(57) The invention presents means for applying negative feedback more powerfully and stably
than before over a frequency range as wide as possible, in the constitution for detecting
a reproduced sound of a speaker used in various acoustic appliances by a microphone,
and applying a negative feedback to an input signal of the speaker by the detected
signal, and correcting the reproduced signal by improving the reproduction frequency
characteristic and other characteristic of the speaker.
A fundamental constitution of an acoustic reproducing apparatus of the invention comprises
a subtractor having an input terminal, a power amplifier for amplifying the output
signal of this subtractor, a speaker for reproducing the output signal of the power
amplifier, a microphone for detecting the acoustic output signal radiated from the
speaker, a microphone amplifier for amplifying the acoustic output signal detected
by the microphone, and an adder/subtractor for adding or subtracting the output signal
of the microphone amplifier and the input signal of the power amplifier, wherein the
output signal of the adder/subtractor is connected to the subtractor to compose a
negative feedback circuit.
Or, in an acoustic reproducing circuit using a speaker box incorporating a passive
radiator, a microphone is disposed in the front side of the magnetic circuit of the
speaker for reproducing the output signal of the power amplifier or speaker rear enclosed
acoustic space, or in the enclosed acoustic space with the passive radiator of the
speaker front side, and the output signal of the microphone is added or subtracted
with the input signal of the power amplifier in the adder/subtractor in the fundamental
constitution above, and the signal is subtracted from the input signal in the subtractor,
thereby composing a negative feedback circuit.
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