Specifying sound measurement procedures
To get the results you want, engineers should be specific when testing for sound and vibration.
My father used to have a saying, "Be careful what you wish for, you might get it." The same holds true for sound measurement specifications. I've seen hundreds of sound measurement specifications that appeared to be copied from past projects or written without putting much thought into what information is needed and why. The end result is a sound report with no clearly defined pass/fail criteria or useful information.
Sound testing should be specified and performed on all projects. It is useful for establishing baseline data of building environments, and is useful for proving that the building systems have been installed and are operating from an acoustic perspective as designed. Sound testing also is useful for identifying any system or systems that are preventing the building environment from being in compliance with the project specifications . Most importantly, sound testing proves to the building owner that the building environment is in accordance with his or her project requirements .
Before developing sound testing specifications for any project, the following questions need to be asked:
• To what sound level was each area designed?
• What is the acceptable sound level for each area ( noise criteria or room criteria )?
• Which areas require testing? All areas, random samples of each room type, etc.?
• What is the purpose of the test being specified? Is the sound measurement solely to evaluate the HVAC system, or the building environment as a whole?
• What specific test procedures will be required? In what mode are the HVAC systems (and other building systems) to be operating in during the test?
At best, a poorly written sound specification results in additional time for the design team and testing firm in project correspondence (writing and answering requests for information, etc.). At worst, a poorly written sound specification results in a project with incorrect testing procedures, which leads to failed test results. This creates the illusion of a problem where the reality is that the building functions normally within the design criteria.
Be careful when specifying the test procedures to be sure you are testing the system as it is intended to be operating. Testing in the noisiest mode is not always necessary or wise. For example, some variable air volume systems are noisiest in the morning warm-up mode, but that mode usually does not occur when the building is occupied. Testing a system in this mode can result in a failed test result, even though the system complies with the criteria under "normal" operating conditions.
Remember when using this specification that it should be modified as necessary to be applicable to your project. My father was right--make sure you are asking for what you want (and need) now. It makes life a lot easier when you actually get it.
Huber is president of Complete Commissioning where he is responsible for the overall operations of the company. As a NEBB Certified Professional, he has extensive experience both in sound and vibration modeling, measurement, and troubleshooting for new and existing facilities.