Acoustic performance of glass partitions: questions to ask of your acoustic test certificate

You’re writing a specification for glass walls and your acoustic consultant has advised you to select a system that achieves a particular Sound Transmission Class (STC) rating. A manufacturer has provided acoustic test evidence, but how do you know it is relevant to the system you are specifying?

Q1. Does the test apply to a representative glass wall assembly?

First, check the dimensions and configuration of the test sample.

Glass walls are full-height assemblies that would normally comprise multiple panes of glass, perimeter framing and glass-to-glass joints. A result obtained from testing a much smaller glazing sample should not be treated as directly equivalent to the performance of a complete multi-module wall assembly.

PurOptima tests representative multi-module assemblies so that the influence of the framing and glazing joints is included in the result.

Q2. Was the system tested using an appropriate laboratory method?

For an STC rating to provide meaningful evidence, the test method and test conditions need to be clearly identified.

In the US, laboratory testing of airborne sound transmission through building partitions may be carried out in accordance with ASTM E90, with the resulting data classified in accordance with ASTM E413 to determine the STC rating. PurOptima also holds test evidence produced to ISO 10140, with the recorded data classified to ASTM E413 where STC values are reported.

The test report should therefore make clear what was tested, the method used and the configuration to which the stated STC rating applies.

Q3. Is the rating tested, assessed or estimated?

Not every possible system and glass combination can practically be laboratory tested, so it is important to understand the basis of the stated performance.

Tested performance is based on physical laboratory testing of the stated configuration.

Assessed performance may be used for some configurations where an independent acoustic consultant has considered physical reference tests using the same system and glass types.

Estimated performance may be used for certain single-glazed configurations where the framing, gaskets and glass engagement remain the same and the principal variable is the glass specification.

These different evidence types should be clearly identified rather than presented as though they are all direct laboratory test results.

Software modeling alone should not be treated as equivalent to physical laboratory test evidence. PurOptima’s approach to assessed performance requires reference to physical test data rather than relying solely on modeling.

Acoustic test report checklist

Before relying on an STC rating, check:

• Was the system physically laboratory tested?
• What test method was used?
• How large was the test sample and how was it configured?
• Did the sample include representative framing and glass joints?
• Does the glass specification match the system you intend to specify?
• Is the stated performance tested, assessed or estimated?
• Is there clear evidence supporting the stated STC rating?
  
  

Acoustic performance should always be linked to the specific configuration and evidence behind it. Asking these questions early helps ensure that the STC value being compared is relevant to the glass wall system being specified.