Kam Ng | Acoustical Solutions

Kam Ng

Vice President of Engineering


Message Kam

  • Virginia

Virginia Commonwealth University Exhaust Fan


A Virginia Commonwealth University exhaust fan was generating a high volume of noise disrupting classes taking place at Sanger Hall. The exhaust unit is a 3.3 horsepower belt drive centrifugal fan, which is mounted on the exterior wall adjacent to one of the classrooms. The fan was generating a noise level above what is typically needed to have good speech intelligibility.

Service Provided

A site survey and sound measurements will allow us to evaluate the levels of sound from the exhaust fan. The noise levels seeping into the plenum above the classroom ranged from 70.5 to 71.8 dB(A). Typically, a classroom should have a noise level below 55 dB(A). The fan was running at maximum capacity to evacuate a large volume of air from laboratories in the basement. The dominant noise sources were the blades of the fan and flow noise created by the air in the passing down through the duct work.

Based on the results of noise measurements and analysis, two options were recommended:

  • Option 1: Use vibration control to isolate the casing of the exhaust fan casing and duct work.
  • Option 2: Reduce the exhaust fan noise by blocking sound and using sound transmission loss approach.

The first option would be the first choice, however, would be more expensive and time-consuming to implement. They chose the second option. Installing sound blocking PrivacyShield® Ceiling Tile Barrier and Light Hoods would be less expensive, easier to install and help the school meet their target date before classes started.

After installing the PrivacyShield Ceiling Tile Barriers and light hoods on the ceiling of the classroom, the total A-weighted sound levels in the classroom dropped from 63.6 dB(A) to 59.4 dB(A). With PrivacyShield, an 8.4 dB noise reduction was observed at the peak noise frequency at 31.5 Hz. Our noise measurements, analysis, research and finds were all summarized and provided in our report provided to the school.

Specific Challenges

Since the original construction design did not include any vibration isolation, it’s difficult to easily retrofit a solution. With fans and air flow, it is best practice to reduce the flow noise and velocity by using bigger duct work. Reducing air speed and the number of sharp right-angle turns also helps. In this case, modifying the long air exhaust ductwork down to the Basement Level 3 would be costly. Last, but not least, the greatest challenge is time. A resolution would need to be in place before students were back at school.

Client Details

As the public research university in the state, Virginia Commonwealth University’s mission is to advance knowledge and student success through its commitments to academic excellence and learner-centered environment. Hence the classroom environment, including sound quality, lighting and comfort are of paramount importance.