Originally Posted by mfrey0118
...Unfortunately, I have zero box building skills. My room is big too, ...I figured 3/4" MDF is a good place to start. I also have a fully activated copy of BassBox Pro 6. ...How to I make the port. If using PVC...What tools do I need? How do I measure out a perfect circle and cut it? ....
The least challenging approach is sealed. It's also smallest, lightest, etc.. Find what size box will keep the driver within Xmax at rated amp power, and build a box that internal volume. Stuff it with low-density (fluffy) insulation or fiber fill until it sounds good. Put it in the corner with the lowest ceiliing, so you get the most efficient coupleing to the room and maximize room gain.
The most challenging (and highest performance) approach is to design a folded horn, but I suspect fabrication alone would be a sufficient barrier.
That leaves ported, and with enough room for the box, I'd second imagic's LLT. You have box design SW, so look at very large volumes and very low tunings to get an LLT. Plan to put it in the same corner as above, for maximum output.
MDF is a good place to start, but plan to double-up on the baffle (side with the driver), especially if you want to recess vs. surface mount the driver. The one advantage to surface mount is that no one sees the hole you cut, so a simple jig-saw is all you need, and the ability to draw a circle (needs a nail, string and pencil) and follow the line. A router and circle jig is commonly used, especially for accurate circles with crisp edges when recessing a driver.
Cutting straight side panels is important. Pay someone to do this if you don't have a good table saw, or you'll need to fill gaps on the outside and add sealant in the interior corners.
PVC makes great ports. Be sure to model with the intended pipe ID. I like to cut a recess on the inner side of the port panel and epoxy the pipe there, where there are no critical dimensions. I then complete the (undersized) through hole and trim with a router roundover bit. I get a smooth transition from MDF to PVC, a nice flare to the port mouth, and no need to worry about how well the PVC finishes as its MDF that I'm painting. Some like to cut a slip-fit through hole, then glue and route the roundover... no functional difference and paint holds well to a routed PVC surface, but you can see the seam.
Assuming ported, you'll want a layer of acoustic absorber on the walls, perhaps 1-2" thick, to damp any harmonics coming off the sub. Anything from air-permenable foams to purpose-designed materials. I use carpet underlayment foam as it's cheap and effective. No one sees what's inside, and in a sub, it's less critical than higher-frequency speakers. Add nothing but braces in the open interior space, especially between driver and port, as you want that volume to resonate, so the port has functional output.
Add cross braces at roughly 8-12" spacings. 1-1.5" hardwood dowels are easy to use and take up minium space for their effectiveness. Cut them a little short and slip some tapered shim stock (like you'd use to align a window or doorway)under when you glue them in. Some do very elaborate braces, but it's inside so audible benefit counts more than visual appeal. The braces don't need to be exactly spaced, and any that touch should be glued or separated to prevent buzzing.
Then be prepared for "room modes;" spatial variation in loudness. Above grade construction with single-layer sheetrock walls and windows/doorways can mitigate a lot of room mode issues compared with a sound-isolated room. If there are obvious issues, you do have options, but hey're more complex than I want to go into here.
Regardless, take the leap and build something. Your first project may not be your best, but it's how you learn...
FrankEdited by fbov - 9/25/12 at 9:02am