What is considered abnormal as far as how much the woofer cone moves when music is playing. I am running some psb image 2b bookshelf speakers with a vintage technics receiver and sony cd player and my woofer seems to be bouncing back in and out noticably. Its even worst when tunning into radio stations. Its usually noticable with bass driven music especially ambient stuff like Brian Eno, it seems as though the woofer wants to jump out , i'm worried I might break my speakers. What is odd is that this does not happen when I use my psb's with my new Rotel RA-02 amplifier. To what degree is it considered normal for a woofer to bounce ? Also, can it be that it is the receiver that is causing this(maybe due to its age)? Thanks