building sub box

Hello Everybody I am trying to build a subwoofer box for 2 12" sundown woofers. The specs say I need 2.5 cubic feet tuned at 32hz. My question is do I need a total of 5cubic feet and can it be tuned at 30hz.? I'm still learning about the hertz stuff so please bear with me.

Your correct about 5 cubic ft. As far as tuning to 30hz yes you can. Look in to bassbox pro software. It will help.Gary Sather

im guessing that you plan on building a ported/vented box for those subs. going off of factory specs can be a bit confusing when you are trying to change the shape of the box but still end up with the same specs so maybe i can clear some stuff up for you that will make it easier to design your box. one thing that most people dont realize is that when they tell you the sub needs 2.5 cubic feet that they mean internal NET airspace after you subtract the volume of the sub woofer, port volume, and any internal bracing. usually when you just build a box going exactly by the manufactures dimensions and cut list they will already take these things into account and you are left with the necessary airspace. if you would go and add it all up what the gross internal volume of the factory spec box you will see that it is going to be a good bit bigger than 2.5 cubic feet. so if you redesign the dimensions of your box you will need to calculate what the overall internal airspace of the original box and go from that number. if you start with 2.5 cubic feet then your box will come out very different from the factory spec box you wanted. did that make any sense to you?

Thank you very much, I was thinking about all that today. Yes it make perfect sense. Also wanted to ask about the tuning frequency please correct me if I'm wrong, so far from what I've read online if I tune the box at a lower frequency like 29hz-32hz does that mean that the subs will hit harder? The subs I have are 2- 12" sundown x- series. The factory specs say 32hz. Any info will greatly appreciated.

the tuning frequency of the box is the frequency at which the port is designed to resonate and if done correctly this gives the subwoofers a boost around the tuning frequency. it is not true that the lower the box is tuned to the harder it will hit, in fact its usually the exact opposite. a low tuned ported box usually will do more for the quality if the sound rather than the actual volume. now that is a big generalization of what happens and with the right combination of a low tuned box and a sub that is designed to work together with that low tuned box then it could be that a sub will get louder as you tune lower, but this depends on a lot of different factors. i said that it usually works the opposite of how you thought meaning that usually the subs will hit harder with a higher tuning frequency, but this also depends on a lot of different factors. BUT, a lot of why it seems that a higher tuned box is louder is that the human ear is more sensitive to higher frequencies than lower ones. in fact most people cant perceive sound lower than around 20-25Hz. so by tuning a box lower than 40 Hz you are really only working to compensate for your ears lack of ability to hear that low. lower frequencies are more felt by your body than heard by your ears. some people will also tune their ported boxes low because it produces a more physical effect and tends to move more air so it will SEEM as if you are hitting a lot harder than you really are and if you were to actually measure the SPL of the low tuned system you would probably be disappointed with the numbers. if you want a good combination of higher SPL numbers and physical effects of low frequency bass then i would stay in the range of 35 - 40Hz maybe a bit higher if you wanted to but i wouldnt go any lower.

I understand thank you you've been very helpful. I will keep all this in mind when I decide to start the project. Do you have any recommendations on an amplifier I could use for these subs they are 1250 rms according to factory specs.