Primary Reflection Point
The wall spot that reflects sound directly from source to listener.
Related terms
See also
Reference
Acoustic glossary — every term worth knowing.
Bookmark this page. 35plain-English definitions of the terms you’ll hear in any acoustic project — from NRC and STC to sabin, gripper, and flanking path.
A
Absorption
Converting sound energy into heat inside a material.
- Acoustic absorption happens when sound waves enter a porous material, agitate air molecules inside its pores, and lose energy to friction — converting sound to a tiny amount of heat. Foam, PET, wood wool, poly wadding, and rockwool are all absorbers. Absorption reduces reverberation inside a room but does nothing for isolation between rooms.
Related terms
B
Baffle
Vertical acoustic element hung below a ceiling.
- A baffle is a vertical acoustic panel suspended below a hard ceiling, exposing both faces to the room. Because both sides absorb, baffles deliver more sabin per square metre than flat ceiling panels — the go-to for double-height spaces and exposed-slab industrial or hospitality interiors.
Bass Trap
Corner absorber for low-frequency control.
- A bass trap is a thick absorber (usually 100 mm+ of PU foam or rockwool) placed floor-to-ceiling in a room corner. Corners are pressure maxima for every standing wave in the room, so absorption there works on the full bass spectrum simultaneously. Non-negotiable for home theatres, studios, and cinemas.
See also
Related terms
C
Cloud
Suspended acoustic panel floating below the ceiling.
- A ceiling cloud is a horizontal acoustic panel suspended with an air gap between the panel and the structural ceiling. The air gap dramatically improves low-frequency absorption vs a directly-fixed ceiling tile. Standard for offices and restaurants where the design brief wants visible ceiling absorption.
Related terms
See also
D
Damping
Reducing vibration inside a material or wall.
- Damping is what you add to a wall assembly to convert vibration into heat before it can radiate as sound on the far side. Green Glue between two drywall layers is the canonical damping treatment; MLV also damps to a lesser degree. Damping is a component of soundproofing, alongside mass and decoupling.
Decoupling
Mechanically separating two sides of a wall so vibration can't cross.
- Decoupling breaks the direct rigid path between the two faces of a wall. Resilient channels, staggered studs, and floating floors all decouple. Combined with mass and damping, decoupling delivers the highest STC per unit wall depth.
Diffusion
Scattering sound to prevent hard reflections without absorbing it.
- A diffuser is an irregular surface (quadratic-residue diffuser, poly-cylinder, or angled facets) that scatters incoming sound in many directions rather than reflecting it in one. Diffusion preserves the sense of a live room while eliminating slap echoes and standing waves. Standard on rear walls of home theatres and studios.
Related terms
Related terms
F
Fabric-Wrap Panel
Acoustic panel with visible decorative fabric skin over acoustic infill.
- Fabric-wrap panels are built by stretching acoustically-transparent fabric over an acoustic infill (poly wadding, foam, rockwool) held inside a uPVC gripper edge track. The fabric is the visible finish; the infill does the acoustic work. Field-serviceable — un-tuck fabric, replace infill, re-tuck.
Fibreglass
High-density spun glass fibre acoustic absorber.
- Fibreglass boards are the highest-performance mid-range acoustic absorber commonly used in construction. Higher airflow resistivity than PU foam means measurably deeper absorption at the same thickness — reference-grade for cinema screen walls, broadcast studios, and premium recording rooms. Must be enclosed inside gripper frames or laminated finishes; never installed exposed.
Flanking Path
Sound bypassing a wall through connected structures.
- A flanking path is any route sound takes around a well-built wall — through shared floor, ceiling, ductwork, or common conduits. The wall may be STC 60, but if the ductwork connects both rooms without silencers, real-world isolation is limited by the flanking path, not the wall.
Flutter Echo
Rapid repeating echo between parallel hard surfaces.
