Wrong. Cold air is more dense and therefore it is more difficult for sound to travel. Any car I have been in has been louder on warm days. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif
On the other hand, the constant cold will keep the voice coil(s) cool, so in theory, they should be able to take more power.