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Acoustics 101

BASICS OF ACOUSTIC CONSTRUCTION

If you are reading this, you are very likely interested in improving your sound through acoustic construction. The concepts put forth in these pages are not new. They are not revolutionary. You can find them in many other texts. Our hope is that our presentation and treatment of these topics will be “down to earth” and easier to understand, putting complex concepts into perspective.

Acoustics is not all common sense. Unfortunately, the subject can sometimes be quite confusing. However, we are confident that you can build a great room by following Acoustics 101. And there is nothing stopping you from taking these concepts and coming up with even better ideas than what we have presented herein. If you do, that’s great! Fax or e-mail us your ideas so future Acoustics 101 readers can benefit from what you have developed. What you are reading right now is the newest incarnation of Acoustics 101. Many contributions from readers like you have been incorporated into this “new and improved” version. The only thing about making changes is to make sure you have really thought through the ramifications of what you are doing. Random substitutions could degrade everything you are trying to accomplish. If you are unsure, contact us.

Some of the basics of how sound behaves are implicit in Acoustics 101. Some examples of concepts we assume you have a basic understanding of include:

• When sound strikes a surface, some of it is absorbed, some of it is reflected and some of it is transmitted through the surface. Dense surfaces, for the most part, will isolate sound well, but reflect sound back into the room. Porous surfaces, for the most part, will absorb sound well, but will not isolate.
• 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.
• Walls need to be isolated from ceilings and floors, usually by means of dense, pliable rubber.
• The main ways to minimize sound transmission from one space to another are adding mass and decoupling.
• Limp mass is most often better than rigid mass (actually, a combination of the two is really what you are after).
• Every object, every construction material has a resonant frequency at which it is virtually an open window to sound - kind of like a tuning fork that “sings” at its particular resonant frequency.
• Different materials have different resonant frequencies.
• Trapped air (a.k.a., air spaces and air gaps) is a very good decoupler.
• Airtight construction is a key concept. Sound, like air and water, will get through any small gap. (Sound can leak through openings as small as 1/32” – in some cases even smaller.)
• Sound bounces back and forth between hard, parallel surfaces.

One of the single biggest concepts to understand and appreciate is that acoustic foam, one of our core products, is not going to "soundproof" your room. It is an extremely effective absorber of ambient, reflected sound and helps make rooms "sound better." Acoustic foam does contribute some sound isolation properties (mostly high frequencies), but is not sufficient by itself to keep sound in or out of a room. Thicker acoustic foam is better at absorbing low frequency sounds. Controlling reflected sound within a room is extremely important in producing good sounding recordings. When you hear Mike Wallace’s voiceovers on 60 Minutes, you might be surprised to find out that they did not spend a million bucks on it. (It is amazing what some good 2" acoustic foam can do for a glorified, yet well-constructed closet!)

Isolation construction – the core concept in Acoustics 101 – is not inexpensive. Acoustics 101 carries with it an assumption that you have a few bucks to spend to make your studio the best it can be. For example, it is important to realize that empty egg cartons, cork squares and carpet scraps are not going to (a) keep sound from leaving or intruding upon your studio and (b) yield that pleasing, neutral, "Mike Wallace" sound within your studio.

If the acoustic construction guidelines, tips, techniques and advice in Acoustics 101 are improperly implemented, the desired results will not be achieved. Auralex cannot be held liable for the advice given because we are not going to be there watching you do the work or assisting with the construction. Please note that these tips are being provided on this website free of charge.

If you cannot handle a circular saw and other common power tools or you do not have the money to hire someone who does, then you should probably stop right here. It is going to be difficult to implement the advice given here if you or someone you hire cannot handle basic construction methods, such as applying drywall tape and mud, creating solid, airtight and level partitions and floors, "measuring twice; cutting once," etc.

There are myriad benefits to constructing your control room to be symmetrical geometrically and building using the best materials you can afford. Money well spent now will benefit you for a long time into the future.

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.

Some of you will be able to grasp all this quicker than others. Please understand 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 are worth whatever work it takes to put them into practice.

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