{
  "name": "Sound Absorption Coefficient Table",
  "description": "Octave-band sound absorption coefficients (125 Hz–4 kHz) and NRC for common building materials and acoustic treatments, with a published reference for every row.",
  "url": "https://roomtreat.com/data/absorption-coefficients/",
  "documentation": "https://roomtreat.com/data/absorption-coefficients/",
  "publisher": "RoomTreat",
  "datePublished": "2026-06-29",
  "dateModified": "2026-08-07T06:48:42.000Z",
  "license": {
    "name": "Creative Commons Attribution 4.0 International (CC BY 4.0)",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Sound absorption coefficient data from RoomTreat (https://roomtreat.com/data/absorption-coefficients/), CC BY 4.0."
  },
  "bands_hz": [
    125,
    250,
    500,
    1000,
    2000,
    4000
  ],
  "unit": "absorption coefficient α, dimensionless (0 = fully reflective, 1 = nominally full absorption)",
  "measurement": {
    "method": "Reverberation-room method (ISO 354 / ASTM C423), random incidence.",
    "nature": "Nominal published values aggregated from standard architectural-acoustics references and manufacturer datasheets. They are planning estimates, not measurements of any specific product — for a purchase decision, check that manufacturer’s current datasheet.",
    "nrc_definition": "NRC = the mean of the 250, 500, 1000 and 2000 Hz coefficients, rounded to the nearest 0.05."
  },
  "limitations": [
    "Values above 1.0 are a known artefact of the reverberation-room method, not a data error: sound diffracts around a finite sample’s edges, so it can absorb as if it were larger than its measured area.",
    "Mounting changes the result. The same porous panel over an air gap reads substantially higher at low frequencies than mounted directly on a wall (ASTM E795 mountings), which is why published figures for the same material differ between sources.",
    "NRC hides the bass. A material can carry a high NRC and still absorb very little at 125 Hz, because NRC excludes the 125 Hz band entirely. Read the 125 Hz value for bass behaviour.",
    "These are absorption coefficients, not transmission loss. They describe how much sound a surface absorbs inside a room, and say nothing about sound passing through a wall. Nothing in this dataset is soundproofing data."
  ],
  "fields": {
    "id": "Stable slug identifying the material within this dataset.",
    "name": "Human-readable material name as published on the site.",
    "category": "One of the 9 categories in `categories`.",
    "coefficients": "Absorption coefficient α keyed by octave-band centre frequency in hertz. Published to two decimal places; JSON numbers drop insignificant trailing zeros, so 0.4 here is the published 0.40 and 1 is 1.00.",
    "nrc": "Noise Reduction Coefficient, as defined in `measurement.nrc_definition`.",
    "source": "Key into the `sources` object.",
    "source_reference": "The resolved full reference text for `source`, repeated inline so a single record is self-contained.",
    "notes": "Caveats specific to this material. Present only where the site publishes one.",
    "page": "Absolute URL of the dedicated reference page for this material, where one exists."
  },
  "categories": [
    "Hard surfaces",
    "Floors",
    "Glass & wood",
    "Soft furnishings",
    "Porous absorbers",
    "Acoustic panels",
    "Bass traps",
    "Ceiling",
    "People"
  ],
  "sources": {
    "vorlaender": "Vorländer, M. — Auralization (Springer), standard material tables.",
    "cox_dantonio": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
    "owens_corning": "Owens Corning 700-series rigid fiberglass board published datasheet.",
    "knauf": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
    "iso354_tables": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
    "bies_hansen": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
    "beranek": "Beranek, L. & Mellow, T. — Acoustics: Sound Fields and Transducers; standard audience/seating absorption tables."
