Confirming sound absorption characteristics of box absorbers that utilize laser-cut micro-slits on the top surface as the means of sound absorption, with an exploration of different architectural installations

Abstract

It is believed that the box absorber utilizes viscous forces present in micro-slits on their surfaces to absorb sound [8]. These box absorbers were developed through research at SINTEF and the Norwegian University of Science and Technology, and current research has tested this sound absorbing technology in standing wave tubes and in a controlled reverberation room. This paper seeks to confirm the sound absorbing characteristics in a less-than-ideal test setup to model how the box absorbers would perform acoustically in an actual installation. It also explores different configurations of the box absorbers in attempts to achieve more sound absorption. To test this, twelve configurations of ten to eleven box absorbers were placed in a reverberation room and the reverberation time of the room was measured in third-octave frequency bands in order to obtain an amount of sound absorption in sabins per module. The sound absorption was confirmed for configurations similar to those tested and published by the manufacturer, though results show that the sound absorption is not as consistent; therefore the box absorbers would not have as strong of an effect in an actual installation as published data may indicate. Tests of different configurations showed that a box absorber with two surfaces of micro-slits exposed to the original sound field gives significantly more sound absorption across the band of frequencies, and a double layer of the micro-slotted surface forming two equal cavities within the box absorber gives a significant improvement in sound absorption above 500 Hz.