Sound transmission through very porous concrete blocks

Abstract

Sound transmission loss measurements through a wall constructed from very porous concrete blocks gave some interesting results. The unfinished block wall had a sound transmission class (STC) rating of 14. This was increased to only 29 by screwing a layer of drywall to one side of the block wall. The drywall, while it provides a sealed surface, is not well enough bonded to the blocks and can still vibrate fairly freely. Plastering increased the STC to 43. The porosity of the block increased the effective depth of the air space behind the drywall. This lowered the mass‐air‐mass resonance substantially and, with drywall supported on steel studs, plastered block wall systems gave very good STC ratings. Walls constructed using this type of block can give STC ratings about as high as those obtained with heavier normal weight blocks. Measurements were made down to 63 Hz and revealed that in many cases there are resonances occurring below 125 Hz that have a strong influence on transmission loss values at and above 125 Hz. Measurement to these low frequencies give a clearer picture of the effect of changes to the wall structure. The results obtained will be presented and discussed.