Misleading Acoustical Information

Green Glue & SilentFX

Many people look for solutions to soundproofing problems online, hoping to be able to resolve their problems themselves without hiring an expert. This is often difficult because there are many cases of misleading information published online by soundproofing product manufacturers, for example, Green Glue.


Misleading manufacturer's information

An example is information provided for Green Glue, a popular and useful noise-damping compound. Looking at the manufacturer's product test data online, this assembly consists of:
5/8" Drywall
Green Glue Compound (2 tubes/sheet)
5/8" Drywall
Wood 2" x 4" Studs // 24" o/c
R13 Fiberglass
5/8" Drywall
has sound attenuation as described below.

An independent lab tested this assembly as having sound attenuation of STC 52. Most people will assume that any wall with wood studs with this assembly will have the stated sound attenuation.

However, most walls have 16 inches of stud spacing, not 24, and the Green Glue information does not provide data about this spacing. I believe this is deliberate to present the maximum possible value, even if misleading.

Note: Green Glue company no longer publishes test data online.  Third-party records are referenced here.

Assembly with Green Glue

Comparison of Green Glue with SilentFX acoustical drywall

Since the manufacturer does not provide sound attenuation value for 16 inches stud spacing, I must search further. I have previously documented that Green Glue assembly performs similarly to assembly with acoustical drywall, such as SilentFX or QuietRock. Looking at data for SilentFX acoustical drywall welwe see that a similar SilentFX assembly with 24” stud spacing provides STC 51, but an assembly with 16 inches spacing provides only STC 45. We know that assembly with Green Glue will perform similarly. There is a big difference between 51 and 45! Assembly with Green Glue on studs with 16 inches spacing will provide a similarly low value as the SilentFX assembly. Another point of interest is that if only ½ inch drywall is used in the assembly instead of 5/8 inch, the STC value is only 41. There is a reason Green Glue company does not publish this result. For comparison, a similar assembly without Green Glue will provide STC 36 to 37.

Always be suspicious of information omitted by a manufacturer of soundproofing products. Usually, there is a reason behind the omission. By comparison, the information for SilentFX acoustical drywall, previously mentioned, provides much more complete information for an extensive range of assemblies.

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About the Author Ivan Koval

The author is the publisher of the Soundproofing.Expert website. He is a soundproofing and building acoustics consultant working in Toronto and GTA, Ontario, Canada. Telephone (416) 471-2130

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