Dimmer noise (acoustic)

[jkowtko]

The lighting crew recently replaced the light dimmers in our theater, and they mounted the new dimmers up high in side loft areas within direct earshot of the audience and stage area. The result is a low buzz from the noisy fans that kick in whenever we have more than a moderately lit scene.

Our tech guys have tried to contain the sound by building wood boxes around them with foam interiors, but that provide only marginal relief. During quiet scenes the dimmer noise is very noticable.

Has anyone dealt with this issue before? If so, any suggestions on a good way to eliminate the noise, other than the obvious one of relocating the dimmers to somewhere they won't be heard? I'm thinking plexiglas enclosures that are vented/fanned in back might do the trick.

Thanks in advance. John

[zip]

we also installed some Dimmers in a Philarmonic Opera, and they were really noisy, the solution was to install them in an nearby room, in an "audio isolated" rack (with foam).
I do not know if this can help you bur i sure hope so.

[BillESC]

What type of foam did you use?

You'd really need real acoustic foam and perhaps even an acoustic barrier as well

Foam of this nature will do a good job.



A barrier of this nature will reduce sound transmission by as much as 40 dB at certain frequencies.

[zip]

we used real acoustic foam, considering that the dimmers were in another room we thought it wouldn't be necessary to use a sound barrier.Although it had another surface profile.
The walls of the Philarmonic are really thick so the problem was really quick solved.
I guess you should consider a solution, the sound isolated rack, but be careful that the one that we installed has 4x120mm additional slow running fans, because the dimmers can produce a considerable amount of heat!
We installed 8 dimmers with each 6x20A/ch, but I guess you have bigger ones considering that in a Theater more lights are used.
As for background noise, the ventilation system gave us much more problems, but the Managers decided on some points to turn it off...

[gafftaper]

Beware of over heating when building your soundproof box. I had a similar problem and managed to make my dimmers do all kinds of weird stuff because they got too hot from the first version of the foam box I built. I suggest a fan with intake and exhaust ports out of the room

[SHARYNF]

Just a box around them probably is not going to do it, you need a double box, where the inside box is considerably smaller than the outside, and the outside box is made such that the air flow enters from the bottom travels up between the two, and then goes to the inside box, if you then cover it with acoustic foam that should do the trick. If you really want to deaden the sound, look at a marine supply company that has acoustic shielding sheets that they use for generators, there is foam and then a high density material that is in between

Sharyn

[Van]

What Sharyn Said. A double boxing system might help as would placing the dimmer rack on a piece of something like "Nike Grind" which is a rubber sheet material about 1/2" thick. Take particular note of Gaff's suggestion, There has to be a lot of air movement into and out of those boxes. Make sure that when they loaded the dimmers up that thy built a balanced load, if the load is not properly distributed across the the rack, often a horendous buzzing is the result. I am assumming this is a portable dimmer pack and not a permenant installation. If that is the case and those dimmers simply have to live right there, then check with you local rental houses and find a set of ET IPS dimmers to install instead, They don't buzz. Period.

[TorontoAlchemy]

Green glue has some pretty impressive sound reduction qualities
http://www.greenglue.org/

[tony]

that green glue stuff is very interesting and impressive !