In article ,
Jeff Liebermann wrote:

isw hath wroth:

I beg to differ. There's no mixing happening in the air. compression
of air is very linear (Boyles Law or PV=constant).

In general, that's true, but take a look at what happens in the throats
of high-powered horn loudspeakers. You can find info in e.g. "Acoustics"
by Beranek.

Isaac

What am I suppose to look for?

Information about the nonlinearity of air; what else? You said
"compression of air is very linear", but there are situations in
acoustics where it is not.

Isaac