TOP TEN" ACOUSTICAL TIDBITS

• Resilient channels are not needed with lightweight (20 gauge or thinner) non-structural metal studs.

Wood stud + resilient channel = metal stud.

• Never trap the resilient channels between layers. Use resilient channels to isolate all of the sheet rock from all of the framing. A hat channel is not the same thing as a resilient channel, and has no useful acoustical properties. Resilient channels are not needed on both sides of the wall.

• Batt insulation inside the wall is almost always a good idea. There is nothing magic about "sound deadening batts" -- regular R-11 or R-19 fiberglass is fine, depending on the wall studs used. Insulation should substantially fill the cavity.

• Dissimilar sides of the wall or window is generally a good thing. Think "1 + 2" layers.

• Solid material (such as a shear plywood layer) on the inside of a double stud wall will drastically reduce the overall sound rating, often from STC 60 down to STC 46. Yes, adding more material reduces the sound rating!

• Triple glazing is worse than double glazing for noise reduction. Thin vinyl interlayers improve R value, but don't count as a third pane. Float glass and laminated glass are dissimilar.

• Think "water tight" when sealing sound rated walls or enclosures. Anywhere that water would leak out, sound will leak too. Leaks are very important -- 1% open area lowers the STC rating by 15-20 decibels.

• With an open plenum above the ceiling tile, you get STC 30-35 room-to-room, regardless of wall type or ceiling tile type. Penetrating 6" above the grid or adding batts on top of the ceiling tiles does absolutely nothing.

• "Sound deadening board" doesn't. Never has, never will. It has absolutely no useful acoustical properties. Really.

• An acoustical "boot" is more than just an elbow. It is 12” of duct plus an elbow plus 4 feet of internally lined duct. External duct insulation is thermal only - it does nothing for noise.

• Inertia bases under mechanical equipment do not help with either noise or vibration. They are not a substitute for an adequate floor slab.

• Plastic waste/drain piping in residential construction will almost always be a noise problem, even with remedial treatment. Adding pipe wrap and appropriate isolators is very labor intensive. Cast iron pipe will almost never have noise problems.

• The supply side of a ventilation system seldom presents a noise problem. The return air side almost always needs noise control, because of the shorter more direct path.

• Active noise cancellation works best in confined areas and for specific low frequency tones. Cancellation won't work for broadband noise in three dimensions, such as a portable generator or traffic noise.

(OK, so it was more than ten.....)