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Build an Effective Room Treatment on the Cheap

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With more and more musicians and engineers able to have their own personal studio, many times the last thing considered is the acoustics of the recording space. This is understandable, since if you don’t have the recording gear in the first place, a great acoustic environment isn’t going to do you much good. But I think that one of the major reasons that the recording environment isn’t given a higher priority in a personal or non-commercial recording space are the perceived costs in attaining something acoustically reasonable.

It’s true that designing a commercial facility with a great designerarchitect is going to cost you anywhere from $300 to 500 USD per square foot (or more) to build, but that doesn’t mean that you can’t improve your present recording environment for much, much less. All it takes is a bit of knowledge about some really basic acoustics principles and some time, and you can improve your studio more than you could’ve imagined in most cases (with no math involved unless you want to go another step).

For this post, I’m going to borrow liberally from chapter 2 of my book “The Drum Recording Handbook ” (written with engineer Dennis Moody), so if you see any references to drum kits, keep in mind that the information applies to just about any acoustic instrument (electric instruments too if you use room mics).

A brief disclaimer first - the construction tips in the first part of the post should help improve most existing rooms, but there are always the exceptions. If you live close to an airport, heliport, train tracks or highway with a lot of heavy truck traffic, you require a lot more drastic measures that what you’ll find below. These situations are difficult for even a pro acoustician and always require extra care and a lot more expense. If you’re located in a quiet neighborhood 20 feet away from a persnickety old lady with great hearing, following the information below still might not be enough to keep her from calling the cops when you record your speed metal band. Once again, you’ll need more drastic measures. But even if you don’t get the amount of isolation that you hoped for, you’ll find that you’ll improve the acoustics of your room enough that you’ll notice it on your recordings, which is exactly what you want. So let’s get started.

I know you already know this but it’s worth saying it again - the room in which you record has a major part in the sound of your recording. The instrument that usually suffers the most in a poor recording environment is the drums, since they depend upon the room acoustics more than any other instrument in the rhythm section (although this can apply to just about any acoustic instrument as well).

You can have a great sounding drum kit that’s tuned to perfection, but it won’t sound nearly as good in a dead garage with an 8 foot ceiling as it will in well-designed studio with a 12 or 14 foot ceiling. With that being said, you can only work with what you have, so here are some tricks on how to optimize your room to make your drum kit (or any other instrument for that matter) sound its best in that acoustic environment. If you feel like swinging a hammer a little and have a few dollars to spend, it’s surprising what can be done without a major acoustic design and an investment to match.


Soundproofing

The first question that both musicians and engineers ask regarding acoustics is, “How can I make sure that my neighbors don’t hear us?” There’s really no secret to this one, although everyone thinks there is. All it takes is mass, which is our first principle. Simply put:

Acoustic Principle #1

The more mass your walls have between you and your neighbors (that includes walls made from cinder block, brick, wood, drywall, etc), the more you’ll be keep the outside sound from getting in, and the inside sound from getting out.

One of the ways that most pro studios accomplish soundproofing is by building a room within a room, which is done by putting the floor on springs or rubber, and building double or triple walls with air spaces in between on top. Needless to say, this gets really expensive and is impossible to do if you start out with a small space like a 10 foot x10 foot to begin with. But there are other ways to improve your isolation that can really be effective (though never as completely soundproof) that are quite a bit cheaper. All it takes are some construction tools and a little time, so here we go:

Step 1 - Add some mass to the walls and ceiling to increase your isolation.

The least expensive way to do this is with 38” cement backing board. This is the same thing that’s used in showers and is sometimes called “Cement Board”. Home Depot sells 3 or 4 kinds and it does a great job for just a little bit of money. Plus, it doesn’t take up a lot of space and is way more efficient than regular drywall. It usually comes in 5’ x 3’ panels, but they weigh about three times what a panel of 4’ x 8’ drywall weighs (and you want all that extra weight to increase the mass, and therefore, the isolation). Make sure that you both glue and screw the cement board to the existing wall, since anything that isn’t absolutely tight will either rattle or give the room an unwanted resonant ring later, and defeats the isolation (see Principle #2).

Acoustic Principle #2

Think of air like water. Any space between any construction joint lets the air out (or in) and acts the same as if the room was filled with water, so the idea is to make sure that there are no air leaks.

Step 2 - Get the thickest solid oak door that you can afford, then make sure you get a doorjamb.

