ASTM E90 & STC Ratings: How Lab Sound Tests Work

How ASTM E90 lab testing produces an STC rating, operable vs non-operable results, and why field performance (ASTC) is usually lower.

Last updated: November 2, 2026

Acoustic Doors · Last updated: 2 November 2026 · Jusen Doors Technical Team · Reviewed by Jusen Doors Engineering Team

ASTM E90 & STC Ratings: How Lab Sound Tests Work

Quick answer: ASTM E90 is the laboratory method used in North America to measure airborne sound transmission loss through a specimen; the resulting one-third-octave data can be classified as STC under ASTM E413. A credible STC report must say whether the door was tested operable with its seals or sealed non-operable into the test opening. The latter can describe the panel while overstating what the installed opening will deliver.

Inside the two-room laboratory test

The specimen is mounted between source and receiving reverberation rooms. Sound pressure and room absorption are measured across frequency bands to calculate transmission loss. Laboratory design suppresses flanking so the test focuses on the specimen. That controlled environment is exactly why lab STC should not be promised as a field result: real walls, junctions, ducts and installation gaps reintroduce sound paths the lab deliberately removed.

Operable versus non-operable specimens

An operable door test includes the actual frame, hinges, latch and perimeter/bottom seals in working condition. A non-operable specimen may be caulked or sealed at the perimeter to characterise the leaf. Both data types have uses, but procurement should price and compare operable assembly data. If a brochure quotes an impressive STC and the report shows permanent perimeter sealing or no latch, the number is not the opening being installed.

STC is a classification, not the raw test

ASTM E90 produces frequency-by-frequency transmission-loss results. ASTM E413 fits the STC contour and produces the single number. Two products with the same STC can sound different at bass or speech frequencies. For music rooms, traffic exposure or mechanical noise, request the TL curve or OITC where appropriate rather than relying on one speech-oriented rating. The report should also identify specimen area, construction and mounting.

Field STC/ASTC will usually be lower

ASTM E336 is used for field airborne sound attenuation between rooms, with ASTC expressing apparent performance in the building. Flanking through the surrounding wall, ceiling void, back-to-back outlets or a lightweight frame can cap the result. A project acoustic target should therefore include wall and junction design, not just a door label. Door seals must remain adjusted after flooring and hardware changes.

Read a door STC report in this order

Who tested it and under which standard editions?
Was the specimen operable and fully latched?
Which seals, threshold, frame and hardware were installed?
Leaf size, thickness, glazing and core identity.
Was the perimeter additionally sealed for the test?
Full TL data and STC calculation, not just a summary badge.

Specification checklist: what to confirm before ordering

Rating system named in the specification (STC, Rw or a field metric), with no informal conversions.
Laboratory evidence for the complete operable assembly, including frame and seals.
Wall, junction, duct and other flanking paths reviewed with the door selection.
Threshold or drop-seal detail coordinated with flooring and accessibility.
Adjustment and seal replacement included in the maintenance plan.

Related guides

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FAQs

Does ASTM E90 itself assign an STC number?

E90 measures transmission loss. The STC single-number classification is determined using ASTM E413.

Why is my installed STC lower than the brochure?

The product may have been tested non-operable, or field flanking and installation gaps may dominate. Compare the exact tested assembly with the built opening.

Is STC enough for traffic noise?

STC is weighted around speech frequencies. OITC or the detailed transmission-loss curve is more informative for low-frequency exterior noise.

Data note: Figures described as typical, common or planning ranges are industry budgeting ranges with the stated assumptions. Building-code duties, tested scope and final quotations depend on destination, selected construction and order schedule.