Sound Proofing -

Our lifestyle has changed significantly since sound proofing began, when it was used to provide privacy between dwellings and protection from traffic and machine noise. We used to sound proof against speech, horse and cart, small slow cars and light machinery. Now we are soundproofing against subwoofers, trucks, aeroplanes and construction sites - the big difference being bass or low frequency noise.

Needless to say the old methods don't work well and sometimes don't work at all. We have gone from soundproofing against mid and high frequency noise to soundproofing against full range noise including low frequency. In the past, adding mass made soundproofing better because it didn't need to cater for low frequency noise. Adding mass does not improve low frequency soundproofing much at all but damping does. Damping is like a shock absorber on a car, it reduces the size of the bouncing or oscillation that would happen if the car just had springs. Just like adding mass to the car wouldn't reduce the size of the bouncing, just the rate or frequency (resonance), adding mass to a wall just shifts the resonant frequency down a little but doesn't reduce its size (and hence doesn't improve the soundproofing). Damping however, like Green Glue, acts like a shock absorber on the car and reduces the size of the oscillation, thereby providing low frequency soundproofing that adding more mass cannot. Green Glue acts as a Constrained Layer Damper (CLD).