Volume 49, Issue 7 - July 2014

feature

Sound Advice
Ten Things to Know About Acoustical Testing
by Brian Stahnke and Douglas F. Winker

 

"You are the expert in the products you send in for testing. The lab staff should be experts in acoustical testing and accurately report testing results for the specimen provided."

How well do you know your windows? If you have never tested them at an acoustical testing laboratory, you probably don’t know them as well as you should. The information gained from acoustical testing is an essential part of architectural specifying and manufacturing and can have an impact on your clients’ satisfaction, contracts and bottom line. Testing shows the acoustical performance of your window and easily identifies leaks and underperformance that can lead to unhappy customers and possibly legal actions. Typically, architects call for Sound Transmission Class (STC) ratings for windows and other noise isolation partitions in buildings; these ratings come from an ASTM E90 test that can only be conducted in a test laboratory. In trying to satisfy ratings requirements, many manufacturers overdesign their products to ensure conformance. A series of laboratory tests with detailed results can identify components that can be modified or even eliminated to meet the needed performance. The end result could likely add up to significant cost savings for a product line.

So what do you need to know to get your money’s worth out of acoustical testing? Following are some tips to ensure a successful acoustical test experience.

1 Use a testing laboratory that is third-party accredited to test to the latest requirements of a specific standard, such as ASTM E90. Examples of widely accepted accrediting bodies are the National Voluntary Laboratory Accreditation Program (NVLAP), the American Association for Laboratory Accreditation (A2LA), and the International Accreditation Service (IAS). Accreditation is a demanding but extremely important process for any testing laboratory. Accreditation is designed to guarantee that the laboratory has a quality program that helps assure results provided to you are verified, open to audit, and meet all requirements of the test standard. These accrediting bodies also ensure that all testing equipment is within current calibration intervals to ensure proper measurements. If you would like to know more about equipment calibration, you can ask to see laboratory accreditation and equipment calibration records.

2 Choose a lab with demonstrated quality procedures and oversight; accredited laboratories are independently verified to have well-documented testing procedures. This is very important as technical competence alone is not enough to be considered a superior acoustical laboratory. A reputable quality policy ensures that staff is well trained and tests are repeatable and reliable. A good example is ISO 17025: 2005, a thorough and rigorous quality program. It is subjected to internal audits on both a scheduled and unscheduled basis. These audits are detailed and company management is required to follow any findings and resolutions. In addition, external assessors that are expert in the acoustical field visit each accredited laboratory biannually. The National Institute of Standards and Technology (NIST) ensures that these assessments are thorough, both from a documentation and technical basis. The unofficial slogan of “continuous improvement” is something that all testing laboratories should
take to heart.

3 Pick your laboratory with care and foresight.
Many acoustical testing laboratories test for both internal and external clients. Talk to the laboratory staff to confirm that they treat both internal and external clients in the same manner; that is, the same level of service, integrity of staffing, and confidentially of results are unmistakably maintained throughout the process. It is essential that all results and data are stored separately from other computer users to maintain control of this confidentiality. Accrediting bodies assure confidentiality of client results to protect your product. With strict controls in place, any experienced acoustical lab can function as an independent test facility for your needs. The performance of the products a lab tests should be just that — a metric that stands on its own irrespective of any specific job or past performance claims.
This is the only fair and impartial way to test for all laboratory clients.

4 Select a lab where you are welcome to visit, participate in, and witness the test program. At the end of the program you should feel confident in the laboratory’s capabilities and have a better understanding of the STC rating that your product received. Be sure to ask questions about any part of the testing process that you do not comprehend and expect a technical but understandable answer.

5 Ensure the lab’s confidentiality program is verified by a third party. A top quality laboratory should have a vigorous, established confidentiality program. At all laboratories, the information, data, and accredited reports are yours alone. You paid a fee for these testing services and you own the results. For your product’s protection, make sure that the testing lab cannot discuss or disseminate in any manner these results to others without your prior written consent.

6 Know that the testing laboratory will produce signals of over 100 dBA to measure your specimen. This high level is needed to ensure test results are not biased due to facility limitations. Sounds used to test the products are closely controlled by the test standard, such as ASTM E90. Know that these test signals will not sound like something you’d expect (traffic, railroad, aircraft noise, etc.). The specific noise spectrum is designed to ensure that the fenestration product being tested is equally subjected to noise at all frequencies so that the specimen’s acoustical performance strengths and weaknesses are ascertained without bias to the test signal.

Efficient and Cost Effective Acoustical Testing
Now that you’ve selected your test lab using the criteria above, below are a few tips to get the best return on your investment in the acoustical testing of your product.

1 Accurately describe the product to be tested. This is crucial to the credibility placed on the product by you and, ultimately, your clients. You are the expert in the products you send in for testing. The lab staff should be experts in acoustical testing and accurately report testing results for the specimen provided. Laboratory staff should be deemed proficient in the specific test methods you are requesting to guarantee proper measurements and precise results. It is the laboratory’s responsibility to confirm independently as much information about the products as is technically feasible. There should be no ambiguity in what was tested and what was reported. Sometimes the laboratory will seek your help with specimen information that is specific to your industry.