The trick here is to make sure that there are no air spaces around the door, and you do this by applying weather stripping around it on both sides. Most commercial studios use a double door “airlock” with a door attached to each side of the wall to maximize the isolation. You might get by with just a single door as long as you eliminate all the air spaces around it (see Principle #2).

Step 3 - Glue and screw some strips of ¼” low grade inexpensive industrial plywood to the cement board, and then glue and screw ½” regular drywall on top of that.

The drywall is there primarily so there’s an anchor to attach the wall treatment outlined in Step 4.


Acoustic Treatment

Now that we’ve increased the isolation, it’s time to treat the surfaces of the room so the decay time is controlled. This is one of the more difficult aspects of acoustics, since you want an even decay time across all frequencies. The following is more brute force than scientific, but will give you a good result with some experimentation for not a lot of money.

Room Resonant Frequencies

Just about every room that has not been acoustically treated has a frequency that, when it’s excited, is a lot more pronounced than others. What’s more, this resonance will occur at even multiples of that frequency again and again. Recording studio designers use many methods, including bass traps, surface treatment and diffusers, to help eliminate these troublesome frequencies. The problem is, if untreated, the resonant frequencies in the bass region are responsible for extraneous noises like the dreaded snare buzz that happens when when certain notes are played.

Rooms that have parallel walls (like almost all buildings) respond much worse than those where the walls are slightly angled (like in recording studios). If this problem frequency happens to fall close to or at the tuning frequency of a drum, or close to a note that a bass, keyboard, or guitar player hit, the buzz will get worse because the volume of that note is accentuated and creates a sympathetic resonance within the drum due to its tuning.

The easiest way to eliminate most of these problems is by treating the walls. Acoustic tiles like Sonex are effective but can be really expensive if you need a lot of them. Here’s another way to accomplish the same thing for a whole lot cheaper, and have it look better too.

Step 4 - Add the wall treatment.

For a more permanent solution to a overly live room, go to Home Depot and get a roll of 12″ (1.6 cm) thick by 6’ (2 m) wide foam rubber carpet padding and attach it to the wall with a staple gun. A 10 yd. (10m) roll costs about $20 US, and with a few rolls you can cover most rooms. The stuff works about the same and takes up a lot less room than the name brand acoustic tiles.

Make a frame for the padding by using 1” x 2” or 2” x 2” plywood, and use the same wood to make runners down the middle. Staple or nail the padding to the frame. You can then snugly cover it with a fabric with staples (but not too tight or it will ripple eventually), then add some cosmetic wood strips to cover the staples (see Figure 1). Now your wall looks great, there’s some acoustic treatment to the room, and most of the sound is kept in or out. This trick works so well that you want to be careful that you don’t deaden the room too much. You can experiment and actually tune the room to get a personalized sound out of your recording area.


Figure 1: Wall Panels

The Curse Of Low Ceilings

Low ceilings are another frequently encountered factor in a room and they’re a problem for a couple reasons. First of all, the sound from the snare, toms and cymbals projects upwards and will splash off the ceiling (especially if it’s a hard surface) back down towards the drums, causing some frequency cancellation and altering the sound of the drums as a result.

Secondly, a low ceiling is the sworn enemy of overhead mics. This is because with an 8’ ceiling (for example), you can’t get the mics up high enough to capture enough of the kit. As a result, the overhead mics are relegated to being cymbal mics (although this may be OK under the right circumstances). If you raise the mics up near the low ceiling, you’ll also be capturing some of those unwanted reflections, thereby altering the sound of the kit. Higher ceilings of at least 10 feet (12 to 15 are best) eliminates these problems, which is why everyone likes recording in studios that have them. If you’re locked into a room with a low ceiling, the only choice you have is to treat it to either deaden the reflections or at least make them sound as good as possible.

Step 5 - Add the ceiling treatment.

For the ceiling, the carpet padding may be both too heavy and add too much acoustic dampening, so it’s best to put selective amounts around the room to get the proper reverb time and break up any reflections. You can make it look good by building it into triangles or squares with the same type of framing as for the wall (see Figure 2). You might want to try carpet squares, which can work as well.


Figure 2: Ceiling Treatment

Step 6 - Control the low frequencies in the control room.

Most control rooms use what’s known as a “bass trap” to keep the low frequency reflections that we discussed earlier under control. The bass trap is usually placed on the back wall behind the console, but can also be placed in the room corners if that’s easier. Check out the following websites for more information and formulas about bass traps.

