Volume 49, Issue 7 - July 2014
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
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
3 Pick your laboratory with care and foresight.
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
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.
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.
Brian Stahnke is a laboratory engineer at ETS-Lindgren’s
Acoustic Research Laboratory.
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
Differences Between STC and OITC Ratings
Created to provide single number rating for…
Calculated over frequency range of…