Hi Bro EngBok, sorry for asking noob question, should i place this acoustic foam all over the wall behind speakers? or just 1 or 2 of standard size?

been studying through forums and articles still couldn't find out how should I utilize them..

also should i go for http://forum.lowyat.net/index.php?showtopi...19&hl=wallcover this or just normal Fabric Wall Covering aka wallpaper for better absorption?