Thin walls? A large ceiling-to-floor tapestry works very well in muffling sound, Al Ubell said. Back-padded with fiber glass, it's even more effective. You can also build a separate wall with pegboard or some other absorbent material and put fiber glass behind that.
Another very effective sound-muffler is to take a carpet, insert grommets and drape it from the ceiling. "A lot of interior designers that work with sound people" tipped him to this one, Ubell said.
If you live above someone and they're complaining about noise, double padding under your carpeting is advised. Ubell suggests a fibrous pad, rather than a foam pad, which is susceptible to air pockets and thus shorter lived. Such fabric padding includes fiber glass, nylon, Orlon and Teflon.
"It feels like you're walking on mush" at first, Ubell said, but it stabilizes. This approach is particularly effective in reducing children's noise. "It's impossible to stop children from running," he said. "They've got to run."
People with pianos should have shock absorbers under the wheels so sound does not travel down through the floor, Ubell suggested.
If you're sensitive to sound, check where the elevator, garbage chute and stairwell are in a prospective apartment. If possible, try to get at least one unit away from mechanical equipment. It doesn't assure you of quiet, Ubell said, but it does assure you that the building's mechanical sounds won't be as intrusive. He also suggests staying away from a chimney line, because noise from the central heating system may carry. He also has had experience with air-conditioning and forced-hot-air systems that can actually carry conversations from one end of a house to another when not in use. When the systems are on, this problem disappears.
For the creme de la creme, the Cadillac of quiet, Ubell said converted factories are about as good as you're going to get. "They're almost--almost--soundproof."