In writing this booklet, I make a few assumptions. I know the old saying about what happens when you make assumptions, but I do so anyway.
- I assume you understand the basic methods involved in how sound behaves. That it gets through any small opening. That it bounces back and forth between hard, parallel surfaces. That the only two ways to stop sound from being transmitted from one space to another are dead air and mass…That limp mass is most often better than rigid mass (ok, a combination of the two is really what you’re after, but don’t get me started on that yet). That every item, every construction material has a resonant frequency at which it’s virtually an open window to sound — kind of like a tuning fork that goes nuts at its particular resonant frequency. That different materials have different resonant frequencies. That trapped air is a very good insulator to sound. That the best way to stop sound transmission through a building structure is to isolate the sound source from the structure before the structure has a chance to vibrate. That walls need to be isolated from ceilings and floors, usually by means of dense, yet pliable rubber. That airtight construction is what we’re after. That sound, like air & water, will get through any small gap.
- I assume you understand that acoustic foam, Auralex’s core product, is not meant to fully “soundproof” your room. That it is an extremely effective absorber of ambient, reflected sound & helps make any room “sound better.” That it does contribute some sound isolating properties, but isn’t sufficient by itself to keep sound in or out of a room. That thicker acoustical foam is better at absorbing low frequency sounds. That controlling reflected sound within a room is extremely important in producing good sounding recordings. That when you hear Mike Wallace’s voiceovers on 60 Minutes you’re smart enough not to sit and say “Boy their studio sounds good. They must’ve spent a million bucks on it.” That you’re smart enough to say, instead, “It’s amazing what some good 2″ acoustic foam can do for a glorified, yet well-constructed closet.”
- I assume you have a few bucks to spend to make your studio the best it can be. That you’re smart enough to realize that empty egg cartons, cork squares and carpet scraps aren’t going to a) keep sound from leaving or invading your studio and b) aren’t going to yield that pleasing, neutral, “Mike Wallace” sound within your studio. That you’ve made a reasonable mental commitment to improving your room, not just a monetary one.
- I assume you realize that these guidelines, if improperly implemented by you, may not yield the desired results. That we can’t be held liable for the advice given because we’re not going to be there watching you do the work or helping you. That these tips are being provided free of charge and we’re not charging you $1200 an hour for our thoughts on how to build a good room. Caveat Emptor ("Buyer Beware"). Enter At Your Own Risk….Void Where Prohibited….Your Mileage May Vary….
- I assume you know the differences between brittle and pliable caulk, and can sense the benefits of & are ready to get messy with silicone caulk, the pliable kind. Be aware, however, that some types of silicone caulk are not paintable, so for caulking that’s going to show in your room, you may want to choose a siliconized type of caulk that’s labeled “paintable.”
- I assume you either know how to handle a circular saw & other common power tools or have the money to hire someone who does. That you can apply drywall tape and mud or can hire someone who can. That you’ve got at least a basic understanding of the importance of solid, level construction techniques. That you know the meaning of the phrase “measure twice, cut once.” That you’re not going to settle for less than perfect (i.e. tight, well-joined) construction.
- I assume that you see the benefits of constructing your control room to be symmetrical geometrically and to be built out of the best materials you can afford. That you realize money well spent now will benefit you for a long time into the future.
- I assume that you’re more concerned with real world results than what a computer printout says. That you believe that one of the keys to getting good, clean sound on tape or hard disk is removing the sound of the room from the equation, to one degree or another. For a great example of this objective successfully implemented, listen to the Eagles’ Hotel California or Pink Floyd’s Dark Side Of The Moon. An interesting aside: the fellow who was chief engineer at Miami’s famed Criteria Studios during the time Hotel California was being recorded there, Steven Klein, now sells tons of Auralex products at his acoustics store in southern California. Small world, indeed!
- If these assumptions I’ve made are correct, you’re gonna do just fine. If not, you might have a bit more work ahead of you than the next guy, but you’ll still be able to grasp the concepts and get excellent results…..it just may take you a bit longer. Rest assured, though, that any extra effort you expend implementing the tips contained in Acoustics 101 will pay you back sonically for a long time to come. Make no mistake: they’re worth whatever work it takes to put ‘em into practice.
