Headroom

[Renato]

A Tech-term usually used in the music-business to describe the MAX level a sound system can go to before distortion occurs:
More commonly known as CLIPPING ......i.e.
A squaring-off(clipped)waveform that occurs when the power output of an amplifier cannot meet the power requirement of the speaker system it is driving: Clipping can be very harmful to high-frequency speakers (tweeters).

[Raeanne Dimick]

the amount of space below a roof, ceiling, or bridge, or below the top of something:

[Tracie Lynn]

The space above a drivers or passengers head in a vehicle.