GC Pro Audio Solutions - Fall 2011 - (Page 42)
D I S P E L L I N G A U D I O M Y T H S
Follow the Bouncing Sound
Busting the myths surrounding acoustics
By Ethan Winer
Figure 1: This roller coaster lowfrequency response measured in a typical bedroom size space is not only common, but also typical.
READERS OF THIS COLUMN KNOW THAT I LIVE TO BUST AUDIO MYTHS, AND SOME OF THE MOST PREVALENT MYTHS ARE THOSE SURROUNDING ACOUSTICS. PERHAPS THE BIGGEST MYTH IS THAT ROOM ACOUSTICS IS AN IMPOSSIBLY COMPLEX, ARCANE SCIENCE THAT ONLY A SPECIALIST HOLDING AN ADVANCED DEGREE CAN UNDERSTAND. NOTHING IS FURTHER FROM THE TRUTH. ALL ROOM ACOUSTIC PROBLEMS — PEAKS, NULLS, RINGING, FLUTTER ECHO, EXCESS REVERB, AND AMBIENCE — ARE CAUSED BY REFLECTIONS OFF THE WALLS, CEILING, AND FLOOR. REFLECTIONS CAN BE ABSORBED OR DIFFUSED, AND SOME CAN BE IGNORED. IT’S THAT SIMPLE!
Of course, the treatment solution for a 30- x 40-foot professional control room is very different than for a 10- x 12-foot bedroom, because reflections from nearby walls are stronger and thus more damaging than reflections from more distant surfaces. So some types of treatment are more appropriate for various situations. Let’s take a closer look.
Myth: You must measure your room’s acoustics in order to know how best to treat it. Fact: I measure rooms as part of my acoustics business, so it may seem strange for me to say that measuring isn’t always needed. To my way of thinking, there are two reasons to measure a room. First, many people have no idea
how bad their rooms are, so measuring can provide a badly needed wake-up call. Figure 1 shows the low-frequency response in a typical 11- x 16-foot untreated bedroom. Fretting over the response of a sound card that’s half a dB down at 20 kHz while ignoring peak/ null spans that exceed 40 dB caused by acoustic reflections borders on insanity. The second reason to measure is to confirm the improvement after adding bass traps and other acoustic treatment. Not that you won’t easily hear the change! The graph in Figure 1 shows only the low-frequency response, but other graph types show comb filtering at higher frequencies, reverb time, the strength of individual reflections, and ringing at specific frequencies. So by measuring before and after treatment, you can assess the improvement in all of these areas and decide whether further treatment is warranted. Measuring can also help you find the best speaker and listener placements. But you don’t usually need to measure to know what or where to treat. Simply adding bass traps in the corners and mid/high-frequency absorbers at key reflection points, including the rear wall behind you, will get you 90 percent of the way there.
whatever happens at low levels happens the same at loud volumes. It’s true that listening softly reduces the audibility of reflections that cause echo, but the response peaks and nulls caused by reflections remain the same. Listening close to the speakers does improve the ratio of direct versus reflected sound, but even at only two or three feet away, which is typical for nearfield listening, the response in an untreated small room is usually similar to Figure 1.
Myth: You don’t need room treatment when using nearfield monitors, and playing music at low volumes also avoids the need for acoustic treatment. Fact: Acoustic behavior is linear, so
Myth: Bookshelves are effective diffusors. Fact: A real diffusor is not simply a random shaped surface. It might be possible to get some amount of diffusion from a shelf full of books, but the books need to be arranged in a specific pattern to be truly effective. One key aspect of diffusion is different depths, to stagger the time between reflections. Most books are a similar depth, so a shelf full of books reflects more or less the same as a flat wall. Myth: You should record vocals in
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GC PRO AUDIO SOLUTIONS
Table of Contents for the Digital Edition of GC Pro Audio Solutions - Fall 2011
GC Pro Audio Solutions - Fall 2011
Table of Contents
Bonzai Vault: Bruce Swedien
Secret Sauce: Just Like Starting Over
Learn to Earn
Gear Trends: Setting Bass Traps
Tech Trends: Living With Loss
Legacy: The ABCs of DSPS
Audio Myths: Follow the Bouncing Sound
GC Pro Audio Solutions - Fall 2011