If you request an STC test on an operable wall from a supplier , how do you know that it accurately reflects or proves the walls ability to stop the transfer of sound? Most reviewers will simply look at the STC number, the higher the better, and confirm that they recognize the manufacturer. Yes? - OK. Good to go. But there is far more to consider. You should carefully look at the test reports contents and compare it to what the test procedure requires to be included in the test report. Look at "what" was tested. Consider the following. Notations in italics - ".." - are direct quotes from ASTM E-90.
Determine the reliability of the Sound test and the STC reported. Questions you should ask
- By what name is the tested specimen identified? If identified as an "operable wall or operable partition" this is acceptable. If by any other name such as a "wall assembly" the test should be regarded as suspect and rejected as not being on an "operable wall or operable partition". It may be on a demountable wall.
- Identify the test procedure. ASTM E-90 alone is not acceptable. Only test ASTM E-90-99 (any tests conducted prior to 1999 should be rejected) and later test procedures and results should be regarded as acceptable and a credible indicator of acoustic quality and conducted on product that is currently manufactured as described.
- Was the sound test conducted in an independent laboratory preferably "NVLAP" accredited and not in a lab owned by the manufacturer; "Independent" is the operative word.
- "..unless the test sponsor wishes to withhold information of a proprietary nature". The test procedure rightly allows sponsors to exclude for obvious reasons, some design and material information. But this exclusion clause is vastly overused and abused. Basic information necessary for a proper evaluation is often left out. Question the manufacturer as to "why" the exclusions especially when it often subsequently appears in the manufacturers published literature. Ask to see the missing information.
- "Because transmission loss is a function of frequency, measurements are made in a series of frequency ranges". In other words the transmission loss - reduction in noise through the partition - varies depending on the frequency. Sound reduction is not uniform. STC is not always a reliable indicator of what you require.
- "…sound ratings obtained using this test method do not relate directly to sound isolation in buildings; they represent an upper limit to what would be measured
in a field test". Because the sound test indicates an STC of 50 (for example) it does not mean that you will get an approximate 50 dB transmission loss through the partition. The transmission loss in the field will be considerably less - usually 10 points less (a TL of 40)
Test Specimens. It is critical to review what was actually tested to ensure that the test was conducted on an "operable wall or partition" specimen.
- "…any test specimen that is to typify a wall shall be large enough to include all the constructional elements in their normal size and in a size and in a proportion typical of actual use". Description should indicate the number of panels, that they were operational, include wall jambs, track and trollies, vertical and horizontal seals, final closure method. If this information is lacking or not included then the veracity of the test is suspect. Ask for information on the missing components.
- "sufficiently detailed to identify the specimen at least for those elements that may affect its sound transmission loss" Does the detailed description clearly identify to your satisfaction those features and elements that are needed to inhibit the transfer of sound? Is the test vague and lacking in detail? Ask questions.
- "the use and type of caulking, gaskets, tape or other sealants on perimeter or interior joints shall be clearly described" Does the sound test describe in satisfactory terms and detail how the specimen was installed in the test opening and what if any additional products and techniques were used to possibly inflate the final STC number?
- "..minimum dimensions shall be 2.4 m…" "Preformed panel structures should include at least two complete modules (panels plus edge mounting elements)…" These two criteria allow a manufacturer to test as few as 2 panels each approximately 8' tall (2.4m) and 4' wide (standard width) for a total of 64 sq. ft. For years the industry standard test size has been 9' tall by 14' wide (4 panels) for a total of 126 sq. feet. In our opinion this size (9' X 14') allows for the inclusion of all constructional elements required to provide a true test of the partition acoustics. Any size less than 9 X 14 is suspect and may provide an inflated STC number. Demand a 9' X 14' test specimen.
- "…report as much information as will allow a clear understanding of how the specimen was constructed" How was the panel made and what materials were used in its construction and assembly? You have to be able to confirm that the panels you are receiving match the description in the test procedure. Ask for the missing required information.
- "Report as much physical information as can be determined about the materials and method of assembly of all components of the partition including weights
and dimensions of the component parts…". You have to know what it is you are buying! Is the product description sufficient?
- "The specimen shall not be designated an operable wall unless it opens and closes in a normal manner. It shall be fully opened and closed at least five times after installation is completed and tested without further adjustments". This statement has to be included in the description. If missing then it is not an operable wall! If it is not there then the specimen cannot be identified as an operable wall.The bottom line is that you have to read the entire test procedure, not just the number. If you have any questions or wish to discuss Moderco sound tests call us at 1 800 363 3150