The first question you should ask is simply this,
is the problem impact noise, or airborne noise (TV’s, Stereos, telephones etc.) coming down from above. Nine times out of ten, impact noise is the main concern. What is impact noise? It is the noise caused by people or animals walking across the floor above (generally hardwood). This type of noise is considered to be structure borne noise and is one of the most difficult noises there is to soundproof from. Impact noise is basically sound that travels directly through the joisting structure from the floor above, directly into the hard mounted ceiling below. Another term for this is known as “foot fall “noise. Impact noise travels through the floor joists structure at speeds of over 1200 times greater than the transmission of sound traveling through ambient air. Keep in mind that most home joist systems as well as studded walls are generally 16 inches on center, so not only do you get the speed of the impact noise shooting downward, but the perfectly spaced joists act as tuning forks thus causing the sound to sustain (last longer) compounding the impact problem. The best and most effective way to stop impact noise from above is to isolate the joist structure and the floor above (which is generally hardwood) from the ceiling below. This can be accomplished in a variety of ways. The most common is to float (suspend on acoustical sound clips or resilient channels) the ceiling using either resilient isolation clips and furring channels (hat channel) or the most common method of floating, RC-1 (resilient channel). The good, the bad, and the ugly of both these methods will be discussed in depth. First we have the industry standard, which is RC-1 or resilient channel. This is a flanged Z channel (generally with only one flange that attaches to the joist) and a larger flange to support the floated drywall ceiling. RC-1 can be purchased from a drywall supply company, or a contractors supply house. The resilient channels are usually attached perpendicular to the joists and the rows are evenly spaced approximately 2′ to 3′ apart. The longer flange (of resilient channels) in a ceiling application will all face the same direction to obtain maximum resilience in the new ceiling assembly. Remember, that the longer flange is the one the drywall screws into. Always use screws when you drywall, never use nails. Once the RC-1 is properly installed across the entire ceiling, you are ready to drywall. The new drywall will be screwed directly through the drywall and into the resilient channel’s (longer) 1″ flange. You will use 1 to 1 ½” self-tapping drywall screws or in rare cases, sheet metal screws. If the resilient (floated ceiling) is installed as per manufacturers instructions, there will be approximately a ¼” gap around the entire perimeter of the new floated ceiling. The floated ceiling must never make direct contact with the adjoining walls. This is NOT negotiable folks. The ¼” gap is then filled with an acoustical caulking, (OSI 175 is a good caulk for this application) and then finally the new ceiling will be taped, mudded, and painted just like a like a hard attached joist mounted drywall installation. The caulk is the interface between the resilient ceiling and the adjoining walls. There you have it, the common mans floated ceiling. Now if you are really serious about soundproofing your ceiling, you have the sound clip and furring channel method of floating. metric to standard