Practical sound absorption coefficient

Professional Definition

Practical sound absorption coefficient (denoted as $\alpha_p$) is a value calculated based on the reverberation sound absorption coefficient ($\alpha_s$), averaged for each octave band. The values of $\alpha_p$ are calculated according to the standard PN-EN ISO 11654 for the central frequencies of the octave bands: 125, 250, 500, 1000, 2000, and 4000 Hz.

This value is rounded to 0.05 and serves as the basis for determining the single number weighted index ($\alpha_w$). This is a conversion of detailed data from 1/3 octave bands to more general octave bands, making design easier.

Acoustics in Simple Words

Imagine that $\alpha_s$ (spectral coefficient) is a detailed record of all your grades from tests, quizzes, and answers throughout the school year. There are many of them, and it's hard at first glance to say how good of a student you are. Practical coefficient ($\alpha_p$) is the grade awarded at the end of the semester for each subject separately.

Instead of analyzing 20 different measurement points, the acoustician receives 6 main values (for low, mid, and high tones). If $\alpha_p$ is 0.90 at 500 Hz, it means that the material in this range "absorbs" 90% of the sound energy that strikes it. This tool allows for a quick assessment of whether a given panel will handle booming in a conference room or just slightly dampen conversations.

Summary

The practical sound absorption coefficient ($\alpha_p$) is a simplified, band-based measure of the acoustic effectiveness of a material. It serves for a quick assessment of absorptive properties in specific frequency ranges and is an essential step towards product classification.