UNE EN 1793-1 defines the laboratory method to measure the sound absorption of flat anti-noise panels or flat coatings for retaining walls or tunnels. It is used to evaluate the behaviour of the intrinsic sound absorption behaviour of noise reduction devices on road traffic which can be reasonably assembled inside the test facilities described in EN 20354.
The results provide a table and a graph that reflect all measuring frequencies of sound absorption αSi for each frequency change during the test.
The evaluation index of sound absorption, DLα, is obtained by rounding to the nearest integer.
If, in addition to the index, the behaviour of absorption is meant to be classified, the standard provides the following table:
| Absorption behaviour categories | |
| Category | DLα dB |
| A0 | Undetermined |
| A1 | < 4 |
| A2 | 4 a 7 |
| A3 | 8 a 11 |
| A4 | > 11 |
The evaluation index DLα is the most suitable to characterize the absorption behaviour in situations where the noise radiation comes from road traffic and is reflected on the absorbent surface. Only in the case of more complex situations in which multiple reflections occur, or when sound waves are diffracted, it is advisable to evaluate the behaviour of the absorbent materials according to the frequency.