  },
  "count": 60,
  "materials": [
    {
      "id": "concrete-block-painted",
      "name": "Concrete masonry block, painted/sealed",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.1,
        "250": 0.05,
        "500": 0.06,
        "1000": 0.07,
        "2000": 0.09,
        "4000": 0.08
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "Lightweight concrete masonry unit (cinder/breeze block) with the surface pores sealed by paint — reflective. Not the same as solid/cast concrete, which is lower still (~0.01–0.05; see “Concrete or terrazzo floor”).",
      "page": "https://roomtreat.com/materials/concrete-absorption-coefficient/"
    },
    {
      "id": "concrete-block-coarse",
      "name": "Concrete masonry block, coarse/unpainted",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.36,
        "250": 0.44,
        "500": 0.31,
        "1000": 0.29,
        "2000": 0.39,
        "4000": 0.25
      },
      "nrc": 0.35,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "This is coarse, open-pored LIGHTWEIGHT concrete masonry block (cinder/breeze block) — NOT solid or cast concrete. Its rough porous surface makes it a genuine mid-band absorber; sealing or painting the pores collapses it to ~0.05 (see the painted row). Solid/dense concrete is reflective (~0.01–0.05, consistent with DIN 18041; see “Concrete or terrazzo floor”) — do not use these figures for a poured-concrete wall. These are nominal aggregated table values (architectural-acoustics/Beranek lineage), not an in-hand primary test report: cross-check the PTB database and verify against the specific block before relying on them for design.",
      "page": "https://roomtreat.com/materials/concrete-absorption-coefficient/"
    },
    {
      "id": "brick-unglazed",
      "name": "Brick, unglazed",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.03,
        "250": 0.03,
        "500": 0.03,
        "1000": 0.04,
        "2000": 0.05,
        "4000": 0.07
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "plaster-on-brick",
      "name": "Plaster on masonry",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.01,
        "250": 0.01,
        "500": 0.02,
        "1000": 0.03,
        "2000": 0.04,
        "4000": 0.05
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "gypsum-board",
      "name": "Gypsum board (12 mm on studs)",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.29,
        "250": 0.1,
        "500": 0.05,
        "1000": 0.04,
        "2000": 0.07,
        "4000": 0.09
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "Resonant absorption near 125 Hz from the cavity.",
      "page": "https://roomtreat.com/materials/gypsum-board-absorption-coefficient/"
    },
    {
      "id": "marble-tile",
      "name": "Marble or glazed tile",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.01,
        "250": 0.01,
        "500": 0.01,
        "1000": 0.01,
        "2000": 0.02,
        "4000": 0.02
      },
      "nrc": 0,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "cork-tile",
      "name": "Cork tiles, 25 mm, on solid backing",
      "category": "Hard surfaces",
      "coefficients": {
        "125": 0.02,
        "250": 0.02,
        "500": 0.03,
        "1000": 0.04,
        "2000": 0.04,
        "4000": 0.05
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "Cork is a poor absorber; useful for floors and pinboards, not treatment.",
      "page": "https://roomtreat.com/materials/cork-absorption-coefficient/"
    },
    {
      "id": "concrete-floor",
      "name": "Concrete or terrazzo floor",
      "category": "Floors",
      "coefficients": {
        "125": 0.01,
        "250": 0.01,
        "500": 0.01,
        "1000": 0.02,
        "2000": 0.02,
        "4000": 0.02
      },
      "nrc": 0,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/concrete-absorption-coefficient/"
    },
    {
      "id": "vinyl-on-concrete",
      "name": "Vinyl / linoleum on concrete",
      "category": "Floors",
      "coefficients": {
        "125": 0.02,
        "250": 0.03,
        "500": 0.03,
        "1000": 0.03,
        "2000": 0.03,
        "4000": 0.02
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "wood-floor",
      "name": "Wood floor on joists",
      "category": "Floors",
      "coefficients": {
        "125": 0.15,
        "250": 0.11,
        "500": 0.1,
        "1000": 0.07,
        "2000": 0.06,
        "4000": 0.07
      },
      "nrc": 0.1,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables."
