That eliminated one noise source, but there was still another to address. Sound from the elevator equipment room was also traveling into the elevator shaft though the holes where the elevator cables penetrated the equipment room floor. To stop the transmission of that noise, Haas created custom rubber gaskets to seal the holes.
Overall, soundproofing has become more difficult, experts say. As buildings become safer and more fire-resistant, they also become more rigid structures and more likely to act as a network of sound-transmitting materials. Just look at party walls and how they have changed. Mike Doty, an architect in Sun Valley, Idaho, says that in his market, party walls in new condos tend to consist of double walls with a 1-inch airspace. This gap has always done a good job at dissipating noise.
But as fire and seismic codes have gotten stricter, the insides of these walls have gotten lined with fire-rated drywall and plywood shear panels. Developers are reluctant to take even an inch of space away from adjoining apartments, so the resulting response has been to narrow or even close the gap, significantly reducing the wall assembly’s sound resistance.
Low-skilled labor and a lack of supervision make matters worse. “When framers build a party wall with an inner cavity, they often let junk fall into the gap,” says Doty. “You design everything right, only to have the wall completely grounded out.”
NOISES OFF Doty’s solution to the party wall problem includes the same material used to help fix the noise problem in the Miami condo: sound-absorbing panels, which have been on the market for about three years. Two companies, Quiet Solution in Sunnyvale, Calif., and Supress Products in San Rafael, Calif., manufacture the panels.
These products use a technique called “constrained layer damping” to modify the behavior of sheet goods, according to Bruce Donaldson, CEO of Supress Products. In a standard sheet of drywall or plywood, when airborne sound waves hit one face of the panel, it starts to vibrate, creating airborne sound waves on the other side.
But a sound-absorbing panel is a sandwich consisting of two layers of standard plywood or drywall separated by a thin polymer layer. “When one face of the panel starts to vibrate, the polymer shears the vibration into a tiny bit of heat,” says Donaldson.
While the consultants and architects we spoke with say that these panels do a great job at absorbing sound, these new products have another advantage. The panels are only slightly different than standard drywall or plywood and require only standard skills for installation. That means these sound-absorbent panels can be easily handled by a builder’s regular framing or drywall crews.
The material also addresses the weaknesses of resilient channels, or RCs, which reduce sound transmission by separating the drywall from the studs. Consultants say that the vast majority of resilient channel installations don’t work because of poor installation. “We usually don’t specify resilient channels because of that,” says Michael A. Schwob, principal acoustical engineer with JBA Consulting Engineers in Las Vegas. The main problem? Short circuiting, which is where sound bypasses the insulation provided by the resilient channels. For an RC installation to work, no screws can connect the drywall to the studs, and adjacent walls can’t touch one another. He says that most RC installations have many such short circuits during installation and that as a result they don’t work as advertised.
Schwob says that Pac International and Kinetics Noise Control make resilient assemblies that do a much better job than standard RCs. But they are best used in conjunction with the new drywall products.