DIY Bass cab(s)

A while back a gentleman gifted me a pair of B&C 12HPL76 drivers. These are 12" neo woofers rated 350/700 watts at 4 ohms.



Though they looked okay, both needed to be reconed. The cost of the recone at Orange County Speaker was less than half that for new drivers, so I figured I made out pretty well. These are fairly high end bass drivers, which gave me the warm fuzzies.

So, with a pair of fresh drivers, I set about designing and building a matched pair of bass cabs.


The plot is actually pretty typical for a 12" driver in a 2 cuft cab. The low frequency tail-off looks a whole lot bigger than it is, as I don't really have to EQ for it. The cab is tuned to 53Hz. Any higher and I'd have lost too much bottom end; any lower and it looked as though it might have gotten a bit farty.

What you see below is a design very loosely based on Epifani UL112 cabs. Height and width are the same as the UL112s, but they're an inch deeper. The extra inch in depth gave me a little additional volume that I could soak into bracing. Good bracing is important in a bass cabs, but even more so here because of the 12mm (about 1/2") walls. I don't have an UL112 to take apart, so could only speculate on what goes on inside with bracing and porting. In the end, I did my own bracing and porting and it all works very well.


The cab carcasses are built using 12mm Baltic Birch plywood with all dado & rabbet construction. Drivers are mounted with 10/32 machine screws. There are brass inserts for the woofer and T-nuts for the tweeter.



Interior corners are gusseted with poplar triangle strip. Extensive bracing is with nominal 4/4 poplar.




All loaded up for a quick test. There was actually a test cab previously built using cheap plywood to test basic functionality. The tweeter is an Eminence ADP80 being fed through a one-way crossover at 1500Hz. The 3" ports will be glued in place with epoxy.



All finished, wired, and fiberfilled. Acoustic damping material is 1" fiberfill purchased at Jo-Ann Fabrics. Paint is Duratex. Handles are spring loaded and mounted at the balance points using 10/32 machine screws. The round objects on the baffle are rubber feet that are used as standoffs for the grill. They're attached with a couple of nails driven through the rubber. Machine screws will extend through them into T-nuts to hold the grill in place.





Grill is aluminum perf sheet hand sanded with 400 grit paper and mounted with stainless steel machine screws through the standoffs.


Finished weight is 37.5 pounds each and the sound is phenomenal. Each cab cab handle 350 watts continuous (equates to RMS), 700 watts peak. Lots of thunder here.

Ken...

Last edited by Ken Baker on Tue Mar 02, 2010 12:39 am, edited 2 times in total.

Nice Rig Ken! Looks great.

What did you use to calculate the dimensions and bracing pattern for the cab? How about the fiber fill? Did you move the fiber around to see how much it changed the sound?

Sorry, inquiring minds want to know....

Gary G

What did you use to calculate the dimensions and bracing pattern for the cab? How about the fiber fill? Did you move the fiber around to see how much it changed the sound?

For cab tuning I used WinISD beta. I had a target volume I was after, 2.2 cuft, based on the dimensions of the Epifani UL112. I then added a little depth to allow volume for the planned extensive bracing and built a test cab to those dimensions. The test cab was gusseted and braced but had no fiberfill. Still, it sounded quite good and green-lighted me for working with real wood, knowing that the fiberfill would improve the sound by damping out waves and echo.

Speakers are motors. To work effectively, they need to be mounted to the baffle as securely as possible so that only the voice coil and cone move - NOT the frame. They also need to be mounted in an enclosure that does not itself act as a speaker through secondary induced vibration cause by either the reaction of the frame relative to the cone or from air pressure waves from the back side of the cone. Whew! The bottom line here is to have the sound come from the driver, not the box. A decent analogy to this would be nailing down your bridge for improved tone and sustain, which works by allowing the strings to vibrate to their fullest.

So...

The bracing was done for one purpose: To have as much of the sound as possible be projected by the driver and NOT the panels of the cab. The cab is made from relatively thin material; 12mm Baltic Birch plywood - a little less than 1/2" thick. Even with the fairly short spans of the box, there is bound to be some flex in the material, particularly the back. Consequently, I braced the Hell out of it. The top & bottom are braced to the sides and all four are braced to the back. And vice-versa. There is a great deal of strength in the frame of the woofer, and it adequately stiffens the baffle to the point that I didn't feel it necessary to brace from the baffle to the sides. There really isn't much in the way of space to do that anyway. Finally, a non-sonic secondary benefit of all that bracing is a box that will take a beating without falling apart.

There was no science and no testing for the fiberfill. It was attached to the back, top, and sides using a minimum number of staples to avoid excess crushing of the material. This is pretty SOP for speaker builders.

I think these worked out pretty well. Even at moderate levels, you can feel the pressure waves coming off the front of the things.

Ken...

Real nice job on those cabinets Ken.

How much do they weigh?
Oh I just re-read your post where you answered this- 37# approx.

I could prob do most of my gigs with just one of those cabinets.
How much did the project cost per cab ? if you don't mind me asking.

Thanks,
Bill

Ken -
I couldn't be more impressed. Wow! I know nothing about bass cabs, but I think I can spot quality in design and implementation (well, after several beers I can).
Thanks for sharing your project. If you ever decide to go into building front porches, my wife wants one and you da man! - ed

Real nice job on those cabinets Ken.

How much do they weigh?
Oh I just re-read your post where you answered this- 37# approx.

I could prob do most of my gigs with just one of those cabinets.
How much did the project cost per cab ? if you don't mind me asking.

Thanks,
Bill

Thanks, Bill. I'd guess cost was $225 to $250 per, which includes everything from start to finish. That's a bunch cheaper than a UL112!

Ken -
I couldn't be more impressed. Wow! I know nothing about bass cabs, but I think I can spot quality in design and implementation (well, after several beers I can).
Thanks for sharing your project. If you ever decide to go into building front porches, my wife wants one and you da man! - ed

Thanks, I think.

Re: the front porch... Lean-to, Zap. A few 2X4s, some nails, and a tarp. Done.

Ken...