Fig. 1. Primacoustic sells turnkey packages as well as individual products. The London 12 Room Kit is a live-end, dead-end (LEDE) room design; it includes 22 panels in a choice of three colors, and is designed for rooms that measure approximately 120 square feet.

 

Fig. 2. This shot shows RealTraps’ Diffusor Modules, MiniTraps in the wall/ceiling corners, and Corner MondoTraps and Fat MondoTraps in the wall/wall corners.

Absorption absorbs sound, so absorptive treatment would seem to diminish most sound that bounces off walls. However, problems are often most pronounced at low frequencies, which require specialized solutions, usually in the form of bass traps. This is because in smaller rooms, the wavelength of a bass sound’s single cycle might be longer than the room itself, and cannot be controlled by thin foam panels and other wall treatments; typically, separate absorbers control midrange/high frequencies and low frequencies (see Figure 1). Fiberglass material designed for acoustics (covered with fabric for both aesthetics and to contain the fiberglass) is a popular absorptive material, as is acoustic foam.

If you can afford to reduce your room size somewhat, creating a second sheetrock wall offset at least a couple inches inward from an existing wall can also help control reflections. Sheetrock has some “give” so it absorbs sound, and the airspace between the two walls also helps. This approach also tends to keep sound within the room by decoupling vibrations from the “public-facing” walls. For similar reasons, absorptive panels are also offset inward from the wall somewhat.

Diffusion Absorption won’t stop all reflections, so diffusion helps make those reflections less objectionable. When rooms have parallel surfaces, buildups happen at frequencies that relate to room resonances. If non-parallel walls aren’t an option, diffusers mounted on walls scatter the sound in multiple directions to defeat these resonances. Diffusors on non-parallel surfaces are even better. Between absorption to reduce reflections and diffusion to create more desirable reflection characteristics, you can cover most of a room’s inherent problems (see Figure 2).

Effective diffusion can reduce leakage if one instrument is reflecting off the wall into a mic for another instrument. Scattering the sound waves can reduce the amount of ambient sound hitting other mics.

Fig. 3. Acoustic Sciences offers Full-Round, Half-Round, and Quarter-Round Tube Traps. The Full Round version rotates to present sides that provide absorption or diffusion; the Half-Round and Quarter Round versions combine absorptive and diffusive properties.	Fig. 4. This plug-in GUI from ARC version 2 shows room response before (orange line) and after (white line) correction.

Wanted: Dead . . . or Maybe Alive Before you go too crazy with absorption, analyze your needs. Absorption reduces a room’s reverb time, which generally a good thing when mixing and mastering, but may not be ideal for tracking—Jon Bonham’s drum sound on Led Zeppelin’s “When the Levee Breaks” proves that room ambience can be a beautiful thing. While that example may be a bit extreme, a little “air” in a room can make guitar amps come alive and add a little depth to vocals. For a more “live” sound, diffusors become more important than absorbers, as the reduction of resonances gives a more “open” feel and less high-frequency information is absorbed.

Fig. 5. sE Electronics’ portable Reflexion Filter Pro reduces room ambience to achieve a “drier” vocal or instrument recording.

Some larger studios have LEDE (live end/ dead end) rooms that conform to a standard design in which one end is live, and the other dead. So you could, for example, set up drums in the live end and guitar amps in the dead end if you plan to add ambience to the guitars during the mix. Even better, scope out your studio to see if there are other options. A nearby tiled bathroom can give a super-live sound, while a large closet that’s filled with clothes can serve as a vocal booth that’s ideal for narration, where you typically record dry and add ambience artificially.

Isolation In addition to room acoustics, “inroom” acoustic considerations include leakage and sound isolation. Acoustical coupling is a common isolation issue with simple solutions: For example, a “floating floor” for drums helps minimize the transference of kick drums, drum hits, impulse sounds from high-hat stands, and the like from working their way into the floor—and then to walls, other mic stands, etc. Some studios also float bass and guitar amps, which often sit on a floor and couple sound into the room.

Minimizing leakage is usually done with gobos—portable panels that absorb sound. For example, when miking a bass amp, you can surround it with gobos and place mics inside the gobo “fort.” Taytrix’s StackIt Gobos are like a Lego setup for gobos; you can stack them, adjust them to different angles, or even enclose a loud sound source such as a guitar amp.

Other isolation methods include isolation shields, such as Primacoustic’s Crashguard, which wraps around drum mics to keep leakage away from cymbals. I’ve also become dependent on their TriPads, which are basically foam isolators for mic stand legs that isolate the mic stand from the floor—if you can’t float a floor at the source, at least you can float a mic stand at the destination. And IsoAcoustics makes speaker stands designed to provide isolation for speakers, which of course produce a lot of vibrations. (If you have the resources, you might even consider a prebuilt iso booth; see sidebar on page 56 for tips.)

Getting Attached Don’t overlook the importance of the way you attach absorption panels or diffusors to the wall, as some adhesives eat away at foam. Auralex has several adhesive products, from Tubetak Pro Liquid, designed for permanent mounting, to TEMP•Tabs, which are designed to be temporary and are ideal if you plan to move your studio around (or want to live with a particular treatment for a while before committing to a permanent installation).

Fig. 6. Auralex’s MAX-Wall lets you set up a mixing or recording space without having to attach anything to the walls—renters, take note.

Quick Fixes I’m generally not a fan of quick fixes, but when all else fails, these simple options can make a huge difference.

