency range. Each divided signal is amplified separately in a channel containing any desired adjustment means, in particular, gain controls, so that the relative contributions of the frequency ranges to the actual output of the system can be chosen. Thus, in the embodiment of the invent~on illustrated, the filter 20 divides the compensated signal into three, the divided signals being amplified in respective variable amplifiers 22, 24, 26. Any suitable number of divided sign~ls may be provided for.
The divided signals after amplification in the amplifiers 22, 24, 26 are recombined in an amplifier 28 and are then fed to the signal loudspeaker 18 or to a group of loudspeakers. Instead however, the divided signals can be supplied to respective loudspeakers or groups of loudspeakers without recombination or with recombination of less than all the divided signals. One or more amplifiers can be provided as desired at appropriate positions in each respective channel.
In the signal supplied to the loudspeaker 18 or other loudspeaker means, the lower and higher frequencies will normally be present in a degree to compensate for the deficiencies of the 4.

, .. . .
, , , l~tl'~ ~ 3 loudspeaker means in reproducing them. So as to be able to reproduce these signal components adequately, the or each loudspeaker unit is preferably provided with a suspension of - compressed rubber or plastics foam material which allows the diaphragm or cone to travel through the rather large excursions necessary to the accurate reproduction of signals down to 20Hz.
In addition, the loudspeaker should have the maximum magnetic field strength than can conveniently be obtained.
The invention can of course be embodied in other ways than as specifically described but will be understood to provide a substantial improvement in the field of high fidelity sound reproduction.

Claims

The embodiments of the invention in which an an exclusive property or privilege is claimed are defined as follows:

1. An amplifier and sound reproduction system for amplifying and reproducing an input signal covering at least a major part of the audio-frequency range, the system comprising a multi-section filter for receiving the input signal, the multi-section filter being arranged to divide the input signal into at least three signals each covering substantially only a respective part of the audio frequency range, at least three variable output amplifier means connected to the multi-section filter so that each amplifier means receives a respective one of the divided signals, loudspeaker means receiving the outputs of the amplifier means, and a compensation circuit arranged to boost the upper and lower frequency portions of the input signal in inverse relation to the frequency response characteristics of the loudspeaker means.

2. A system as claimed in claim 1 in which the compensation circuit output is connected to the multi-section filter input.

3. A system as claimed in claim 1 or 2 having a preamplifier of which the output is connected to the compensation circuit input.

4. A system as claimed in claim 1 or 2 in which the compensation circuit incorporates an amplifier.

5. A system as claimed in claim 1 in which the compensation circuit includes means for selectively adjusting the compensation characteristics thereof.

6. A system as claimed in claim 1, 2 or 5, in which the loudspeaker means comprises a single loudspeaker unit.

7. A system as claimed in claim 1 in which the loudspeaker means comprises a plurality of loudspeaker units.

8. A system as claimed in claim 7 in which the output of each variable output amplifier means is applied to a respective loudspeaker unit.

9. A system as claimed in claim 7 in which the outputs of at least two of the variable output amplifier means are combined before application thereof to the loudspeaker means.