Stereo & Electronics - help my horns don't work at all

I've already done a search on horns, and have found most of the info i'm looking for. My question is this: My horns are no longer weak - they just don't sound at all. Do I replace both the high and low tone horns, or do I just replace the low tone horn?

Thanks in advance.

I went ahead and replaced just my low horn. It works perfectly now. But anyways, thanks to the guys that answered all the other horn questions. It helped me a lot.