<hardware, communications> A device used to connect a modem to a
telephone line via an ordinary handset. The acoustic coupler converts electrical
signals from the modem to sound via a loudspeaker, against which the mouthpiece
of a telephone handset is placed. The earpiece is placed against a microphone
which converts sound to electrical signals which return to the modem. The
handset is inserted into a sound-proof box containing the louspeaker and
microphone to avoid interference from ambient noise.
Acousitic couplers are now rarely used since most modems have a direct
electrical connection to the telephone line. This avoids the signal degradation
caused by conversion to and from audio. Direct connection is not always
possible, and was actually illegal in the United Kingdom before British Telecom
was privatised. BT's predecessor, the General Post Office, did not allow
subscribers to connect their own equipment to the telephone line.
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