does temperature affect speaker performance?

My system always seems more dynamic on a warm day. Is it the case that drivers have an optimum working temperature and are more flexible within certain perameters?
I can't be certain but years ago I had a Magnepan 1D. I live in south Florida and I have no doubt that it sounded better in the winter when the humidity was low and the temperatures were lower than in the summer. No idea if cone speakers behave the same. Right now I have Merlins and I think they sound the same all year.
Maybe your ears are affected by the weather?
Dynamic driver speakers run pretty hot after just a few seconds play - so I doubt if external weather would make much of a difference.
I have Maggies, and have heard that humidity affects them substantially. My experience in humid NC seems to support that.
From my experiences living in Pa., where temps run from 90+ summers to 30 and lower winters, I will have to agree with you. My first house did not have AC and can attest to the dramatic sound changes with temperature that I experienced. A typical mid-summer day brought interior temps of 84-86 degrees in my listening room....add the heat from the old Krells and it would reach a shirt soaking 90 degrees. I'm sorry, but that will loosen up any flexible edge materials that I know of. As for the winter, temps would be right around 60-65 degrees causing materials to stiffen up.

The one pair of speakers that acted completely different from winter to summer in my house were the Thiel CS3.6's I had. I know exactly what you mean, as I can easily remember playing the soundtrack to "Glory" in which the opening track has some serious bass drum work and ends with a rumble and pipe chime. Winter time it sounded fine to me but summer time seemed to let the bass drum become much more the point of feeling like there was a subwoofer added to the system. The same thing was evident with Pat Metheny's "Secret Stories" on track 3 about 3/4 through the track. Just after the orchestra swells to a fortissimo there is a nice set of pedal tones that underscore the ensueing melody of sustained notes by french horns. These pedal tones can only be heard from a FULL range speaker or a Sub. Again the same effect was felt in summer heat of a visceral impact and sustain of the pedal tones like a sub was added, where as winter just let the notes be heard but not really felt.
I think temperature has a greater effect on the speed of sound than on the speaker driver's mechanics. This can throw your system off if the speakers were carefully positioned and the room reflections/nodes treated and optimized at different ambient conditions. Sound travel is faster in warmer air temperatures - probably explains what Bryhifi experienced.
Here's an interesting site that can provide a lot of insights with regard to venue acoustics and temperature/sonic speed: ( Of course the lower humidity in the winter time will affect sound propagation as well. The expanse of Mylar that makes up the Maggie's main diaphragm, and narrower(but still long) Quasi-Ribbon driver would certainly be subject to expansion and contraction with changes in temp also. My Maggies are in a climate controlled environment, so I don't notice any seasonal difference in sound.