# Room Sound Absorption - Sound Absorption Coefficient

## Room sound absorption and absorption coefficients for common materials like plaster walls, brickwork, plywood panels etc...

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The sound absorption coefficient is the ratio of *absorbed sound intensity in an actual material* to the *incident sound intensity* and can be expressed as

α = I_{a}/ I_{i }(1)

where

α= sound absorption coefficient

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

I_{i}= incidentsound 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 |

Carpet, heavy on concrete | 0.3 - 0.6 |

Carpe, heavy on foam rubber | 0.5 - 0.7 |

Concrete block, coarse | 0.3 - 0.4 |

Concrete block, painted | 0.05 - 0.07 |

Cork sheet, 6 mm | 0.1 - 0.2 |

Fiberboard on battens, 12 mm | 0.3 - 0.4 |

Floor, concrete or terrazzo | 0.02 |

Floor, linoleum, asphalt, rubber or cork tiles on concrete | 0.03 |

Floor, wood | 0.06 - 0.1 |

Hardwood | 0.3 |

Glass, large panes heavy plate | 0.03 - 0.05 |

Glass, ordinary windows | 0.1 - 0.2 |

Gypsum board, 12 mm | 0.04 - 0.07 |

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 sound absorption coefficient varies with the frequency.

### 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:

α_{m}= A / S(3)

where

α_{m}= mean absorption coefficient

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

The acoustic characteristics of a room can be calculated with the formulas above, or estimated for typical rooms.

### Example - Room Acoustic Absorption

The total sound absorption in a room with

*10 m*concrete floor with absorption coefficient^{2}*0.02**10 m*^{2}concrete roof with absorption coefficient*0.02**40 m*fiberboard walls with absorption coefficient^{2}*0.3*

can be calculated as

*A = (10 m ^{2}) (0.02) + (10 m^{2}) (0.02) + (40 m^{2}) (0.3)*

* = 12.2 m ^{2} Sabine*

The mean absorption coefficient can be calculated as

*α*_{m} = (12.2 m^{2} Sabine) / ((10 m^{2}) + (10 m^{2}) + (40 m^{2}))

* = 0.2*

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