An attenuator that provides 30dB performance reduces the energy transmitted by 99.9%. This rises to 99.99% for 40dB performance (i.e. only 0.01% of the original sound energy can be permitted to pass through—or around—the attenuator). This performance can only be achieved if the attenuator is able to function properly, which can be affected by damage occurring before, during or after installation. In addition to more obvious damage, such as deformation of the casing, or the internal components, this can be difficult to detect, as in the case of damage to the acoustically absorptive infill, resulting in its loss over time, particularly when exposed to airflow during use.
Acoustical Control Engineers’ attenuators incorporate a perforated steel facing to protect acoustically absorptive surfaces against mechanical damage. An acoustically transparent inter-layer is also used to prevent fibre migration of the infill through the perforations in the protective facing.