Recording - March 2014 - 50

drove in a bunch of toed-in nails (no nail gun), stuffed in some
R19 pink insulation, nailed up the drywall and mudded it into
place. I had built a wall!
It was a satisfying feeling, it shrank my tracking room by a
crucial 7 inches with an attendant big improvement in sound,
and it even cut my heating bills a tad-this project was built on
a north-facing outside wall, and that R19 insulation did its job
admirably. If I could build a wall, I suspect you could too.
Absorb and diffuse
Okay, you've found a room with acceptable dimensions (or
perhaps made a room acceptable). How are you going to treat
it for good sound? Elsewhere in this issue, Bruce Black offers a
DIY solution for tweaking low end via a Helmholtz resonator; I'm
going to focus on the highs and mids in this next bit.
There are only two things a sound wave can do when it
encounters an object: it can be absorbed, or it can bounce off.
(Most likely it'll do a bit of both.) In the 1970s, studio design
was all about absorption, and we got a lot of dead-sounding
rooms as a result. These days a combination of absorption and
diffusion is considered preferable.
What's diffusion? Diffusion is what happens when sound
bounces off an object or surface, not in a single direction, but
every which way. Smaller objects help sound become diffuse;
the small decorations in old-fashioned churches (and concert

Another excellent resource can be found at sweetwater.com/
shop/studio/acoustic-treatment/room_analysis.php, where you
can download a form that gets you a custom-designed studio
treatment from the makers of Auralex sound-absorbing foam
(auralex.com). These sites will naturally emphasize the use of
their respective products in designs, but that's only fair; they have
to feed their families too. Auralex, a large manufacturer of
acoustically-absorbing foam, sells a kit expressly designed for
home studios, the Roominators Project 2. The kit contains a broad
variety of absorbent pieces, and some information on their use;
you can also find information in Everest's books, or at the online
resources discussed below. The Roominators kit would be a good
start for many rooms of average size, and I've made it the default
acoustic treatment for our Startup Studio.
Auralex isn't your only choice; foam isn't the be-all and end-all
for absorption by any means, and Primacoustic (primacoustic.com)
offers an alternative set of packaged solutions in its London series
of room kits, which use fiberglass rather than foam as an absorber
(check out the London 12 kit as an example). My DIY alternatives
also use fiberglass; I'll get to those in a minute.
Don't forget that, if your control room/mixing area is separate
from your tracking room (it usually is), that will need some
acoustical treatment too, along the same lines as the recording
space. As I mentioned above, a reverb time of about 0.5 seconds is often appropriate for control rooms.
Build your own
Let's say you've decided on your plan of absorption, but don't
have the money to buy foam or other products-or you want to
keep this a 100% do-it-yourself project. Fear not; you can. Everest
shows designs for some do-it-yourself absorbers in his books, and,
as mentioned, there are some on the RealTraps website and elsewhere on the Internet.

Contrary to Urban Legend, the cardboard from egg crates will not work
as absorption or diffusion, EVER. I've heard egg-crate studios for forty years,
and they all sound like what they are: rooms with no diffusion at all.
halls) are a prime example. We'll get to diffusion in a bit, but
first let's talk about absorption.
I'm going to oversimplify a bunch here, but basically absorption controls the reverberation time of a room-the time it takes
a sound to decay to inaudibility, defined as 60 dB below its
original level. A good number to aim for in a small recording
studio is about 0.6 seconds, and in a control room probably 0.5
seconds will be appropriate. There are charts in Everest's books
that enable you to choose a reverberation time for various-sized
rooms; my numbers are just ballpark figures.
The problem is, a given room will have different reverberation
times at different frequencies, because most materials absorb
different amounts of sound at different frequencies. If, for example, you line the walls, floor and ceiling with deep-pile carpet,
you'll do a great job absorbing high and high-mid frequencies,
a poorer job absorbing low-mid frequencies, and a terrible job
absorbing low frequencies. Result: a room that imposes a
boomy, muddy, bottom-heavy sound on everything you record.
Sorry, blankets do the same thing.
There are a couple of online resources that can help you plan
out sound absorption for a better-balanced sound. I'll start with
a nod to a fellow Recording contributor, Ethan Winer, and the
folks at RealTraps (realtraps.com), who present a great deal of
material about absorption, including plans for some effective
absorbers you can build yourself.
50

RECORDING March 2014

I've written a couple of articles on sound treatment for this magazine
in years past ("Build a Broadband Acoustic Panel," Recording, August
1996) and "Sabins on a Shoestring," Recording, January 1997) that
provided designs for DIY absorbers which provided reasonably uniform absorption down to 125 Hz or so. Both used Fiberglass insulation
in 6" thicknesses (R19) rather than 4" (R11); the extra thickness makes
a big difference down in the lower-frequency regions, around 125 Hz.
Both of these articles are available for free on Recording's website now,
in their Resource Library; look under Do It Yourself > Acoustics.
For what follows, here is a major caution: WEAR RUBBER
GLOVES THAT GO WELL UP YOUR ARMS, AND A BREATHING MASK. Fiberglass is nasty stuff; it provokes itching that
rivals poison ivy, and it's not at all nice to inhale.
Okay, here's the more formal absorber. Build a 6" D x 17.5" W
x 48" H wooden frame from 1 x 6 lumber (the crosspieces should
be 16" long); nail and/or glue it to a piece of 17.5" x 48" chipboard (you can get 5 of these from a 4' x 8' sheet, with a bit left
over). When the glue has dried, staple a 20" length of picture wire
to the back, so you can hang it from a hook on the wall. Fill the frame
with unfaced R19 Fiberglass (remember the gloves and mask), then
cover the frame with thin fabric. (The fabric used on the bottoms of
couches is good for this application.) Staple the fabric to the sides or
back of the frame, and voilá-you have a sound absorption panel.
Each frame will use one 1" x 6" x 12' board; add in the fiberglass and cloth, with a few pennies for picture wire, staples and

http://sweetwater.com/shop/studio/acoustic-treatment/room_analysis.php http://sweetwater.com/shop/studio/acoustic-treatment/room_analysis.php http://www.auralex.com http://www.primacoustic.com http://www.realtraps.com

Recording - March 2014

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