Hello, I'm a newby at audio electrical engineering. I would like to build headphones that can do double duty as room speakers (in both situations they would be plugged into an ipod headphone jack). What I mean is, I would like to incorporate speakers that are sufficient for playing music ambiently, but then, when a (volume-limiting?) switch is thrown, the speakers max out at a certain volume that makes them able to safely be used as headphones. Would 85db speakers be loud enough for this? Should it be more like 90db speakers? Do I need to have an amplfier built in as well as a volume limiting element? Any help or advice would be greatly appreciated!! Thank you!