PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES
According to that site, a single 12" driver with a 17mm one-way excursion, tuned to 34Hz needs a minimum port area of 31.66". And the lengths of the port sides to be 5.6" to achieve that area. However, even if I bring the port down to a 5x5 square opening, the length of the vent has to be 25". The problem is that in order for the box to successfully utilize this port, it has to be almost 3cu.ft. - while the specs on the Eclipse sub we're getting suggests a 2cu.ft enclosure.
My question is, would using a 4.5x4.5 port, tuned to 33Hz be a wise alternative? This would shorten the necessary port length to 21". Allowing for a smaller volume. From my calculations (and I'm not up to drawing another diagram at the moment) a H17.5 x W17.5 x D16 would allow for the 4.5" square port. The effective port length across the top would be 13", and I'd have 8" going down towards to the bottom of the box.

I'm having a really difficult time determining if I'd still end up with enough room to mount the woofer on the front of the box. I think it will. My problem is that I don't know how far away from the edges the mounting hole has to be so that I don't fudge up the structural integrity of the box. It'll be made out of .75" MDF.

Also, it seems logical to me to measure the length of the port through the middle. Is that correct? You wouldn't measure the longest are shortest side to get the length of the port. The average would be a line right down the middle, I think. That's how I've been figuring it out.

I'll draw another box up at the new dimensions. I get 80% through each diagram and I notice something else that won't work... lol

This is hard.

 

Hopefully that makes sense to you experienced box builders as well.
17.5 x 17.5 x 16 will give me a 2.15cu.ft box. Then I'd subtract the volume the vent walls take up from that amount. And I end up close to the 2 cubes. 2.07 by my calculations.

Can this thread be moved to the proper section? I screwed up.

 

your drawings look to be fine. your right where you wanna be, betweent 33 and 34hz. a one hz different wont make a noticible difference in a daily setup

 

Jalat, what would you consider the minimum allowable distance of the sub mounting hole from the perimeter of the MDF? An inch? Or is that too close.

 

I tend to use 12-16sq inches of port area per cubic foot.
Generally work out ok for me

 

I'm not going to get that much out of this 4.5 x 4.5 port opening. It'll only yield 20.25 of port area for this box. So just over 10 square inches per cubic foot. Are we going to experience port noise by having that small of an opening? I keep reading that keeping the port square, or as close to square as possible, is ideal. So that's the direction I've gone. Yet I'm struggling with keeping the volume just above 2 cubes. And in a configuration that meets my fiancee's requested size - SMALL. lol

I still need to know how close to the edge of the MDF the mounting hole can be without causing any issues.

 

When the manufacturer states the recommended volume, have they already taken the displacement of the driver into account? This 12" Eclipse has a displacement of .52 quarts, or about .02cu.ft. I would have thought it was more than that.

 

i dont think you will experence a large amount of port noise. the woofer may become a bit choked because of the lack of sq. in. of port but it really shoulldnt be an issue. as far as the sub mounting, i like to make the piece an inch and a half larger that the cutout. so a 12" sub gets a 13.5" baffle. an inch does cut it close but can be done.

 

Just got in from Lowes. $30 for a sheet of 3/4 MDF, and I figure $5 for woods screws, and $5 for a bottle of wood glue that I would not use up completely. How long should the screws be, 1.5"?

I don't have the tools to cut the MDF, but I have what's necessary to put it together.
How much would someone charge me to have them cut the board up to the sizes I need? I also want the outlet and inlet 'mouths' of the port to be rounded off with use of a router.
When putting the walls together, what should I use for spacing between the screws? I helped a buddy build a simple sealed box a few years ago. I remember pre-drilling holes for each screw location due to the MDF cracking along the edges without pre-drilled holes.

 

i space my screws about 2 inches from the edges of the two pieces your putting together. countersinking is always a bonus cause it looks cleaner. just remember not to use too many screws, cause it can honestly hurt then enclosure. one screw every 3-4 inches