Regarding that box...Make sure you brace the inside of it really well. I dont think 1/2" MDF will stand up to 2 15's very well...If not properly braced, the panels will resonate resulting in significantly lowered output...PS and also get rid of the 6 x 9 's on it...

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smpl_gy running a smpl system...
one amp, one sub and 1.6 kilowatts of 50hz and below...

yea i said a few posts ago i was going to remove the 6x9s, and 1/2 mdf will stand upto it with the 2 inch nailers on all of the edges on the inside, just need sound help me and my father have a combined of like 65 years of construction/automotive experience and knowledge, but about 2 hours of sound knowledge