CEILINGS

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.