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.  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.

For a complete treatment of acoustical terms defined, two additional sources are recommended (besides the overview of the most important terms discussed in Acoustics 101):

Rane’s Pro Audio Reference (free web-based dictionary of audio and acoustical terms)
- and -
ANSI Standard S1.1-1994 ($150.00 – official, standardized acoustical definitions)

Acoustics 101 Definitions:

STC

As mentioned before, mass and decoupling 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 Sound Transmission Classes (STCs) of various types of walls. The following illustrations of wall constructions represent a small sampling of the myriad possibilities:

Note: "Gypsum board" is a generic name. Brand names include "Drywall™" and "SheetRock™." Also, metal studs (instead of wood) will provide incrementally higher STC for each of the configurations above.

The following table gives a subjective equivalent for different STCs:

And finally, we would encourage the reader to review the STC FAQ for a more complete discussion.

Absorption Coefficients and NRC The table below shows absorption coefficients and Noise Reduction Coefficients (NRCs) for some common building materials. They plainly illustrate the need for specialized acoustic treatments in studios that require well-controlled sound.

Some other useful links include:
- The Auralex Master Acoustical Data Table (PDF)
- The NRC FAQ for a more detailed discussion.

A point that is worth reiterating here is the fact that absorption coefficients and NRCs are not percentages. In other words, if a material has an NRC of 1.10, it simply means that more sound (on average) is absorbed than a material with, say, an NRC of 0.50. A few more facts about NRC that you may want to know when comparing acoustical materials:

NRCs can only be multiples of 0.05. For example, and a material that is reported to have an NRC of 0.72 was probably not tested in accordance with the standards.

Absorption coefficients and NRCs can only be reported for materials tested in accordance with very specific mounting methods. Beware of absorption coefficients and NRCs that were "calculated" using numbers that were only reported by the testing lab as "Sabins per unit." (One of our competitors is notorious for this.) Since there was not standard area under test, converting to absorption coefficients and NRCs is forbidden per the ASTM standards. A final thought STCs and NRCs are both very useful numbers for comparisons. However, if two (or more) materials or constructions are being compared and their STCs or NRCs are very close, the octave band or 1/3-octave band data should be compared. This is discussed more thoroughly in the FAQs mentioned above. Should you be unsure of how to make certain comparisons, please contact us and we'll be happy to assist!

In Acoustics 101 a few general materials, as well as specific Auralex products are discussed. You may or may not be familiar with all of them, so we will cover them here in detail to get that out of the way! Your local lumberyard or hardware store can probably guide you if you do not know exactly where to pick up the items discussed, just be careful not to let them steer you wrong with substitutions or deletions. What worked once to construct a tight, good-sounding recording studio will always work because sound never changes. Auralex has no interest in reinventing the wheel, which is exactly what we would be doing if we attempted to make claims that were counter to the proven construction techniques that are “out there.” The acoustic construction 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, do not add multiple layers of the materials specified; in this case more is not necessarily better due to diminishing returns. (For reasons we will cover, going from two layers of gypsum board to four is a good thing. Going from four layers to six or eight, however, might not be worth the added cost/trouble.)

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 are to have a good room. The materials discussed herein are available at any decent lumberyard and will not set you back two years’ salary.

Wood and metal studs and joists – construction framing members with which most of you are familiar. The most common framing for walls is either 2x4 wood studs or 3.5” metal studs. Which is more cost effective – metal or wood – will largely depend on the relative price of wood and steel in different parts of the country. For acoustical purposes, metal does offer resiliency benefits worth considering for maximum benefit. For those of you that are not used to building things, bear in mind when figuring your dimensions that lumber is not really the actual dimensions indicated by the name. For instance, a 2x4 is not; it is actually 1½"x3½". A 2x6 is 1½"x5½", etc.

Gypsum wallboard (“GWB,” “drywall,” “SheetRock”) is commonly available in ½” and ?" thicknesses. It is far and away the most common building material in North America for interior finish construction. Unless you have a home built prior to the 1950s, you probably have gypsum board finish to your walls and ceilings. (Plaster on lathe was much more common – and incidentally much better for sound isolation than gypsum board – in homes prior to the construction boom of the 1950s.)

