Tech Question

[30 ips]

I am interested in setting up some kind of system that will allow a light to glow when the speaker recieves a voltage from the amplifier. Since this is my first project of this kind I would prefer not to modify the amp, but rather introduce a some kind of transducer into the chain between the amplifier output and the speaker input. Has anyone done this before at a resonable cost. Any info or a point in the right direction would be most appreciated. Thanks.

[triez]

Many electronics kit sellers have sound-to-light disco style boxes to build, or you may be able to buy one complete from a DJ shop.

[usetheforce]

I have seen some PA/studio speakers where the manufacturer put a light bulb in series with the tweeter which glowed when the level increased.

I got the call at 3am by a concerned producer who saw the flickering light through the bass port and thought his speaker was about to blow!! I was rather shocked to find a light bulb.

I dont know how this effected the sound but the manufacturer claimed it didnt and it was there as a fuse and surge protection.
Im not naming ma,es but i would like to see the proof befor attemping such a modification.

[30 ips]

Thanks fo rthe reply(s). I was hoping on doing the modifications myself as opposed to purchasing something. I think this maybe a good starting project to get a better understanding of schematics and transducers. I was hoping someone could recommend a site or a book where I could find out a good way to do this and then maybe get a greater understanding of how it all works in the process. Thanks

[usetheforce]

This site is a good starting place for theory and links...

http://www.proaxis.com/~iguanalabs/Begtut.htm


And this is a good site for circuits with helpful explanations on the design and theory.

http://www.hut.fi/Misc/Electronics/circuits/#audiocir

But you must think of electronics as another language and learning it is a time consuming process but from my own experience its worth it.
good luck and chip away at it.

[30 ips]

Thanks very much. Just what I was looking for!

[Doug Ring]

Hiya, the light bulb works as a passive compressor.

The resistance of a cold lightbulb is much less than a hot one, so under normal power-draw conditions, the bulb doesn't get enough juice to light up and so the resistance stays low. Start to crank up the volume however, and the increased power starts to heat the bulb filament. This causes its resistance to increase, the power draw is reduced, the filament cools...and the cycle repeats.

If you choose the correct values for the system, the cycling effect isn't a factor and you get a smooth compression effect that protects the tweeter.

It's neat and simple, but hard to condone in this era of minimalist crossover circuits.

[usetheforce]

Thats a good explanation.... and that makes sense to put them in studio monitors as at the higher volumes your just after a vibe rather than an acurate mix.

[Paul Frindle]

Originally posted by usetheforce
I have seen some PA/studio speakers where the manufacturer put a light bulb in series with the tweeter which glowed when the level increased.

I got the call at 3am by a concerned producer who saw the flickering light through the bass port and thought his speaker was about to blow!! I was rather shocked to find a light bulb.

I dont know how this effected the sound but the manufacturer claimed it didnt and it was there as a fuse and surge protection.
Im not naming ma,es but i would like to see the proof befor attemping such a modification.

I came across a certain UREI monitor system in the mid 80's that had automobile type lamps in series with the drivers. I think the woofer had one too (not entirely sure after so long), but the mid and top were definitely fitted with correspondingly smaller lamps. The effect was a type of compression at high sustained levels because as the series impedance increased dramatically as the filaments heated up. Maybe this was a mis-guided attempt to protect the drivers from damage (they seemed to blow often enough)? But certainly the response changed badly under loud programme conditions in ways I wouldn't want to put up with if I were engineering :-(

I dunno, I kinda collected those blown bulbs with pride!
(813 was the model number????)

[Tim Farrant]

IMHO putting a such a unpredictable and non-linear device in series with a speaker where the speaker is used for monitoring is not such a good idea. In the case of the UREI's, it wouldn't have mattered as they sounded so damn bad anyway !!

Also IMHO, the light bulb theory does not really work. In most cases where I have had to replace a light bulb in a speaker enclosure, I have also needed to replace the speaker it was supposedly protecting !!

Tim