Friday, November 26, 2010

Coordinating Construction Trades to Optimize Noise Control

Coordinating Construction Trades to Optimize Noise Control
By Harry Alter & Norman Varney

  You've spared no expense to make sure your state-of-the-art studio or home cinema is designed to offer the most realistic experience. Ceiling, walls, doors and floor systems have been designed to achieve a minimum STC (Sound Transmission Class) performance rating of 60 and IIC (Impact Isolation Class) of 55. HVAC ducts were designed to make sure ambient noise levels within the room are quiet to an NC (Noise Criteria) rating of 20. You've crossed your T's and dotted your I's, there's nothing left to do... Right?  Wrong! The fun is just about to begin because what happens in the field will determine whether all your hard design work will pay off.

  Planning to reduce potential field problems before they happen is your key to success. So what more do you plan for? First, plan for flanking noise and second, plan for the trades in the field to work as they usually work. That means that if you want the various trades in the field to work together and do what needs to be done, you must provide clear and concise information and instructions (both visually and verbally) to help them through what will probably be a new and atypical construction process for them. It is important that all the trades are on the same page and understand what the goal is. Express to them how important their skill and care is in accomplishing the goal. Ask them to review the scope of work in advance and to ask any questions or concerns ASAP. 

  A few examples of how field conditions can affect a room's final noise performance level:

  1.  Poor caulking around the frame of an acoustical door, or along gaps at the floor plate can cut a high STC door or wall system in half.
  2. If a high STC wall assembly is built over an OSB or plywood subfloor, the performance level of the wall will (as a result of flanking noise) typically never achieve an STC rating above 50.
  3. The improper installation of plumbing lines through wall studs and ceiling joists can take the room's ambient noise level from a quiet NC 20 to a distracting NC 40.
  4. The direction of floor joists relative to a partition wall beneath it will affect the amount of airborne and impact noise flanking through the floor assembly to adjacent rooms. 
  5. Lined duct runs alone don't assure a quiet environment. Typical HVAC installations can be very noisy even with lined duct runs.
  6. Using heavy floor toppings such as gypsum-concrete can dramatically increase the STC (airborne) performance of a floor system, but can dramatically decrease the IIC (impact; footfall) performance when not properly addressed for noise control.
  7. The fanciest electrical system cannot deliver instantaneous and continuous current, and will be susceptible to noise, if there are any connections along the path that are not clean and tight.  
  It is attention to detail that you must rely on from each of the trades in order achieve the invested potential. Dynamic range and low-level resolution are only as good as the noise floor allows.  Give the construction trades good information and they can give you the desired results. 

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