You want to run a voltage reducer. It's the best option. Given the size of the sound bar you purchased this is the reducer you want to use. I have the same size sound bar and this works perfectly.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It's best to hook it to a fuse panel so you don't run the risk of damaging your cart with any shorts. This is what I used:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1