Blocking Airborne Sound The weatherstripping that seals outside windows against drafts also seals out airborne sound, at least while the windows are closed. You can take the same tack with an interior door, weatherstripping it just as you would a door to the outside, complete with a threshold or sweep. If you're adding a door as part of a remodel, use a solid-core door rather than a hollow-core for better sound control. Electrical outlets in open-cavity stud walls are another easy sound path between rooms. These can be plugged by removing the outlet from the wall, stuffing some mineral fiber insulation behind the box, sealing the holes in the box with silicone caulk, and re-installing the box. Ductwork. Cutting sound transmission through ductwork is not as simple. The problem shows up in cases where the duct outlet that serves a "quiet" room shares a common duct with an outlet in an adjacent noisy room. A lot of sound can be transmitted if the outlets are close together, less if they are distant from each other. The best fix is to separate the takeoff points as much as possible. If you can't do this, you'll help things somewhat by lining the inside of the duct with acoustic insulation. Be sure to size the duct to compensate for the added insulation.

In many cases, noise transmitted directly through walls or floors may be a much greater nuisance than airborne noise. These sounds are caused either by noise in one room that vibrates the intervening floors or walls or by physical impact, such as doors slamming and footfalls. To get a feel for how this works, think of the drywall surface on one...

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