We turn our attention to uprating studio walls, as well as techniques for building sound‑isolating partitions.
If you're lucky enough to have solid brick or stone walls in your studio room or premises, this gives you a head start in achieving a reasonable amount of sound isolation; lighter walls — studding partitions, for example — are far from ideal. However, even solid walls can be improved upon, and partition walls can be constructed to give a surprisingly high level of sound isolation.
If you are building a new, solid wall, always go for cavity construction using brick or concrete blocks. Cavity ties tend to transmit sound, so omit these if at all possible, and ensure that there are no spurious bits of mortar bridging the cavity. Breeze blocks are too light and consequently offer poor low frequency attenuation, even for internal walls, though breeze block walls can be uprated using a panel and studding system.
Studding walls are obviously lighter than brick or concrete, but by using a double construction, you can achieve reasonable isolation. Work on this type of partition was pioneered by the BBC, and most modern studio construction is based on their 'Camden' partition. Single‑skinned partitions have their uses, but in all honesty, their sound isolation value is too small. A double‑skinned structure is far preferable, a four‑inch air‑gap being a sensible compromise between wasted space and isolation.
The frame for your partition should be built up from 2 x 4‑inch studding, which should be isolated as thoroughly as possible from the existing structure using Neoprene strip. Sound travels quite efficiently within solids, so it's important to ensure that the frame doesn't make a good acoustic contact with the floor, the walls or the ceiling. The best way to achieve this isolation is to insert quarter‑inch thick (or thicker) Neoprene sheeting between the frame and the floor to support it, and to use a similar approach where the wall touches other walls and the ceiling. Some screws will have to pass through the Neoprene to hold the studding wall in place, and these will cause some sound leakage, but this shouldn't be too serious.
Even though this is a lightweight frame construction, the rules of physics apply, so the heavier you can make it, the better it will perform for sound isolation. Use at least two layers of plasterboard, preferably the 12mm thickness, on each side, and use more layers if you can afford the space. It can help to sandwich a layer of softboard between the plasterboard, as this helps damp the structure. Having at least two layers increases the mass of the partition and the layers damp each other, reducing resonances. The joins in the plasterboard should be staggered, and isolation performance is noticeably better if the finished partition is skimmed with plaster. However, care must be taken that the plaster does not reach all the way to the floor, ceiling or other walls, as it could carry sound directly to the main structure. When plastering, it may be best to insert a removable plastic spacer at the corners, and once the plaster is dry, this can be removed and the resulting gap filled with mastic or silicon rubber.
Figure 1 shows how a simple studding wall is constructed. Some improvement can be made by building two separate frameworks with the studs staggered, as in Figure 2. This takes up very little extra space and provides better mechanical isolation between the two sides of the partition. The inside of the partition should be filled with Rockwool insulation or compressed Rockwool slab for best results.
The techniques used for building the free‑standing partition can be applied to uprating existing walls. Construction is along the same lines, but only one side of the frame need be panelled; the other side of the frame is screwed directly to the wall via Neoprene spacers. The cavities within the frame, between the existing wall and the new skin, can be filled with Rockwool and then the plasterboard skin nailed in place. Rockwool is purported to work rather better than fibreglass and 2‑inch Rockwool slab is slightly more effective and easier to handle than the more common rolled insulation.
Greater mass can be added by using two (or more) layers of plasterboard, or by layering plasterboard, chipboard and fibre insulation board to form a sound‑deadening sandwich. Layering different materials is a good idea, as it provides a deliberate acoustic mismatch, causing vibrations to reflect back and forth within the structure, which increases the likelihood of absorption of the sound — exactly what you want! The more layers you can use, the better the sound isolation will be, which is why professionally constructed studio walls sometimes have panels four inches or more in thickness, made up from layers of plasterboard and chipboard. If you intend to go this far, make sure that the floor of your room will take the weight! Figure 3 shows this method of uprating.
Finally, remember that the effectiveness of your soundproofing is determined by the weakest spot in the room. For example, there's no point in building huge walls with layer upon layer of plasterboard if your doors and windows haven't been uprated or if the ceiling is untreated. Always tackle the weak spots first and then move on to the next weakest area. By an amazing coincidence, next month's installment looks at the problems posed by poor floors and ceilings, and offers a selection of remedies that can be applied even when there's very little headroom left to play with.
- The greater the mass, the more work the sound has to do to move it, so a large mass equates to better isolation.
- Two layers of isolation are better than one, and the greater the distance between them, the more effective the low frequency isolation will be.
- Sound travels efficiently through solids, so anything you can do to isolate one solid section from the next, such as incorporating rubber, air gaps or other absorbent materials, will help.
- Acoustically absorbent material such as Rockwool can help when placed between partitions, though you must ensure that everything is absolutely airtight.
- You could put the Rockwool in fabric bags to reduce the dust and to make it easier to handle, but beware that plastic bags will prevent sound being absorbed efficiently. Air needs to be able to move in and out of the fibrous structure for absorption to occur. Glass fibre and Rockwool are potentially dangerous irritants, so wear gloves and a face mask whilst working with these materials.