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MATERIALS & PRODUCTS SPECIFIED
In Acoustics 101 a few materials and products are specified which you might not be familiar with, so I’ll cover them here in no particular order. Your local lumberyard or hardware store can probably guide you if you don’t know exactly where to pick up the items discussed, just be careful not to let them steer you wrong with substitutions or deletions. You don’t want to fall victim to the old “Ya know, my brother-in-law used to date a girl whose cousin knew a guy who got fired as a janitor at a radio station once, & you know what they used….” The reason I wrote Acoustics 101 in the first place was to combat bad or misguided advice being given by other so-called “experts” in the field!
Regarding substitutions, the second reason I wrote Acoustics 101 was to keep our staff and phone system from being tied up so often arguing….uh, I mean, uh, gently reasoning….with some weenie who can’t understand why he can’t just rip down his drywall, slap up some $8.99 paneling and call hisself a recording studio. I’m not suggesting that a good-looking, intelligent and well-dressed individual like you could possibly think and act like that, but I’m sure you see my point and that you can realize how these sorts of conversations can really gobble up 800 line time and monopolize business days. Stop to think about it: what worked once to construct a tight, good-sounding recording studio will work umpteen thousand more times because sound never changes. Auralex isn’t equipped to, nor is there any legitimate reason to, reinvent the wheel 90 dozen times each week, which is exactly what we were doing before Acoustics 101. So please, have a heart and don’t call to ask us why you can’t substitute 1/8″ masonite for 5/8″ drywall. The methods and materials outlined here have proven themselves to work many times over and should prove more than sufficient for your needs. Also, with few exceptions, don’t add multiple layers of the materials specified; in this case more isn’t necessarily better due to the resonance issue noted previously.
For more information on any of the Auralex products mentioned in Acoustics 101, please visit www.auralex.com.
Lumber & Construction Materials
You can construct a perfectly good-sounding, airtight recording studio with common, easily-located materials. There is simply no “magic” material that you absolutely must use if you’re to have a good room. The materials discussed herein are available at any decent lumberyard and won’t set you back two years’ salary. They’re common items like 2x6s, 1/2″ & 5/8″ drywall, 3/4″ tongue & groove chipboard or plywood, 3/4″ particle or MDF board (compressed sawdust mixed with glue; MDF is more dense than regular particle board), drywall screws, construction adhesive, silicone caulk and more. For those of you who aren’t used to building things, bear in mind when figuring your dimensions that lumber isn’t really the actual dimensions it’s called by. For instance, a 2x4 isn’t; it’s actually 1½"x3½". A 2x6 is 1½"x5½", etc.
SheetBlok™ Professional Sound Barrier
Auralex’s proprietary limp mass, dense vinyl sound barrier material available in 10’x4’ sections or 30’x4’ rolls. It is 1# per square foot, 1/8″ thick, highly flame retardant, easy to install with plastic-cap nails, staples, trowel-applied multi-purpose flooring adhesive or our peel-&-stick pressure sensitive adhesive and yields a great Sound Transmission Class (STC) of 27. Compared with a sheet of solid lead which only yields an STC of 21, SheetBlok is safer, cheaper, easier to work with, more effective, easy to cut with scissors or an ordinary utility knife and UPS shippable (when necessary if one of our dealers isn’t near you) right to your door. It is used to “float” walls, floors & ceilings (isolate them from the rest of the structure), or as one or more of the layers in a wall, floor or ceiling intended to block the transmission of sound to neighboring spaces. It has been used with great success by our most famous clients & is simply unbeatable. SheetBlok is quite simply one of the best investments in good sound control that you’ll ever make. That’s why we sell truckloads of it!
