Box Building/Relays

Hello-

I have a few questions on building an enclosure. Ok say I am building a box for 1 subwoofer out of 3/4 inch MDF. I understand the formula of H x W x L will give me the internal volume. Say H = 15 , W = 25, and L = 20 for my Box. Using the formula that comes out too 7500. I know 1728 Inches is 1 cubic foot, so my box would be 4.34 cubes? Now if i did that right i am assuming, in what part of that formula would i take out my material, minus 3/4 or .75 from H/W/L? Do i take 3/4 out of all of those numbers (H/W/L)?

Off the subject, I also have some questions on relays. Using 2 5 prong relays for in an amp rack. I want to use one for turning on 2 cooling fans, and 1 for turning on neon lights in the amp rack. Could some one explain proper realy hook up for me in dummie terms. I could not understand the terms used on the site for explanation. What I am looking for is what prong is the remote wire hooked into from the head unit to send the signal to turn on the lights/fans. What prongs are for constant power, ground, and to the lights/fan from the relays?

Any help from any one is greatly apperciated! Thank you for your time.

pin 86 = remote wire

pin 85 = ground

pin 87 = constant 12v fused

pin 30 = to accessories

Hi Dose3782, if your material is ¾ inch thick, you'll need to subtract 1.5 inches from your outer dimensions. So if your outer dimensions are 15H x 25W x 20L, then you would multiply 13.5H x 23.5W x 18.5L to determine the interior volume of your enclosure. ( 5,869.125 ÷ 1728 = 3.396484375 or 3.4 cubic feet ) If you are using any dividers or braces, you'll need to subtract the volume of each divider and/or brace from your interior volume.

For your relay question, wire each of them as hot_shot_guy123 explained above.

the12volt

Thanks for the help on the formula, been a while since i have done any box building and lost all my notes. On the relay wiring, can i wire it like this..

pin 86 - remote

pin 85 - ground

pin 87 - constant 12v fused

pin 30 - wire to another pin 86 for the remote wire

Just curious, i wanted to dedicate a relay to sending the remote signal as to not branch off the one remote wire ran back to  my amp rack.

Thanks again guys great site and very friendly people!