Solving an Acoustical Problem in a Retrofit Environment

 

Stan Gatland

Stan Gatland is Manager, Building Science Technology for CertainTeed Corporation

It can be a challenge to control the acoustics in older buildings when they are repurposed for multiple business uses.  One example is a call center situated in the middle of an office building, surrounded by cubicles of other workers and offices with many hard surfaces – glass, wallboard and wood doors. The perimeter of the call center has a low suspended ceiling with a decorative hard wood finish that amplifies and reflects the various sounds typical in an open plan office setting – loud telephone conversations and office equipment – carrying the disruptive noise throughout the floor.

The building owner had some ideas on how to improve the space but decided to work with an acoustical consultant to confirm the noisy conditions with measurements, as well as make recommendations on how to improve the space acoustically.

Acousticians commonly refer to highly sound reflective rooms as “live” or “reverberant.” Open plan office space should be designed for both good speech privacy and poor speech intelligibility.  Typically, you design for privacy at work stations and make speech unintelligible between adjacent areas by controlling background noise levels and reverberation time – the length of time it takes for a sound pressure level to decay or dissipate.

The results confirmed that background noise levels were high and intermittent and reverberation times exceeded the maximum recommendation of 0.60 seconds at most locations on the floor.

Another metric that was used to characterize the space was the speech transmission index (STI). STI is a measure of the ability to understand speech in a given space with the sound source coming from different directions or locations.

In open plan office settings, you want STI values to be low or poor meaning that people can’t understand each other from different locations.  Most locations had fair to excellent ratings creating a poor acoustical environment.

The recommendations provided by the consultant to solve the problem in this office space were:

  • Change the entire ceiling to high absorption suspended tile or use functional absorbers (hanging panels in the box like orientation)
  • Add some absorptive treatment to office doors or walls facing the open office
  • If not enough, use background masking noise.

It is expected that if the summary improvements were made it would improve comfort and maybe morale and productivity for the employees.

Time will tell. Do you have any examples of acoustical retrofit to share?