# Sound Absorption Coefficients for some common Materials

## Sound absorption coefficients for some common materials as plaster walls, brickwork, plywood panels etc...

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The sound absorption coefficient indicates how much of the sound is absorbed in the actual material. The absorption coefficient can be expressed as:

α = I_{a}/ I_{i }(1)

where

I_{a}= sound intensity absorbed (W/m^{2})

I_{i}= incident sound intensity (W/m^{2})

Absorption coefficient - *α* - for some common materials can be found in the table below:

Material | Sound Absorption Coefficient - α - |
---|---|

Acoustic belt, 12 mm | 0.5 |

Acoustic tiles | 0.4 - 0.8 |

Asbestos, sprayed 25 mm | 0.6 - 0.7 |

Brickwork, painted | 0.01 - 0.02 |

Brickwork, unpainted | 0.02 - 0.05 |

Cork sheet, 6 mm | 0.1 - 0.2 |

Fiberboard on battens, 12 mm | 0.3 - 0.4 |

Hardwood | 0.3 |

Mineral wool, 100 mm | 0.65 |

Persons, each | 2.0 - 5.0 |

Plaster walls | 0.01 - 0.03 |

Plywood panel, 3 mm | 0.01 - 0.02 |

Polystyrene, expanded on 50mm battens | 0.35 |

Polystyrene, expanded rigid backing | 0.15 |

Polyurethane foam, flexible | 0.95 |

Rubber sheet, 6 mm porous | 0.1 - 0.2 |

Slag wool or glass silk, 50 mm | 0.8 - 0.9 |

Snow | 0.75 |

Wood wool cement on battens, 25 mm | 0.6 - 0.07 |

Note! The absorption coefficient varies with the frequency of sound.

### Total Room Sound Absorption

The total sound absorption in a room can be expressed as:

A = S_{1}α_{1}+ S_{2}α_{2}+ .. + S_{n}α_{n}= ∑ S_{i}α_{i}(2)

where

A= the absorption of the room (m^{2}Sabine)

S_{n}= area of the actual surface (m^{2})

α_{n}= absorption coefficient of the actual surface

### Mean Absorption Coefficient

The mean absorption coefficient for the room can be expressed as:

a_{m}= A / S(3)

where

a_{m}= mean absorption coefficient

A= the absorption of the room (m^{2}Sabine)

S= total surface in the room (m^{2})

A rooms acoustic characteristics can be calculated with the formulas above, or estimated for typical rooms.

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