Plywood is usually ¾" (but is available in a variety of thicknesses from larger lumber yards) and is either available with flat edges, or with tongue and groove edges for tight floor construction.

The Particleboard family:

• Low density fiberboard, or LDF, is typically called chipboard. It’s the stuff out of which most inexpensive, DIY furniture is made.
• Medium density fiberboard, or MDF, is more typical of shelving and loudspeaker enclosures. It has some very good acoustical properties and we like using it for many varied applications.
• High density fiberboard, or HDF, is also available, but is quite rare and quite heavy. Very high-end cabinetry will often employ HDF.
• Oriented strand board, or OSB, is often used in residential construction as a low-cost floor underlayment.
• Straight up particleboard is usually a version of LDF, but can also be the name given to a higher grade of OSB.
• Other materials we make mention of in Acoustics 101 include gypsum board screws of various thread sizes and lengths, construction adhesives including vinyl flooring adhesive, silicone caulk, etc. Wherever possible, we have provided make, model and cost information as appropriate for any non-Auralex materials we mention.

Soundboard is often misunderstood, so I will try to set the record straight here. Many people mistakenly use the term to describe materials like regular gypsum board or even particleboard. When people refer to soundboard, they are usually referring to a product trademarked SoundStop®.

SoundStop® is a brown, compressed paper board that is usually 1/2" thick and is manufactured by Knight-Celotex. The best way to describe it for you here is to say that it is a lot like a sheet of Masonite or pegboard, only thicker and a bit softer. A similar material is Homasote. If you describe SoundStop® or Homasote to your building materials supplier, he or she 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" gypsum board, 3/4" particleboard or MDF and SheetBlok™, it is really effective at blocking the transmission of sound. (It should be noted that when compared side by side with gypsum board, SoundStop® is not quite as good in a straight up STC comparison. It is not clear what sort of performance Homasote offers versus gypsum board or SoundStop®. Bearing that in mind, SoundStop® is good if you want to change up the composition of the layers in your construction. This will dissipate resonances well. However, for sheer mass, gypsum board is a much more cost-effective alternative.)

Blueboard is also a very misunderstood material. This is typically an expanded polystyrene board that's been dyed blue, though there are also pink versions available. It's all the same—mostly useless in terms of acoustical isolation. The density of the material is very low and the material itself is a closed-cell foam. Thus, there is no mass benefit to be gained for isolation and no absorptive benefit to be gained when using it in wall cavities. Unless there is a specific code requirement for this type of material in your construction, we would encourage the use of glass fiber or mineral fiber insulation products in lieu of blueboard.

Figure 3.1a and Figure 3.1b show good designs for those of you who have the vertical space to spare and need to float your floor (and your walls). These are perfect when a studio and control room are both going to rest on a common floor, either wooden or a concrete slab. If yours is concrete, consider (carefully) cutting a gap in the concrete between the two rooms first, then proceeding as shown. Cutting the slab is no minor undertaking, but you will be relieved to know that if you decide to do it, the gap does not need to be any wider than the width of the saw blade. N.B.: The cut must bisect the entire slab. If you are unfamiliar with the structural ramifications of doing this, please consult a local expert. Auralex cannot be held responsible if your building caves in.

Figures 3.1a-b show 2x6 joists and 2x4 walls, but if you do not have the space you can use 2x4s, 2x3s or even 2x2s for the floor. The specific material used may not matter as much as the proper implementation of the materials. I.e., the general method stays the same. The preference if you have the space is 2x6 or larger because they allow for more trapped air space and better overall decoupling. It is advisable to caulk all edges, seams and corners (as well as any penetrations – more on that elsewhere) particularly where different materials meet. Leave about a ¼” gap in parallel seams and perpendicular corners and use our new acoustical sealant, StopGap™. (StopGap is an approved substitute for gypsum board “mud.” Tape and finish as you normally would.)

