Eletro Magnetic Interferince from Moving Lights

[deadpixel]

Hi Guys,

 

So I am trying to solve an ongoing problem that has been plaguing the sound guys my music venue. In our lighting rig we have Martin Mac 700 profiles that seem to produce a fair bit of EMI coming from the ignitor on one side of the yolk. this always causes problems with humming (not 50hz) on Guitar pickups when coming in to close proximity to the fixtures.

 

I wondered if anyone had any insight to this problem and ways to remedy it. is it a problem with insufficient shielding on the unit itself?

 

Thanks in advanced.

[jonathanhill]

...and ways to remedy it.

 

Move the lights away from the guitars?

[Grum]

I've had similar problems with other fixtures and after a lot of trial and error we think we narrowed it down to unshielded pickups too. Sadly there's not much that can be done about it other than to move the fixtures further away from the guitarist.

 

How far will depend on the fixture, we found that Sharpys weren't an issue at all but QWO 800s couldn't be within 3 feet.

[deadpixel]

...and ways to remedy it.

 

Move the lights away from the guitars?

 

Truss trim height is 2.6m :)

 

I've had similar problems with other fixtures and after a lot of trial and error we think we narrowed it down to unshielded pickups too. Sadly there's not much that can be done about it other than to move the fixtures further away from the guitarist.

 

How far will depend on the fixture, we found that Sharpys weren't an issue at all but QWO 800s couldn't be within 3 feet.

 

Yes there is defiantly a case for vintage guitars being more susceptible to EMI as they have little if no shielding but why doesnt the fixture have the EMI better suppressed considering the environment they are built for?

[Grum]

Are you sure it's EMI? Our monitor engineer has some pretty good equipment for scanning RF and couldn't find anything. He was insisting it couldn't be the lights.

 

Rather than EMI it could be a mechanical issue (i.e. vibration) producing a harmonic frequency that the guitars are picking up. During our tests we found that the problem didn't occur when the guitars didn't have any strings.

 

Having said that, 2.6m is a very reasonable distance, perhaps a call to Martin? Could be something they've encountered in the past and have a fix for.

[deadpixel]

I am fairly convinced that it is EMI as it is only when the lamp is struck and only really on certain axis and is proportionally loud to the distance from the fixture. I suppose that it would be reasonable that the strings pickup the the RF and maybe transfer it to the pickup in some way. Next time we have a gig I am going to experiment a little more.

[niclights]

I have the same issues with the electronic ignitors in Varilite fixtures. Certain pickups are sensitive. It is proximity related and I can't see any solution other than moving further away or using different pickups. When I mentioned to PRG they had not heard of the issue. I was surprised given that any floor units would usually be close enough to cause a problem.

[timsabre]

Guitar pickups are very sensitive to electromagnetic fields in the audio band - it's most likely not a RF (radio frequency) problem but a magnetic field coming from the wound components in the lamp gear. If changing the orientation of the guitar affects the level of noise then the chances are it's magnetic. And that is virtually impossible to screen out.

[DeMe-X]

I have the same problem in the venue that I am working with Mac700's. The interferences are present in Fender style guitars with single pickups, the oldest the noisest. Guitars with humbuckers (Gibson SG and LesPaul, heavy guitars, ...) have not any noise at all.

 

The only solution I have found is switch off the nearest MAC's...