    },
    {
      "id": "parquet-on-concrete",
      "name": "Parquet on concrete",
      "category": "Floors",
      "coefficients": {
        "125": 0.04,
        "250": 0.04,
        "500": 0.07,
        "1000": 0.06,
        "2000": 0.06,
        "4000": 0.07
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "carpet-thin",
      "name": "Carpet, thin, on concrete",
      "category": "Floors",
      "coefficients": {
        "125": 0.02,
        "250": 0.06,
        "500": 0.14,
        "1000": 0.37,
        "2000": 0.6,
        "4000": 0.65
      },
      "nrc": 0.3,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/carpet-absorption-coefficient/"
    },
    {
      "id": "carpet-medium-underlay",
      "name": "Carpet, medium, on felt underlay",
      "category": "Floors",
      "coefficients": {
        "125": 0.05,
        "250": 0.15,
        "500": 0.35,
        "1000": 0.55,
        "2000": 0.65,
        "4000": 0.7
      },
      "nrc": 0.45,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/carpet-absorption-coefficient/"
    },
    {
      "id": "carpet-heavy-pad",
      "name": "Carpet, heavy, on foam pad",
      "category": "Floors",
      "coefficients": {
        "125": 0.08,
        "250": 0.24,
        "500": 0.57,
        "1000": 0.69,
        "2000": 0.71,
        "4000": 0.73
      },
      "nrc": 0.55,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/carpet-absorption-coefficient/"
    },
    {
      "id": "rug-medium",
      "name": "Area rug, medium pile, on hard floor",
      "category": "Floors",
      "coefficients": {
        "125": 0.04,
        "250": 0.08,
        "500": 0.2,
        "1000": 0.45,
        "2000": 0.6,
        "4000": 0.65
      },
      "nrc": 0.35,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "A loose rug covers only part of the floor — scale by the area it actually covers."
    },
    {
      "id": "rubber-floor",
      "name": "Rubber / PVC sports floor tile",
      "category": "Floors",
      "coefficients": {
        "125": 0.02,
        "250": 0.03,
        "500": 0.04,
        "1000": 0.04,
        "2000": 0.04,
        "4000": 0.04
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "glass-window",
      "name": "Ordinary window glass",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.35,
        "250": 0.25,
        "500": 0.18,
        "1000": 0.12,
        "2000": 0.07,
        "4000": 0.04
      },
      "nrc": 0.15,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "glass-heavy-plate",
      "name": "Heavy plate glass",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.18,
        "250": 0.06,
        "500": 0.04,
        "1000": 0.03,
        "2000": 0.02,
        "4000": 0.02
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "plywood-panel",
      "name": "Plywood panel (10 mm, air gap)",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.28,
        "250": 0.22,
        "500": 0.17,
        "1000": 0.09,
        "2000": 0.1,
        "4000": 0.11
      },
      "nrc": 0.15,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
      "notes": "Panel resonator — useful low-mid absorption."
    },
    {
      "id": "wood-paneling",
      "name": "Wood paneling on battens",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.3,
        "250": 0.25,
        "500": 0.2,
        "1000": 0.17,
        "2000": 0.15,
        "4000": 0.1
      },
      "nrc": 0.2,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "solid-wood-door",
      "name": "Solid wood door",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.14,
        "250": 0.1,
        "500": 0.06,
        "1000": 0.08,
        "2000": 0.1,
        "4000": 0.1
      },
      "nrc": 0.1,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "osb-panel",
      "name": "OSB / chipboard panel (10 mm, air gap)",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.25,
        "250": 0.2,
        "500": 0.15,
        "1000": 0.1,
        "2000": 0.1,
        "4000": 0.1
      },
      "nrc": 0.15,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
      "notes": "Panel resonator — modest low-frequency absorption over a cavity."
    },
    {
      "id": "hardboard-panel",
      "name": "Hardboard (3 mm) on battens, air gap",
      "category": "Glass & wood",
      "coefficients": {
        "125": 0.2,
        "250": 0.15,
        "500": 0.1,
        "1000": 0.1,
        "2000": 0.1,
        "4000": 0.1
      },
      "nrc": 0.1,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
      "notes": "Thin panel resonator tuned low; little mid/high absorption."
    },
    {
      "id": "curtains-light",
      "name": "Curtains, lightweight, draped",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.05,
        "250": 0.06,
        "500": 0.39,
        "1000": 0.63,
        "2000": 0.7,
        "4000": 0.73
      },
      "nrc": 0.45,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/curtains-absorption-coefficient/"
    },
    {
      "id": "curtains-heavy",
      "name": "Curtains, heavy, deep folds",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.14,
        "250": 0.35,
        "500": 0.55,
        "1000": 0.72,
        "2000": 0.7,
        "4000": 0.65
      },
      "nrc": 0.6,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "page": "https://roomtreat.com/materials/curtains-absorption-coefficient/"
    },
    {
      "id": "upholstered-seat-fabric",
      "name": "Upholstered seat, fabric, empty",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.19,
        "250": 0.37,
        "500": 0.56,
        "1000": 0.67,
        "2000": 0.61,
        "4000": 0.59
      },
      "nrc": 0.55,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press)."
