Measurement of the airflow resistivity, porosity etc.

• determination of the airflow resistivity with airflow resistivity meter AcoustiFlow^® on the basis of the static-airflow method (direct-airflow method) described in DIN EN ISO 9053-1 (former DIN EN 29053); in the case of thin layers determination of specific airflow resistance, which allows the calculation of the sound absorption coefficient

• measurement of the gross density and the porosity (accessible void content) by volumetric method with gas pycnometer according to DIN 51913

• determination of the hydraulic tortuosity and the structure factor by measurement of the electrical tortuosity; in the case of electrical conductors by indirect calculation by using the frequency-dependent characteristic absorber values

• determination of the characteristic viscous lengths and the thermal lengths by indirect calculation by using the frequency-dependent characteristic absorber values

• tomography and polished cut images

Sound absorbers

Materials with sound absorbing properties are e. g.:

• synthetic materials (e. g. open-cell foams)
• glass wool, mineral wool
• granulates, fills
• felts, fibers
• perforated plates
• foils
• open porous asphalts and concretes
• elastomer compounds
• metal fiber sound absorbers
• metal hollow sphere structures

Optimization of sound absorbers and mufflers

• calculation of the sound propagation (sound absorption, sound reflexion, sound insulation) above layered absorbers by applying different absorber models (e. g. homogeneous model, phenomenological model) with sound absorber software AcoustiCalc^® Absorber

• prediction and optimization of the sound absorption in mufflers and silencers as well as absorbent-lined ducts by both analytical models with muffler software AcoustiCalc^® Silencer and by numerical calculation (see FEM)