Noise: Thoughts on quieting a lab

This AP (Associated Press) article about new products on the market for quieting home environments got me thinking about my experiences quieting a few laboratories and what I learned along the way. Here are my thoughts, arranged in no particular order:

• The frequency of the noise matters. High frequency noises can be reduced or eliminated by light-weight materials such as fiberglass, curtains, carpet, and rubber seals (e.g. around doors). Reducing low frequency noise requires MASS; in other words, it takes heavy materials to absorb the large amounts of sound energy contained in low frequency noise, such as from machinery, engines, air handlers, and the like.
• Solid-core doors can make a big difference in the amount of sound coming from the hallway (or leaking out into it, for that matter) and cause little, if any, disruption to the work environment when used to replace existing hollow-core doors. Most doors that come standard in home and office environments are hollow in the middle and therefore don't absorb low frequency sounds very well at all.
  
• If the room has a drop (also called a "false") ceiling, then replacing the standard ceiling tiles with acoustic ones can make a significant difference and is minimally disruptive.
• Wall and door treatments, such as barium-loaded vinyl hangings and acoustic panels, offer the benefit of being able to be installed to an existing room without requiring tearing down the walls, but installing them may require significant effort and it will almost certainly be quite disruptive to the existing workspace (think about shelves and such that are on the walls).
• If you have hollow walls (e.g. gypsum board on stud), then blowing insulation into the wall cavity can reduce middle and high frequency noises without being too disruptive.
• If full-scale remodeling is an option, consider adding an extra layer of gypsum board or other massive material to the walls. If you go this route, then you should advise the workers to install the boards so that the seams (between boards) of the new layer do not over-lap the seams of the underlying layer. Of course, there may be complications with window and door frames fitting the non-standard thickness of the walls, but a competent carpenter can solve those issues.
  
• Speaking of windows, if the building is located in an area where the external noise (e.g. vehicular traffic or aircraft) is an issue, then it will likely make things much simpler if you pick a room without a window for your lab in order to avoid having to acoustically shield it. Likewise, locating away from internal noise sources, such as elevators and air-handlers, is also a good idea where possible.
• Quieting noises in your lab itself is also a good idea. Computer workstations and other electronic equipment fans are the usual culprits here. A variety of options now exist for quieting computers ranging from low-noise replacement fans to liquid cooling systems that can be added to existing computers.
  
• If the acoustic environment is so poor that you need to go beyond the simpler of the measures listed above, then consider getting professional help (i.e. a consultant who specializes in this area) to evaluate the situation and recommend appropriate steps.
• Choosing a room that isn't a strict rectangular box can be a good idea as it can mean significantly less resonance.

As I said above, my comments are based on my own personal experience on quieting existing rooms. I did not mention options that I am not personally experienced with, such as bass traps. Finally, I have not addressed anechoic chambers or designing sound studios as that is outside of the scope of this post.