Acoustic panels control sound within a room by converting acoustic energy into a small amount of heat through friction as sound waves pass through a porous or fibrous material. This is distinct from soundproofing, which blocks sound transmission between spaces. Absorption reduces reverberation time, eliminates flutter echo, and improves speech intelligibility within a room. The effectiveness of an acoustic panel is quantified primarily by its Noise Reduction Coefficient, or NRC.
Understanding NRC Ratings
The Noise Reduction Coefficient represents the average sound absorption across four octave-band frequencies: 250 Hz, 500 Hz, 1,000 Hz, and 2,000 Hz. An NRC of 0.00 means perfect reflection with zero absorption. An NRC of 1.00 means 100% absorption at the tested frequencies. An NRC of 0.85, typical for a 2-inch-thick fibreglass panel, means the material absorbs 85% of incident sound energy on average across the tested range.
NRC values can technically exceed 1.00 due to diffraction effects at panel edges and the calculation method, which rounds up to the nearest 0.05. A panel reporting NRC 1.05 is not absorbing more than 100% of sound energy; the value reflects measurement methodology rather than a physical impossibility. The more precise Sound Absorption Average (SAA) uses a third-octave band method that reduces this anomaly but is less commonly cited in product literature.
Fibreglass and Mineral Wool Panels
Owens Corning 703 rigid fibreglass board, with a density of approximately 3 pounds per cubic foot (48 kg/m3), is the reference standard for professional acoustic treatment. In 1-inch thickness, 703 achieves an NRC of approximately 0.70. At 2 inches, the NRC rises to 0.90 to 0.95. At 3 inches, NRC reaches 0.95 to 1.00 across the full frequency range. The 700-series products use a formaldehyde-free binder, addressing indoor air quality concerns.
Rockwool mineral wool panels, specifically Rockwool Safe'n'Sound at approximately 2.5 pounds per cubic foot (40 kg/m3) or Rockwool ComfortBatt at higher density, offer comparable acoustic performance to Owens Corning 703. NRC values for 2-inch Rockwool panels range from 0.85 to 0.95. Mineral wool has the advantage of being naturally fire-resistant to temperatures exceeding 1,000 degrees Celsius without requiring additional fire-retardant treatments, and it is hydrophobic, meaning it does not absorb moisture.
Both materials are typically wrapped in acoustically transparent fabric, with Guilford of Maine FR701 being the most widely specified commercial fabric for this application due to its combination of acoustic transparency, fire rating, durability, and colour range of over 60 stock options.
PET Felt Panels
PET felt acoustic panels are manufactured from recycled polyethylene terephthalate, typically sourced from post-consumer plastic bottles. The material is formed into a non-woven felt with densities ranging from 1.5 to 4 pounds per cubic foot. PET panels achieve NRC values of 0.40 to 0.75 depending on thickness, which ranges from 9 mm to 24 mm for typical commercial products. While PET does not match the raw absorption performance of fibreglass at equivalent thicknesses, it offers significant practical advantages: it is safe to handle without protective equipment, does not shed fibres into the air, can be cut to custom shapes with waterjet or CNC routing, and comes in a wide range of colours without requiring fabric wrapping.
Major manufacturers include Autex (New Zealand), EchoPanel (Australia), and numerous brands sourcing from Chinese production. PET panels carry LEED credentials for recycled content and are increasingly specified for commercial interiors where fire-rated, low-VOC, and sustainable materials are required.
Diffusion versus Absorption
Sound diffusion scatters reflected sound energy in multiple directions rather than absorbing it, preserving the acoustic energy in the room while eliminating focused reflections and flutter echo. Quadratic residue diffusers, or QRD panels, use wells of varying depths calculated according to number theory sequences to scatter sound evenly across a specified frequency range. A QRD diffuser designed for a base frequency of 500 Hz requires a maximum well depth of approximately 17 cm.
Absorption and diffusion serve complementary roles. Absorptive panels are placed at first-reflection points on side walls and ceilings to control early reflections. Diffusive panels are placed on the rear wall and ceiling to maintain a sense of spaciousness while preventing focused echoes. Recording studios and critical listening rooms typically use a combination of both, with absorption targets set to achieve a reverberation time appropriate for the room's purpose, typically 0.2 to 0.4 seconds for control rooms and 0.6 to 1.2 seconds for live rooms.
Perforated Wood Panels
Perforated acoustic wood panels combine absorption with an architectural finish. The panel consists of an MDF or plywood substrate with regularly spaced holes, typically 3 to 8 mm in diameter, backed by a black acoustic fleece. The perforation percentage, usually 8% to 20% of the surface area, determines the acoustic performance. Behind the perforated panel, a fibreglass or mineral wool absorber provides the actual sound absorption. This system is widely used in auditoriums, concert halls, and commercial atriums where visible acoustic treatment must meet architectural standards.