If it were not for these drawbacks, ALL sound absorption treatments would utilize thick blankets, with no further worry about targeting specific frequency ranges. Unfortunately, it is not cost effective to provide thick absorbing layers when only a limited frequency range requires treatment. The Tuned Resonant Absorbers, described below, can achieve comparable sound absorption efficiency in a limited frequency range, with lower cost and reduced space requirements.

Material thicknesses, intermediate between the 1 II and 6" treatments shown in the figure, exhibit sound absorptive efficiencies intermediate between those two curves, which can be roughly matched to the noise spectrum for which noise control is desired. A general discussion of the relation between the thickness of the glass fiber blanket and the effectiveness of absorption at low frequencies is presented at the end of this booklet in Appendix A.

The next step is the selection of a suitable protective covering.