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JPH02228196

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DESCRIPTION JPH02228196
[0001]
A. Field of the Invention The present invention relates to a headphone device for converting an
electrical signal into an acoustic signal and outputting it, and in particular, an amplifier circuit for
amplifying a human power electrical signal and supplying it to a headphone unit The present
invention relates to a so-called active noise reduction headphone device having a function of
reducing noise by converting the noise into an electric signal and performing negative feedback
in a microphone unit. SUMMARY OF THE INVENTION The present invention amplifies noises by
converting an acoustic signal near the microphone unit into an electric signal by the microphone
unit and negatively feeding it back to an amplification circuit that amplifies an input electrical
signal and supplies it to the microphone unit. In a so-called active noise reduction headphone
device having a function to be reduced, the reduction amount with respect to external noise can
be varied by variably setting the gain of the amplification circuit. C. Prior Art As disclosed in, for
example, Japanese Patent Application Laid-Open Nos. 60-220698 and 62-2798, in a headphone
device for converting an electric signal into an acoustic signal and outputting the same, An
acoustic signal in the vicinity of the headphone unit, which is converted into an acoustic signal
and output, is converted into an electrical signal by the microphone unit, and so-called active in
which noise in the vicinity of the headphone unit is reduced by the negative feedback loop A
conventional noise reduction headphone device has been employed. The active noise reduction
headphone device has a microphone unit (6) in the vicinity of the headphone unit (4) attached to
the listener's ear (20), as its principle configuration is shown in FIG. And an input electrical signal
S applied from the signal source (10) to the signal input terminal (1) to be supplied to the
headphone unit (4) at the input side of the amplifier circuit (3). An acoustic signal in the vicinity
of the headphone unit (4) is converted into an electric signal by the microphone unit (6) and
supplied to the signal synthesizer (2) through the feedback circuit (7); A configuration for
performing negative feedback control of the amplifier circuit (3) by combining the output of the
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feedback circuit (7), ie, the feedback signal, with the input electrical signal S in (2) and supplying
it to the amplifier circuit (3) Going on. As in this active noise reduction headphone device, an
acoustic signal in which an acoustic output signal from the headphone unit (4) and an external
noise signal are added is obtained near the entrance of the ear canal of the listener's ear (20) The
acoustic signal to which the noise signal from the outside is added is converted into an electrical
signal by the microphone unit (6), and the amplification is performed via the feedback circuit (7)!
Negative feedback to the input side of (3) can reduce the noise level of the acoustic signal input
to the listener's ear (20). D Invention tries to solve! l By the way, in the active noise reduction
headphone device having the function of reducing external noise, if the noise reduction amount
is too large, for example, while listening to music in a state where external noise is reduced,
There is a possibility that it will not be heard even if a voice is heard, and it may miss listening to
the 9A sudden broadcast and the like. In addition, when the noise reduction amount is too small,
it is not practical in a factory or a construction site where the noise level is high. In the
conventional active noise reduction headphone device, since the noise reduction amount is fixed,
there is a problem that the noise reduction amount can not be used according to the situation.
Therefore, in view of the conventional problems as described above, the present invention aims
to realize a practical active noise reduction headphone device that can be used with a noise
reduction amount according to the situation, and output from the headphone unit It is an object
of the present invention to provide a headphone device of a novel configuration in which the
amount of noise reduction can be varied without affecting the signal level of the acoustic signal
to be reproduced. ELli! Means for Solving the II In order to achieve the above object, the
headphone device according to the present invention amplifies a headphone unit for converting
an input electrical signal into an acoustic output signal and an input electrical signal supplied to
the headphone unit. An amplifier circuit capable of variably setting gain, a microphone unit
disposed in the vicinity of the headphone unit and converting an acoustic signal into an electric
signal, and negative feedback of a signal obtained by the microphone unit to an input terminal of
the amplifier circuit A feedback circuit, wherein the gain A of the amplifier circuit can be variably
set within the range of l AHMβ I) 1 with respect to the transfer function M of the headphone
unit and the transfer function M of the microphone unit and the transfer function β of the
feedback circuit. It is characterized by having done. F Action In the headphone device according
to the present invention, the signal level of the input electrical signal is S, and an acoustic signal
with a sound pressure level P of 1 + A summer IMβ 1 + AHM β is obtained in the vicinity of the
headphone unit as the signal level N of external noise. By variably setting the gain A of the above
amplification circuit in the range of I AHMβ I) 1, the level of the external electrical noise is
maintained at a constant level of 1 / Mβ with respect to the signal level S of the input electrical
signal. The signal level N is reduced to 1 / AHMβ.
