That's to add some harmonics higher up in the audible range, giving it more colour and augmenting the perception of low frequency force...woooahhh - should be reposted on production thread. Can anyone explain to me how this works, theoretically speaking?:
"We always add subtle amounts of distortion/saturation for added tone on our subs so they can be heard on smaller speakers, not just massive club systems."
wiki said:Missing fundamental
A sound is said to have a missing fundamental, suppressed fundamental, or phantom fundamental when its overtones suggest a fundamental frequency but the sound lacks a component at the fundamental frequency itself. However, the brain perceives the pitch of a tone not only by its fundamental frequency, but also by the ratio of the higher harmonics. Thus, we may perceive the same pitch (perhaps with a different timbre) even if the fundamental frequency is missing from a tone.
For example, when a note (that is not a pure tone) has a pitch of 100 Hz, it will consist of frequency components that are close to integer multiples of that value (e.g. 100, 200, 300, 400, 500.... Hz). However, smaller loudspeakers may not produce low frequencies, and so in our example, the 100 Hz component may be missing. Nevertheless, a pitch corresponding to the fundamental may still be heard.