<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.
