I haven't experienced that as it doesn't get that cold here in Arizona, but I would have to say that it wouldn't surprise me. Electronics are temperature sensitive, not to mention the mechanical action of a speaker. Most electronics have a temperature range listed somewhere on them, and I imagine the Sportage radio is no different.

It sounds fine once the interior starts to warm up right?

 

I thought anybody knew that woofers have to be warmed up in severe cold. You can kill your speakers by trying to make them play before they're ready. Warm the car up before expecting high performance out of it or anything in it. You can play music, but just quietly - this helps warm the drivers up. When you start hearing the bass, you can add a little volume - work your way up to 'window rattling'. I always turn the volume down before shutting down for the night - this helps prevent damage if its cold the next time I start the car.
BTW, even the EX has a pretty good system in it - capable of more bass than I like to use. Being an actual musician, I like the sound to be 'real', and I have to control the volume in the attempt to save what I have left of my hearing.

 

Not an issue with navigation stereo system

Below 32 degrees F my stereo does just fine from what I experienced as I do crank it up everytime I drive. I won't say this system Kicks Butt, however for most people it sounds great. I will someday upgrade the amp and put some woofers in back and replace all the stock speakers.

The front speakers and Tweeter are about the strongest sound then the back doors then the 1 woofer that came stock. I can tell by cranking up the volume to full blast then fading from the front to the back.

I hate to say this as I love the car but the woofer in back is about useless as it is underpowered and it seems the back doors are too. But the front doors Rock Hard.

I guess tapping into the back woofer and adding a amp with a couple of subs would work for me. As I will do that first as when I am ready I will spend good money upgrading all the speakers but right now I am Car poor. Plus my wife doesn't understand why the need for noise.

 

Below 32 degrees F my stereo does just fine from what I experienced as I do crank it up everytime I drive. I won't say this system Kicks Butt, however for most people it sounds great. I will someday upgrade the amp and put some woofers in back and replace all the stock speakers.

The front speakers and Tweeter are about the strongest sound then the back doors then the 1 woofer that came stock. I can tell by cranking up the volume to full blast then fading from the front to the back.

I hate to say this as I love the car but the woofer in back is about useless as it is underpowered and it seems the back doors are too. But the front doors Rock Hard.

I guess tapping into the back woofer and adding a amp with a couple of subs would work for me. As I will do that first as when I am ready I will spend good money upgrading all the speakers but right now I am Car poor. Plus my wife doesn't understand why the need for noise.

They rarely do. new toys = good times!

 

I live in Anchorage, Alaska and it has been as low as -10F for the past month. I've noticed when the car has been outside for a long time the bass is noticeably quieter than when it's parked in the garage and warm. After the car has warmed up a bit the bass gets fuller and sounds great after about 10 min. I just leave it at a normal volume while it warms up. I think it's probably normal in such cold temperatures; everything takes a little longer to warm up.

I also have the UVO system and granted it's no million watt super system; I think it sounds very good for a stock system.

 

I've only heard radio on the stock system so far.

I don't think anyone will be offended to say that stock subwoofers are not good. In my last car, I bought the "Premium Package", which came with a subwoofer in the trunk. I later found out that it was a "6in subwoofer". My background is in home audio, where anything less than 8in is a midrange "woofer" because they can't hit 40hz. My music tends to be more about soundstage, but electronica can hit low notes, and when I heard that 6in subwoofer fart in the midrange, I bought a 15in JL. Sportage SX supposedly is 7in, which is better, but I'll be installing my sub.