Quick ?

[jkh04200]

How big do speaker boxes need to be? I'm installing some 6.5" under the rear seat. I could go as shallow as 2".

[thmper321]

6.5" speakers unless they are specified as woofers are typically designed to be run free air. Theis means there is no need for an enclosure. As long as you have the speaker mounted to a good solid surface you should be good. If you put it in an actual enclosure limiting the space it will negatively effect the sound of the speaker.