# Example

The figure below presents the Sabine sound absorption coefficients in third octave bands for a 40-mm thick rock wool. Measurement were performed by Mickael Duranteau in 2006 [Dur06] at ENTPE (two vertical red lines are reported at frequencies 200 Hz and 2 500 Hz to identified absorption values considered to compute the SAA).

The measured sound absorption coefficient $\alpha_{i}$ per 1/3 octave band are reported in the table below.

1/3 octave freq. | Absorption measured |
---|---|

100 | 0.19 |

125 | 0.15 |

160 | 0.50 |

200 | 0.67 |

250 | 0.89 |

315 | 0.86 |

400 | 1.04 |

500 | 1.05 |

630 | 1.01 |

800 | 1.07 |

1 000 | 0.67 |

1 250 | 0.80 |

1 600 | 0.76 |

2 000 | 0.82 |

2 500 | 0.71 |

3 150 | 0.74 |

4 000 | 0.71 |

5 000 | 0.74 |

6 300 | 0.78 |

8 000 | 0.99 |

From the measurement values above, the SAA is found to be equal to 0.86.

# Comments

The Sound Absorption Average should be used with care:

- The frequency range used to compute the SAA is quite limited compared to the human hearing frequency area [20 - 20 000] Hz. In particular, the third octave bands around 4 000 Hz are not used in its computation.
- The third octave values used are equally weighted which does not correspond to the natural sensitivity of sound by a human ear.

# Script

Follow the link compute_SAA.m to download a Matlab/GNU Octave script which compute the Sound Absorption Average from 1/3 octave band measurements.% Compute the Sound Absorption Average (SAA) % from absorption measurements in diffuse field. % % Measurements performed on a 40 mm-thick rock wool % by Mickael Duranteau during his 'DEUST VAS 2' % internship at ENTPE in 2006. % % Commands for the rotation of tick labels are % borrowed from rotateticklabel.m % Written Oct 14, 2005 by Andy Bliss % Copyleft 2005 by Andy Bliss % % Everything else is copyleft 2006 luc.jaouen@matelys.com % cf. APMR on the web, % Standards/SAA % for more information