If you're serious about cutting noise from your studio, you'll have to explore the mysteries of studding and neoprene rubber. Paul White explains that it's not quite as exciting as it sounds...
When you've dealt with sound leakage from your studio via doors and windows (see last month's instalment), usually the weakest areas when it comes to soundproofing, it's time to look at walls, floors and ceilings. As with most improvements I'm suggesting in this series, you can probably do the work yourself if you want to keep the cost down.
The first area I'd like to cover is the studding partition wall, because if you need to divide a large room into two — for example, to create a separate playing area and control room — the only real alternative to permanent masonry is plasterboard and studding. Lightweight studding walls don't have the necessary mass to act as effective sound isolators, especially at low frequencies, so we need to fall back on the two mainstays of soundproofing — a double barrier and as much mass as possible. If you have the space, two separate studding walls are best, but if you don't want to lose too much room, a simple 4‑inch‑thick frame with several layers of plasterboard on each side can be quite effective. However, you have to be careful how you fix this in place, as sound energy travels quite happily within solids. You need to find some way of isolating the frame from the rest of the structure, so that vibrations don't travel to or from the floor, the walls or the ceiling. This isolation can never be perfect, as the frame needs something to rest on, but providing you use something resilient rather than solid, the improvement will be worthwhile.
Perhaps the best option is to use quarter‑inch neoprene rubber sheet between the frame and the floor, and also where the wall touches other walls and the ceiling. Alternatively, use thick rubber car mats, or something similar, cut into strips. (Try the Yellow Pages for rubber, foam and plastics suppliers if you don't know where to find Neoprene.) Some energy leakage is inevitable via the fixing screws, but this probably won't be too serious in the case of a studding wall.
Once the frame has been constructed, it must be panelled on each side with at least two layers of plasterboard — use the thicker 12mm grade if you can get it, to keep the mass as high as possible. Ensure that the boards are staggered so the seams don't coincide, and use temporary spacers, made from hardboard, to ensure that the plasterboard stops just short of touching the existing walls, floor or ceiling. Putting a layer of lightweight fibreboard between the two layers of plasterboard can improve the damping of the wall without adding much to the mass. Having the surface skimmed with plaster on completion will also help, but try to keep that small gap around the edges. When the plaster is dry, you can seal the gap with frame sealer using a mastic gun. Figure 1 shows how a studding wall can be constructed.
Though it's simple to build, this type of wall suffers a little because the frame itself can conduct vibrational energy from one surface to the other. To improve on this, you could nail the plasterboard to the frame via rubber or felt spacers, but probably the best approach is to build a double‑frame structure. as shown in Figure 2. Here the timbers are staggered to fit between each other, so that the wall isn't much thicker than before. In either case, stuffing the void between the two sides of the wall with Rockwool loft insulation will help absorb any energy trying to pass through the void. The diagrams only show the timber fitted in one direction, but in practice, studding walls comprise both vertical studs and horizontal noggins.
Of course, you may have an existing wall which doesn't provide enough isolation, either because it's too thin, or because it's made from a lightweight building material such as breeze block. Such walls can be lined with studding and plasterboard, using similar constructional techniques to the free‑standing studding wall just described, except that you only need to cover one side of the frame. Ideally, you should leave a small gap between the frame and the existing wall, and, again, this is best achieved with the use of neoprene spacers. The cavity can be filled with Rockwool before the plasterboard skin is nailed into place.
Two or more layers of plasterboard are required to build up a worthwhile mass, and a fibreboard middle layer may also help. Layering different materials creates an acoustic mismatch, reducing transmitted vibrational energy and damping out resonances. Figure 3 shows an existing wall uprated by the addition of a studding/plasterboard layer. In all multi‑layer walls, where two or more layers of board are being used, it helps to seal the gaps between boards using a flexible mastic or frame sealer before fixing the next layer. It also helps to use dabs of plasterboard adhesive between adjacent layers of plasterboard, to prevent the panels resonating independently, and if you can afford the space to add even more layers of plasterboard, that's all to the good, providing your floor can take the weight.
Unless you use many layers of plasterboard to create a very heavy wall, the attenuation offered by this type of wall at low frequencies will probably be less than that offered by a solid brick or concrete wall, but the improvement should still be significant.
If you do need to build an internal wall, look at the ratio of the height, width and length of your newly created rooms to see if you might be inviting acoustic problems. As a rule, having equal dimensions for width, height and depth is the worst possible case, as you'll end up with strong room resonances at specific frequencies, and you should also avoid one dimension being an exact multiple of either of the other two, for the same reason. Keep the ratios as random as possible, and if you can slope one wall slightly to avoid having parallel surfaces in the room, this will help minimise flutter echo. However, don't worry if you can't avoid parallel walls, as the acoustic treatment needed to kill flutter echoes is fairly simple.
If you have a concrete floor, you're probably starting from a reasonably good position, but if the studio is in a bedroom with a wooden floor, you're going to have problems. Not only is a typical domestic floor a relatively poor sound isolator, most of the noisy gear, not to mention tapping feet, will be in contact with the floor, which only makes things worse. Because of this latter consideration, structurally‑borne sound needs to be tackled, and the cheapest first step is to fit heavy felt underlay beneath the studio carpet.
