Hi,

I'm afraid your offering is more foreign to me than the original.  I think you probably know way more about it than I do.

Comparing to conventional sound, the velocity changes with the medium through which it travels, eg., 343 meters per second through dry air at room temperature.  It's much different when travelling through water, or through a steel railroad rail, all of which I'm sure you know.  
 
I take "perturbations" to be upsets in the speed at which the waves are travelling, as they encounter various media.

I'm not sure if "propagation" refers to the original generation of the sound at the source, or the "passing" of the waves through the media   -   I think the latter (at least that would fit better into your expression   -   the continuation, or progress of the wave).  I don't think the frequency changes as the media change   -   only the velocity.

Anyway, that's about all I can say without looking it up, which you've probably already done.

Best wishes,  A.