Focus on Acoustics: Containing Fan and Duct Noise

By Steven J. Thorburn, PE, CTS-D, CTS-I
Thorburn Associates

edit-acoustic-0110During a recent tour of an existing campus, we were shown a classroom that was in the process of having a complete, bells-and-whistles audiovisual package installed to support a distance learning program. However, our project meeting quickly took an unscheduled detour when we noticed an acoustical issue with the space.

The issue was you needed to be within six feet of the person speaking to be able to understand what they were saying. The fan that supplied the air for that wing of the building was located directly over this room, creating sound levels that masked over the speaker and making their speech unintelligible. Until the rumble from the ductwork and the hiss of air flow is properly mitigated, the client is not going to be get full value from their AV investment.

The only way to fix this issue at this point in the project is to remove the ceiling and rework and box the duct work. This can be very costly and is obviously it’s the kind of thing one wants to try to anticipate and avoid, if possible, in the first place. Next best is to discover and resolve it during the construction phase. That’s where dialogue at an early stage of the process can really save the day. Members of the core team — the audiovisual designer, the acoustical engineer, the architect, the project manager — should be asking questions and sharing an understanding about how a room is going to be used, before it is built. The next best scenario, although less than desirable, is to discover and resolve these issues during the construction phase; however, this can lead to dealing with change orders that result in unnecessary expenses.

In the case of this particular building, the as-built drawings showed that there was an adjacent restroom, and by lengthening the ducts, the fan units could have been positioned over that less sensitive area. There are a number of tricks and methods available, including silencers, shaft enclosures, double wall duct or just plain heavier gauge duct work to reduce noise from the HVAC system. As always, your acoustical consultant can help you decide the best option for your scenario.

Steve enjoys helping others understand the principals of acoustics and audiovisual technology almost as much as he enjoys sipping a good single malt scotch.  He’s been InfoComm’s Educator of the Year, is a two-time InfoComm Facility Design Award Winner, author, teacher and has AV design experience on more than 2000 projects including Universal Studios Toon Lagoon, Hershey Park and Six Flags Great America. Find his company Thorburn Associates online at http://www.TA-Inc.com