noun
telephone transmitter; mouthpiece
Technical term for the part of a telephone that converts sound into electrical signals; often contrasted with 受話器 (receiver).
古い電話機では、送話器と受話器が別々になっている。
On old telephones, the transmitter and receiver are separate.
送話器に向かって話すと、声が電気信
When you speak into the mouthpiece, your voice is converted into electrical signals.
マイク is a general term for any microphone, while 送話器 specifically refers to the telephone transmitter component.
Compound of 送 (そう, 'send') + 話 (わ, 'talk') + 器 (き, 'device'). The reading is on'yomi throughout.