If the coupling system is a set of earphones, the electrical signal is changed to acoustic energy (sound) at the loudspeakers (like the receivers of hearing aids) of the earphones and directed into the ear.
(the coupling system; is; a set of earphones) (the electrical signal; is changed; to acoustic energy; L:at the loudspeakers (like the receivers of hearing aids) of the earphones) (the electrical signal; directed; into the ear)
the coupling system the electrical signal the electrical signal
is is changed directed
a set of earphones
to acoustic energy L:at the loudspeakers (like the receivers of hearing aids) of the earphones
into the ear