Terms
150+
Defined concepts
Categories
8
Organized sections
Standards
12
Industry references
01 — Measurement
Ratings &
Standards
STC (Sound Transmission Class)
Quantifies how effectively a building partition attenuates airborne sound. Scale ranges from 25 (minimal blocking) to 70+ (essentially soundproof). Calculated by measuring sound transmission loss at 16 frequencies from 125 Hz to 4000 Hz per ASTM E90 and ASTM E413 standards.
NRC (Noise Reduction Coefficient)
Measures a material's ability to absorb sound energy across frequencies most relevant to human speech (250-2000 Hz). Values range from 0.0 (perfect reflection) to 1.0 (perfect absorption). Determined per ASTM C423.
IIC (Impact Insulation Class)
Rates a floor/ceiling assembly's ability to absorb impact sound (footsteps, dropped objects). Scale ranges from 25 (poor) to 85+ (excellent). Minimum IIC 50 required by most building codes for multifamily construction.
SAA (Sound Absorption Average)
Similar to NRC but averages absorption at 12 one-third octave bands from 200-2500 Hz per ASTM C423. Provides more detailed frequency-specific data than single-number NRC.
ASTM Standards
ASTM E90
Laboratory measurement of airborne sound transmission loss
ASTM E413
Classification for rating sound insulation (STC calculation)
ASTM C423
Sound absorption and NRC measurement of acoustical materials
ASTM E492
Laboratory measurement of impact sound (IIC)
ASTM E1007
Field measurement of impact sound rating
ASTM E336
Field measurement of airborne sound insulation
02 — Concepts
Core Acoustic Principles
Absorption
The process by which materials convert sound energy to heat, reducing reflection and reverberation. Measured by NRC. Absorptive materials include fiberglass, foam, fabric, and natural fibers like wool.
Diffusion
Scattering of sound waves in multiple directions to create uniform sound distribution. Diffusers use irregular surfaces or mathematical sequences (QRD, primitive root) to scatter energy evenly.
Isolation
Prevention of sound transmission between spaces. Achieved through mass, damping, decoupling, and sealing. Measured by STC for airborne sound and IIC for impact sound.
Reflection
Bouncing of sound waves off surfaces. Controlled reflection is desirable in some spaces (concert halls), while excessive reflection creates echo and reduces clarity.
Reverberation
Persistence of sound in a space after the source stops. Measured by RT60 (time for sound to decay 60 dB). Optimal RT60 varies by space use: 0.4s for speech, 1.5-2s for music.
Resonance
Amplification of sound at specific frequencies when excitation frequency matches a system's natural frequency. Room modes are resonances caused by standing waves between surfaces.
Standing Waves
Wave patterns formed when sound reflects between parallel surfaces, creating areas of constructive (loud) and destructive (quiet) interference. Cause uneven bass response in rooms.
Decibel (dB)
Logarithmic unit measuring sound intensity. 10 dB increase = 10x intensity (roughly 2x perceived loudness). Normal conversation: 60 dB. Pain threshold: 120-140 dB.
03 — Components
Treatment Components
Acoustic Panels
Flat or slightly contoured absorptive panels mounted on walls or ceilings. Typically 1-4 inches thick with fabric wrapping over fiberglass or mineral wool core.
Bass Traps
Thicker absorptive treatments designed for low-frequency absorption. Placed in corners where bass energy concentrates. Types: porous (broadband), resonant (tuned), and VPR.
Diffusers
Geometrically complex surfaces that scatter sound. Quadratic residue diffusers (QRD), skyline diffusers, and binary amplitude diffusers use mathematical sequences for optimal scattering.
Clouds & Baffles
Suspended horizontal (clouds) or vertical (baffles) absorptive elements. Absorb sound from both sides, increasing absorption per square foot of floor space.
Resilient Channels
Metal strips that decouple drywall from studs/joists. Allow drywall to flex independently, reducing vibration transmission. Critical for high-STC wall assemblies.
Mass Loaded Vinyl
Flexible, heavy sheeting (1-2 lb/sq ft) that adds mass to assemblies without significant thickness. Used in walls, ceilings, and floors for improved STC ratings.
04 — Materials
Acoustic Materials
Absorptive
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Fiberglass
High NRC, cost-effective, fire resistant
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Mineral Wool
Excellent low-frequency absorption
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Acoustic Foam
Lightweight, affordable, mid-high frequency
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Natural Wool
Sustainable, biophilic, effective absorption
Natural/Biophilic
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Cork
Renewable, natural absorber, attractive
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PET Felt
Recycled plastic, moldable, colorful
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Wood Fiber
Natural aesthetic, moderate absorption
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Mycelium
Bio-based, growing material innovation
Isolation
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Mass Loaded Vinyl
Flexible mass barrier for STC improvement
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Green Glue
Viscoelastic damping compound
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Acoustic Sealant
Flexible caulk for sealing gaps
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Isolation Clips
Decoupling hardware for ceilings