Does altitude change the sound of speakers??

Heh Chorus, I met Mark L. at a Boston audio store years ago.

I moved from 800' to 7220' about a dozen years ago, and do not recall any significant change in speaker sound due to altitude. The ability to listen at volume levels that do a system justice was an improvement very much more readily noticeable.

I do have a premium system in my truck and I experience substantial altitude changes in my travels. What I notice is that my ears plug up and things overall don't sound right. After I clear them, everything sounds much better. Meaning that there are other factors involved and I can't discern any change in the sound of the speakers directly due to attribute.

Humidity also a factor. 

The effects of gravity are reduced at higher altitudes. Thus, it is slightly possible that a speaker cone will behave slightly different at high altitudes compared to sea level. It would not be audible.