ASTM E90 Explained: How the Test Produces STC Ratings

ASTM E90 is the laboratory test that rates how much airborne sound a wall or other building assembly blocks. The current edition is E90-23.

One drill behind a thin partition can empty a hospital waiting room. We build reusable temporary walls for occupied buildings like that, so we read a wall’s E90 report before we spec it. Here's how the test produces an STC rating and how to specify one for your project.

What Is ASTM E90?

ASTM E90 is a test method from ASTM International that reports transmission loss, the decibels a specimen removes from sound passing through it.

The method covers everything from operable partitions to roofs, so one standard tests a temporary wall and the door set into it.

ASTM lists E90-09(2016) as historical in its store, so a report citing it predates the latest version. Name the edition on every submittal, so reviewers know which version the lab followed.

How the ASTM E90 Test Works

An E90 test isolates the specimen between two reverberation rooms and measures how much sound it strips out on the way through. Five things make that measurement work:

1. The specimen, sealed in place. Technicians install the wall in the opening and seal the perimeter to match real construction. Walls must measure at least 2.4 meters (about 8 feet) in each direction.

2. The only sound path. Labs design the rooms so the specimen forms the only significant route for sound between them.

3. A diffuse source field. A sound source creates an approximately diffuse (evenly spread) field in one room. The specimen then carries energy into the other room.

4. Levels on both sides. Microphones record space- and time-averaged sound levels on each side. Technicians also measure the receiving room's absorption and background noise.

5. Transmission loss per band. The lab converts those readings into decibel loss for each one-third-octave band, using the specimen's area and the receiving room's absorption.

The finished report plots the curve from 100 to 5000 Hz, and engineers calculate single-number ratings from it.

ASTM E90 STC Ratings by Wall Assembly

ASTM E413 converts E90 results into one STC number. The lab slides a reference contour against the test data across 16 frequency bands from 125 to 4000 Hz.

A contour fits when total shortfalls stay at or below 32 dB and every band stays within 8 dB. The highest fitting contour sets the STC, which is its value at 500 Hz.

Lab values for common ⅝″ drywall assemblies run from STC 33 to 57.

ASTM E90 vs. Field Testing and Related Standards

ASTM E90 is a laboratory test, so its ratings run higher than the same wall measured in the field. The standard sends field testing to ASTM E336, which measures sound between real rooms and counts every path.

Flanking, where sound travels around the wall through the surrounding structure, makes field results land lower. E336 reports the apparent loss, which runs below the wall's actual performance.

STC starts at 125 Hz, so it tells you little about bass. If low-frequency equipment will run behind the wall, ask the lab for the loss values in the lowest bands it reports.

E90 only measures airborne sound, so other standards cover the rest. E492 rates impact sound through floors as IIC. E1332 turns E90 data into OITC, which rates how well a facade element reduces transportation noise and counts bands down to 80 Hz.

RealWall and FireblockWall Sound Ratings

RealWall™ foam core cuts renovation noise by up to 50% (STC 21), based on ASTM E90 laboratory testing. Top and bottom gaskets and tongue-and-groove joints seal the panels. It also carries ASTM E84 Class A for flame and smoke, which is a material rating separate from fire resistance, so RealWall itself isn’t a fire-rated wall.

RealWall has kept noise down on real occupied jobs. At Sarasota-Bradenton International Airport, Modular Wall Solutions used it for noise control around a 30-foot-atrium escalator renovation, and passengers walked past the double doors while crews cut through structural slab on the other side.

At Fresenius Medical Care’s Waltham headquarters, J. Calnan & Associates ran a three-phase, fast-track build-out with RealWall between the work and occupied offices, and staff kept working nearby without hearing it.

When a job needs fire rating too, FireblockWall™ is the first reusable one-hour fire-rated wall, tested to ASTM E119 and ASTM E84. It still reaches STC 40, between a batted wood-stud and a batted metal-stud wall in the table above, so it delivers moderate noise reduction while meeting fire code.

How to Specify Sound Performance for Temporary Walls

Run these five checks before you approve a wall:

1. Find the owner's target. Hospital sound management targets can start with the FGI Guidelines, which set minimum composite STC at 45 between patient rooms on the same floor and 60 between an operating room and an MRI room. Use those permanent-wall minimums as a benchmark for temporary walls.

2. Request the E90 report. Confirm the lab's accreditation, which ASTM spells out in Annex A4. Results apply most directly to similar specimens in similar sound fields, so ask whether the tested wall included your doors and joints.

3. Pair it with the fire report. Fire ratings come from separate third-party testing, so ask for that report beside the E90 report on any rated wall.

4. Add a margin. Building codes typically allow a 5-point tolerance between lab STC and field results, so specify a lab rating 5 points above your site target. A site target of STC 45 means a lab rating of 50. Put an E336 field test in the contract when the owner sets noise limits.

5. Match the wall to the driver. Pick RealWall for long-term, high-visibility renovations where noise control and finish drive the spec. Pick FireblockWall when code calls for a one-hour fire-rated temporary wall.

Match an ASTM E90 Target to a STARC Wall

Lab STC runs higher than field STC, so spec a wall a few points above your target and confirm it covers your doors and joints.

Tell us the STC you need and the space you’re protecting, and we’ll match you to a STARC system that holds up on site and goes back up on the next occupied job. Request a quote and we’ll take it from there.

Frequently Asked Questions

What does an STC rating mean?

An STC rating scores how well a wall assembly blocks speech-range sound, and higher numbers block more. At STC 25, you can understand normal speech through the wall, and at STC 50 only very loud sounds come through.

What is the ASTM E413 standard?

The ASTM E413 standard is the classification for rating sound insulation, and its single-number result is the STC. It works from the one-third-octave data an E90 test produces.

How to calculate STC rating?

To calculate an STC rating, take E90 transmission loss for 16 bands from 125 to 4000 Hz and fit the highest E413 contour that keeps total shortfalls at or below 32 dB, with every band within 8 dB. The contour's value at 500 Hz is the STC.

What are typical STC ratings for batt insulation?

Batt insulation typically adds about 3 to 6 STC points to a framed wall, lifting a 3⅝″ metal-stud wall with ⅝″ drywall from STC 38–40 to 43–44.

Where can you get the ASTM E90 PDF?

You can get the ASTM E90 PDF from the ASTM store, which lists E90-23 as the active edition.