As stated already by others, AFAIK it's the condensated humidity that can be a risk. If you take gear in from cold,
you must be sure they are thoroughly dry before switching them on. If they are kept in cold/cool room, and the temperature rises slowly, there should be no problem. Though, I can imagine that actual freezing/warming repeatedly must be a strain for many components and soldered joints etc.
 
 

Dave I did a bit of digging around for you. Here to begin with is a SOS article which brings up a few points:
 
http://www.soundonsound.com/sos/mar10/articles/qanda0310_4.htm
 
I looked up some specs for the following items and they indicated some temperature ranges:
 
Quest speaker  -10 C to +55C Other speakers though specified operating ranges as low as -25C and -35C in some cases.
 
Shure PG57 Mic -29 C to +57 C
 
Soundcraft Mixer +5 C to +40 C
 
Korg Kronos synthesiser +5 to +35C
 
Notice the mixer and the Korg Kronos did not like going down too far. The Korg synth obviously does not like getting too hot either +35 is easily obtainable on a pretty hot day. That would run pretty hot inside I would imagine under those conditions. In the manual also the Korg synth is very clear if there is condensation it also should not be used. Speakers and Mics seem to be OK although the Quest speaker is borderline in your case. (Other speakers went well below that though) These are operating and I guess storage temps too. The point that Mike mentions is important but also I have never felt great about all the soldering inside a lot of gear being kept at super cold temps. (and then coming into hot venues and going back out into cold temps again for longish periods) I lived in Canberra (Australia) for a long time and the temps there in the winter go down to 0 C and under. After doing gigs and getting home late I often brought the electronics gear inside. Left my drums out there though! Mechanical things like tape machines definitely don't like the cold.
 
Personally I don't think it is great for anything but that could just be me being paranoid.

Good stuff, Jeff. Thanks. You have to wonder how they came up with those numbers. Engineers routinely do mechanical tests such as drop and shake tests, but I'd be surprised if a speaker manufacturer actually left a pair of speakers out in -10C temperatures and measured them for performance and microscopically inspected them for mechanical damage. Shure, OTOH, I can believe that they might have actually done such a thing. 
 
It's true that electronics generally don't care about cold, and may indeed perform better at low temperatures. High-performance supercomputers' CPUs are intentionally kept very cold, it's commonplace for radio transmitter gear to be kept in an outside shed, and I have frozen ICs on many occasions, as a troubleshooting tool. Transistors and integrated circuits don't care, and tubes provide their own heat. It's mechanical parts that are most likely to be affected.
 
I found this interesting warning in an ADAM manual: "Never expose this product to extremely high or low temperatures. Avoid exposing the speaker's back panel to direct sunlight. Never operate this product in an explosive atmosphere."
 
Sunlight? I'm guessing they don't want the heatsink getting hot. They also warn against getting close to the speakers when using them at high volumes, and using flammable chemicals to clean them. And here I've been swabbing my cones with gasoline. 

Quest does make speaker systems for outdoor use.

Going from very cold to hot (if you have hardware that runs hot when on) can cause solder joints to fail. Not that common of a problem but it can happen. I've had to re-solder the odd power supply capacitor twice now in one of my ASR-10 samplers - which runs very hot. Quite a job taking it apart so I could get at them, but not that hard to do really. I'm not an electronics guy by any stretch, but I can solder OK as I've made a lot of cables over the years.

Bonzos Ghost
Going from very cold to hot (if you have hardware that runs hot when on) can cause solder joints to fail. Not that common of a problem but it can happen. I've had to re-solder the odd power supply capacitor twice now in one of my ASR-10 samplers - which runs very hot. Quite a job taking it apart so I could get at them, but not that hard to do really. I'm not an electronics guy by any stretch, but I can solder OK as I've made a lot of cables over the years.

I've seen that. Having worked at an electronics mfr - seen lots of tests of devices being shock heated and cooled (mostly industrial mobile devices). Best to let your avg electronic things acclimate for a couple hours before use.

While acclimating, it can be smart to leave them in their cases. I lived in Colorado for a while. A friend brought his guitar in from the car and removed it from the case looking beautiful. After a minuet or two the finish expanding to room temp at a different rate from the body, shattered and cracked like crazy!

Yup, you learn that trick when you tour Canada, Alaska and the northern tier states. Guitars stay wrapped until they've had time to warm up. Applies to groupies, too.

I remember playing clubs waaaay back when during the winter time. Among others things I had an ARP Odyssey that on occasion would go suddenly waaay out of tune if I happened to be setup near an outside door that let in a big blast of cold air. Usually just one oscillator was the culprit, so I could quickly kill it and carry on. The not-so-wonderful side of analog gear. I had to tune up all my gear between each set. Oh…to have had the luxury of digital gear c/w memory presets back in those days!

as I have an interest in old 8 bit computers.. a lot use old paper disc caps etc. that *DO* need replacing as they age and you will get a stink and a pop when they eventually do go.. extreme temps e.g. lofts / basements do them no favours.... same goes with vintage electronic stuff that needs re-capping.. and some stuff is probably well known for the PSU going pop because of not being used in 10-30 years.