Monday, January 2, 2017

SHHHHH!: Quieting That Confounded Noise

That confounded noise!
Ugh, that confounded noise! Whether it’s the rush of freeway traffic, the drone of a furnace fan, or just the faint tap-tap-tapping of your kid texting in the next room, noise in the home can drive you crazy.

Noise is simple to define: It’s any sound you don’t want to hear. For example, while you may happily tolerate the whine of jet engines at an airport, hearing them in your living room would be something else entirely. Their sound is transformed into noise.

A solid wall is a little like a giant drum head.
Staggered double-stud construction reduces
impact noise by "de-coupling" wall surfaces.
Noise consists of sound waves whose behavior, while theoretically predictable, is very complex. Even acoustic engineers can’t always figure them out—witness the number of concert halls with bad acoustics, or those freeway sound barriers that actually increase traffic noise in homes some distance away. Nevertheless, there are a few simple guidelines that can help you keep out unwanted sounds.

Noise travels via two paths—through the air (airborne noise), and through materials (impact noise). Both have to be addressed in order to contain a noise problem. The sound of that drunken twit banging on the wall next door is an impact noise. It’s usually of low frequency, and it’s best contained by isolating (or “decoupling”) the two surfaces. One way is to build a double wall between the spaces, sometimes using different stud sizes and gypsum board thicknesses to prevent sympathetic vibration. Other methods use special resilient channels to “float” the gypsum wallboard on its supports.

Resilient channels are used to
"float" gypsum board atop
the wall studs, allowing it
to absorb some of the sound energy.
Airborne noise—the screech of somebody else's kid playing a violin, for example—is usually of higher frequencies, and it’s relatively easier to damp. Sound-absorptive materials such as fiber glass blankets can be placed inside walls and ceilings or, in existing buildings, materials such as acoustic tile or tackboard can be installed on the face of surfaces. The softer and more absorbent the material, the more airborne sound is absorbed. That’s why carpet is often used as a sound dampener on airport walls.

A gap this size around an outlet box is
enough to completely negate any
soundproofing in the wall. 
However, putting sound insulation in a dividing wall can only solve part of an airborne noise problem. Any penetrations in the wall—even as small as the cracks around receptacles—will continue to transmit a surprising amount of sound. Such penetrations have to be carefully tracked down and filled with calk or foam materials. The idea is to get the wall literally airtight, since without a pathway of air available, airborne sound waves can’t travel.

A commercial water hammer
arrestor, especially advisable
near laundry machine faucets.
Many common noise problems are best addressed in the construction stage. Water hammer in pipes can be reduced by making sure that all piping is securely attached to the framing, and by placing isolators or expansive foam in the holes that pipes pass through. Commercial water hammer arrestors are also available.

The drone of a forced-air furnace fan can be muted by locating the furnace outside  the living space, and by placing the return-air intake (which is like a superhighway for furnace noise) some distance from the furnace itself. The rushing sound of air exiting from registers can be reduced by increasing the register size and hence reducing the air velocity through the diffuser vanes. External sounds such as highway noise can be damped by using triple glazing in windows, adding drapes, and even by planting leafy greenery outside the house.