@janlopes really? Where are all the details of your setup? you even say you have tried things? What things? What did you edit? Which file? What did you type? Did you enable audio out properly? What do you have the volume level set to? What emulators have no sound? Which games? Which image? Official? Or a pre-loaded one? To enable others to help you please go back and read this
I picked up one of these cables from a Goodwill for $0.50 but I couldn't get it to work on my older 32" 720p HDTV. I guess I should note that I have an RCA switch box that I was running through (so I can switch between my Blu-ray player, Wii, GameCube or PSX on that TV). There's probably something I needed to put in /boot/config.txt. I didn't really try very hard because it already works great with my HDMI cable.
@Jakob-Holz glad to see it is working for you. Unfortunately so many guides tell you to add lines to the bottom of the config but fail to mention it is already on the page somewhere else and may or may not be # hashtagged out.