If for whatever reason you cannot build your wall/floor exactly as pictured, be it a space limitation, lack of funds, etc., first try to grasp the concepts used in the construction pictured. If you are serious about wanting to stop sound transmission, it is imperative that you isolate the sources of sound from the structure. Air and mass are your friends. Give strong consideration to making a layer of SheetBlok part of your floor sandwich.

The sill plate (bottom framing member of the wall) actually rests on two layers of SheetBlok to decouple it from the existing or floated floor. In a perfect world it would be preferable to glue the SheetBlok to the bottoms of the wall plates and joists instead of nailing it; in fact, wherever possible throughout the framing, glue any materials you can together rather than nailing or screwing them. The reason gluing is always recommended is that the adhesive itself will contribute some degree of sound isolation, too. Nails or screws serve as bridges acoustically and transmit sound from one layer to the other too well, so you want to avoid them whenever possible. Pick screws over nails (preferably used in conjunction with glue) because they form a tighter bond that yields fewer resonances. Example: We suggest gluing the particle board down and caulking the seams and boundaries. Repeat for each layer, gluing one atop the next. This makes fewer penetrations than if you screwed down each layer.

If you must screw the layers (this is very often the practical reality), be aware that it is not “the end of the world.” Just be sure to go with the absolute least number of screws possible. We recently completed a build-out on a new facility. You should be aware that most “drywallers” will simply use as many screws as they think is necessary. Even as often as every 4”! This is far too many for acoustical purposes. So keep an eye on any hired help and let them know that as few screws as they can get away with is preferred.

Same goes for when you are anchoring the walls to an existing floor (Figure 3.1b). If you must bolt, screw or otherwise secure the sill plate, use the least number of connection points that you can get away with. And if you are anchoring to concrete slab, look into spending a little extra on isolated bolt mechanisms. These devices provide rubber grommets for the solid bolt to go through so it does not come into direct contact with your sill plate, thereby maintaining the level of decoupling you need!

When layering, subsequent sheets of material should be rotated 90 degrees so no seams line up (see Figure 3.2; this staggering applies to wall, ceiling and floor materials) and, if used, the preferred “tongue and groove” (T&G) materials should be glued together at each T&G joint. As mentioned previously, all seams – regardless of material used – must be sealed up tight with something like StopGap.

Where applying baseboard or other trim you can line the bottom of it with foam weatherstrip tape to help decouple it from the floor if you are installing flat flooring like vinyl or parquet instead of carpeting. Naturally, if you are installing carpet, your carpet pad should be the thickest and densest you can afford and accommodate from a space standpoint; 8#, 1/2" re-bond carpet pad has worked well for us under certain types of carpet like plush or Berber, while ¼" ComfortWear-200 (made by GFI and sold under a variety of trade names; it is usually purple or blue and has a honeycomb pattern embossed on one side) works well under short-pile commercial-type carpet.

Where your raised floor meets the existing walls, it is better to build it in such a way that the two have a slight physical separation (note the airspace in Figure 3.1b), but if you must attach them, run StopGap at the juncture first before attaching the final wall layer.

Do you have pretty good isolation except for when, say, someone plays piano or acoustic drums? Instead of constructing an entirely new floor, you can fashion an effective riser using Platfoam™ to put on the floor under the offending instrument. A prefabricated riser is also available, the HoverDeck™. This also applies to those of you in basements who do not want to frame new floors as earlier described. Kenny Aronoff and many other famous Auralex users are using our PlatFoam and HoverDeck. The amount of extra sound isolation you gain, as well as the dramatic improvement in the purity of the instrument that rests on the riser, make either of them an all-around winner! Kenny Aronoff is so impressed with his riser that he now has them in all the major recording markets with his identical drum kits so no matter where he is playing, he can be on an Auralex riser. How's that for an endorsement?????

Auralex also offers a small, portable riser called the GRAMMA™ (patent-pending). GRAMMA stands for Gig and Recording Amp and Monitor Modulation Attenuator, and it is designed to float guitar cabinets, bass rigs, subwoofers, studio monitors, stage monitors and more for greatly improved isolation and purity of tone. Tower of Power, Lee Roy Parnell and many other famous recording artists are using GRAMMAs on-stage and in the studio and LOVING them! If you are unable to construct your room to be as sound-isolated as you would like due to budgetary constraints, physical constraints, etc., perhaps you can improve your sound AND your isolation by strategically implementing GRAMMAs under some of your amps, monitors, etc. You will be quite happy and quite surprised at the improvements!

In situations where you simply have no vertical room to spare or cannot install a floated floor, you should consider floating a couple new layers of alternated T&G flooring on two layers of SheetBlok. This yields increased STL and decoupling, but obviously does not give you the benefit of any trapped air space.

The method for controlling structureborne sound that is passing through ceilings is much the same – see Figure 3.3a. Generally, we suggest layering SheetBlok and gypsum board either over the existing ceiling, preferably hung on RC8 Resilient Channel, or as part of a lower, separated ceiling resting atop the new walls. If you are lucky enough to have vertical height to spare, drop down 3½" and frame another ceiling resting it only on top of your new walls (which, in turn, might be on top of your new floated floor). Insulate it with Mineral Fiber and cover it with two (2) layers of ?" gypsum board mounted on RC8. If you have an unfinished existing ceiling, insulate it with Mineral Fiber, cover the joists with two (2) layers of ?" gypsum board mounted on RC8 (you can use ½" gypsum board if you want, but ?” has been verified to be better if space, time, funds and motivation permit) and then drop down 3½" and frame your new ceiling.

In reality, most of us fall into the "I do not have the height to spare" category. If that is you, you should add a layer of SheetBlok to your existing ceiling and then add one (or two) layers of gypsum board (½” or ?”).

Should you be in a situation where you need more sound isolation, but absolutely cannot add any more gypsum board, consider adding a layer of SheetBlok Plus mounted with our pressure sensitive adhesive. A piece of wood trim is recommended at each vertical seam and across the top and bottom of each piece of SheetBlok Plus due to its weight. If the black color does not match your decor, your SheetBlok Plus may be painted with high-quality latex paint (note that you may need to prime it first). In order to use it as a finish layer, obviously you should be very careful during installation so as to not nick up the SheetBlok Plus. By the way, while the pressure-sensitive adhesive (PSA) backing for the SheetBlok Plus is very strong, we definitely recommend some type of mechanical fasteners be used, too. Plastic cap nails, screws with grommets, furring strips at the edges, etc. have all been used with good success. Also, for standard SheetBlok, multi-purpose flooring adhesive is recommended because it is made for use with vinyl materials. We have not tried this type of adhesive ourselves, so do not yell at us if it does not work for you.

No matter which method you use, the less light fixture boxes set in the ceiling, the better: They serve as open windows to sound. Track lighting is preferred to recessed lighting and you should StopGap any wire holes as outlined elsewhere in Acoustics 101 because holes sonically weaken a wall or ceiling. So much so that in some instances people have virtually wasted their time. Floor lamps or surface-mounted conduit may be your best bet.

(Non-)Flat Ceilings

Have you ever seen pictures of world-class studios? Sure you have. Have you ever seen one with a flat ceiling? Rarely, if ever. The reason for this is that it is widely acknowledged that rooms with more cubic volume (space inside them) sound better than small rooms. Why is this?

Small rooms tend to sound, well, small, because they have less space for sound waves to develop and breathe. Think about it. In a 10’x10’ room, a sound wave that is traveling 1130 ft/s (feet per second) can get from wall to wall to wall to wall in no time at all. This effectively means the room does not allow time-delayed reflections to develop; reflections that would give the room a sonic "acoustical space" signature. Implementation of good diffusors (such as Auralex T’Fusors™) can definitely help a small room sound larger by properly diffusing the sonic energy in the room, giving the sound more room and time to breathe. Further, digital delays and reverbs have improved enormously over the last decade and we can now add our own "acoustical space" signatures to sounds — and best of all, only when we desire to have them. It is often desirable to have a drier room and add ambience digitally rather than rely on the room to interject the ambience. The reason for this is that there are quite a few times when ambience is not desirable and other times when a different ambience than the room has is desirbable. Still, there are plenty of instances where a room’s ambient sonic signature is desirable. It is for this reason we started this talk about non-flat ceilings. Discussing room sound over lunch one time with Ross Vannelli, he hit the nail on the head: "Once it’s on disk (or tape), there’s no knob for it."

Few of us have unlimited budgets — budgets big enough to allow us to buy real estate with as much square and cubic footage as we would really love to have. Does this necessarily and always mean that we are forever resigned to suffer with tiny little rooms with flat ceilings? No way.

Square footage is expensive, but cubic footage is not. Look at Japan — what have they done? Because Japanese real estate is at such a premium (i.e. they have run out of it), they have chosen to grow up instead of out. We can put the Japanese principle to work for us in order to gain cubic volume for our rooms. Maybe to a relatively small degree, but we can gain some amount of useful cubic space to be sure. Non-flat ceilings are an easy way to do so. See Figure 3.3b and Figure 3.3c for some examples of good (and bad) ceiling designs. Also not that “cathedral” or “A-frame” ceilings can be quite helpful in live rooms. (They are generally discouraged in control rooms due to focusing effects.)

Cathedral Ceiling Treatment for Live Rooms

Figure 3.4 shows an example of how we would suggest you to treat a cathedral ceiling for live rooms. This also would work in a control room or studio room you have put in, for example, an attic space because that’s the only place your spouse would let you! In it, we show 4" Studiofoam™ on the two ceiling surfaces that come together to form the peak of the cathedral ceiling. Below that (the farther down, the more effective it is), a horizontal piece of material forms the face of the “trap.” In this example, the face material is ¼" pegboard and it is covered on both sides with 4" Studiofoam. Instead of using two (2) separate pieces of 4" Studiofoam leading up to the peak, a viable and perhaps even more effective alternative is to span the peak with a piece of Studiofoam, forming a small, triangular-shaped airspace behind it. One way to control sound in general and low frequency sound in particular is to force the sound waves to fight their way through multiple layers of different materials and dead air before they can strike the room boundary.

You can also build the faces of these panels out of strips of 1x2, 1x3 and/or 1x4 lumber (normally pine, but that is your choice; based on your budget you might want to try oak or some other hardwood). One approach would be installing the slats in an alternating, random fashion (1x2, 1x4, 1x3, 1x3, 1x4, 1x3, 1x2, etc.) and leaving spaces of varying widths between them (¼", ½", ¾", etc.).

The last variation on this theme is to substitute plywood, masonite, or some other hard material for the pegboard, caulking the it tight to the ceiling surfaces so you end up with a sealed, resonant air cavity. This is technically known as a diaphragmatic or panel absorber. You can cover the face of the plywood with Studiofoam to broaden the effective range of the trap and help control your room’s acoustics. The Studiofoam inside the trap broadens the range of frequencies the trap affects, kind of like changing the Q of a parametric equalizer.

The preceding three paragraphs have described perforated panel absorbers, slat-Helmholtz absorbers and diaphragmatic absorbers, respectively. For more information on exact designs of these devices – designs that will help you tune them to target a specific frequency range – please refer to the titles – particularly the Master Handbook of Acoustics by F. Alton Everest – on our Book Referrals page. Many of the titles are probably available through your local library.

Using any of these methods is viable; which you use is really up to you and depends on how much time you want to put into the device(s). They all work, so just pick one depending on your needs. Some people have even combined a couple of these variations. For example, wooden slats can be placed over the face of the plywood for extra reflection and diffusion.

An often overlooked method of gaining extra bass trapping in a small room is to "steal" some of the wasted space that may be above an adjacent room. Famous acoustician and talented surfer dude Chris Pelonis (who has used LENRDs when 90° angles are involved) has built Helmholtz resonator types of bass traps in the attic space over rooms adjacent to studios and control rooms. This is a great way to give a room’s low frequency waves more room to develop and breathe and to utilize what is often wasted space. Auralex implemented this type of adjacent trapping in our acoustical design of the 1999 CEDIA Home Theater of the Year and the room tested flat (±3dB) from 70 Hz to 20 kHz. Down to 38 Hz, the room was subjectively flat; i.e., it had no audible peaks or dips. On paper, this corresponded to ±6 dB down to 38 Hz. See the SJPT Case Study for more details.

Mr. T (Bar)

Many times a customer with an existing T-bar (suspended, or "drop") ceiling will ask if he should remove it to expose the bare gypsum board ceiling above, then treat the gypsum board ceiling with foam. If the existing ceiling tiles are the really cheap, not-very-absorbent type (the absorption coefficients and NRC of which you might be able to verify with the help of your local hardware store or lumber yard), then we would say “yes.” If the existing ceiling tiles’ acoustical properties are able to be verified and the NRC is 0.75 or above, leave them, but over the top of them and the T-bar roll out at least one layer of 4" Mineral Fiber or 6"-12" unfaced traditional insulation. Doing so not only helps alleviate the reflected sound that can bounce around between the top of the suspended ceiling and the gypsum board above, it improves the NRC of the ceiling as a whole, especially with regard to its low frequency absorption. It is also likely to marginally improve sound isolation from whatever is above the room, be it a neighbor or the great outdoors.

If you are in a space that has an existing drop ceiling that has decent NRCs, but you desire absolutely the maximum amount of sound transmission loss from above and are absolutely unable to frame a new false ceiling, we have a couple solutions for you. The first involves rolling out unfaced insulation or Mineral Fiber as noted above then rolling out SheetBlok over the top of the insulation. SheetBlok weighs 1 lb/ft², so some reinforcement of the T-bar suspension will probably be necessary. Overlap the SheetBlok by at least an inch, then tape the seams with foil duct tape or at the least regular cloth duct tape.

Alternatives:

• Cut SheetBlok to the size of each of your ceiling tiles, then glue it to the back of each tile or simply lay it over them.
• Buy T’Fusors™ and lay a piece of rigid material like 1" Mineral Fiber, SonoFiber, or even rigid glass fiber board (preferably with SheetBlok cut to fit and glued to it) in the cavity molded into the back of each T’Fusor. This yields improved diffusion, quite a bit of low frequency trapping and improved isolation.

Some suspended ceilings are not the sturdiest things, so be sure to check yours out and make sure it will support the weight of the composite panels before you go ordering the materials. Nothing ruins a session like a heavy ceiling crashing down on top of you!

If you feel the need to install a suspended ceiling in a room where there is not one already, the tile manufacturers recommend that it be dropped down from the existing ceiling 16" to 18" for the best acoustic performance. We agree, especially if you implement the insulation over the top of it as described above. Some ceiling tiles we would encourage you consider – in lieu of the “cheapies” you get from the hardware store – are as follows:

• Armstrong High-NRC tiles include Optima Open Plan and Painted Nubby Open Plan.
• USG High-NRC tiles include (PDF downloads) Orion 270 ClimaPlus and Premier Nubby ClimaPlus.

For those of you sharing space with neighbors, especially in commercial settings, a commonly overlooked route of sound transmission is the space above the drop ceiling and over the wall separating you from your neighbor. Many times this area will be totally open, so the only things stopping sound from your neighbor getting to you (and vice versa) are your and your neighbor’s ceiling tiles. This will typically provide an STC of only 10-15. Grossly inadequate for sound isolation – especially a studio! There are two main solutions to this problem:

1. Replace your ceiling grid or – ideally – both ceiling grids with a solid, drywall ceiling as described above.

2. Continue the common wall up to the roof or floor deck above, seal it airtight, and possibly consider adding to its construction as outlined below in the section on Walls.