    },
    {
      "id": "upholstered-seat-leather",
      "name": "Upholstered seat, leather, empty",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.15,
        "250": 0.27,
        "500": 0.39,
        "1000": 0.34,
        "2000": 0.48,
        "4000": 0.52
      },
      "nrc": 0.35,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press)."
    },
    {
      "id": "mattress",
      "name": "Mattress, bare",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.22,
        "250": 0.55,
        "500": 0.7,
        "1000": 0.7,
        "2000": 0.73,
        "4000": 0.75
      },
      "nrc": 0.65,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables."
    },
    {
      "id": "bookshelf-filled",
      "name": "Filled bookshelf",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.3,
        "250": 0.4,
        "500": 0.4,
        "1000": 0.3,
        "2000": 0.3,
        "4000": 0.3
      },
      "nrc": 0.35,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
      "notes": "Acts as a partial diffuser/absorber."
    },
    {
      "id": "audience-occupied-upholstered",
      "name": "Audience, occupied upholstered seats (per m²)",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.39,
        "250": 0.57,
        "500": 0.8,
        "1000": 0.94,
        "2000": 0.92,
        "4000": 0.87
      },
      "nrc": 0.8,
      "source": "beranek",
      "source_reference": "Beranek, L. & Mellow, T. — Acoustics: Sound Fields and Transducers; standard audience/seating absorption tables.",
      "notes": "Per m² of seated audience — use for occupied home-theatre seating."
    },
    {
      "id": "wooden-chairs-empty",
      "name": "Wooden chairs, unoccupied (per m²)",
      "category": "Soft furnishings",
      "coefficients": {
        "125": 0.02,
        "250": 0.02,
        "500": 0.03,
        "1000": 0.04,
        "2000": 0.04,
        "4000": 0.04
      },
      "nrc": 0.05,
      "source": "beranek",
      "source_reference": "Beranek, L. & Mellow, T. — Acoustics: Sound Fields and Transducers; standard audience/seating absorption tables."
    },
    {
      "id": "mineral-wool-50",
      "name": "Mineral wool, 50 mm, on wall",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.15,
        "250": 0.55,
        "500": 0.9,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 0.85,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
      "page": "https://roomtreat.com/materials/mineral-wool-absorption-coefficient/"
    },
    {
      "id": "mineral-wool-100",
      "name": "Mineral wool, 100 mm, on wall",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.45,
        "250": 0.95,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 1,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
      "page": "https://roomtreat.com/materials/mineral-wool-absorption-coefficient/"
    },
    {
      "id": "mineral-wool-50-gap",
      "name": "Mineral wool, 50 mm, 50 mm air gap",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.4,
        "250": 0.85,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 0.95,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
      "notes": "Air gap boosts low-mid absorption.",
      "page": "https://roomtreat.com/materials/mineral-wool-absorption-coefficient/"
    },
    {
      "id": "owens-703-25",
      "name": "Rigid fiberglass 703, 25 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.11,
        "250": 0.28,
        "500": 0.68,
        "1000": 0.9,
        "2000": 0.93,
        "4000": 0.96
      },
      "nrc": 0.7,
      "source": "owens_corning",
      "source_reference": "Owens Corning 700-series rigid fiberglass board published datasheet."
    },
    {
      "id": "owens-703-50",
      "name": "Rigid fiberglass 703, 50 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.17,
        "250": 0.86,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 0.95,
      "source": "owens_corning",
      "source_reference": "Owens Corning 700-series rigid fiberglass board published datasheet."
    },
    {
      "id": "owens-703-100",
      "name": "Rigid fiberglass 703, 100 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.65,
        "250": 1,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 1,
      "source": "owens_corning",
      "source_reference": "Owens Corning 700-series rigid fiberglass board published datasheet."
