Recording - March 2016 - 24

GPS to find our way through all the noise out there, and discover where our sonic serenity lies... where what you hear is the
unadulterated sound on your track, and your confidence in its
accuracy grows and flourishes.
The (beginnings of a) solution
The very first task is to understand what your setup will be
used for. If you're using it strictly for listening, like a home theater, then accuracy is not necessarily the most important thing.
Yes, I said it. If the room is only for your entertainment, then it
needs to sound good, to your ear.
But if you're reading this magazine, it's likely you want to
create something for others to listen to, and perhaps even pay
for. So you want what you hear to be what they will hear. Or
you might be part of broadly collaborative work, like post production sound (my milieu). In this situation, what you need is
accuracy. You need to know that what you're hearing is an
accurate representation of what's on your track, so you can
have a good idea of how the person at the end of the line, the
consumer of your product, will hear it.
We all want our music to play the same for everyone. But
there are so many playback and listening devices around that
it's impossible to do some sort of quality check for every playback system your project will encounter. There are formats
from vinyl to CD to MP3. There's Dolby's universe of formats
like AC-3 and Atmos. And there's a staggering array of speakers, headphones, earbuds, and car entertainment centers, with
more climbing on board every day. We're aiming for sonic
neutrality, not sonic perfection.

Speakers
The first step is to get speakers that are accurate. That
means you shouldn't chose them because your favorite artist,
engineer, or producer uses them. Your heroes' hearing is different, their rooms are different, their listening experiences will be
different in every way. And in the case of artists who perform
live, they may very well be half deaf! (Pete Townshend has
gone very public about his hearing loss.)
Your should look for neutral speakers with published and verified data about frequency response, directivity, distortion, and
the like. Educate yourself not only on what the specs mean and
what numbers are good, but also learn how manufacturers can
fudge the data to make their product look better (remember VW
and their fudged emissions data?). It's easy to get fooled.
Personal aside here: I have to admit I am partial to JBL's latest offerings. While there are a number of manufacturers who
have excellent products, many of which are reviewed in these
pages, I've had multiple opportunities to examine JBL's speakers in detail. I've found the JBL data to be honest, I've spoken
to the designers and found them to be excellent scientists who
are enabled to do their best work, and their research is a solid
quest for knowledge, started decades ago with Dr. Toole and
continuing under Dr. Sean Olive. End of personal aside.
Room
You also have to pay attention to the room you work in. I like
to say that the room is the other half of the speaker-it's that
important. Speakers and room acoustics interact with each other,
and you can't separate the effects of one from the other. Poor
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RECORDING March 2016

room acoustics can make the best speaker sound bad, and good
acoustics bring out the best that even a poor speaker has to offer.
The goal is to have a room where the overall response is as
flat as possible, with special attention paid to the low frequency
range. This is where much of our perception of audio quality
resides, due to the low number and wide spacing of resonances.
Your low frequencies should be brought under control by addressing the individual resonances and problems, without using "bass
traps" (a long story for another article). One of my more interesting
projects was fixing a complaint of "boominess". It turns out that the
problem was two narrow +18 dB resonances. Addressing those
specific frequencies instead of using a broadband bass trap fixed
the problem without impacting the overall LF sound.
It's also important to carefully control reflections, especially
from windows, doors, and the ceiling. Spurious reflections can
mess up localization, where the sonic image jumps around the
room. I've even experienced this in some very high-end rooms;
I was surprised that the big names that worked in there didn't
notice this. This is best fixed with diffusion. But you can't go
overboard with it, as too much diffusion can make it difficult to
have any localization at all.
Perhaps the most important aspect of a room is its most overlooked-the ceiling. It is the largest flat, reflective surface, so it
needs to be addressed just like any other surface. You can
deal with this with acoustical clouds, which can be as simple
as fabric covered absorptive panels suspended from the ceiling. (Hang them carefully-even the lightest panel can hurt
you if it falls.) See my article in the September 2014 issue of
Recording for specifics on this rarely-addressed topic.

Then you adjust the room's decay using absorption. But there
are pitfalls here too. The lowest frequency absorbed is determined by the thickness of the absorber. You should use a material
(fabric-covered Owens-Corning 703, for example, or supported
Bonded Logic R-7 if you don't like fiberglass) around 2 inches
thick. This has good absorption down to around 300 Hz. Below
this frequency, you're better off using devices that respond better
to pressure, like my ever-favorite Helmholtz resonators.
These simple things will take you a long way to getting an
accurate sound in your room and building your confidence in
the accuracy of what you're hearing.
Room acoustics is a complex thing, so randomly slapping up
panels of stuff you buy from the guys who sell picks at the music
store is not an effective way to go. Do a little research first,
which will help you avoid spending money on things that won't
give satisfactory results. And if you really want to dive into studio acoustics, I highly recommend The Master Handbook of
Acoustics, fourth edition, by F. Alton Everest. It's a long read,
around 600 pages, but his presentation of the material makes it
easy, and he doesn't overwhelm you with mathematics.
In the end, an excellent set of speakers in a well designed
acoustical environment will give you a neutral listening experience, so you know that, to paraphrase a popular saying,
"what you hear is what they get."
Bruce Black (black@recordingmag.com) is a recording and
post-production engineer now working as an acoustics consultant
with Media Rooms Tech in Ventura, CA. Learn more at media
roomstech.com and read Bruce's blog at manofacoustics.com.

http://www.mediaroomstech.com http://www.mediaroomstech.com http://www.manofacoustics.com

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