At the very least, SheetBlok hung vertically above the wall and sealed as tightly as possible to the structure can help. The more airtight the better, so grab your caulking gun and go wild.

If you have already leased such a space or are contemplating doing so we would encourage you to bargain with your landlord; ask him to share the expense of making the space habitable for your needs. Many landlords will step up; a landlord who is in it for a quick buck will not and will likely be tough to deal with down the road.

Unfortunately, the basic walls built in most homes and businesses are simply not dense enough or thick enough to be good barriers to neighboring sound. This page will show you proven methods for adding additional layers of materials to your existing walls to make the most of them. For those of you doing new construction, these tips are applicable as well. The choice of how to retrofit your existing walls, ceiling, etc. is entirely up to you, your ears and your pocketbook.

Existing Walls

First, determine as best you can what the materials are which comprise your existing walls. You hope you find out that you have 2x6 walls, heavily insulated and caulked, floated on SheetBlok, then covered with a layer of ?" gypsum board, a layer of SheetBlok, a layer of ½" gypsum board and surface treated with Studiofoam.

If so, go directly to Park Place, collect $200 and have dinner at a fancy restaurant. If not, read on. If your problem sounds severe to you and you learn that the existing wall has no insulation in it, it is advisable to install Auralex Mineral Fiber in it by removing the gypsum board and placing the Mineral Fiber between the wall studs. Alternatively, you can look into blowing insulation into the wall with a machine (see your local hardware store for details).

Having done that, the more closely you can retrofit your wall to resemble the one shown in Figure 3.5 above, the better off you will be. You can choose to alter materials or leave off layers, but the performance of the wall may be lessened, so delete or change at your own risk. Naturally, you should use good construction techniques, taping, mudding and caulking seams all the way, making sure to stagger all seams and rotate adjoining layers 90° from each other.

If you determine your problem to be relatively minor, you might be able to get by with as little as adding one (1) more layer of gypsum board. If you previously found out your existing wall is one layer of ½" gypsum board or plaster on lathe (older homes), add a layer of SheetBlok and then another layer of ?" gypsum board.

Do you want to go to the trouble to fur out from your existing wall to hang your new wall boards on? We think so. It is neither a waste of time nor money and, if you have both, we would encourage it...but with a twist. At least cover the faces of the furring strips with strips of SheetBlok (it is considerably more effective to actually mount a layer of SheetBlok across the faces of the furring strips versus just putting strips of SheetBlok on the furring strips' faces, but it also costs more). Then mount RC8 across the furring strips. Then mount a layer of ?” gypsum board to the channels.

New Construction

If you have the opportunity to build your space taller, allowing for a false/lowered ceiling and giving your studio more cubic space, then you are indeed lucky. If that’s the case, there are a few things to note that you might implement to improve on the wall/ceiling described above.

• You should definitely build a "room within a room," meaning that there is air space and no physical contact between the exterior walls and the new walls of your studio! There is no substitute for doing it this way. You can build just one wall and can add layers to the wall until you are blue in the face and poor as Patty’s pig, but chances are that you will never achieve the level of sound transmission control you will if you go the extra mile and build a room within a room. You know what they say about an ounce of prevention being worth a pound of cure? In the practice of acoustics, an ounce of prevention is worth considerably more than a pound of cure!

• Sound can slip through very tiny gaps (1/32” and smaller) which might seem to you to be insignificant. So it is of extreme importance to construct your place as airtight as humanly possible. When humanly possible is not good enough, StopGap can be of great benefit. The specific gaps we are talking about here are, e.g., the gaps around electrical boxes (remove the outlet and switch plates to find them), underneath door trim, baseboard, crown-molding, around HVAC vents (remove the grilles to find them), and so on. This is all part of the attention to detail we’ve been talking about!

