How does a speaker work?.

[Steve P]

I have classic looking DAB radios in my Herald and Vitesse, Both using the dealer option housing and speaker on top of the tunnel, the Vitesse recently started giving intermittent sound which has progressed to no sound. I tested the radio on the kitchen table with a spare speaker I had from on old Peugeot I used to have, no sound at all, the radio display and function is all normal. Peugeot speaker had 3.5 ohms across it.

Today I measured the resistance on the old speaker as the supplier said it should be around 4 ohms. The speaker has a dead short across the connections.

I had a spare original one In the shed so I measured that, 3.2 ohms, swapped them over and it works in the Herald, but the Vitesse radio has to go back to the supplier as It looks like the speaker short has killed the output.

So I wondered, how is the speaker constructed and where does it get the resistance, Is there a coil in there?.

Steve

[Nigel Clark]

There is a cylindrical coil of fine copper wire at the centre of the speaker cone. This coil sits inside a cylindrical permanent magnet. Current from the radio output causes a magnetic field which varies with the current, moving the speaker cone. Thus the electrical energy output from the radio is connected to sound. It's similar in principle to a solenoid.

I suspect there is a short circuit inside your speaker. This may have overloaded the output stage of the radio, causing a blown fuse, or electronic damage if you're unlucky.

Nigel

Edited July 27, 2023 by Nigel Clark

[Steve P]

Thanks Nigel,

The only fuse on the outside is an in-line one for the main feed. Would there be internal fuses?. It`s out of warranty so it doesn`t matter if i take it apart.

Steve

[Nigel Clark]

There may be one or two small fuses inside the radio, though many older units don't have them.

Nigel

[Steve P]

This is a new Dab unit,I opened it up, no fuses.

Steve