Impedance tube, Kundt’s tube, sound absorption and transmission loss
The impedance tube (also know as Kundt Tube) measurement obtains the normal incidence absorption coefficient of a layer of textiles with a small diameter (usually less than 10 cm)
The results can be used to compare the basic absorption performance of the material and for acoustics simulations.
In practice, the absorbers can be quite large and their structure and configuration may be complex and part of acoustic designs. Furthermore, they will be exposed to real sound fields where the incident sound may come from many directions.