• Primacoustic Recoil Stabilizers These mount under speakers, providing isolation and stabilizing speaker motion. It seems like snake oil, but after extensive testing (because frankly, I didn’t see how the “miracle cure” claims could be true), there’s no doubt it makes a major, audible difference in terms of bass, imaging, and an overall “tighter” sound.

• Bright Star Audio Isonodes These reject vibration—put them under your portable hard drive, tube amps, units with transformers, and the like to quiet them down and minimize “bad vibrations.”

IK Multimedia ARC (Advanced Room Correction) System This is one of the best-kept secrets for those who want better mixes: It’s a system for DAWs that combines a measurement microphone and measurement software, but the unique element is a correction plug-in (Figure 4 on page 55) that compensates for room issues. You can mix and record with the plug-in inserted in the master bus, so your mixes are targeted to acoustics with a flat response. When it’s time to render to a stereo mix for duplication or other environments, bounce without the plug-in . . . very clever. Recently upgraded to Version 2 (with upgrade pricing for Version 1 owners), ARC works well because it doesn’t do pinpoint EQ for just one sweet spot, but the measurement process takes the entire room into account for broader, more forgiving correction. It even lets you create alternate references like TVs, club P.A. systems, radios, and the like so you can mix to a specific target playback medium.

• JBL MSC-1 This monitor system controller incorporates their RMC (Room Mode Correction) process. As a controller, it can switch among three input source and two sets of speakers (including subwoofer management); it includes EQ, mute, sub on-off, and level. Like ARC, the RMC process requires using the included reference mic, but it corrects mostly low frequencies where errors tend to be most egregious.

• sE Electronics Reflexion Filter This is primarily for vocalists and narrators, as it provides an “acoustic shield” (Figure 5 on page 38) that blocks your voice from reaching the walls and creating echoes, but also shields against those reflections returning back into the microphone. It’s a highly effective concept.

• Instant Recording Space Can’t do permanent acoustic treatment? Check out Auralex’s MAX-Wall (Figure 6).

Super Silencers: Prefab Vocal Booths

Sometimes the only thing that’s needed is a really quiet place to record vocals or voiceovers. You can build that space yourself, but if you’re in an apartment, condo, or some space that you plan on leaving someday, it’s best to be as portable as possible. That’s where a prefab vocal booth comes in.

The beauty of a prefab vocal booth is that not only is it portable, but it’s capable of giving you great isolation as well. Most of them are easy to float, so it can become a room-within-a-room, and the acoustics are controlled, so it’s not too dead. They’re so quiet, some night owls in big cities like New York even use them to sleep in during the day. So what’s not to like?

If you’ve ever spent more than 15 minutes in a totally isolated area, you know that the heat soon becomes oppressive, which means that some sort of climate control is required, and that’s where the expense comes in. While most manufacturers of vocal booths have an option for HVAC, the whole idea becomes a lot more costly and complicated once that factor is introduced. Most vocal booths will have a heat exchanger that will keep the heat down, but still may be too hot for extended sessions.

Another issue with prefab vocal booths is that they provide excellent isolation at mid and high frequencies, and only good isolation at low frequencies. If you’re only concerned about recording vocals or narration, this will never be a problem, but if the booth is large enough for drums, you have to take that factor into account. One of the best reasons to purchase a prefab vocal booth rather than attempt to build one yourself is that building a small room that actually sounds good is far from trivial. You may end up with a worse-sounding space than when you started if you try it yourself and do it incorrectly. Manufacturers of portable booths spend a lot of time perfecting the acoustics of the space, so the products are pretty good right out of the box. Many manufacturers also make enclosures for guitar amplifiers so you can crank till your heart’s content without affecting your neighbors. While these work pretty well, remember that an enclosed space could cause your combo amp to overheat unless it has ventilation, which might compromise the isolation that you’re getting in the first place. Non-ventilated enclosures should work well with speaker cabinets, though. Just like with premade acoustic components, be sure to check out the shipping and packaging costs before you order, as they can be prohibitively expensive. Vendors for vocal booths, drum booths, and speaker enclosures include acousticalsolutions.com, soundsuckers.com, vocalbooth.com, clearsonic.com, whisperroom.com, and realtraps.com.

 

Acoustic Sciences acousticsciences.com
Acoustimac acoustimac.com
Audimute audimutesoundproofing.com
Auralex auralex.com
Clearsonic clearsonic.com
Creative Insanity Designs creativeinsanitydesigns.com
Delta H Design deltahdesign.com
Ghost Acoustics ghostacoustics.co.uk
GIK Acoustics gikacoustics.com
IK Multimedia ikmultimedia.com
IsoAcoustics isoacoustics.com
IsoNode brightstaraudio.com
JBL jblpro.com
Pelonis Sound & Acoustics pelonissound.com
Primacoustic primacoustic.com
Pro Acoustics proacoustics.com
RealTraps realtraps.com
RPG Diffusor Systems rpginc.com
sE Electronics seelectronics.com
SoundProofCow soundproofcow.com
Taytrix taytrix.com
VocalBooth vocalbooth.com
WhisperRoom whisperroom.com

Auralex: auralex.com
RealTraps: realtraps.com
John L. Sayers: johnlsayers.com/phpBB2/index.php
Ethan Winer’s acoustics forum on MusicPlayer.com:
forums.musicplayer.com/ubbthreads.php/ forums/24/1/Ethan_Winer_Acoustics_Forum