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G. Embodiment Hereinafter, an embodiment of the kM collection processing apparatus according
to the present invention will be described in detail with reference to the drawings. The
embodiment shown in the equivalent block configuration diagram of FIG. 1 is an application of
the present invention to the conventional active noise reduction headphone device shown in FIG.
2 described above, and the synthesized output signal by the signal synthesizer (2) is It is
configured to be supplied to the headphone unit (4) through a variable gain amplification circuit
(13) which can be set with variable gain A. An acoustic output signal from the headphone unit (4)
is added to the noise signal N from the outside in an equivalent signal adder (15) in an acoustic
space near the headphone unit (4). The synthesized output according to 15) is converted into an
electrical signal by the microphone unit (6) as an acoustic signal near the headphone unit (4) and
supplied to the signal synthesizer (2) through the feedback circuit (7). There is. In this head-pon
apparatus, the variable gain amplification circuit (13) transfer function, that is, the gain A is the
transfer function H of the headphone unit (4), the transfer function M of the microphone unit (6),
and the transfer function of the feedback circuit (7). The transfer function A of the variable gain
amplifier circuit (13) is expressed in the frequency domain, and is variably settable in a range of
AI (Mβl> 1). In this headphone device, assuming that the signal level of the input electrical
signal applied to the signal input terminal (1) is S and the signal level N of the external noise
signal applied to the signal input terminal (18), An acoustic signal with a sound pressure level P
of 1 + AHMβ 1 + AHMβ as a combined output according to 15) is obtained at the signal output
terminal (19) that hits the ear canal entrance of the listener wearing this headphone device. The
acoustic signal of sound pressure level P obtained at the signal output terminal (19) has a
constant level of 1 / Mβ with respect to the signal level S of the input electrical signal, and the
signal level N of noise from the outside is 1 The noise signal level N, that is, the noise reduction
amount according to the gain A of the variable gain amplification circuit (13) is reduced to /
AHMθ and variably set in the range of 1 AHMβl) 1. That is, in the headphone device of this
embodiment, the signal level S of the input electrical signal is fixed by variably setting the gain A
of the variable gain amplifier circuit (13) in the range of I AHMβ I> 1. Thus, an acoustic signal in
which only the noise level is reduced according to the gain A of the variable gain amplifier circuit
(13) can be obtained at the signal output terminal (19).
In order to adjust the volume of the sound signal obtained at the signal output terminal (19), that
is, the sound output, a volume adjuster may be provided at the front stage of the signal input
terminal (1), that is, the sound source side. Effect of the Invention In the headphone device
according to the present invention, the transfer function M of the headphone unit, the transfer
function M of the microbon unit, and the transfer function β of the feedback circuit, the transfer
function of the amplification circuit, ie, the gain A is IAHMβ1)! Can be reduced to 1 / AHMβ
with the level of 1 / Mβ fixed with respect to the signal level of the input electrical signal. The
noise reduction according to the noise situation can be used by setting the gain A of.
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[0002]
Brief description of the drawings
[0003]
FIG. 1 is an equivalent block diagram showing an active noise reduction headphone device to
which the present invention is applied.
FIG. 2 is a schematic diagram showing the principle configuration of a commonly used active
noise reduction headphone device according to the present invention.
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