Re: [Frameworks] 16mm in the classroom - projector noise!

From: Ken Bawcom (email suppressed)
Date: Tue Oct 26 2010 - 18:02:33 PDT

Just to add a few thoughts to Dave's -

There is a "sound insulation board," a fiberboard that comes in 4'x8'
sheets that is cheap, and deadens better than particle board. There
are different grades of particle board. The soft stuff used for
underlayment on floors is cheapest, but wouldn't hold up to well as a
piece of cabinetry. High-density particle board, like that used for
countertops is far more durable, but costs a bit more. Both are
heavier than plywood.

A double walled box would be best. In home construction, the top grade
of sound deadening wall is a double wall, with studs offset, so they
aren't opposite each other. Fiberglass insulation is placed between
the walls. They are covered first with sound insulation board, then
sheet rock, or plaster.

If building a double-walled box for a projector, I would place
fiberglass, or soft foam, between the walls. In theory, just air may
be best. In theory, theory is the same as practice, but in practice,
it isn't. So, I say put something in there, to dampen movement. Inner
and outer walls could be joined at the edges by gluing them to thin
spacer strips of sound insulation board, or perhaps better, Styrofoam
insulation. Be sure and use appropriate glue. They make special
construction adhesives for Styrofoam. Don't use nails or screws, they
transmit sound.

It wouldn't be necessary to build inner and outer doors. Double-walled
doors could be made in the same manner as the double-walled box. One
could use stick-on foam weather stripping to seal the edges.

On the projection window - I'll admit I have never knowingly seen
something projected through a double wall of glass. Might there be
some sort of reflective artifacts? I'd want to be sure, before I made
it, that there weren't. If double glass is suitable, then a small
thermopane window would be ideal, as it is air tight. One might call
some local glass companies, and see if they had any small ones that
were in their bargain bin.

Also, I agree with Fred about needing ventilation, in a sealed box.
Projectors produce lots of heat. There are nearly silent ventilation
fans available from home audio/video system suppliers, for use in
equipment cabinets. For best results with a fan, I would recommend
that there be a small intake vent, low on the back side of the
enclosure. It should be covered with foam, or an air filter medium, to
reduce sound transmission, and clean the incoming air. If there is no
near-by vent hole, like Fred had, perhaps a dryer vent hose, leading
from the exhaust fan, would suffice.

Ken B.

Quoting David Tetzlaff <email suppressed>:

> If you actually attempt to build a projection blimp, I'd suggest
> looking at some books about building home sound studios, which
> usually have good info about creating sound isolation.
> A big issue is whether the blimp would have to move regularly, or
> could sit in one place for, say, a semester (and if it has to move,
> can it be rolled on a cart, or would it have to be lifted and
> carried). The cheapest and most sound deadening stuff you could make
> it out of would be particleboard, which is pretty heavy. Also, to
> kill sound, you want a double wall, a box inside a box, with space
> between them. Foam doesn't really help that much, at least if it's
> attached to single walls. If you have a double wall box, it's not
> necessarily best to fill the space between the walls with foam. Just
> air might be better. In permanent installations I think they fill
> the spaces with sand...
> If I had (or could build) a suitable rolling cart that could handle
> the weight, or if the box could sit in place, I'd probably make the
> walls out of 1/2" or 3/4" particleboard, with a 1/2" to 1" gap
> between the inner and outer walls. To separate the two walls on the
> bottom, which would have to bear the weight of the projector, I'd
> probably use a series of rubber spacers. For the sides i'd try
> squares of foam glued between the walls, just enough to provide some
> structural integrity, leaving most of the gap as air (unless some
> expert source pointed me to a type of foam that definitely improves
> on air.)
> If the whole thing had to be lighter, I'd probably try 3/8" plywood
> for the outer walls, and the inside layer of the floor. But I might
> try to make the inner box out of the stiff yellow insulating foam
> they sell at Home Depot or Lowe's.
> In any case, I think both inner and outer layers of the box ought to
> be tightly sealed with something like silicone caulk (though I doubt
> that would work with foam inner walls).
> For sure, the window for the projection beam needs to be double wall
> glass, (or maybe inside and outside windows both of insulated glass.
> The tricky part, I think, would be designing the doors. I think to
> make it practical you'd need separate doors, a larger one for the
> outer box, and a slightly smaller one for the inner box (so that it
> would fully open inside the opening for the larger outer door).
> Again, I type this out of memory from guides to studio construction
> I read over 20 years ago. So I'd definitely do some more research
> before actually heading of the the store.
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