Speakerphone and microphone case for the same

Details Speakerphone and microphone case for the same Speakerphone and microphone case for the same

1998-06-26

2001-07-24

Chiang, Jack (Department: 2642)

Telephonic communications

Terminal

Having loudspeaking conversation capability

Reexamination Certificate

active

06266410

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a speakerphone which enables a user to talk to the other party over the telephone without lifting a handset and to a microphone case for use in the same.
2. Prior Art
Heretofore, there has been known a speakerphone which incorporates a speaker and a microphone for amplifying a voice in a housing to enable a user to talk to the other party over the telephone without using a handset.
In general, in a speakerphone, a speaker and a microphone are incorporated at a relatively close distance in a same housing. Therefore, there is available a speakerphone which incorporates a voice switch circuit to prevent acoustic coupling between them, that is, a phenomenon that the voice of the other party output from the speaker is picked up by the microphone.
FIG. 17
is a block diagram showing a configuration of a speakerphone incorporating a voice switch circuit. As shown in this figure, the speakerphone comprises a hybrid circuit
1
, a voice switch circuit
2
, a speaker amplifier for amplifying a voice (to be referred to as “speaker amplifier” hereinafter)
3
, a louder speaker for outputting an amplified voice (to be referred to as “speaker” hereinafter)
4
, a microphone amplifier for amplifying a voice (to be referred to as “microphone amplifier” hereinafter)
5
, and a speech microphone for inputting a voice to be amplified (to be referred to as “microphone” hereinafter)
6
.
The hybrid circuit 1 is an interface for connecting the speakerphone to a telephone line network
10
, which outputs a received signal to the voice switch circuit
2
and a transmitted signal to the telephone line network
10
and prevents the transmitted signal from being input into the voice switch circuit
2
. The voice switch circuit
2
reduces the transmitted signal level during reception and the received signal level during transmission, and comprises a reception suppression circuit
11
, a transmission suppression circuit
12
and a control circuit
13
. The control circuit
13
compares a transmitted signal and a received signal, controls the reception suppression circuit
11
to attenuate the received signal during transmission (transmitted signal level>received signal level) and controls the transmission suppression circuit
12
to attenuate the transmitted signal during reception (received signal level>transmitted signal level).
Since an audio output from the microphone
6
can be suppressed by the audio switch circuit
2
even when a voice from the speaker
4
is picked up by the microphone
6
, acoustic coupling between the speaker
4
and the microphone
6
can be suppressed.
FIG. 18
shows a block diagram illustrating acoustic coupling between the speaker
4
and the microphone
6
. As shown in the figure, a received signal Sr from the other party is output from the speaker
4
on a user's side as an audio signal, the audio signal is picked up by the microphone
6
on the user's side and output to the other party as a transmitted signal St. In this case, without any voice switch circuit
2
, the level of the transmitted signal St input from the microphone
6
may become larger by picking up the received signal, resulting in the occurrence of howling or acoustic echo. However, as this conventional speakerphone incorporates the voice switch circuit
2
, the level of the transmitted signal St picked up by the microphone
6
is reduced, thereby suppressing the occurrence of howling or acoustic echo.
As shown in
FIG. 17
, the speaker amplifier
3
amplifies a received signal from the voice switch circuit
2
to a predetermined level, while the microphone amplifier
5
amplifies a transmitted signal from the microphone
6
to a predetermined level. In this case, when an appropriate speech acoustic level is 74 dBSPL (SPL; sound pressure level), a gain for the speaker amplifier
3
is set to produce an acoustic output from the speaker
4
larger than 94 dB so that a received voice from the speaker
4
is heard at 74 dBSPL. Furthermore, since an acoustic level of ca. 94 dB is added to the microphone
6
when a user speaks, a gain for the microphone amplifier
5
is set such that the acoustic level should become the regulated audio level of a telephone circuit. The received signal amplified by the speaker amplifier
3
is supplied to the speaker
4
to generate a sound while the transmitted signal amplified by the microphone amplifier
5
is supplied to the voice switch circuit
2
.
FIG. 19
is a perspective view of the outer appearance of the speakerphone. As shown in this figure, sound output holes
16
for the speaker are formed in a center portion on a front left side of the housing
15
, and a sound input hole
17
for the microphone is formed in a right portion on a front side of the housing
15
. The speaker
4
is arranged inside the housing
15
at a position where the sound output holes are formed and the microphone
6
is arranged inside the housing
15
at a position where the sound input hole
17
is formed.
FIG. 20
is a transverse sectional view of
FIG. 19
,
FIG. 21
is a sectional view of the key parts of
FIG. 19
, and
FIG. 22
is an enlarged sectional view of a portion where the microphone
6
is installed. In these figures, the microphone
6
is stored in a rubber case
20
, and a sound introduction surface
6
A (see
FIG. 22
) of the microphone
6
is arranged to face the sound input hole
17
. A wire
6
B of the microphone
6
is connected to a circuit board
22
. The rubber case
20
excludes sounds output into the inside of the housing
15
and covers all the portions of the microphone
6
except the sound introduction surface
6
A. Further, a handset
18
is generally provided to the speakerphone in addition to the speaker
4
and the microphone
6
for amplifying a voice so that the user can talk through the handset
18
.
However, the above conventional speakerphone has the following problems. When the user talks over the telephone at an appropriate speech level, most of a voice from the speaker
4
may be picked up by the microphone
6
and the other party may hear his/her voice like an acoustic echo. According to fluctuations in the AC impedance of a telephone circuit, a transmitted signal may leak into a received signal to generate a hybrid echo in the hybrid circuit
1
. Therefore, the sound suppression loss of the voice switch circuit
2
is set large in the prior art. However, by setting the sound suppression loss large, a slight lag is produced when priority is shifted from the speaker
4
to the microphone
6
, and a first portion of a word input from the microphone
6
is missing, whereby speech becomes unnatural.
Further, when big sounds are output from the speaker
4
, sounds output from the rear side of the speaker
4
may stay in the inside of the housing
15
of the speakerphone and form an effective acoustic coupling passage with the microphone
6
. However, it is extremely difficult to cancel it. Even when the rear side of the microphone
6
is covered by the rubber case
20
, sounds from the speaker
4
are transmitted too large to the microphone
6
through a cover and base forming the housing
15
and mechanical parts such as a circuit board. If mechanical vibrations of the cover, base, printing circuit board and the like are transmitted too large to the microphone
6
, the voice switch circuit
2
carries out transmission operation, the switch is electrically kept switched to the microphone
6
in the worst case, and normal communication becomes impossible.
To solve this problem, the following methods have been considered: (1) the distance between the speaker
4
and the microphone
6
is increased, (2) the rear of the speaker
4
is completely covered by another part, (3) the microphone
6
is removed from the housing
15
and installed outside the housing
15
to eliminate acoustic coupling within the housing
15
, and (4) a special directional microphone is used.
However, in either case, there is no design freedom because the housing
15
beco

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