To verify the model, we measured the complex acoustic admittances of a series of circular tubes as a function of length between 200 Hz and 10 kHz using a three-port acoustic coupler
. The absolute magnitude of the specific acoustic admittance is approximately one.
A "Y"-splitter single-to-dual RJ-11 jack, or an acoustic coupler
that attaches to almost any phone handset, lets the modem communicate audibly with the phone system.
TDDs are special phones that incorporate a standard typewriter key board, alphanumeric display, and an acoustic coupler
and/ or standard RJ-11 jack for network connections.