Laboratory Testing and Acoustic Trials — A Guide for Architects and Specifiers
What happens inside an acoustic test chamber, how STC and Rw values are derived, why laboratory values differ from field performance, and how to read a test report correctly when specifying a partition or movable wall system.
Acoustic performance claims in partition and movable wall specifications are only meaningful when they are traceable to a specific laboratory test of a specific configuration. A single STC or dB Rw number on a product data sheet — without a referenced test report — is not a specification value. It is a marketing claim.
This guide explains how acoustic laboratory testing works, what the ratings mean, and what you need to verify in a test report before incorporating a performance value into your project specification.
How Laboratory Testing Works
Acoustic laboratory tests for partition and movable wall systems are conducted in purpose-built paired reverberation chambers — two acoustically isolated rooms separated by a test aperture into which the partition specimen is installed. The test measures how much sound is transmitted from the source room (high sound pressure) to the receiving room (low sound pressure) through the partition.
Specimen Installation
The partition panel or movable wall panel assembly is installed in the test aperture under standardized conditions. For movable walls, the assembly includes the panel, seal system, track, and closure configuration — because all of these affect the measured performance.
Sound Source Generation
A calibrated sound source (random noise generator or loudspeakers) produces a diffuse sound field in the source room across the frequency range 100 Hz to 3150 Hz (1/3 octave bands per ASTM E90) or 50 Hz to 5000 Hz (ISO 10140).
Sound Level Measurement
Precision microphones measure the average sound pressure level in the source room and the receiving room simultaneously. The difference between these levels — adjusted for the receiving room absorption and specimen area — gives the Sound Reduction Index (R) at each frequency.
Rating Calculation
The R values across all 1/3 octave bands are fitted to a reference contour (ASTM E413 for STC, ISO 717-1 for Rw) to produce the single-number rating. The fitting method differs between the two standards, which is why STC and Rw values for the same specimen are not directly interchangeable.
STC vs. Rw — Technical Differences
ASTM E90 / E413 (USA)
- · Frequency range: 125 Hz to 4000 Hz (16 bands)
- · Contour fitting: E413 reference contour
- · Tolerance: Sum of deficiencies ≤ 32 dB
- · No adaptation terms — single value only
- · US, Canada, Latin America codes
ISO 10140 / ISO 717-1 (International)
- · Frequency range: 100 Hz to 3150 Hz (18 bands)
- · Contour fitting: ISO 717-1 reference curve
- · Reports Rw + C + Ctr adaptation terms
- · C: correction for pink noise spectrum
- · Ctr: correction for traffic noise spectrum
- · EU, UK, Australia, international codes
Never convert between STC and Rw using a simple arithmetic offset. The two rating systems use different frequency weighting, different contour-fitting rules, and produce different numerical values for the same physical specimen. Always request the test report in the standard applicable to your project jurisdiction and use that value directly in the specification.
Laboratory vs. Field Performance — The Flanking Problem
Laboratory test values are measured in ideal conditions: a rigid, acoustically isolated test aperture with no gaps, no flanking paths, and perfect installation. Field conditions are never ideal. The gap between laboratory and field performance is caused by flanking transmission — sound traveling around or through the partition via the floor slab, ceiling void, service penetrations, or poorly installed perimeter seals.
Typical flanking paths in office partitions
- →Sound through ceiling void above partition (if partition does not reach structure)
- →Sound through raised floor void
- →HVAC duct penetrations through partition
- →Electrical service boxes back-to-back in adjacent panels
- →Poorly installed perimeter seals leaving air gaps
How to minimize the laboratory-to-field gap
- →Specify partition to ceiling structure (not false ceiling)
- →Seal all penetrations with acoustic putty or mineral wool and flanking tape
- →Specify independent HVAC supply to each room
- →Avoid back-to-back electrical boxes in the same panel
- →Conduct field test (ASTM E336 or ISO 16283-1) after installation
How to Read an Acoustic Test Report
When reviewing a test report in support of a partition specification, verify the following:
The report must describe the exact panel configuration tested: panel thickness, core construction (mineral wool, glass, air), glass type and thickness, frame profiles, and perimeter seal type. If the specimen differs from what is being installed, the test value does not apply.
Confirm whether the test was conducted per ASTM E90 (giving STC) or ISO 10140 (giving Rw). For international projects, ensure the standard matches the code jurisdiction.
The test laboratory must be accredited by a recognized body (NVLAP in the US, UKAS in the UK, DAkkS in Germany, ENAC in Spain). Non-accredited laboratory results should not be used for compliance submissions.
Use only the most recent revision of the test report. Older reports may reflect product configurations that have been superseded. Confirm with the manufacturer that the current product matches the tested specimen.
The STC or Rw value is on the cover page. Also note the Rw + C and Rw + Ctr values (if ISO 10140) — for traffic-adjacent projects, the Ctr adaptation term may be the relevant specification value.
Request Acoustic Test Reports
Stylewall provides full laboratory test reports for each system and configuration. Request the report package for your project specification.
