Garbage Can Acoustics

Often I get asked how to “soundproof” a practice room. A band wants to rehearse and record without bothering their neighbors too much. The first thing I ask is “Which is it, soundproofing or sound treatment?”

WHAT’S THE DIFFERENCE?

Soundproofing is a way to keep annoying sound from escaping (the stuff that bothers the neighbors) and sound treatment is what you do to make a space sound good! A room that sounds good but also keeps all the sound in is actually pretty hard to do.

SOUNDPROOFING

The typical garage (the preferred choice of many a “garage” band) does little to block sound. While high frequencies are mostly attenuated, low frequencies (the constant boom, boom, boom) goes right through the walls. The only way to really block this effectively is with massive, heavy construction (like cinder blocks and concrete).

Professional studio spaces, especially in urban areas, are usually built like a kind of “thermos” (a room within a room). This keeps noise transmission down to an acceptable level, though it does nothing about the actual SOUND in the room.

THE ULTIMATE ROOM

A good sounding space just sort of disappears – its sonic signature does not adversely affect the sounds produced within. The larger the room, the less sound problems. The cleanest, driest room possible is – outdoors!

Unfortunately the typical garage/living space available for practice rooms tends to be on the small side (11 x 11, 11 x 16, etc.) with low ceilings and muddy, boomy acoustic properties. While our ears and brain can subjectively compensate for these shortcomings, recordings cannot. Any sound recorded in such a space will take on the sound of that space.

THE LAWS OF PHYSICS

No matter what whiz-bang tech comes along, the principles of acoustics don’t change much. Many the techniques for improving room sound were devised years and years ago,and they all still work! It doesn’t have to take a small fortune to fix most sound problems. You just have to know what’s going on.

FREE SOUNDPROOFING

Here’s a tip: You can get the same soundproofing results as the big boys and girls by setting up your band a cellar! With dirt on all four sides your isolation is pretty much complete (except for straight up). Want to build a quiet practice room/studio? Pretend you’re building a swimming pool (or a bomb shelter).

Another tip is to try not to “excite the resonances” of the room too much. The quieter you play, the less the room affects your sound. Any room will reach a point of saturation where nothing sounds good anymore. Past this point the sound has no choice but to leave the room and entertain the neighborhood (in other words, play quieter).

DRYWALL IS YOUR FRIEND

Sound escaping a room can also be useful sometimes. You’ve probably pulled up alongside someone playing loud music in their car with the windows rolled up and heard their subwoofer pumping away. This escaping low frequency energy actually can improve the sound inside – imagine how boomy and deafening it would be if it all stayed in there (yes, I know you’d probably rather it did)!

Similarly, most modern residential construction uses drywall – gypsum boards mounted on 2 x 4s which creates hollow walls. While this attenuates high frequencies pretty well, the more powerful bass sounds mostly just pass through them like they didn’t exist. This actually cleans up the sound  a bit since the offending resonant  low frequency information has passed out of the room.

Professional studios spend a lot of money and time installing acoustic treatment to tame these low frequency sounds, yet drywall basically gives you basically the same effect for free!

ACOUSTICS ON THE CHEAP

Even with all that low frequency loss, small rooms still contain a lot of muddy sounding lower and upper midrange resonances. Learning how to control these is one of the the “secrets” of making a better sounding room.

Forget about stuff like egg cartons and foam mattresses and carpet on the walls – they don’t work! They only absorb/diffuse high frequencies, making your room sound dull. The “mud” still remains (and the bass sound still escapes).

Stick a couch in the room. The heavier the better. A couch is actually a pretty good low/mid absorber (now your groupies have somewhere to sit and admire you!).

WHAT’S WITH ALL THE GARBAGE CANS?

There’s lots of formulas and techniques that you can use to “fix” a room, but right now we’re just trying to improve it some. Take a few plastic garbage cans (the big ones) and fill them up with loose fiberglass insulation, then put on the lids and toss them into the corners. These will “suck up” a lot of low resonance. Use as many as you want, you can’t really overdo it.

On the wall behind your mixing station install a large bookshelf and fill it from floor to ceiling with books, the more irregular the better. This helps break up slap echos and even out the room. Add a few cheap curtains on the walls. Throw down some rugs. Tack some heavy sheets on the ceiling at 2 foot intervals leaving some “droop” between. The room is starting to sound better, and we’ve hardly spent anything!

BASS TRAPPING

bass traps

For something more permanent (and effective) get a couple of 4 x 8 sheets of heavy pegboard and cut them in half making four 2 x 8 pieces. Install these into the corners of the room from floor to ceiling and fill the space behind them with loose fiberglass insulation. Use wooden trim to hold it all in place. These act as broadband “resonators”, sucking up and dissipating low and mid frequency energy. If one of the corners is not available, mount them  up above between the wall and ceiling.

If you are fortunate enough to have a ceiling higher than eight feet you can stuff a couple of 1 x 3 x 3 foot boxes with insulation (faced with pegboard) and mount them on it.

I once visited a home studio where the owner had used pegboard instead of drywall on ALL the walls, nailed over fiberglass insulation. Every gap between the 2 x 4s was an absorber! That was one dead room!

FIX THE LEAKS

Seal any spaces you can find around wall boxes and on the underside of doors. You might be surprised how much closing those little gaps help.

Get rid of those paper-thin doors – try installing some “outside” type metal doors with built in frames and seals. make sure there’s a window. If you have the space,create an “airlock” using two doors with a closet-sized space between them.

The worse leakage challenge is the typical thin metal garage door. Seal it up as best you can (or build a temporary wall over it).

GOING CRAZY

wall traps smallBroadband Absorbers – Tracking Room
Authors Studio

ceiling trap small

Ceiling Bass Trap – Tracking Room
Authors Studio

mixing room

Bass Trap/ Diffusers – Mixing Room
Authors Studio

Time to get out the sledgehammer! Having two (or more) optimised spaces for recording and mixing is a great way to go if you can manage it. But don’t let “tech perfection lust” get in the way of your ultimate goal. Once you know the basic principles, You can get pretty good, even excellent results by keeping it simple. Just use your ears!

Here’s a good practical guide on studio acoustics:

http://www.amazon.com/Build-Budget-Recording-Studio-Scratch/dp/0071782710

© 2015 Leo Bidne

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