It may register below 0dB SPL (in an anechoic chamber, anyway) depending on the manner in which it's measured, which is a complex discipline in itself. Sound pr

It may register below 0dB SPL (in an anechoic chamber, anyway) depending on the manner in which it's measured, which is a complex discipline in itself. Sound pressure dissipates over distance, for example, so the distance at which the measurement is made has bearing, as does the angle at which it's measured. (This is unabashed pedantry. But I'm on my lunch break, so...)