Is it bad to have more cubic feet then recommend by the company,
Example 10"=1cb another 10"=1cb and a 12"=2cb adds up to 4cb but the box is 8cb is this bad

 

Yea, it can damage the sub and it will destroy sound quality, think of it kind of like backpressure on exhaust haha you want just the right amount. Also when doing this you have to account for the subs displacement too, and bracing, and hopefully your going to put some kind of wall in between the subs. And I wouldn't run two 10's and a 12 at the same time, it can cause noise cancellation issues. Not really sure how or why but I've read it and heard it in a lot of places. Hope this helps man

 

At 8 cubic feet, I hope that box is going in the bed. Also, 2 cubic feet is an awful lot for a sealed box. And yea, running different size subs is a no no.