Oddness

[robocow]

 

Curious. I feel I should now why this is, but I don't - the light buzzes when a black sleeve is in the beam. Note there is no buzz with just hand!

 

Anyone know?

[adam2]

I can not think of any plausible mechanism whereby a black sleeve placed in the beam of an LED light would cause the light to emit any noise that was not emitted otherwise.

 

I consider it more likely that the change in the picture content/video signal is in some way interfering with the digital audio stream and thereby producing a buzz. Or put another way, I don't believe that the buzz would be audible to a human observer in the room at the time, as distinct from being heard on a recording.

 

 

 

[DrV]

I'm always up for a convoluted explanation!

 

Does this fixture have a feedback loop which is monitoring the light output in some way? My convoluted explanation would then be that the LED drive current is being changed (most likey increased) and that is making its power supply do something a bit different which is in turn making the noise. In support of my theory, you can see how the structure surrounding the LEDs goes darker when the sleeve is there but not when the hand is there.

 

Dave

[timsabre]

Is this your video, and if so could you tell where the buzz comes from?

 

The only thing I can think of is infrared being reflected back into the lenses and causing some sort of thermal effect (or output reduction as Dave suggests). I do know that black jumpers are very reflective to infrared due to a curious project I once worked on which used infrared detection to sense when people stood at a urinal.... you probably didn't need to know that.

[robocow]

I can not think of any plausible mechanism whereby a black sleeve placed in the beam of an LED light would cause the light to emit any noise that was not emitted otherwise.

 

I consider it more likely that the change in the picture content/video signal is in some way interfering with the digital audio stream and thereby producing a buzz. Or put another way, I don't believe that the buzz would be audible to a human observer in the room at the time, as distinct from being heard on a recording.

 

 

 

 

I made the video BECAUSE I heard the buzz! What a daft thing to say?

And trust me, its louder than the rubbish phone mic would suggest.

 

Is this your video, and if so could you tell where the buzz comes from?

 

The only thing I can think of is infrared being reflected back into the lenses and causing some sort of thermal effect (or output reduction as Dave suggests). I do know that black jumpers are very reflective to infrared due to a curious project I once worked on which used infrared detection to sense when people stood at a urinal.... you probably didn't need to know that.

 

 

Ah, I didn't localise the sound in the light, and they are no longer with me to test. I would have asumed the lamp housing or driver...

 

I like IR as the differentiator, can only be that really. Do we know why IR / light relecflected back would make a buzz?

There must be a good EE on here that will say somelthing like its an inductor in the led engine driver not being able to pass current.

[timsabre]

I can not think of any plausible mechanism whereby a black sleeve placed in the beam of an LED light would cause the light to emit any noise that was not emitted otherwise.

I consider it more likely that the change in the picture content/video signal is in some way interfering with the digital audio stream and thereby producing a buzz. Or put another way, I don't believe that the buzz would be audible to a human observer in the room at the time, as distinct from being heard on a recording.

I made the video BECAUSE I heard the buzz! What a daft thing to say?

And trust me, its louder than the rubbish phone mic would suggest.

 

OK calm down, it was not clear if it was your video or just something you'd seen on youtube.

 

Can you confirm where the buzzing was coming from? i.e. top/bottom of the light? Does the light make that noise in any other situation e.g. when dimmed by DMX?

[Whiskers]

Try other bits of black materiel and other colours of sleeve, double check for bracelets and watches.

 

PWM LEDs certainly make IR translation and hearing aid headsets buzz.

 

Buzz on video - keep your hair on - a badly transmitted PAL can cause audio buzz, Rarely seen now bit was most common when Hotels & Theatres combined several video channels. Sound should be 5.5 MHz above video, unlimited or enthusiastic video will stray into audio and the dominant is 50Hz field rate - sounds like Buzz but "modulated" by how much white is in the picture. I am sure poster was only trying to help