A type of modem that has rubber cups that fit on the mouth and ear-piece of a normal phone. This converts data from the PC into sound that is then transmitted across the phone network to another computer with a modem. Most modems plug directly into a telephone socket and provide better quality sound, which means that they are more reliable. An acoustic coupler sends data more slowly than a modem. But it is useful if you are travelling and need to use public or hotel phones to send data.
