Recording - November 2016 - 12

By Aaron J. Trumm

Ask an amateur recordist what they consider most important
in their studio, and the answer is likely some piece of gear. Ask
a professional audio engineer what the most important thing in
the studio is, and they'll almost certainly call out room acoustics.
Anyone who's mixed in a boxy room knows how hard it can
be to hear what's going on, and many of us have experienced
the sadness of a poorly translated mix that's boomy, tinny, or
muddy in other rooms. Or you may have noticed the horror of
vocals recorded in an empty room-that hollow, boxy sound that
should be reserved for bad indie movies and teleconferences.
The reason for these problems is sound waves reflecting and
interacting, creating nodes (where a given frequency is cancelled by its out-of-phase reflection), peaks (the opposite condition), comb filtering, ringing, flutter echo, and plain old reverb.
The size and dimensions of a room determine where and at
what frequencies problems occur, but any conventional rectangular room has three sets of parallel surfaces, which is the
worst possible situation for acoustic interaction.
These facts are becoming more apparent to musicians, and
nowadays there are fewer square boxes with $10,000 DAWs
and no treatment. There are still plenty of expensive studios
built to spec, but what about bedroom studios, renters, and lowbudget recordists? Can they build a trustworthy space they can
use to get great results? Yes they can, and it's not that hard.
Before we begin
First off, let's distinguish acoustic treatment from soundproofing. Soundproofing means isolation: making a room that lets
no sound in or out. Doing this effectively takes structural work
(which renters can't do), and is a very different approach than
treatment. Treatment is making a room sound and function better as an acoustic space, by taming or eliminating reflections
inside the room that cause problems. In this article we're talking about treatment, not isolation. The great thing is, we can
do all of our acoustic treatment ourselves.
We also won't talk about measurement. While measuring a
room's acoustic response with testing equipment and calculat-

ing modes and resonances using room dimensions can be useful in some situations, generally the solutions are going to be
the same. So we're leaving measurement outside the scope of
this article.
Lows first!
Often home recordists just tack a lot of acoustic foam or egg
shell mattress on every wall (Figure 1). This can be ugly, and it
doesn't work very well. In a room like that, you might clap
your hands, hear no reflections, and think you're done. The
problem is, clapping can't tell you what's happening at low
frequencies. When you tack up acoustic foam, you're only
dealing with highs and mids.
1

To illustrate, consider this chart of absorption coefficients for
three common materials, in a 2" thickness applied directly to a
wall, at six standard frequencies in Hz.

Material

125 Hz

250 Hz

500 Hz

1000 Hz

2000 Hz

4000 Hz

OC 703

0.17

0.86

1.14

1.07

1.02

0.98

OC 705-FRK

0.60

0.50

0.63

0.82

0.45

0.34

Sculpted Acoustic Foam

0.11

0.30

0.91

1.05

0.99

1.00

RECORDING NOVEMBER 2016

Table of Contents for the Digital Edition of Recording - November 2016