Just to make it a little more fun: (NRR -7/2) = dBA.
So stacking NRR 29 (11 dBA) on top of NRR 27 (10 dBA) results in a total NRR 34 (13.5 dBA) 
Just to make it a little more fun: (NRR -7/2) = dBA.
So stacking NRR 29 (11 dBA) on top of NRR 27 (10 dBA) results in a total NRR 34 (13.5 dBA) 