Editing Acoustic coupler (section)

==Design==
Usually, a telephone handset was placed into a cradle that had been engineered to fit closely (by the use of rubber seals) around its [[microphone]] and earpiece. A modem would modulate a [[loudspeaker]] in the cup attached to the handset's microphone, and sound from the speaker in the telephone handset's earpiece would be picked up by a microphone in the cup attached to that. In this way signals could be passed in both directions. Despite the use of seals, acoustic couplers were sensitive to external noise and depended on the then-widespread standardization of the size and shape of handsets.

Once direct electrical connections to telephone networks were made legal, they rapidly became the preferred method of attaching modems, and the use of acoustic couplers dwindled. Acoustic couplers were still used until at least the late 1990s by people travelling in areas of the world where electrical connection to the telephone network was illegal or impractical.<ref>{{cite web | url=http://web.media.mit.edu/~nicholas/Wired/WIRED6-04.html | title=Wired 6.04 - Rj-11 }}</ref> Many models of [[Telecommunications Device for the Deaf]] (TDD) still have a built-in acoustic coupler, which allow more universal use with [[Payphone|pay phones]] and for emergency calls by deaf people.