Audio reproducing apparatus

Details Audio reproducing apparatus Audio reproducing apparatus

1999-04-15

2001-08-28

Mei, Xu (Department: 2644)

Electrical audio signal processing systems and devices

Loudspeaker feedback

C381S056000, C381S057000

Reexamination Certificate

active

06282296

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an audio reproducing apparatus that can excellently reproduce signals even at a noisy place such as a factory and transportation means including cars and trains.
BACKGROUND OF THE INVENTION
There are a lot of opportunities to reproduce audio signals at a noisy place, where a noise level is high and varies, such as a factory, and transportation means including cars and trains.
FIG. 6
is a block diagram illustrating a conventional audio reproducing apparatus that is utilized in a noisy environment. In
FIG. 6
, an audio signal received at input terminal
1
travels through variable gain circuit
2
and is amplified by power amplifier
3
. An output signal tapped off from amplifier
3
is fed into speaker unit
5
disposed in speaker box
4
, thereby reproducing the signal into audio form.
Microphone
6
disposed around speaker unit
5
collects the sum of the signals which speaker unit
5
radiates and noises around speaker box
4
. An output signal supplied from microphone
6
together with the output signal from amplifier
3
are fed into subtractor
7
.
Subtractor
7
subtracts an input signal component from the sum of the signal radiated from speaker unit
5
and the noises around speaker box
4
so that an output signal proportional to the surrounding noise is extracted. The output signal supplied from subtractor
7
runs through low pass filter
8
where a frequency band of the signal is limited, and then runs through rectifier
9
where the output signal is converted into direct current (dc), which then is fed into variable gain circuit
2
.
Because variable gain circuit
2
is automatically controlled its amplifying rate by the output signal supplied from subtractor
7
, speaker unit
5
can radiate signals free from being cancelled by the surrounding noise, i.e. free from being masked. As already discussed, the output signal supplied from subtractor
7
varies proportionally to the surrounding noise, which contributes to this automatic controlling.
However, in the conventional audio reproducing apparatus utilized in the noisy environment, differences exist between the audio signals supplied from speaker unit
5
and the output signals supplied from amplifier
3
so that subtractor
7
cannot completely remove the radiated signal from speaker unit
5
. Therefore, it is difficult to extract only the noises around speaker box
4
, and a user is thus obliged to control variable gain circuit
2
within a narrowly limited frequency band. The conventional audio reproducing apparatus utilized in a noisy environment thus has not been provided with a sufficient masking correction.
SUMMARY OF THE INVENTION
The audio reproducing apparatus of the present invention comprises the following:
(a) a power amplifier;
(b) a speaker box including a speaker unit which reproduces output signals from the power amplifier;
(c) a first microphone disposed outside the speaker box;
(d) a second microphone disposed inside the speaker box;
(e) a low pass filter (LPF) coupled to the first microphone;
(f) a high pass filter (HPF) coupled to the second microphone;
(g) an adder for adding an output from the LPF and an output from the HPF;
(h) an ac/dc converter for converting an ac output signal to a dc output signal; and
(i) a variable gain circuit disposed at an input side of the power amplifier, and an output signal of the circuit being varied responsive to a level of the dc output signal supplied from the ac/dc converter.
A gain of the variable gain circuit is changed by the output signal of the adder so that the better masking correction responsive more faithfully to the surrounding noise can be achieved.


REFERENCES:
patent: 4254303 (1981-03-01), Takizawa
patent: 4628526 (1986-12-01), Germer
patent: 4864246 (1989-09-01), Kato et al.
patent: 5107539 (1992-04-01), Kato et al.
patent: 5434926 (1995-07-01), Watanabe et al.
patent: 5896450 (1999-04-01), Kurihara
patent: 6122385 (2000-09-01), Konno et al.
patent: 53-108419 (1978-09-01), None
patent: 63-82197 (1988-04-01), None
patent: 1-29154 (1989-01-01), None

Affiliated with

Also associated with

Rating

Audio reproducing apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Audio reproducing apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Audio reproducing apparatus will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2442262