light bulb in series with speakers

[Gaston]

why do some speakers have a light bulb un series with them? to limit the current somehow?

 

[Nigel Goodwin]

why do some speakers have a light bulb un series with them? to limit the current somehow?

Yes, a light bulb has a positive temperature coefficient, so as more current passes through it and it heats up, it's resistance increases. So while it's cold it's a very low resistance, and passes pretty well all the power to the tweeter, as the power increases the current through the bulb does, it starts to warm up, and it's resistance increases, dropping the power to the tweeter.

By careful selection of a suitable bulb you can protect the tweeter nice and cheaply, without any significant impact on the sound.

 

[audioguru]

I think a powerful light bulb in series with a speaker will react slowly, providing an audible delayed compression of the sound volume.
Many modern digital compressors at radio and TV stations work like that and sound awful like a hammer.

 

[Hero999]

Are you talking about an automatic gain control?

I've seen bulbs used in amplifiers for this purpose but never in speakers.

 

[audioguru]

An audio limiter suddenly reduces sound volume that is too loud. When it is too slow, the attack is loud like a hammer to your hearing then it cuts the volume a little later.

High power speakers compresss the sound a little when they heat due to the voice coil's resistance increasing due to the heating.

 

[Gaston]

so the bulbs only go in series with the tweeters not the woofers?

 

[audioguru]

Tweeters are very fragile. Continuous high power like from severe clipping distortion or from acoustical feedback howling will burn out a tweeter in one second. So a light bulb will protect it.

A woofer is big and strong and has a high continuous power rating. It doesn't need a light bulb.

 

[Nigel Goodwin]

so the bulbs only go in series with the tweeters not the woofers?

Yes, it's a cheap effective method to protect the tweeter, and has a minimal effect on the sound - obviously the bulb needs to be a specific exact type though!.