A.Bonnie Schnitta, an acoustic consultant at SoundSense in East Hampton, N.Y., responds: Resilient channel will add flexibility to the ceiling assembly, which is needed to deal with foot traffic and other types of structure-borne noise. But when you fasten the drywall to the metal channels, be sure your screws don't penetrate the old ceiling or framing, a common installation error that short-circuits their effectiveness. Adding a layer of insulation between the channels will also help absorb some sound frequencies and prevent the airspace from reverberating. Make sure that the added insulation won't be compressed after the drywall is installed - we typically use 1/2-inch-thick hvac duct liner, which is reasonably priced and works well with 7/8-inch channel.
If the budget allows, use decoupler clips instead of resilient channel. Though less widely available and considerably more expensive than channel, decoupler clips will give the ceiling assembly a higher STC (sound transmission class) and IIC (impact insulation class) rating (see chart, below). Most of the time we use standard RSIC-1 clips (866/...
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