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Is this box okay? Its in a Mazda 3 sedan.

 

for ground and pound that box needs to be deeper.

 

How much deeper should the box be? Right now its at 14". Would I hear/feel drastic results with a change? I want to be able to massage my kidneys with these subs lolll.

 

Your ports could be too small to push enough LF air inside the cabin...even if they are tuned to 30HZ etc. Build a deeper box. You'll get louder with less power required from your amp. Simple Box physics, a low power amp can push a sub to it's max excursion limits without having to use alot of current to do so, when the sub is placed inside a large box cavity, compared to the amp having to fight rear cone displacement in a smaller box....just to be as loud. Although freq's above 60HZ can also be labour-ous for an amplifier also. I had the same set-up as you, except I ran my ports through my rear deckofmy car...my box was about the same size as yours...I hit about 139db SPL with only 380-423Watts rms off an old RF amp....and 2 12's.

 

solid bro!