River ,'Safe'
Got a question about technology? Ask it here. Discussion of hardware, software, TiVos, multi-region DVDs, Windows, Macs, LINUX, hand-helds, iPods, anything tech related. Better than any helpdesk!
I have an off the wall question that probably noone can answer (and it really has little impact on my life) but I figure asking's free.
You know the noise only teenagers can hear? I can still here it, and the light fixture in my parents' dining room makes the noise, but it's on a dimmer, and I only hear the noise if the light is dimmed. If I turn it up to full brightness, the noise stops. Why would the light fixture make a noise when it is dimmed?
Why would the light fixture make a noise when it is dimmed?
For the exact same reason that theater and set light dimmer packs make more noise when they are at a dimmed level. All dimmers work by adding resistance to the current to prevent electricity from reaching the lamp. The more you dim the light, the more of the current is being dissipated at the dimmer instead of being turned into light energy at the lamp. When the dimmer is full, all of the electricity is passing through the resistance coil and going straight on through to the lamp. The sound is a byproduct of that.
It's an SCR dimmer which works by interrupting the waveform. This action creates harmonics where the hard edge of the chop in the waveform happens. These harmonics can get picked up by the filament in the lamp causing it to vibrate. Part of what you are hearing is the vibration of the filament. Higher quality dimmers put chokes on the dimmer which cut down on the harmonics, but those are more expensive and also take up quite a bit more space.
Sean, actually theatrical dimmers haven't done their work via resistance dimming in a few decades. They do it with SST or SCR dimmer.
Also, in many dimmers, if the sound has gotten louder over the years, the dimmer probably needs to be replaced.
Also? That sound only teenagers are able to hear? I can hear it too. Which really surprised me, because between work and liking loud rock music, I know I've suffered some frequency loss.
Sean, actually theatrical dimmers haven't done their work via resistance dimming in a few decades. They do it with SST or SCR dimmer.
Ooh! What's the difference? I mean, most lighting packs still buzz when dimmed to some degree, so what's going on there?
SCR dimming makes the buzzing much worse, but there is less wasted energy. Basically SCR dimming works by rapidly pulsing the energy on and off at a specific point in the waveform.
Take a look at the dimming section on wikipedia:
Specifically you are looking at Thyristor dimmers.
You guys are awesome!