Acoustics 101 - Chapter 3: Floors
Practical Guidelines For Constructing Accurate Acoustical Spaces
Floors
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, StopGapT. (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 PlatfoamT to put on the floor under the offending instrument. A prefabricated riser is also available, the HoverDeckT. 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 GRAMMAT (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.
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