Box specs

when building a box, is it better to have the specs bigger or smaller than the suggested volume? i know it would be ideal to get the exact specs the manufacturer says, but i'm wondering if bigger or smaller air volume is better?

also, what's the deal with polyfill? i've heard some people say it makes the box act like there is more air volume than there actuall is.

As to your first question, are you talking about making mistakes in your enclosure volume?  It really depends on what you're trying to accomplish and what the overall system is made up of, but I suppose in general a smaller than optimal sealed enclosure is safer for the woofer, since it will dampen it more than a larger enclosure and thus make it harder to overpower the speaker.  But the real answer to your question is "neither."  Build your enclosure to the correct size and if it comes out differently from what your speaker requires, rebuild or modify it.

Poly-fill inside a sealed enclosure forces the air inside the enclosure to move more slowly than it would without the filling, so it forces the enclosure to act like it is larger than it really is.  Good quality acoustic-grade polyfill stuffed loosly into an enclosure at a ratio of about 1lb per 1cuft can cause the enclosure to function like it is 30% to 40% larger than the raw dimensions.  It allows speaker builders to under-size an enclosure or to compensate for unpredicted enclosure behavior.

Using two layers of MDF for the front baffle board (or using thicker MDF or extra braces) stiffens the front baffle and helps reduce flexing which is made more likely on the front baffle due to the weight of the speaker mounted there.  It is a common professional technique.

I highly recomend reading www.diysubwoofers.org and purchase of the Loudspeaker Cookbook.

Well... A few good reasons to double up are:  1. Stiffens the mounting surface of the box, the giant whole you cut for the woofer is a weak point.  2. The more solid your box, the better your SPL and SQ (refer to 1).  3.  Ever screwed a woofer in and had the screw strip out the wood? Doubling up will help prevent that.  https://www.jlaudio.com/tutorials/index.html A good site for tutorials, learn more there about all aspects of enclosure (box)_building.  Slightly bigger is usually better then smaller.  If we are talking a sealed box then you will need more power to achieve the same SPL the smaller the box is.  Bigger boxes tend to have boomier, looser bass.  If your porting the use a box calculator to get the port size.  Subs come with a recommend enclosure range like 1.0-.7 feet squared, not one solid number.  If you're building your own its easy to go with one of the designs in the sub manual.  They are usually easy to construct and will deliver a good blend of sq and spl.

Not at all.  Remember that you need to account for the displacement of the woofer or any ports you may add.  Good luck!

sweet. the specs on the sheet include the driver displacement