Noise reduction coefficient
Sound absorption performance of a material
The noise reduction coefficient (commonly abbreviated NRC) is a single-number rating intended to describe the average sound absorption performance of a material, derived from reverberation-room measurements. In common usage it is reported on a scale from 0.0 (very low absorption) to 1.0 (very high absorption), though values greater than 1.0 can occur in reverberation-room testing due to measurement effects such as edge diffraction and non-ideal diffuse-field conditions rather than “more than 100%” absorption.
NRC should not be confused with the sound transmission class (STC), a single-number rating derived from laboratory measurements of airborne sound transmission loss through building elements (for example walls, doors and windows). In general terms, STC relates to sound transmission loss through a construction element, while NRC relates to sound absorbed within a room by surfaces and treatments, such as to dampen echos and reverberations.
Technical definition
The noise reduction coefficient is "a single-number rating, rounded to the nearest 0.05, of the sound absorption coefficients of a material for the four one-third octave bands at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz". (note: it is commonly assumed that NRC is calculated based on the arithmetic average of the octave band absorption coefficients; however this is not in accordance with the ASTM C634-22 definition). The absorption coefficients of materials are commonly determined through use of standardized testing procedures, such as ASTM C423 that is used to evaluate the absorption of materials in eighteen one-third octave frequency bands with center frequencies ranging from 100 Hz to 5000 Hz. Absorption coefficients used to calculate NRC are commonly determined in reverberation rooms of qualified acoustical laboratory test facilities using samples of the particular materials of specified size (typically 72 square feet [6.7 m2] in an 8 ft × 9 ft [2.4 m × 2.7 m] configuration) and appropriate mounting.
In reverberation-room methods, absorption coefficients are derived from changes in measured reverberation time between an empty room and the room with the test specimen present; NRC is then reported as a rounded average of the selected one-third octave band coefficients.
History
Wallace Clement Sabine was the first scientist to study the sound-absorbing characteristics of materials in a scientifically rigorous manner.
Begin with the source’s own compact description: “Noise reduction coefficient” is sound absorption performance of a material. The dossier treats that line as a proposition to test through Noise, reduction and coefficient, not as a finished interpretation.
Why this record matters
The phrase “sound absorption performance of a material” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Aug 21, 2026. The linked authority identifier is Q17083791. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1000 and 2000.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Noise reduction coefficient”, its source revision and the description used here.
- Expand the search: follow Noise reduction coefficient primary sources, Noise reduction coefficient archive and Noise research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Noise reduction coefficient”?
- Which institution is responsible for the underlying evidence?
- Which cited source is closest to the event, object or claim?
Search terms from this dossier
This entry incorporates text from “Noise reduction coefficient” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.