Can a PTC thermistor prevent overheating in a DIY speaker heater?

[MattRSK]

Hi

My brother has a logitech pure fi anytime alarm clock radio. The problem with it is that when it is cold the speakers do not work properly distorting the sound. This is not very useful as it is cold in the mornings when the alarm goes off (playing a song from the ipod).

Now I had an idea that I could use a bank of resistors to heat the speakers so that they would operate normally all the time. I have basically used the same idea as a dew heater for a telescope (http://www.dewbuster.com/heaters/heaters.html ).

this is my idea

I am just a bit worried that the resistors would end up overheating. My question is would it be possible to use a PTC thermistor in the circuit to prevent overheating?

 

[vk6kro]

It is unlikely to be the speakers themselves that cause distortion.
It would possibly be something in the amplifier driving the speakers.

Easy to check. Just plug another set of speakers in one cold morning.
Or use a hair dryer to warm up just the speakers or just the amplifier.
If a warm amplifier gives clean sound into cold speakers this means the amplifier is at fault.

Or put the amplifier in the fridge for a while and see if it is distorted after that.

So, having worked out where the distortion is coming from, you need to fix it.

Assuming it is the amplifer, you could open it up when it is warm and working OK and get a can of freezer spray and try to identify which part you spray that makes it get distorted again.

But look for obvious faults like burnt resistors.

Forget about heating it up with resistors etc. It needs to be fixed because whatever is faulty now will probably get worse.
You really need some test equipment and a schematic diagram to be sure of fixing it, but you might be able to get lucky and fix it just by having a look.

Also look at the power pack if it has one that plugs into a wall socket. It could give low voltage if it is cold.

 

[MattRSK]

Good points to think about. I will give it a try. Thanks!

 

[russ_watters]

I had never considered the possibility of building my own dew heater - thanks for that!

Unrelated aside: I had my telescope outside last night and based on dewpoint and predicted low temperature, didn't expect to need my dew heater. But the absolute humidity ended up rising through the night in advance of a new weather pattern and I found when I woke up this morning I had lost 2 hours of exposure to dew. Clear weather is so rare here I need to make a policy of using the dew heater even if I think I won't need it.

 

[Bob S]

One passing thought. I once had problems with the speaker coil in a sagging speaker cone rubbing against the magnet. I turned the speaker upside down and the problem went away.