All I know is for noise insulation, building a party venue for example, inner wall spacing should be about 20cm. Though I don't see how that helps with anything but one frequency and It's harmonics. But im not buildingthe venue from scratch, so I want to sound-insultate the walls by adding panelling internally.
There must be some good physical solutions akin to electronics high/low pass fiters? I saw one with a layer of wood and either rubber or accoustic foam. The absorption was only 10dB.
What would be a standard modern solution to reduce noise by 40+ dB? 100hz -2khz roughly will be the biggest problem I think