This is 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 loudspeaker and microphone to avoid interference from ambient noise. Acoustic couplers are rarely used today since most modems have a direct electrical connection to the telephone line.