If you’re going through the trouble to expand the walls in this way, you’ll want to do the same with the ceiling. Otherwise, you won’t gain much in terms of mitigating sound transmission (Fig. 1).
You also need to consider the doors and windows in the room. If they’re not sealed properly, sound will escape. While recording studios often have industrially built doors and windows, there are a number of books that show you how to build your own for a fraction of the cost.
When done properly, a sound-isolated room will be airtight, so you’ll need to figure out how to ventilate it. Again, a variety of DIY studio books show examples of ventilation systems that don’t compromise the isolation you’re trying to achieve.
The next level of isolation comes from adding an air gap of at least 2" between the walls and ceiling in your studio and the surfaces surrounding it (Fig. 2). At this point, you’re building a room within a room.
Although this approach can get pricey, it’s not as expensive as you might think, particularly if you or a friend are handy with carpentry tools. In cases where the room you’re planning to use will be a source of income, either through teaching or remote recording, it’s worth exploring the room-within-a-room concept.
At the high end are prefab systems, which include the same technology used for industrial-level sound isolation. Omar Hakim chose this type of solution for his suburban New York loft, where he installed a 12' x 16' x 8' “modular music room” designed by Industrial Acoustics (industrialacoustics.com). The studio is large enough to hold his full kit, as well as a small recording setup and perhaps an extra musician or two. The design includes a floating floor, acoustic doors with magnetic seals, and a ventilation system, and it is quiet enough that he can play for hours without worrying about complaints from his neighbors. And because the room is modular, he didn’t have to build anything into the loft structure itself. When Hakim recently moved to Brooklyn, his new space made this unit unnecessary, but it broke down and stored away relatively easily.
The DIY method, on the other hand, is practical in situations where you have the ability to modify the structure appropriately. Berkeley-based drummer John Hanes took this approach when he dedicated one of the rooms of his house to a drumming booth for practicing and giving lessons. With the help of a contractor, he built a raised floor in it, where the joists sit in rubber, U-shaped vibration isolators on the pre-existing wooden floor. The riser is hollow and it doesn’t touch the walls.
“The inner walls have thick layers of sheetrock with sound board in between,” explains Hanes, “and there’s a 6" airspace between the inner and outer walls. We installed two doors. The inner door is a metal, industrial-insulated door — fairly soundproof. There are a few inches of airspace, then the outer door. That second door makes a huge difference.” (Fig. 3.)
Hanes spent about $4,000 on the project. And while the results in this roughly 10' x 10' room aren’t perfectly soundproof, he feels it is a major improvement. “The low end is not completely isolated, and out in the house you can hear the muffled sound of someone drumming. However, when I close both doors, I can’t hear my wife giving voice lessons,” he says with a laugh. More importantly, he can play as loud as he wants and it doesn’t disturb the neighbors next door.