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Q: Sound dampening a small, resonant room. ( No Answer,   8 Comments )
Subject: Sound dampening a small, resonant room.
Category: Science
Asked by: juststeve-ga
List Price: $5.00
Posted: 13 Jun 2006 08:04 PDT
Expires: 13 Jul 2006 08:04 PDT
Question ID: 737787
I need to dampen the echos in a small room with a high, cathedral
ceiling. The room is 12x14 ceiling starts at 8' on a 45 degree angle
for 5" then flattens. Effectively it makes for 3 panels of 5x12...2 of
them facing the floor at 45 degrees. 5/8" sheetrock.

The floor is concrete - slab heating so I don't want to carpet it.
It's not a sound studio....i don't need perfection....just looking to
get better than it is.

Studio grade acoustic foam is too expensive. 

It's been suggested that the best (cheap) way to approach this is
Walmart bed foam - the egg crate stuff. I'm not overly concerned about
looks but that seems just a bit too tacky - even for me.

I'm considering just a flat, 2" foam sheet with the 'popcorn', texture
paint covering it.

Question is would i get a worthwhile sound reduction off the flat (vs.
convoluted) foam?
There is no answer at this time.

Subject: Re: Sound dampening a small, resonant room.
From: ashaman5-ga on 17 Jun 2006 20:01 PDT
hello there,

i believe you only have one central question, so i'll address that: 
would there be a substantial reduction in echos moving from flat to
corrugated surfaces.

the answer is absolutely.  sound propogates optimally in dense,
structured media.  sound propogates poorly in sparse, unstructured
media.  this is why solid-state physicists are able to calculate sound
velocities in crystalline materials so well and haven't a clue how to
do the same in glasses (which are essentially disordered media).

anyway, i'm wandering a bit, but the point is that sound is a wave
and, as such, it will diffusely scatter (ie spread in all directions)
if it encounters a surface which is "bumpy" or corrugated on that same
length scale (ie if the bumpiness in your surface is about the same
length scale as the wavelength of sound coming in).  if you have a
flat surface the sound just reflects off of it more or less
untrammeled and continues on its way (that leads to huge echo

so, i've written a lot, but the ultimate point is that the more small
bumps you can introduce into your surface (popcorn surface) the better
chance you have at eliminating echos.

hope that was helpful


Subject: Re: Sound dampening a small, resonant room.
From: juststeve-ga on 22 Jun 2006 02:49 PDT
Thankx Jeff...yep, you've focused on the central part of the question.
I can refine it even a bit further...

Having determined I'm going to apply cheaper than acoustic-grade
egg-crate foam I'm nexted faced with trying to keep it from looking

I'll be cutting bedding foam into 4x4 squares, cemeting to a stiff
backing (to keep from drooping) and framing the edges off. That'll
help a lot and will be adaquate for my purposes.

But it'd be nice to hide the egg-crates behind some thin material - if
i knew I weren't counteracting the deflection properties of the
egg-crate to a significant degree. Common sense tells me that i would
not ...that most sound would be unaffected by the covering and would
still be defected by the foam behind.
Subject: Re: Sound dampening a small, resonant room.
From: myoarin-ga on 22 Jun 2006 03:51 PDT
Good idea, covering the faom with something.  I would think a very
thin and loosely woven material would be best, something like
"see-through" curtain material, but probably a cheaper material is
available that is similar.
This is the principle of the cloth used to cover loudspeakers, the
lighter it is, the less it deflects the sound.  In your case, this is
not so important, since any sound deflected/absorbed by the material
is part of the desired effect.
If you used cheap cotton, and people will be smoking in the room, I
would try to find something other than plain white, since it will
catch the smoke and begin to look dingy.
Subject: Re: Sound dampening a small, resonant room.
From: knowitawe-ga on 22 Jun 2006 19:37 PDT
The least expensive solution with allowances for aesthetics, safety,
and effectiveness is to apply inexpensive surplus acoustical ceiling
tiles (0.20$/sq.ft) on wall and ceiling surfaces.  You have something
less than 600 square feet in total wall and ceiling area, so you could
spend $50 to $150 to eliminate the echo.

The tiles are nice because they can be cut to any shape and stacked to
create interesting shapes that will break up flat echoing surfaces. 
Also, you don't have to cover the entire wall or ceiling surface to
eliminate the echo.  A few visually pleasing geometric patterns using
even a few tiles on the wall will improve the acoustics.  Start with a
pattern on the wall behind the seating area at head height and see if
that resolves the echo for the preferred listening position.

A good method to affix the tiles to the wall is with long thin strips
of wood - ~1" wide x ~1/4" thick - positioned and nailed either
vertically, horizontally or diagonally to hold multiple the tiles
against the wall/ceiling.  Then if later you decide that they aren't
visually pleasing, you'll only be left with a few tiny nail holes to
patch rather than pieces of tile glued to the wall.

You can always pre-paint the wood strips (e.g., white, grey, whatever)
to match your acoustic tiles.  Just pre-drill each nail hole in the
wood strips to avoid smashing the wood and under-lying tiles.  I don't
think I would recommend painting the tiles because that would fill
surfaces making them more flat, but I suppose you could try it.  They
sell interesting spray paints that have rough surfaces but that would
add cost you are attempting to avoid.

If you don't like the color or surface of the acoustical tile you can
cover them individually with an inexpensive cloth or you can tack the
tiles to the wall in a random pattern and just hide them behind
floor-to-ceiling curtains.

And lastly, if you don't have on already, put a rug on the concrete
floor in the center of the room - that may do the trick altogether...

Example effort:

Example materials:

Kind regards,

Subject: Re: Sound dampening a small, resonant room.
From: eestudent-ga on 14 Jul 2006 14:28 PDT
Curtains! Big, heavy, thick curtains.
Subject: Re: Sound dampening a small, resonant room.
From: martin_g-ga on 18 Jul 2006 12:33 PDT
The foam idea would work ? kind of.

But you should be very wary of it as a fire hazard ( esp. if there are
any hot lights around ) If it were to catch fire ? think  : burning
drips of polyurethane . . .

Much better to use thick wads of fibre-glass wool. Say, 12x12x4 (
inches)  ( lots of ?em )  will do the job pretty well ? but the more
wool you put up there, the better it will work. To make them look
reasonable, put them in wooden surrounds with a ?grille cloth? over
the front. ( any non-flammable open weave material as per loudspeaker
grilles )

Bye the bye - there?s always a huge confusion between ?sound proofing?
and ?sound treatment? - bear in mind that your fibre-glass wads will
do a great job at cutting down reflections within your room -  but
will do next to nothing to stop any loud sounds leaking out to annoy
the neighbours.
Subject: Re: Sound dampening a small, resonant room.
From: ukbikerman-ga on 13 Oct 2006 03:25 PDT
The pro way is to isolate where possible. The best way is to build a
room within a room and minimise the points of contact. Ideally you
float a new floor over the old one and then build wall and ceiling
from that base without tying to the existing structure. The floor can
sit on rubber gromits happily (like big thick rubber washers). Add
some accoustic 'rubber' between the old and new rooms and you have a
proper job :-)

Subject: Re: Sound dampening a small, resonant room.
From: ronnieyours-ga on 16 Nov 2006 20:43 PST
You could also use heavy velvet curtains. I have seen a lot of my
friends using that. You can get them custom made for chear from

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