Originally Posted by jake515
What would it look like if I built (2) well braced 2' x 4' x 4' cabinets with dual 15's in each with a large slot port?
Only 2 cabinets to build and finish and my theater has lots of space to hide big subwoofers away.
I did a 42" tall one that would work well adopted for you: Need help desining subwoofer enclosure for 2 x 15" subs.
The big one on the left:
You can see what it was like inside here: (before bracing)
Basically a big slot port with a 90 degree turn down the long side in the back. I used dual 15" but this modified for one driver would be ok too. Or even two 18".
I used 42" instead of 48" because it just seemed to work better, but you can go 48" if you don't have a table saw to make it easy. I used 3/4' MDF and I used PL premium construction adhesive in all the corners and glue in braces or quarter round trim, which you can see in all the corners. This helps give it extra strength and ensure it is air tight.
Something like this might work for you ?
Basically you want to design it so you can build it easy. 24" x 24" by 48" (or 42") That way you can make efficient use of the wood, but if you do 42" instead of 48" you use the left over for braces. So either will work good. You can have home depot make your cuts for you too. They are simple cuts.
Make it 24" deep by 24" wide by 42" tall. That is about 14 cubic feet before the port and speaker.
If you make it 48" then it would be 16 feet cubic before port, bracing and speaker.
The ideal slot port would be 21.75" x 4" (24" wide minus 3/4" each side+ 3/4" brace down center) and run the full width and depth almost. This will determine what port tune you can get.
So let's take a look at tuning this bad boy:
It's really your choice on tuning but I find the higher tune is more impressive in real life. Don't be fooled chasing ultra low frequencies, because you give up something doing that. It's noticeable IMO. and it's usually not worth it.
I used a 12.5 cubic foot box in my guessing because after braces and driver and port it probably would be about that.
So basically your box is: 48" high, by 24 wide and 24" deep. You can cut the wood exactly like that and make either the depth or width slightly less or more because the wood takes 3/4" which is 1.5" total difference when you assemble it. Or you can do 25.5" x 24" too. You will need to compensate for the width of the material (.75") in determining outside size. But I will proceed with the simple assumption of 2x2x4 feet for simplicity.
A 2x2x4 foot box has 16 cubic foot of volume, and you will likely lose about 2-3 cubic feet of volume for the port, another .35 for the driver, and perhaps a little more for bracing. So I just used 12.5 cubic feet as a guess, but when you build the actual box you can get a more realistic volume using this:
I am close enough though. A little bit difference changes the tune about .5hz so hardly noticeable or important. Close enough is close enough usually.
For the 17hz tune your port would be 4" height by 21.75" wide by 57" Long. That would work for you? 24" down from front to back. Then another 33" or so down the back. Longer ports = lower tune. You need to account for the opening of the port too, so you need to leave a reasonable amount of space to start the port inside. A 14" tune would be really long, you'd need to make it less height (which will increase chuffing and port turbulence noise) and it also can be more problematic for a 90 degree slot port turn. I think 17hz is as low as you'd want to go. You can shorten the port easily to raise the tune to anything you want. 48" gives you a lot of room to go low in tune if you wanted, but if you tune higher you will get increased output in the regions that are exciting with music.
If you raise the port tune a little higher you get something that would work better for music and you pick up a few db of SPL where you will hear and appreciate it even more.
Port volume of a 57" slot port with 4" height and 21.75" width would be this:
57" x 21.75" x 4" or 4.75' x 1.8125 x .3333 which is 2.869 cubic feet. That is the volume of your 17hz port so you need to subtract this from the total box volume. 16 - 2.89 = 13.13
Brace and driver will bring you close to our estimated 12.5 cubes in the model I think. Close enough is close enough
So you need 3/4" MDF (one sheet plus a little more probably, or use other wood for braces)
1 tube of PL premium construction adhesive.
I would use a brad nailer to build it- and use the brads (or screws) as a pernmanent type of clamp. You won't want to use clamps on a box this big. Get a helper, load the PL premium on heavy, fit it and nail or screw it to hold until the PL Premium hardens (24 hours in your climate). Then it's forever. That stuff is strong.
You want to make sure you have a 4" brace down the center of the port- this will help you make sure it's exactly 4" but also keep it strong. PL premium all sides that touch, and shoot brads from the sides, and also into the brace from inside the box. If you want to go back and add glue in 1/4 round or small mdf rips in the corners to make it extra strong and air tight you can do that too. It takes a very small amount of volume away from the box, but can accommodate for a less perfect and skilled construction technique. PL premium is good for filling gaps and very strong. Wood glue is ok, but not good enough for a monster box IMO. If your cuts are perfect and exact wood glue will work, but less optimal PL premium can make up for slight mistakes.