Measurement of the airflow resistivity, porosity etc.

• determination of the airflow resistivity with airflow resistivity meter AED 300 – AcoustiFlow^® on the basis of the direct-airflow method described in DIN EN 29053 (ISO 9053); 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 AED 3001 – 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 AED 8001 – AcoustiCalc^® Silencer and by numerical calculation (see FEM)