I really don't know what is but I've seen Chris martin using it in a lot of acoustic performances, somek ind of rubber thing in the sound hole?

 

Does anyone know what they're called and what they are for?

 

Greetings from the Bear

Don't really know what they're called, but i just call it a soundhole plug. They're used on acoustic guitars with pickups, so that the majority of the sound comes from the pickup, and not the soundhole. This way the microphone in front of the guitar(vocals) won't pick up as much sound from the guitar. This is desirable when you want a separate channel for every instrument/voice..

Ah thanks for the info. I think I'm gonna buy one then since I am singer and rythm guitar dude in a new band and I just bought a micced acoustic guitar. Cheers.

I have one...but I don't have many uses for it...I had to look it up, but it is called a "feedback buster"

ohh I've been wondering about that thing for a while and I have another question, is that the reason why the sound of the string of the guitar sound like "wahh" or so like in AROBTTH tour if you listen to see you soon for example in live 2003 or any other with acoustic guitar the sound of the guitar is not the same as the normal or the sound of their guitars on the most recent tours ohh and in the scientist also live 2003 the acoustic guitar doesn't sound it's just the struming.

 

PS: would anyone know the name for the "feedback buster" in spanish???