Situation #1 :
A guy walks into a GM dealership and asks: “What mileage does a Chevrolet get?” Sales man hands him a piece of paper on a GM letterhead saying “Chevrolet” which indicates that the car described gets 53 mpg on the highway and 44 mpg in the city for a combined 48 mpg. The guy says “Great. I’ll take one” and drives away. The problem is that the piece of paper is dated 1986, the car is a Chevy Sprint designed and manufactured 27 years ago, had 3 cylinders, a 1 liter engine with a manual transmission and was only made for 2 model years.
Situation #2 :
A guy asks a prominent operable partition manufacturer “What STC is your partition?” Manufacturer/distributor provides a test result showing name of company and an STC number of say 52. “Great! I’ll specify/buy/use it”. The problem is that the test was conducted in 1994 in a laboratory that is no longer in business, using a test procedure developed in 1990 and describes a product that the manufacturer obviously no longer makes as described because the partition design is almost 20 years old.
Can this happen?
Situation #1 – never!!! Situation #2 – happens on a regular basis.
The moral of the story: “Just because it is written down does not mean it is true.” If you are purchasing/specifying an operable partition with acoustics being one of the important criteria then you have to carefully read the entire sound test. Here are some items to consider
- Ask for a complete copy of the most recent sound test conducted on a partition that is the most similar to the model that has an STC value that you intend to use or specify.
- Confirm that the name of the company for whom the sound test was conducted is the same as the company that you intend to use or specify. Also that the name of the testing company is on the test along with confirmation that the testing laboratory is NVLAP accredited. NVLAP is an acronym for National Voluntary Laboratory Accreditation Program.
- Understand that “ASTM E-90” by itself is not a sound test. It is the original (1961) “standard test method” around which the sound testing is based. The “sound test procedure” that determines the method of testing for the STC of the partition will be indicated by the pre-fix “E-90” followed by a suffix that identifies the year in which the test was accepted by the E-90 committee: example “E-90-09”. E-90-09 then becomes the test procedure used to determine the STC number. Other than in 1961, E-90 by itself is meaningless. When looking at a sound test, look for E-90 followed by a number that indicates the year of approval by the E-90 committee
- A general rule is that only the last 4 tests - currently ASTM E-90-99, E-90-02, E-90-04 or E-90-09 - should be considered as acceptable. According to a study conducted at a prominent Independent NVLAP Testing facility, a manufacturer retesting a particular model under each succeeding revision of ASTM E-90 would find a lowering of STC results (from 2 to 5 levels) because the standard continues to improve, evolve and change. Read the test report to determine the test procedure used to acquire the STC number. If as of today, it is prior to ASTM E-90-99 then it is suspect.
- The current ASTM E-90 standard test method is 15 pages in length the majority of which is technical in nature, explanations & definitions. The parts that are germane to operable partitions in particular are limited.
The specific size that a test specimen must be is not defined other than to say it must be large enough to include all essential constructional elements in their normal size and in a proportion typical of actual use, the minimum dimension of the specimen shall be 2.4 m (7.87 feet), there must be at least two complete modules (panels) and the specimen installed in a manner similar to what would occur in the field. It is a common belief that test specimens must be 9’ tall X 14’ wide and that there must be a minimum of 4 panels plus a closure. This is not true. You can, as noted above, test a 2 panel specimen, sealed at both ends with fixed jambs with each panel being approximately 47.5” wide and acquire an STC number.
This test specimen could be approximately 62 square feet and have a total of 23.6 L/F of seam (potential places for transfer of sound) between panels or between panels and fixed walls. Compare this to Moderco’s 9’ X 14’ test specimen (which is the size that is most often specified and used by manufacturers) with 4 panels. It is logical to assume that the test using the smaller specimen will achieve a higher number than the larger specimen. Check the test specimen size and the number of panels.
Conclusion. Read more than the name and number! When test was conducted, the test procedure, where it was conducted and the size of the specimen should be determined before you accept the test as an indication of acoustic quality.