How does this stuff work?

[amir.razzaqi]

Hello
The following pictures are related to the disassembled parts of the speaker inside the handset of an old desktop phone (Belgacom maestro 350)
The diaphragm of the speaker is made of two thin metal sheets that act as a 62nf capacitor.
Behind the speaker diaphragm, there is a coil (with gap) that one pins common with diaphragm first pin and the other pin of coil connected to second pin of diaphragm trough a 1K8 resistor.
Does anyone know how this speaker works?

[T3sl4co1l]

Piezo disc I guess?

I suppose the coil would be loading, compensation for the disc capacitance, then.  I mean, you have the parts in front of you, you can trace the circuit -- then measure the coil, and see what the impedance of the whole thing is at audio frequencies.

POTS was 600 ohm, wasn't it?  Should have a peak or valley impedance around that, in the phone range (500-3000 Hz).

Tim

[Andy Watson]

My guess would be that the 62nF disc is the piezo "speaker" - producing sound. The coil is probably there to be used with hearing-aids which have an induction coupling option.

[SiliconWizard]

My guess would be that the 62nF disc is the piezo "speaker" - producing sound. The coil is probably there to be used with hearing-aids which have an induction coupling option.

Yes.