    },
    {
      "id": "acoustic-foam-50",
      "name": "Open-cell acoustic foam, 50 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.08,
        "250": 0.25,
        "500": 0.6,
        "1000": 0.9,
        "2000": 0.95,
        "4000": 0.98
      },
      "nrc": 0.7,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Weak below 250 Hz despite popularity.",
      "page": "https://roomtreat.com/materials/acoustic-foam-absorption-coefficient/"
    },
    {
      "id": "acoustic-foam-25",
      "name": "Open-cell acoustic foam, 25 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.05,
        "250": 0.12,
        "500": 0.3,
        "1000": 0.65,
        "2000": 0.85,
        "4000": 0.95
      },
      "nrc": 0.5,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "page": "https://roomtreat.com/materials/acoustic-foam-absorption-coefficient/"
    },
    {
      "id": "egg-crate-foam-50",
      "name": "Convoluted egg-crate foam, 50 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.05,
        "250": 0.18,
        "500": 0.45,
        "1000": 0.7,
        "2000": 0.85,
        "4000": 0.9
      },
      "nrc": 0.55,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Profiled foam performs like thinner flat foam — weak below 250 Hz."
    },
    {
      "id": "mineral-wool-150",
      "name": "Mineral wool, 150 mm, on wall",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.65,
        "250": 1,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 1,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
      "notes": "Thicker slab extends absorption further into the bass.",
      "page": "https://roomtreat.com/materials/mineral-wool-absorption-coefficient/"
    },
    {
      "id": "polyester-batt-50",
      "name": "Polyester acoustic batt, 50 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.12,
        "250": 0.45,
        "500": 0.85,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 0.85,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Recycled-PET batt; planning estimate modelled as an equivalent porous absorber."
    },
    {
      "id": "wood-wool-board",
      "name": "Wood-wool cement board, 25 mm",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.1,
        "250": 0.2,
        "500": 0.45,
        "1000": 0.55,
        "2000": 0.6,
        "4000": 0.55
      },
      "nrc": 0.45,
      "source": "vorlaender",
      "source_reference": "Vorländer, M. — Auralization (Springer), standard material tables.",
      "notes": "Cement-bonded wood fibre (e.g. Heraklith); a mid-range absorber."
    },
    {
      "id": "acoustic-plaster",
      "name": "Acoustic plaster, sprayed (~25 mm)",
      "category": "Porous absorbers",
      "coefficients": {
        "125": 0.17,
        "250": 0.4,
        "500": 0.66,
        "1000": 0.65,
        "2000": 0.62,
        "4000": 0.68
      },
      "nrc": 0.6,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Seamless porous finish; performance depends on thickness and backing."
    },
    {
      "id": "fabric-panel-50",
      "name": "Fabric-wrapped panel, 50 mm",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.16,
        "250": 0.55,
        "500": 0.95,
        "1000": 1,
        "2000": 1,
        "4000": 0.98
      },
      "nrc": 0.9,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets."
    },
    {
      "id": "fabric-panel-100",
      "name": "Fabric-wrapped panel, 100 mm",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.52,
        "250": 0.96,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 0.99
      },
      "nrc": 1,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets."
    },
    {
      "id": "fabric-panel-50-gap",
      "name": "Fabric panel, 50 mm + 100 mm gap",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.45,
        "250": 0.9,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 0.98
      },
      "nrc": 1,
      "source": "knauf",
      "source_reference": "Knauf / Rockwool mineral-wool acoustic board published datasheets.",
      "notes": "Best broadband value for the money."
    },
    {
      "id": "pet-felt-panel-12",
      "name": "PET felt panel, 12 mm",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.03,
        "250": 0.07,
        "500": 0.32,
        "1000": 0.62,
        "2000": 0.78,
        "4000": 0.82
      },
      "nrc": 0.45,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press)."
    },
    {
      "id": "pet-felt-panel-24",
      "name": "PET felt panel, 24 mm (double layer)",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.05,
        "250": 0.15,
        "500": 0.5,
        "1000": 0.8,
        "2000": 0.85,
        "4000": 0.85
      },
      "nrc": 0.6,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press)."
