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Acoustic treatment for the home

By: Steve Manes , Contributing Writer
In: Home Improvement Tips, Technology

An apartment dwelling friend called me last week and complained about her upstairs neighbors who sounded like they were raising cattle. The clomping noise was driving her nuts and she wanted to know how much acoustic ceiling tile would cost her. I told her that ceiling tile would be virtually useless in this application. That’s not what it’s made for.

There are two basic types of noise control: one that alters the acoustics inside a room (absorption) and one that contains that noise and keeps it from invading neighboring spaces (transmission). The respective technical approaches are about as similar in function as a kitchen sponge and a sea wall. In other words, different.

Acoustic tile is an absorptive treatment. It’s also a limited one insofar as it’s mostly effective at the frequency range and sound pressure level (SPL) of ordinary speech. It’s intended to reduce the reverberation time, a/k/a echo, inside a room. It does very little to prevent sound transmission to the room next door.

My friend complained, “But I see it used in expensive hotels and I never hear anyone walking around in the room above me.” That’s because what she doesn’t see is the eight inches of concrete under that tile nor the thick carpet and padding on the floor above. Hotel builders know what they’re doing. That acoustic tile is mostly there to make the room feel cozier. And heavy carpet actually does a better job of it.

Sound transmission comes in two flavors: airborne noise and structurally borne noise. Airborne noise is like standing outside your neighbor’s front door and yelling, “Hey Joe! Get your car outta my driveway!” Structurally borne house is banging on his door with your fist. Airborne noise is much easier to deal with because air is a fairly poor conductor of sound.

Sound likes density as a medium — like the water around a sonar head or the the wood joists in your ceiling. It’s a bit more complicated than that but it’s the answer to why acoustic tile doesn’t work in this application. Acoustic tile works on airborne noise. Your neighbors upstairs sound like a team of Clydesdales because they’re creating structurally borne noise which travels through the floor joists to the building’s framing to which, of course, your apartment is rigidly attached.

So how do you fix it? The most doable solution is to buy your neighbors thick, fuzzy slippers. Or a plush hotel carpet. Beyond that, it gets complicated, expensive and crazy impractical.

I built a couple of commercial audio recording studios and the way we dealt with structural noise was to remove any pathways for sound to move through the structure. Commonly, this is done with box-within-a-box construction.

The control room is typically a very tight room built on a concrete slab which is floating on spring-and-neoprene vibration absorbers similar to those used to isolate vibrating heavy machinery. Then another air tight room is built around it with no rigid physical connection between them, not even a screw. Access is typically through a sound lock, which is a pair of very heavy, air tight solid core doors.

To kill airborne noise, the windows are double or triple glazed glass of different thicknesses to prevent harmonic resonance, with several inches of air space between them. Even the plumbing is isolated with vibration absorbing connectors. In fact, that was one of the most difficult jobs because FDNY inspectors weren’t very accommodating with regard to the floor’s fire sprinkling system.

These techniques work very well but you can see how something like this would never be practical as a retrofit for an apartment or a house.

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  1. 5 Responses  to “Acoustic treatment for the home”

  2. Aug 29, 2011
    Great tips for minimizing noise of the footsteps. Great pots
  3. Aug 29, 2011
    I like your post. It gives me great ideas on how to help minimize the noise of our footsteps to be heard in the apartment below our apartment. Thanks
  4. Lucy
    Aug 29, 2011
    I hope you got unlimited free admission to the disco in return for your efforts!
  5. Aug 29, 2011
    Carpeting your apartment would help to muffle the noise of your footsteps being heard in the apartment below you. It wouldn't do much for a loud stereo downstairs though because your walls are rigidly attached to the same framing that your floor is. The #1 rule for quieting structurally borne noise is to silence it at the source. Keep the noise generator from coupling to the building structure. For instance, when I had my Broadway loft there was an after-hours disco two floors above me that went till 8am. I worked with the owner to isolate his huge speakers from the floor. I came up with an elaborate affair using two plywood platforms with double durometer neoprene absorbers and stacks of bricks (for weight -- to make the bass wave have to do more work to move the speaker, which helped burn off some of its energy). It worked very well and -- bonus -- the club owner was happy because he got a tighter bass sound.
  6. Lucy
    Aug 29, 2011
    Fascinating! Thanks for putting that in laymen's terms. So if I understand correctly, a way to muffle the noise from the neighbor's below us (who play games on their x-box with their surround sound blasting) is to carpet our apartment (but can't bring myself to carpet over beautiful hardwood floors...) Yet there is no real fix for them if I were to take up tap dancing heh heh heh.