Natural Science Forum / Physics / Acoustics / March 2006

I think you can forget about pyramid foam unless its cheaper than other
solid foam. Fabric does reduce some high frequency absorbtion.
Use a breathable fabric. What to do about the ceiling? Probably need a contractor.
Throw rugs on the floor or wall to wall is going to do wonders.

greg

Unless you use a very unusual fabric it won't make a significant difference.
But shaped foam is not worth the money over plain foam, if it costs more.

Depending on the price of the foam and the cost of labour, it might well be
cheaper to buy sound absorbent panels covered with fabric that are ready to
install.

Don't overdo the coverage otherwise you will kill the mid and high frequency
reverberation and leave lower frequency reverberation so that will make the
place sound boomy.  Covering the upper part of two adjacent (important - not
opposite!) walls is usually
enough.

No.  If you want to make the panels your self, use loft insulation (I
would recommend something like Rockwool rather than a glass fibre based
insulation) mounted inside wooden frames and held in place with chicken
wire.  Then stretch an open weave fabric such as Hessian over the face.

Alternatively, take a look at http://www.realtraps.com  You could buy
the products from there or see what they look like and build then yourself.

Chris W

May I presume that "is" really means "would be"?

The heavier the "nice fabric", the better the sound absorption.
Anywhere from 12 to 40 ounces per square yard (carpets) will do.

The most important parameter is the distance from the wall; the greater,
the better, but in no case should it ever be less than one inch.

Pyramid foam is pure hokum. You get more beneficial sound absorption
(250 Hz, etc.) if the pyrimida are turned onto the wall!

Foam is not only a waste of money, it is also dangerous because of the
fire load (pounds of combustible material) it adds into the room.

The heavier the fabric, the less important is the filler (fiberglass
duct liner board, etc.).

A wide air gap and slightly heavier fabric are by far the more
cost-effective measures.  Such spacing from the wall is most readily
achieved by mounting the fabric of stand-offs from the wall. Fireproof
fabrics are preferred,

Edging or trim about the edges is another waste of money. They are pure
vanity with no acoustic gain; they are actually an acoustical loss as
they prevent sound from entering under the edges to be absorbed.

    Angelo Capanella

Sorry I accidentally sent this by email initially

You did not say what the ceiling is.  If it is plaster or gypsum, that may
be the most important place to start depending on the proportions of the
room.  Since you said the ceiling is high, the walls may be most
appropriate, but I would want to know the overall room dimensions before
offering an opinion.

As others have said, foam is a potential fire hazard. Some is reasonably
safe, but you have to be careful.  Also, the pyramids and wedges are mostly
marketing.  Cloth covered fiberglass panels are readily available from many
suppliers in 1 inch and 2 inch thicknesses, or for more durability slightly
thicker with a higher density layer just behind the cloth.  These are
considered furniture for tax purposes.  There are also companies that can
build a frame on the wall, fill it with fiberglass and stretch cloth over
it.  This is considered a building improvement for tax purposes.  Mineral
wool can be used instead of fiberglass.  Cloth must be fire resistant.  Two
inch thick panels are preferable if you are adding much to keep the lower
range of voice sounds under control.Unless the room is relatively small and
you intend to play and listen to music, you do not need to spend a lot of
money on small thick panels intended to have strong low frequency absorption
to treat problems that are common in small rooms.

The classic combo begins with Owens-Corning 703 rigid (compressed)
fiberglass boards. They typically come in 1" or 2" thicknesses and are
2' x 4' rectangles. These are then usually covered with Guilford 701
fabric (the full company name is "Guilford of Maine"). You certainly
want a fire rated fabric, or at least treat whatever you get with fire
retardant. The fabric should be a coarse weave, not tight or shiny. You
can build 1 x 2 wood frames to hold each fiberglass board and stretch
the fabric over them and staple to the back. You can also trim them
however you like if it makes your office cohorts happier. There are also
other potential solutions to an office noise problem, but regarding
absorptive panels, the above is a pretty typical construction. I'd pass
on the foam.

Thank you all!  You were very generous in your responses and I am grateful.

That's a lot to consider; I didn't realize it was so complicated.  I looked
at realtraps.com and some others and was surprised at the cost of these
solutions.  I thought we could make something in the $000's not thousands.

Some asked about the room.  It's an old building -- open plan with
moderately sparse furnishings.  The room is roughly rectangular:  50'x25'
with 14' ceilings.  All surfaces are textured plaster (roughened on the
walls and "stucco'd" on the ceiling) except the short ends of the rectangle
are mostly windows.  Lighting is suspended from the ceiling on tracks, so a
tile grid won't work.  We do have carpeting wall to wall.

It looks like some firms recommend putting the panels in the corners, on a
diagonal.  Would just treating the 4 vertical corners and a couple of the
horizontal ceiling corners make an effective solution?

What about adding some white noise generators?  Is that a good second step:
masking the noise to make conversations and mp3 playing less noticable?

Thank you,
SC