Sound emitter - Diaphragm
Diaphragm (in an electrodynamic or electromagnetic sound emitter)
That part of the emitter which forms the principal sound radiating or receiving element; it usually consists of a rigid or semirigid membrane specially adapted to respond to or to generate sound.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM