How to protect the wood finish of speakers.

Another wax product I use is Sunwax with UV protection...combines UV inhibitors with a unique blend of carnauba wax, beeswax and orange oil.

Bees wax is the best I have found. Liquid Gold can tend to dry out and require more applications. I have switched to a bees' wax product and buff it it lightly between applications. And as a accasional measure I use a citrus cleaner to remove any wax build up and re-apply the bee's wax. As a a final not I mean no offense to those who use Liquid Gold I used it for years and have just found something I like better.

One thing an owner needs to consider is the type of finish on wood. Most speakers of modern manufacture are going to be finished in some sort of catalyzed impermeable finish. No amount of beeswax, oil, or whatever is going to have an iotas effect on the wood. It may make the surface look pretty, but it's not going to affect the actual underlying wood unless you have an oil or wax finished veneer. And those are fairly rare these days. Conservators wouldn't trust sunscreen products to protect any valuable wood item. They may help a little, but don't be lulled into a false sense of security and think they'll stop sun bleaching, especially in places like Florida, Arizona, or Hawaii.

curtains on windows work pretty good

Photon46 is correct. Two options, curtains, or a UV filter film (made by 3M) installed on your windows. Also, periodically, switch your left with your right speaker around to get an even tan.