2 Request a detailed testing proposal that clearly defines the scope of work being contracted. Communication is key before the test program begins or is undertaken to ensure that everyone has the same understanding. The test proposal should cover all window configurations you anticipate testing, clearly define pricing, and allocate appropriate time for the test series. The test plan agreed upon by you and the laboratory should demonstrate knowledge and foresight by the lab on proper specimen handling and give you a clear point of contact for the day of testing. Having a formal proposal and agreed upon test plan make the entire test program much quicker and more efficient.

3 Provide testing specimens of the size requested and stated in the mutually agreed upon proposal. Most laboratories have specific window size test capabilities and deviations from the agreed upon size can delay testing your product. Efficient labs have specific sizes to increase throughput of test samples. Ask for the lab’s specimen throughput and price advantages for multiple tests of the same size and type. Remember to supply all associated hardware for operation and set-up shipping/specimen return instructions. Good communication between you and the laboratory will ensure that test results are received in a timely manner.

4 Review, evaluate and approve test results individually. It is important to know that all test results apply only to the sample tested. The graph above shows the graphical test results for a well-defined sample window specimen; it is important to discuss anything you don’t understand about the transmission loss curve and test report with your testing laboratory. Remember that significant effort goes into testing before the test specimen arrives on-site. Quality assurance initiatives, calibration programs, and proficiency test programs ensure the test equipment is ready to use and the personnel are continually trained and provide exemplary service, which are all part of your window ratings.

Once you are onsite at your test lab, be patient and keep in mind acoustical testing involves much more than the time the data is collected. The pivotal part of a product test takes under 30 minutes in most labs once the test is set up. Much more time is normally spent on receiving the specimen, uncrating it, ensuring appropriate climate acclimation, properly mounting the specimen in the test opening, and sealing the specimen in place so as not to influence the results. These are all activities that are part of the final acoustical test. After testing is complete, laboratories can provide preliminary test results the same day. If final reports bearing the accrediting body’s logo are requested, these should be available within two weeks.

These tips have been provided to aid in the selection of a quality acoustical test lab and help prepare manufacturers for cost-effective use of their test time on site at the acoustical laboratory.

Acoustical testing can be an expensive undertaking, but expenses can be minimized by selecting a credible acoustical testing lab and adequately preparing for the test in advance. In addition, quality test results can determine if you are overdesigning a product to pass industry standards; in which case, product designs may be revised to lower manufacturing costs.

Brian Stahnke is a laboratory engineer at ETS-Lindgren’s Acoustic Research Laboratory.
Dr. Douglas F. Winker is the acoustics product line manager for ETS-Lindgren.


A Glance at OITC vs. STC Ratings

Almost all fenestration products provide both Sound Transmission Class (STC) and Outdoor-Indoor Transmission Class (OITC) ratings, but the former is the inherited and informal standard—despite what might be its shortcomings.

While the range in which both ratings are calculated goes all the way to 4000 hertz (hz), there is a significant difference between the two on the lower end.

STC is calculated from 125 hz and up, while OITC uses frequencies all the way down to 80. Because of that, OITC is more precise as it encompasses a wider frequency range. And the lower-end of the spectrum is especially important when looking at sound transmission loss from the outside buildings to in. Hence the name.

According to information from Architectural Testing Inc., STC was created to provide a rating for interior building partitions subjected to mid- to high-frequency noises, such as speech and radio, while OITC was created to provide a rating for exterior walls, doors and windows subjected to low- to mid-frequency noises caused by cars, trains and airplanes.

Still, STC rules the roost in North America despite the advantages of OITC.

“The industry is somewhat split on this,” says Valerie Block, senior marketing specialist at Kuraray America Inc. “The proper use of the OITC would be to look at sound transmission loss from outside the building to in. But everybody is very comfortable with STC, and, for most people, it’s the most commonly asked for form.”

Adds Kolbe & Kolbe product and marketing manager Lance Premeau, “STC is kind of just the general term used in the industry … Most window and door manufacturers will report both, but in my opinion, people just associate with STC.”

OITC has, however, built somewhat of a presence in U.S. metropolitan areas. New York City for example has used OITC requirements in its building department regulations and technical manual in the last ten years.

“Basically there are parts of the city where there’s a certain sound attenuation requirement for people living in that area or working in that area,” says Block. “They made this transition (to OITC) because they knew they were looking at this relationship between outdoor noise and sound attenuation in inside space.”

According to a report, in 2011, most cities have “gradually made the transition from the STC metric to the OITC metric for building façade design evaluation,” but New York’s implementation of OITC in its technical manual is the “first time this design requirement has been officially prescribed.”

—Nick St. Denis

Differences Between STC and OITC Ratings
Calculated in accordance with…

STC: ASTM E413 (Originally published in 1970).
OITC: ASTM E1332 (Originally published in 1990).

Created to provide single number rating for…
STC: Interior building partitions that are subjected to noises from speech, television, radio, office equipment and other mid to high frequency noise sources.
OITC: Façades (exterior walls) and facade elements (windows and doors) that are subjected to transportation noises (aircraft, trains, automobiles, and other low to mid frequency noise sources).

Calculated over frequency range of…
STC: 125 to 4000 hertz.
OITC: 80 to 4000 hertz.

Calculated by…
STC: Comparing the measured sound transmission loss to a reference contour curve.
OITC: Subtracting the logarithmic summation of the transmission loss values from the logarithmic summation of the A-weighted transportation noise reference spectrum. n Source: Architectural Testing Inc.

Source: Architectural Testing Inc.

 

 

 

 

 


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