Reference
Acoustics glossary
The terms that appear on an acoustic panel's test report and in a specification — defined in plain English.
Absorption coefficient (α)
The fraction of sound energy a surface absorbs rather than reflects, from 0 (fully reflective) to 1 (fully absorptive). It is measured separately in each frequency band, because most materials absorb high frequencies far better than low ones.
αw (weighted absorption coefficient)
A single-number rating to BS EN ISO 11654, derived by fitting a reference curve to a material's measured absorption values. Reported in 0.05 steps from 0.00 to 1.00 — the headline figure most acoustic products quote.
NRC (Noise Reduction Coefficient)
A single number that averages the absorption coefficients at 250, 500, 1000 and 2000 Hz, rounded to the nearest 0.05 (ASTM C423). The North-American counterpart to αw; the two are similar but not identical.
SAA (Sound Absorption Average)
The ASTM successor to NRC — the average of twelve one-third-octave bands from 200 to 2500 Hz, giving a more detailed single-number rating.
ISO 354
The reverberation-room test method that measures how much sound a material absorbs across frequency bands. It is the source measurement behind every αw and NRC figure.
BS EN ISO 11654
The standard that converts ISO 354 measured values into the single-number weighted coefficient αw and a sound-absorption class from A to E.
Absorption class (A–E)
A BS EN ISO 11654 rating band: Class A (αw ≥ 0.90) is the most absorptive, down through B, C and D to Class E. A quick way to compare products without reading every frequency.
Reverberation time (RT60)
The time it takes for sound to decay by 60 decibels after the source stops. The primary measure of how 'live' or 'echoey' a room is, and the number most acoustic treatment is designed to control.
Sabine's equation
RT60 = 0.161 · V / A, relating reverberation time to a room's volume V and its total sound absorption A. Adding absorptive panels increases A, which lowers RT60.
Euroclass (reaction to fire)
The BS EN 13501-1 classification of how a product reacts to fire — A1, A2, B, C, D, E or F — with sub-classes for smoke (s1–s3) and flaming droplets (d0–d2). A fire-rated panel is typically specified as B-s1,d0.
Reaction to fire
How a product itself contributes to the early growth of a fire — ignitability, flame spread, heat release and smoke. It is a different property from fire resistance, which is about holding back an established fire.
Acoustic slat panel
Timber slats mounted over an acoustic felt or backing board. Sound is absorbed in the gaps between the slats and by the backer, while the face presents a continuous wood finish.
Baffle
A vertical acoustic element suspended from the ceiling, absorbing sound on both faces. Used to add absorption where covering the walls or the full ceiling is impractical.
Porous absorber
A material — mineral wool, acoustic felt, open foam — that absorbs sound by turning the energy of air moving through it into a tiny amount of heat. Most effective at mid and high frequencies.
Frequency (Hz)
The pitch of a sound, in hertz. Acoustic performance varies with frequency, so absorption is measured band by band — usually 125 Hz to 4000 Hz — not as a single figure.
Decibel (dB)
A logarithmic unit of sound level. Because it is logarithmic, a 10 dB increase is perceived as roughly twice as loud, and small dB changes can matter.
Speech intelligibility
How clearly speech can be understood in a space. It falls when reverberation is too long or background noise is too high — the core reason classrooms and offices are treated.
BB93
Building Bulletin 93, the acoustic design standard for schools in England. It sets reverberation-time and noise limits by room type, and is a statutory reference under the Building Regulations for school buildings.
Declaration of Performance (DoP)
The document in which a manufacturer declares a construction product's tested performance under the UK/EU construction products regime — the formal record behind a marketing figure.
FSC (Forest Stewardship Council)
A chain-of-custody certification that timber comes from responsibly managed forests. It is a documented claim, published when the certificate is held — not an assumption.