- Flutter echo is the tin-can, buzz-saw sound you hear when you clap in an empty tiled room. It happens when sound bounces rapidly between two parallel hard walls. Cured by treating one of the parallel surfaces with absorption or breaking the parallel geometry with diffusion.
Related terms
See also
Related terms
G
Gripper
uPVC edge track that snaps and locks fabric on a panel.
- A gripper is the uPVC extrusion that runs around the perimeter of a fabric-wrap acoustic panel and locks the fabric edge in a snap-in channel. Acoustimart's gripper system uses three profile families (edge, butt, cove) and delivers a fully field-serviceable finish that outlasts three redecorations.
Related terms
See also
H
HVAC Noise
Noise from heating, ventilation, and air-conditioning equipment.
- HVAC noise is the persistent low-level background rumble from ducts, fans, and diffusers. In studios and cinemas, target background is NC 15-25 (below 25 dBA). Requires duct silencers on intake and exhaust, low-velocity air handling, and rubber-isolated fan-coil units.
Related terms
See also
I
IIC
Impact Insulation Class — single-number impact-noise isolation rating.
- IIC is the impact-noise counterpart to STC. It measures how well a floor / ceiling assembly attenuates impact noise (footsteps, dropped items). IIC 50+ is code-standard for multi-family construction; IIC 60+ is desirable for premium residential.
Isolation
Stopping sound from crossing a boundary between rooms.
- Isolation is the acoustic problem of preventing sound in one room from being heard in another. Solved with mass, decoupling, damping, and airtightness — not with absorption. MLV inside walls is the canonical isolation upgrade for retrofits.
Related terms
Related terms
M
Mass
Weight per unit area — the primary driver of isolation.
- The mass law says every doubling of wall mass adds ~6 dB of transmission loss. MLV adds mass to lightweight walls without adding depth; concrete walls have mass built in. Mass is one of the four pillars of soundproofing (mass, air, damping, decoupling).
MLV
Mass Loaded Vinyl — dense flexible sheet for adding mass to walls.
- MLV is a limp, dense vinyl sheet that installs inside wall assemblies to add mass without adding significant depth. Available in 2, 3, and 5 mm thicknesses; 2 mm is the residential and studio standard. Every seam must be sealed with acoustic caulk — the wall is only as good as its weakest gap.
See also
N
NC
Noise Criterion — rating for background HVAC noise.
- NC curves plot allowable octave-band noise levels for HVAC systems. NC 25 is typical for offices; NC 15-20 for studios; NC 30-35 for retail. Achieving low NC requires duct silencers, oversized ducts (low velocity), and isolated equipment.
NRC
Noise Reduction Coefficient — single-number absorption rating.
- NRC averages a material's absorption coefficient across 250, 500, 1000, and 2000 Hz. Rated 0 to 1: 0 = perfect reflector, 1 = perfect absorber. Doesn't cover bass (below 250 Hz) — use full absorption curves for cinema or studio work.
Noise Floor
Ambient background noise level in a space.
- The noise floor is the persistent background level of a room when nothing is deliberately playing — HVAC, traffic bleed, computer fans. Broadcast studios target 25 dBA or lower; residential 30-35 dBA is typical.
Related terms
Related terms
See also
Related terms
O
Open-Cell Foam
PU foam with interconnected air pockets — the standard acoustic foam.
- Acoustic foam is open-cell polyurethane — the pores are interconnected, allowing sound waves to enter and get absorbed. Closed-cell foam (packaging foam, insulation) reflects sound and does nothing acoustic. Density and geometry (pyramid, wedge, flat) determine absorption performance.
Related terms
P
PET Panel
Non-fibrous polyester acoustic board.
- PET (polyester) acoustic panels are made from spun polyester fibre pressed into rigid boards. Non-friable, low-VOC, wipe-clean — safe for offices, schools, hospitals. Available in wide colour range and CNC-cuttable into custom patterns. The mainstream acoustic panel for commercial fit-outs.