    },
    {
      "id": "perforated-wood-panel",
      "name": "Perforated wood panel + backing",
      "category": "Acoustic panels",
      "coefficients": {
        "125": 0.25,
        "250": 0.55,
        "500": 0.8,
        "1000": 0.85,
        "2000": 0.6,
        "4000": 0.4
      },
      "nrc": 0.7,
      "source": "vorlaender",
      "source_reference": "Vorländer, M. — Auralization (Springer), standard material tables.",
      "notes": "Helmholtz behaviour, tuned mid absorption."
    },
    {
      "id": "corner-trap-broadband",
      "name": "Broadband corner trap (300 mm)",
      "category": "Bass traps",
      "coefficients": {
        "125": 0.5,
        "250": 0.85,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 0.95,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Floor-to-ceiling triangular corner fill."
    },
    {
      "id": "superchunk-corner",
      "name": "Superchunk corner (mineral wool)",
      "category": "Bass traps",
      "coefficients": {
        "125": 0.6,
        "250": 0.95,
        "500": 1,
        "1000": 1,
        "2000": 1,
        "4000": 1
      },
      "nrc": 1,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press)."
    },
    {
      "id": "membrane-trap-tuned",
      "name": "Tuned membrane trap (~60 Hz)",
      "category": "Bass traps",
      "coefficients": {
        "125": 0.75,
        "250": 0.45,
        "500": 0.2,
        "1000": 0.12,
        "2000": 0.1,
        "4000": 0.1
      },
      "nrc": 0.2,
      "source": "vorlaender",
      "source_reference": "Vorländer, M. — Auralization (Springer), standard material tables.",
      "notes": "Narrowband — targets a specific room mode."
    },
    {
      "id": "tube-trap",
      "name": "Cylindrical tube trap (corner, ~280 mm)",
      "category": "Bass traps",
      "coefficients": {
        "125": 0.45,
        "250": 0.7,
        "500": 0.85,
        "1000": 0.9,
        "2000": 0.85,
        "4000": 0.8
      },
      "nrc": 0.85,
      "source": "cox_dantonio",
      "source_reference": "Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press).",
      "notes": "Free-standing cylindrical corner absorber; one side can be reflective."
    },
    {
      "id": "ceiling-tile-mineral",
      "name": "Mineral-fiber ceiling tile (15 mm)",
      "category": "Ceiling",
      "coefficients": {
        "125": 0.34,
        "250": 0.55,
        "500": 0.68,
        "1000": 0.78,
        "2000": 0.8,
        "4000": 0.78
      },
      "nrc": 0.7,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "ceiling-tile-suspended",
      "name": "Suspended acoustic tile + plenum",
      "category": "Ceiling",
      "coefficients": {
        "125": 0.55,
        "250": 0.68,
        "500": 0.72,
        "1000": 0.78,
        "2000": 0.82,
        "4000": 0.8
      },
      "nrc": 0.75,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured).",
      "notes": "Plenum gap improves low-frequency absorption."
    },
    {
      "id": "gypsum-ceiling",
      "name": "Gypsum board ceiling",
      "category": "Ceiling",
      "coefficients": {
        "125": 0.15,
        "250": 0.1,
        "500": 0.06,
        "1000": 0.04,
        "2000": 0.04,
        "4000": 0.05
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "plaster-ceiling",
      "name": "Plaster ceiling",
      "category": "Ceiling",
      "coefficients": {
        "125": 0.02,
        "250": 0.02,
        "500": 0.03,
        "1000": 0.04,
        "2000": 0.05,
        "4000": 0.05
      },
      "nrc": 0.05,
      "source": "iso354_tables",
      "source_reference": "Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured)."
    },
    {
      "id": "person-seated",
      "name": "Person, seated (per m² of audience)",
      "category": "People",
      "coefficients": {
        "125": 0.16,
        "250": 0.4,
        "500": 0.55,
        "1000": 0.65,
        "2000": 0.7,
        "4000": 0.7
      },
      "nrc": 0.6,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables."
    },
    {
      "id": "person-standing",
      "name": "Adult, standing (per person, sabins)",
      "category": "People",
      "coefficients": {
        "125": 0.18,
        "250": 0.4,
        "500": 0.46,
        "1000": 0.46,
        "2000": 0.51,
        "4000": 0.46
      },
      "nrc": 0.45,
      "source": "bies_hansen",
      "source_reference": "Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables.",
      "notes": "Value is per person, not per m²."
    }
  ]
}