• Never mount electrical boxes or connector panels back to back; always stagger them as shown in the Figure 3.6. Seal the holes your wires go through, or (preferably) run wire through conduit, stuffing foam or insulation in the ends to help seal it. Isolating the conduit from the structure with SheetBlok or hanging it with resilient hangers can really offer some improved isolation. Remember: Sound control is a game of inches.™

• Of course, the less wires and boxes you have poking holes in your walls, the less chances sound has to get through where you do not want it. It may be prettier having all your boxes flush mounted, but there is a lot to be said for surface mounting your phone cables and jacks, audio connector boxes, light switches, etc. Not only does this method yield better isolation, your artsy friends might consider you "retro", "industrial" and just plain "cool." Studiofoam and other Auralex treatments applied to room surfaces can often mask surface-mounted goodies.

• It is always better to keep wires away from each other than in big globs; especially audio, video, data and phone lines that might be in proximity to electrical wires. If wires have to cross, doing so at a right angle lessens the chance of interference occurring. Otherwise, keep all the different typs of wires at least 12” away from each other and use shielded cable wherever possible.

Stringers

There is quite a bit of debate about whether adding “stringers” to your wall, ceiling and floor construction is worth the effort. We believe it is a great benefit to run stringers at uneven intervals between wall studs and floor and ceiling joists before insulating them, as shown in Figure 3.7. This helps tie the whole wall, ceiling, or floor together so it is less likely to move and transmit sound. As Philip Newell has pointed out in many of his books, a stiffer construction will make it less able to vibrate at lower frequencies. Our research is ongoing and we certainly acknowledge that stringers may not be completely applicable to each and every construction. However, in the context of Acoustics 101, we believe it is a necessity. I.e., since the budget for construction is usually tight, we believe stringers to be a very cost-effective way to help maximize isolation.

Figure 3.7 shows stringers mounted between studs or joists. Stringers are short (14½" normally if your studs/joists are 16" on center) pieces of the same material as your joists that run perpendicular to the joists and are nailed and glued between them in a random, staggered fashion. It might seem like a pain putting them in, but it’s time well spent. We know because we have done it. We let people talk us out of them once and lived to regret it!

Other than the above, the wall construction we generally suggest is shown in Figures 3.1a-b from the section on Floors.

We have compiled many great links on acoustics here. If you have some you’d like to share, feel free to contact us!

Professional Organizations
• Acoustical Society of America (ASA)
• Audio Engineering Society (AES)
• Custom Electronic Design and Installation Association (CEDIA)
• International Communications Industries Association (InfoCOMM)
• Institute for Noise Control Engineering (INCE)
• International Music Products Association (NAMM)
• National Systems Contractors Association (NSCA)
• Percussive Arts Society (PASIC)
• Synergetic Audio Concepts (Syn-Aud-Con)

Professional Design Assistance
• Russ Berger Design Group
• National Council of Acoustical Consultants
• Consultants page on Acoustics.org

Acoustical Prediction, Test and Measurement
• CARA software for small room modeling from Rhintek
• ULYSSES software for large room modeling from IFBSoft
• Audio Toolbox™ from TerraSonde
• ETF software from AcoustiSoft

Cool Corporate (non-Auralex) Stuff
• The British Broadcasting Company (BBC) now has many of their acoustical research papers available for download from the BBC R&D page.
• Genelec white papers
• Rane Libraryincludes an excellent online audio dictionary, the Pro Audio Reference
• Rosebrand is the company we turn to for our heavy curtain needs.
• Sound Construction and Supply is the only place to go for Iso-Box™, as well as all of you studio furniture needs.

Cool People
• Eric Desart, one of the worlds best acoustical minds, has created and assembled some wonderful tools available for limited download from his Acoustics-Noise.com website.
• Bob Golds has assembled and discussed the absorption coefficients of a bunch of different materials.
• David Griesinger of Lexicon fame has his own technical website – very cool stuff.
• Worshiptech.com is Kent Morris’ site. Kent is a world-renowned expert in church systems integration.
• Bruce Richardson has written a review of Auralex products and services for ProRec.comhere.
• Keith Yates is a leading home theater design expert. Of particular interest are Keith’s articles on myriad home theater sound topics.