Poly Wadding
Non-woven polyester fibre — the hidden infill inside gripper walls.
- Poly wadding is a non-woven polyester fibre material used as acoustic infill inside fabric-wrap gripper walls, stud cavities, and behind PET panels. Non-friable, dust-free, dimensionally stable — the modern replacement for fibreglass batting.
- In a mixing room or home theatre, the primary reflection points are the wall spots where sound from a speaker bounces once and arrives at the listener. Mirror trick: slide a mirror along the wall — anywhere the listener sees the speaker is a primary reflection point. Panel there.
Related terms
See also
Related terms
R
Reflection
Sound bouncing off a hard surface.
- Any surface that isn't absorbent reflects some proportion of incoming sound. Untreated hard walls (concrete, glass, tile) reflect over 95% of incident energy. Reflection is what creates reverberation, echo, and comb-filtering.
Reverberation Time (RT60)
Time for sound to decay by 60 dB after the source stops.
- RT60 is the single most-used number in acoustic design. Different room types target different RT60: studios 0.2 s, home theatres 0.3 s, offices 0.5 s, restaurants 0.7 s, auditoriums 1-2 s. Measured with a phone app or lab instrument; controlled with absorption.
Rockwool
Non-combustible mineral-fibre insulation with acoustic absorption.
- Rockwool is stone-based mineral wool made by spinning molten basalt. Delivers acoustic absorption similar to fibreglass with non-combustible fire behaviour (A1 class). Standard for isolation-shell cavities, fire-rated partitions, and thermal-plus-acoustic insulation.
Room Mode
Standing wave at a specific room-dimension-driven frequency.
- Room modes are standing waves that build up at frequencies determined by the room's length, width, and height. They cause bass frequencies to be exaggerated at some positions and cancelled at others. Corner bass traps and thoughtful listening-position placement are the main mitigations.
Related terms
Related terms
Related terms
Related terms
S
Sabin
Unit of sound absorption — 1 m² of a perfect absorber.
- A sabin is a unit of absorption: one square metre of surface with an absorption coefficient of 1.0 (perfect absorption). Used in the Sabine reverberation equation to calculate RT60 from room volume and total absorption.
Sound Masking
Adding low-level background noise to reduce speech intelligibility.
- Sound masking is the counterintuitive solution for open-office privacy — engineered background noise (typically 45-48 dBA pink-noise-like signal) makes speech from adjacent desks less intelligible without adding disruptive noise. Works best when reverberation is already controlled with absorbers.
Standing Wave
Sound wave that reinforces itself between parallel surfaces.
- A standing wave forms when a sound frequency's wavelength matches a room dimension exactly (or its half or double). Creates pressure maxima at the walls and minima in the room centre — audible as boomy bass or missing bass depending on where you sit.
STC
Sound Transmission Class — single-number wall isolation rating.
- STC rates how well a partition attenuates airborne sound across 125 Hz-4 kHz. STC 45 is a good residential wall; STC 55 is a studio wall; STC 60+ is a cinema inter-hall wall. Does not predict bass isolation — use full transmission-loss curves for home theatres and cinemas.
Related terms
See also
See also
T
Transmission Loss
The amount of sound blocked by a partition, in dB.
- Transmission loss (TL) is the frequency-by-frequency reduction in sound energy passing through a wall. STC is a single-number summary of the TL curve. For bass-critical applications (home theatres, cinemas), specify the full TL curve, not just STC.
W
Wood Wool Board
Cement-bonded wood-fibre acoustic + thermal panel.
- Wood wool boards are made from cement-bonded softwood excelsior. Impact-tolerant, non-combustible, moisture-tolerant — the pick for schools, cafeterias, corridors, and industrial spaces where durability matters as much as acoustics.
Related terms
See also
Term you can't find?
Ask us — we’ll add it.
If a term you're looking for isn't here, let us know. We update this glossary continuously with reader-requested entries.