Sound absorption of microperforated duct systems

In recent years, the concept of microperforated sound absorbers has been successfully implemented in various applications, such as transparent panel absorbers, microperforated foils or suspended ceilings. For the first time, interior design and room acoustics were merged by using various benefits of microperforated absorbers. In order to introduce the principle of microperforation to further engineering areas, microperforated ducts have been investigated as a visible element of the room. In this case, air flows through the microperforation. Hence, not only the ventilation aspects have to be designed but also the sound absorption effects need to be taken into account. For this purpose, the theory of a microperforated absorber was extended to include the effects caused by airflow through the microperforation. A frequency dependent factor ùc was introduced to describe the influence of the superimposed averaged flow velocity. Experimental evidence is provided. First, measurement results using a modified impedance tube are presented. Furthermore, measurements of microperforated ducts in a reverberation chamber were conducted keeping feasible duct dimensions and flow conditions in mind. Calculated and measured values for the pressure loss due to the microperforation were compared. The investigations show a high sound absorption characteristic, which results in an attractive and flexible room acoustic element that can be easily integrated into duct systems.