How do walls block sound?
Most solid walls with no open leaks will provide 40 to 50 dB of blockage for middle frequency sound. This is somewhat amazing if you consider that 40 dB amounts to blocking 99.99% of the sound, and 50 dB amounts to blocking 99.999%. With special care, blockage up to 60 dB or more can be achieved. However, success beyond 50 dB depends on careful construction, and is often limited by flanking or sound leakage by paths around the wall, door or window. A small leak can have a major effect on a wall with otherwise high blockage. Higher frequency sound is easier to block than low frequency or bass sound. The bass sound has longer wavelengths. The wall looks thinner to the low-frequency sound. Walls are rated in their ability to block speech or speech-like sound by the Sound Transmission Class (STC). Their blockage of bass sound will be less than the STC. The wall with the higher STC may actually be a poorer blocker of bass sound. The major factor that influences the blockage of the structure
