Recording - November 2015 - 16

Acoustics
One of the problems that is very common in
home studios is the lack of room symmetry for the
control room. Regardless of how the room is
going to sound, whether it sounds good, bad, or
anything in between, ideally you want the left
speaker to sound like the right speaker, so that's
why you need to set the room up in a very symmetrical fashion. You don't want it to be off center one way or the other. So you can get a huge
improvement just by thinking in those terms.
The next thing is just basic room geometry,
which you may or may not be able to do anything
about. But if you have a choice between two
rooms and you are trying to decide which room
might be better, higher ceilings are always better than lower ceilings; a low ceiling is kind of the Achilles' Heel of rooms.
Let's talk actual numbers-what is low, and what is high?
A very typical construction has an 8' ceiling. So if you can end
up with a 9' or a 10' ceiling, you are much, much better off.
What is it about the height that hinders or helps your sound?
The room modes, which produce nulls or dips in certain frequencies and bumps or loud areas in
certain other frequencies. For an
average person that's seated in a typical chair, the height of their ears is
about 4' off the ground-exactly in
the middle of an 8' high room, precisely where your first room mode is!
It almost always produces some challenges when you have an 8' ceiling.
So you're hearing exaggeration at
certain frequencies, just because
of where your actual height is?
Yeah, and that would be a significant null. The other challenge is to
apply any acoustic treatment to the ceiling that is effective at all. Let's say we
have a cloud as an example, which is
a good inexpensive solution. You might
want a 2" to 4" cloud, and it might be
4" to 12" off the surface of the ceiling,
so now, all of a sudden, you've come
down anywhere up to 16". So now
instead of having an 8' ceiling, you
have a 6'8" ceiling, which won't work.
So that is even worse than an 8'?
No, it has more to do with aesthetics. It's a very low ceiling and it doesn't feel very comfortable, you feel very restrained, and imagine
if you were particularly tall, it would really feel cramped. So it's
not that you can't get away with an 8' ceiling, it's just not ideal.
Basically, if you have a choice between an 8' ceiling or a 9' or
a 10', pick the room with the higher ceiling!
The other component is trying to find a room that doesn't have
square dimensions. Square dimensions are the absolute worst
case scenario because all rooms have those room modes; it's just
the physics of how sound travels in space. If the length is, let's
say, 10' and the width is also 10', the nulls and peaks in one
direction are exactly the same as in the other direction, so you're
accentuating those problems even more. What you're hoping to
have in a perfect world is lots of nulls and peaks that are at different frequencies, so when they average out it smooths the frequency response out. No amount of acoustic treatment that you
16

RECORDING November 2015

could put in a 10' x 10' x 10' room would make
that room sound acceptable.
Even gobos that artificially reduce the length
of the room?
You could improve it, but you would be hard
pressed, it would be challenging. Try to avoid
those rooms.
If you have a choice of a number of rooms in a
house, try to pick a room that is leaning in your
favor. There are a number of free on-the-web
room mode calculators that you can use. This
might help someone just trying to figure out if a
room might be a better choice; you can enter the
height, width, and length, and it will plot out the
frequencies for each of the axial, tangential, and
oblique modes, but the most important ones are the axial modes.
Just try to find a room that is more rectangular in shape and
where, if you had an 8' ceiling, avoid another 8' dimension.
Seeing the designs you've created, what I remember seeing
is no dimensions repeated-rooms with symmetry but no
matching dimensions... even rooms where walls all have different lengths.
Yes, but that's virtually impossible to have unless you start a building from scratch. Let's say you've got
two parallel walls and you have flutter
echo. One of the solutions would be to
apply something to the wall that would
be absorptive, or put something on the
wall that would be diffusive. But what
happens if those two parallel walls
have windows on them and you can't
apply absorptive or diffusive material
to them? The only solution is to splay or
angle those two walls so they are not
parallel to each other. And they need
to be not parallel to each other by at
least 15 degrees for it to work without
causing more problems than it fixes, so
that's a design consideration when
you're dealing with glass, because
glass is so reflective.
Can you talk about actual treatments that can help or hinder the
sound? Many of our readers might
have misconceptions regarding
this. Surely some have thought, at
some point, "I'll just put all this
foam on my walls, and it will be
awesome."
Use your ears. Walk around the
room clapping your hands. Do you
hear any flutter echo, or excessive reverb? Talk loudly, do you hear
any room resonances or boomy or thin sounding areas? One of the
most common problems you see is people applying too much
absorption in a room, which ends up sounding pretty hideous. When
you put a lot of absorptive material, the room becomes overlydamped, very dead-sounding, it doesn't sound natural at all.
This thin material only absorbs down to about 500-800 Hz. So
you walk into a room with this kind of treatment and it sounds particularly dead, but it sounds very boomy and big as well. It's like
the low end is out of control, like someone turned the bass way
up. What's actually happening is you've damped out all the highfrequency information, but the absorptive material is doing nothing for the low end. All that's left is all this low-frequency information that's feeling accentuated. It's not that it's been turned up, it's
that the top end has been turned down; it's a relative perception.

Table of Contents for the Digital Edition of Recording - November 2015