Once you've done that, try to get noisy gear off the floor by using speaker stands for your monitors (placing the speakers on blobs of Blu Tack on top of the stands), and try putting things like guitar amps on blocks of thick foam rubber. Drum kits are more problematic, and it's unrealistic to expect a DIY approach to provide anything like complete isolation. The most effective way to reduce drum kit noise is to make a shallow plinth or raft, on which to set up the drum kit, and isolate this from the floor by standing it on thick foam rubber. If this doesn't provide isolation, the next step is to consider a complete floating floor (see box for details).
Ceilings have all the problems associated with floors, but you don't have the benefit of gravity to help you keep your sound isolation treatments in place. Acoustic foam tiles stuck to the ceiling might look good, but in practice they'll keep out very little sound. A professional studio designer would probably specify a false ceiling, probably quite a heavy one, but in the home studio you have to be a little more pragmatic. As mentioned in last month's instalment, your first step should be to fit underfelt to the room above your studio. Even if this room belongs to someone else, offer to pay to have it fitted.
If you're serious about going further, you need to know whether the floor above consists of floorboards or chipboard. Chipboard floors are reasonably airtight, but floorboards may well have gaps, in which case you'll need to remove the ceiling plaster or plasterboard to expose the joists (don't do this if it isn't your property!). This will give you access to the floorboards of the room above, whereupon you can set about filling all the gaps with mastic. A more thorough approach is to fit barrier mat between the joists, as shown in Figure 6. Barrier mat is a material that has many uses in studio construction, but you're unlikely to find it anywhere other than at a studio materials suppliers — they don't have it at the usual DIY superstores! Barrier mat is a mineral‑loaded plastic material that looks rather like a black, flexible lino and is very heavy. It may be fixed in place using a powered staple gun, but you'll need somebody to help you take the weight until you've got enough staples in to hold the material up.
Once the barrier mat is in place, the gaps between the joists can be stuffed with loft insulation‑grade Rockwool and the underside of the joists covered with at least two layers of 12mm plasterboard. Get a plasterer to skim the plasterboard for you and you have a smooth new ceiling, as well as reduced sound leakage.
If you have the necessary room height, fitting a false ceiling can help with sound insulation, but if you don't know exactly what you're doing this is a job for a professional builder, as the size of the required joists depends on the length they're required to span. This approach is shown in Figure 7. You still have to strip the old ceiling of plasterboard and treat it, as per the previous example, before you start. Notice that the joists for the new ceiling are fixed in between the existing ceiling joists to minimise height loss, though if you have plenty of headroom you can simply leave the original ceiling untouched and build the new one beneath it. The void between the original ceiling and the suspended ceiling should again be stuffed with Rockwool, otherwise it may resonate.
The suspended ceiling is built from joists and plasterboard, in much the same way as a studding partition wall, but here it rests on wooden wall plates fixed to the original walls. Obviously, the original walls must be of solid construction. The heavier the false ceiling, the better the isolation, but you can introduce a layer of lightweight insulation board between the plasterboard layers without incurring much of a weight penalty. Whether or not you isolate the edges of the ceiling from the existing wall is up to you, but as there is no sound‑producing equipment in direct contact with the ceiling, the difference will not be nearly so significant as it is with a floor. For the best isolation, you need to build a complete room within a room, and that will be discussed next month.
WARNING! Commercial studios may have up to four inches of plasterboard and chipboard screwed to the ceiling, but don't go to extremes without proper architectural advice.
Professional floating floors can be massive and complex affairs, but for the smaller studio you can build your own quite simply. A floating floor is just a false floor mounted on acoustic isolators above your existing floor, with resilient material around the edge so that it doesn't come into direct contact with the walls. A commercial floating floor may be cast from reinforced concrete, several inches thick, and may be supported over a void several feet deep, the weight being borne by springs or machine‑rubber mountings, but clearly this is impractical for most bedrooms!
There are less massive floor designs based on studding and chipboard, or you can even buy a specially made floating floor material comprising chipboard with Rockwool bonded to the underside. This type of structure won't be too heavy for a typical domestic floor to support, and though it won't work as well as six inches of concrete on springs, it will make a very noticeable difference. One commercial material, known as Lamella, is flooring‑grade chipboard backed with a tightly packed Rockwool material where all the fibres are perpendicular to the board, rather like the bristles on a scrubbing brush. Fitting the floor would involve fixing a felt strip around the room, somewhat like a felt skirting board, and then laying the Lamella boards atop the existing floor. Once the floor is down, a second layer of flooring chipboard is glued and screwed to the top, with the joints staggered. This adds strength and rigidity to the floor, as well as preventing the individual panels from drifting apart. Figure 4 shows a Lamella floating floor in place.
This type of flooring may also be used as a base on which to build a small studding/plasterboard room‑within‑a‑room type of studio, as long as the weight of the inner room isn't so great as to cause the floor to bow. I'd be inclined to consider adding a third layer of chipboard to the floor if you're thinking of going for the full room‑within‑a‑room treatment.
An alternative to using Lamella is building a wooden 2x2‑inch or 2x4‑inch frame and covering it with two layers of flooring chipboard. This may be separated from the original floor by blocks of Neoprene, though the most usual approach is simply to cover the existing floor with Rockwool loft insulation, then lay the studding raft on top of that. Observe the rules of isolation by not allowing the floor to touch the existing walls at any point, and fill any gaps with mastic to ensure the floor is airtight. Figure 5 shows a studding floor.