Tubetak™ Permanent Liquid Adhesive
The world’s best acoustic foam adhesive, guaranteed to keep your foam up for as long as you want it there and not to “eat” your foam. Also works great to attach various materials to each other during construction of your studio. Tubetak applies easily with a standard caulking gun and gives a solid, permanent bond that actually improves the sound isolation of your construction. You don’t want to use Liquid Nails brand because its very manufacturer published a memo some time back advising that it not be used with acoustic foam due to possible chemical interactions that can cause the foam to disintegrate prematurely.
Foamtak™ Spray Foam Adhesive
Auralex’s own proprietary brand of spray adhesive that has to be the easiest foam mounting solution on the planet. Using Foamtak can save you tons of time & effort! Foamtak features a unique “web-like” spray pattern that gives it a real competitive advantage—it doesn’t soak into the foam & dry out like other brands do, which is why they so often fail. Foamtak absolutely rules!
Studiofoam™ Sound Absorbent Wedges & Pyramids
Simply the world’s best and most complete line of acoustic foams at prices that make our competitors cry, modify their product lines to try to be more competitive with us or even leave the business entirely. Acoustic foam is such an important component of any studio’s sound control that some mention of our various foam products and their functions is warranted in Acoustics 101 and may be found in the following pages. Overall, there is no better or simpler way to make any room sound better.
U-Boats™ Rubber Floor Decouplers
We developed what we think is the world’s best solution to an age old acoustical problem: how to physically decouple ("float") a floor without having to use rigid mechanical fasteners like screws or without having to take out a second mortgage. Described in full detail in our brochure, U-Boats make quick work of floating a floor at a price virtually anyone can afford. They are much smarter than the super-expensive “pucks” that have been used by acousticians in the past. Not only don’t you need a PhD to use ‘em, U-Boats yield better sway resistance than pucks, are not rigidly attached to your existing structure in any way and are much more affordable to boot. What else is there? Famous studios and recording artists are using ‘em & loving ‘em. Many multi-million-dollar studios and home-theaters-of-the-stars are floating on U-Boats and you’ve heard ‘em at work on numerous chart-topping records.
Auralex RC8 Resilient Channel (aka “Z” Channel)
This is a piece of specially shaped metal to which drywall or other building materials can be mounted to isolate them from the framing members (studs) of a wall or ceiling. One leg of the resilient channel attaches to the stud, the other leg to the layer of building material being hung. This isolation helps improve the structure’s ability to achieve greater sound transmission loss (see definition below). Screws of the correct length must be used so they don’t penetrate through the resilient channel and get into the studs, which would defeat the whole purpose of the channel. Z channel isn’t widely available to those of us who aren’t licensed contractors, so Auralex now keeps thousands of 8’ pieces of RC8 on hand. We sell ‘em in bundles of 24 that are UPS shippable and are available through your favorite dealer.
Soundboard
The term soundboard is often misunderstood, so I’ll try to set the record straight here. Many people mistakenly use the term to describe materials like regular drywall or even particle board. This isn’t accurate. Soundboard is actually a trademarked name for a brown, compressed paper board that is usually 1/2″ or 5/8″ thick & is manufactured by the Celotex company. The best way to describe it for you here is to say that it’s a lot like a sheet of masonite or pegboard, only thicker & a bit softer. It may go by other names like “Homosote” in your neck of the woods, but if you describe it to your building materials supplier, he can probably direct you to it. It is pretty dense, so it makes a good layer in a multi-layered wall configuration. In conjunction with layers of 5/8″ drywall, 3/4″ particle board or MDF & SheetBlok, it’s really effective at blocking the transmission of sound.
Auralex Studio-Grade Mineral Fiber Insulation
This is a special, way more dense type of insulation that the million dollar room guys are known to use to improve a room’s level of soundproofing. Like resilient channel, this product isn’t one that’s normally available to the general public, so Auralex literally stocks truckloads of it. The greatly increased density of this type of insulation as compared to the “pink stuff” makes it way, way more effective at stopping the transmission of sound from one room to another. Plus, our mineral fiber features a much higher burning point than standard fiberglass insulation and has a radically lower rate of moisture absorption (these are both big benefits). Our studio-grade mineral fiber is available in 1″, 2″, 3″ and 4″ thicknesses in 2’x4’ sheets. Is it worth the money? More than you’ll ever know until you use it instead of the “pink stuff” in your new studios! We never build rooms without it.
