Does altitude change the sound of speakers??

I like D_S answer.. hee hee.

The air is thinner, thing are bound to be a little faster and with less pressure on the old ear drum, ay? But give it a little time, just like you for the altitude change.. Interesting though.. Humidity is right in there with SQ to...It all plays into "The sound", ay?

Would it actually be a lower spl with the same watts or not? I gotta think on that one a bit. $ for $ would you get the same SPL at sea level as one, two, or what about 4 miles up. Everest? Can you hear anything up there. 
With no air, no pressure, little air, little pressure, Right?

Regards

That is why EBM live's in a Penthouse. Ultimate SQ!!! 👍

So if the rooms are not exactly the same, of course there would be a difference in sound.

The change in the listening room itself probably dwarfs any changes in altitude. 

Correct.

Sound is pressure waves transmitted by molecules bumping and bouncing off each other. The greater the density the faster and more efficient the wave. Air at sea level being more dense the sound will be louder with more dynamic impact. Go higher, air gets thinner, more tenuous, sound and dynamic detail are less. The difference the first mile is however much less than a dozen other things that change such as for example the room. The room and setup contributes far more to the sound than changes in atmospheric pressure.

To hear a difference greater than all the other differences you need to go higher. At some point high enough density falls to zero, no molecules, no waves, no sound. Thus the expression, In space no one can hear you fart.