acoustic coupler

noun2

1. •
   An interface device for coupling electrical signals by acoustical means.
2. •
   (old-fashioned) A terminal device used to link data terminals and radio sets with the telephone network.

   • The call will be answered with a high-pitched tone; no human voice will be heard. The phone receiver should be placed in the acoustic coupler, if one is used, with the cord in the proper position. — 1984