BRIEF DEFINITIONS & STATISTICS
The two ratings of how sound control is measured are listed here with their respective definitions so you’ll know what the heck Acoustics 101 is talking about.
The first is NRC (Noise Reduction Coefficient), a numerical rating given a material which tells us how much airborne sound the material absorbs. This rating generally applies to soft materials like acoustic foam, fiberglass, fabric, carpeting, etc. but also applies to much lesser degrees to harder materials like brick and drywall. A material’s NRC is an average of its absorption at various center frequencies between 125Hz & 4000Hz. The higher the number, the better an absorber the material is. (Be careful if you’re gonna compare Auralex’s numbers with those of other companies ‘cause some use their own brand of funny math to figure theirs. Auralex, on the other hand, uses only the nation’s oldest, most respected and widely acknowledged as most accurate laboratory, so you know you can take our numbers to the bank.
The second is STC (Sound Transmission Class), a numerical rating of how effective a material is at blocking the transmission of sound through itself. This rating generally applies to hard materials like rubberized sound barriers, concrete, brick and drywall but also applies to a much lesser degree to softer materials like mineral fiber (although it isn’t tested by itself; it’s tested as part of a wall system to verify its effectiveness). Virtually every material filters out some of the sound that travels through it, but dense materials are much better at this than are spongy materials.
Another Important Definition
If you’ve read any books or articles on acoustics, you’ve probably run across the term “room modes.” A room mode is a bump in a room’s frequency response that is facilitated by the room’s dimensions and the way those dimensions cause soundwaves to interact with each other. There are three types of room modes: axial, tangential and oblique. While there’s no such thing as a “good” room mode, tangential and oblique ones are much less detrimental to good sound than are those dastardly axial modes. There are intricate formulas in books at your library that can help you determine your room’s modes; there is also software on the market that can do the same. Auralex has such software and would be glad to work with you or your salesperson in figuring your room’s modes to help steer you in the direction of the proper acoustical treatments. (This offer only goes for those of you who are in square or rectangular rooms; no weird-shaped ones please. They get really tricky & can take the fastest computers and whiz-bang engineers days of computations if you want ‘em to do the job to the “nth” degree.)
Common Wall Configurations & Their Sound Transmission Coefficients
As mentioned before, trapped air and mass are the two components that are most effective at stopping the transmission of sound from one space to a neighboring space. This fact is plain to see when you examine the STCs generated by various types of walls.
• Single wood stud wall, 16″ o.c., with 3½” R11 insulation and a single layer of ½” drywall on each side: STC 38
• Same wall, but with a double layer of ½” drywall on both sides: STC 41
• Same wall, but with the double layer of drywall on one side mounted to resilient channel: STC 53
• Staggered stud 2x4 wall, double layer of ½” drywall both sides, with 3½” R11 insulation: STC 53
• Two identical 2x4 walls, each with 3½” R11, built ½” apart, outside face of each with double layer ½” drywall: STC 60
• Single metal stud wall, 24″ o.c., with 3½” R11 insulation and a single layer of ½” drywall on each side: STC 49
• Same wall, but with a double layer of ½” drywall on both sides: STC 54
Clearly, while some of these designs yield STCs that approach those necessary for studio construction, none of them hits a home run. The addition of a layer of SheetBlok, with its fantastic STC of 27, Auralex resilient channel and our mineral fiber insulation can yield the extra control necessary — saving you time, money and floor space in the process.
Useful Absorption Coefficients
Here are absorption figures for some common building materials. They plainly illustrate the need for specialized acoustic treatments in studios that require well-controlled sound.
• Heavy carpet on concrete: 125Hz NRC=0.02, 4KHz NRC=0.65
• Wood floor: 125Hz NRC=0.15, 4KHz NRC=0.07
• Plate glass: 125Hz NRC=0.18, 4KHz=0.02
• Painted concrete: 125Hz NRC=0.01, 4KHz NRC= 0.08
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