Soundproofing 101

May 13, 2013 | Comments

Watching movies on a big screen with surround sound is a wonderful source of family entertainment, but domestic tranquility can be quickly destroyed when the sonic mayhem of a Hollywood blockbuster invades the rooms adjoining your home theater space, or a washer on a noisy spin-cyle intrudes on the cinema.

That's why it pays to weigh the costs and benefits of soundproofing while you're making plans for a media room or home theater. And don't be fooled into thinking that adding an extra layer of sheetrock is all it takes to keep an adjacent space quiet — far from it. Proper soundproofing is a specialized discipline that requires several key ingredients for success. In other words, if you want to do it right, you'll need to consult a professional.

Paper-Thin Walls

When you think about it, there's not much to the walls in a typical home, just sheets of half-inch thick drywall screwed or nailed to 2 x 4 studs. Rap your knuckle on the wall and it sounds hollow, which helps explain why standard walls don't do a very good job of containing sound.

When your speakers are cranked up, walls vibrate, and that vibration travels through the studs (or joists) to walls (or floors/ceilings) on the other side. Sound also leaks through electrical outlets, lighting fixtures and other openings.

It's a common misconception that adding a second layer of sheetrock and stuffing insulation in the walls will improve sound isolation, but because of these traveling vibrations, it barely has an effect.

Another common fallacy is that putting foam or acoustic panels on the walls will stop sound. Not so. Sound-absorbing panels are intended to control echoes inside a room, not block sound.

The Fundamentals of Successful Soundproofing

So what does it take to successfully soundproof a home theater? The science of soundproofing boils down to three words: mass, damping, and decoupling. You can achieve varying degrees of soundproofing by adding mass, dampening wall surfaces, and most importantly, decoupling adjoining structures so they are not physically connected. The ideal solution is a combination of all three.

The most common way to add mass is to double up on sheetrock, while damping can be achieved by using specialty drywall made with a viscoelastic compound that absorbs vibration, which helps mitigate sound transmission.

A "mass-loaded vinyl barrier" — a 1/8-inch rubbery sheet filled with metal particles — can be added to walls to increase mass and improve damping. The barrier is attached to the studs before the drywall goes up is or sandwiched between a layer of plywood and drywall.

Adding mass and reducing vibration through damping will do a decent job of impeding middle frequencies, but you need to take additional steps if your goal is to contain the rumble of alien spaceships bumping through your audio system. The most effective method for isolating low frequencies is to literally build two walls — one in front of the other with a gap in between — to physically separate (decouple) the sheetrock from the studs.

Of course, it's also labor-intensive and expensive. When double-framing isn't feasible, the pros use isolation bushings, or "clips," to decouple sheetrock from studs or joists. The rubber bushing side of the isolators attaches to the studs while the opposite side supports a horizontal rail, or "hat channel," onto which the drywall is fastened.

The basic techniques outlined here apply to both new construction and retrofit projects, but starting fresh is always easier since you don't have to tear down existing sheetrock and the like.

We've just scratched the surface here, but hopefully, you now have a better understanding of what it takes to successfully soundproof a room. To learn more, consult an acoustical consultant or CEDIA professional. Click here for a list of CEDIA-member home technology professionals in your area.

Special thanks to Anthony Grimani, president and founder of Performance Media Industries, who provided key information for this article. PMI is a Novato, CA-based firm that designs and engineers world-class home theaters and professional studios.