A simple bass trap is pretty cheap and easy to make. Just make a 1” or 2” frame to the specs from the above formulas, fill it with R18 encapsulated fiberglass, and cover it with some sort of fabric. Again, don’t pull the fabric too tight as it will ripple over time and you’ll just have to tighten it again. Make sure you use the encapsulated fiberglass since it’s easy to handle without any of the health hazards and itching that comes when you handle raw fiberglass.

Step 7 - Treat the floor

For the recording room, you usually want to keep the floor reflective, so wood or cement is fine. Just put a light carpet under the drums or other acoustic instrument to keep them from moving and also keep the reflections down. That being said, the smaller the recording room becomes, the more you want to contain the ambience. That’s because the reflections of a small room usually aren’t that great sounding and we actually start to hear the smallness of the room. The more we keep them under control, the better the kit (and everything else) will sound.

You might want to keep the control room pretty dead so you can hear just the direct sound from the monitors, so a low-pile carpet on the floor usually works fine. If you’d like to put some wood under the engineer’s chair so it rolls around easier, it usually won’t hurt anything.


Air Conditioning

Now that you’ve isolated your room, you’ll notice that you’ve insulated it pretty well too. That means that it’s going to get plenty hot with a few bodies rocking out inside (especially in the summer), so you’ll have to consider some kind of air conditioning unit to keep everyone from falling over from heat exhaustion. Usually this is where things get really expensive in a professionally designed studio, since quietly exchanging the inside air with the outside takes a fair amount of expertise. Luckily there’s a fairly inexpensive solution.

Step 8 - Keep the room cool.

There’s an air conditioning system called a “mini-split” that’s very popular in Europe were the compressor for the unit is physically located outside the building (see Figure 3). It requires that a 1″ hole be cut through the wall to allow access for a hose that goes to a cooling head, which is mounted on a wall and is very quiet. Just make sure that the compressor is located about a foot away from the building and has about a foot of space on either side.

For a garage or a bed room, a 9,000 BTU unit should give you plenty of cool air and its quiet enough that you can actually leave it on during drum and even vocal recording. Just make sure that the filter is cleaned often to keep the noise down and have the unit serviced annually. Some units also contain a heater which, believe it or not, has come in handy here in the winter in Southern California!


Figure 3 - The Mini-Split Air Conditioner

When You Can’t Make Physical Changes

If you’re unable to make any physical changes like adding mass or carpet to your room, there are still things that are simple and easy to do that will make a difference for the better.
If you are unhappy with the sound of your kit because the room that you are recording in is too live, you can alter it by changing the ambiance of the room. To do this, try either taping up blankets, heavy cloth, or packing blankets to the walls (Figure 4), or lean an old mattress or some couch cushions up against the wall. (Figure 5)


Figure 4: Changing the Room Acoustics Using Blankets

Figure 5: Changing the Room Acoustics Using Cushions

On the other hand, if you find your room is too dead, you can lean sheets of 38″ (1 cm) plywood up against the wall. In a pinch, you can use some plastic sheeting or large plastic garbage bags opened to flat and duct tape them to the walls. These create a reflective surface that should liven up your recording room. I’ve tried this many times and it works great.


Placing The Kit In The Room

If you do nothing else, positioning your kit in the best acoustic place in the room will do wonders for the sound. What you’re looking for is a spot where the drums or acoustic instrument sounds relatively live without any of the room cancellations. Try these following steps to find the best room placement:

  1. It’s usually best to stay out of a corner. The corner normally causes “bass loading”, meaning that the low frequencies will be increased causing your kick and floor tom to be louder than the other drums. This can also lead to increased ringing and snare buzzing. That being said, don’t rule the corner out without trying it first since the extra fullness of the kick might be just the thing you’re looking for.
  2. Pro engineers will usually test a room by walking around and clapping their hands. That’s a good way to find a place in the room that’s has a nice even reverb decay. If the clap has a “boing” to it (a funny overtone), then so will your drums so it’s best to try another place in the room.
  3. Ideally, you don’t want to be too close to a wall. The reflections (or absorption if the wall is soft) can change the sound of the kit. The middle of the room usually works best.
  4. Ideally, you want the place in the room with the ceiling height is the highest. If the ceiling is vaulted, try placing your drums or acoustic instrument in the middle of the vault first, then move as needed.
  5. Whatever you do, stay away from glass if you can. Glass will give you the most unwanted reflections of just about any material. If you have no choice because of the way the room or the band is situated, try setting up the kit at a 45° angle to the glass.
  6. These tips will really help get your room in shape with the least amount of financial outlay. All it takes is some time and experimentation, and only one optional mathematical formula. But remember, if you need the real thing it’s still best to hire a pro.
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