The Eminence Kappalite 3012HO is not usually on the short list to use for a DIY 212 bass guitar cabinet because of its somewhat attenuated low end response and pronounced high mid peak. It is, however, a powerful light-weight woofer and I've been impressed for some time with its WinISD profile versus a number of other twelves. With the proper cab design, HF crossover, and matching amp this box should slam. I have cabs built around the 3015LF and 3012LF woofers which have all the low end extension I'll ever need. This is a different flavor I wanted to check out. Three things prompted me to go through with this build:
1. The Genz Benz Streamliner 900 amp. I'm pretty fond of the tube sound and heft this little amp delivers. Its bottom heavy, mid-scooped profile matches up well with the attenuated lows and juiced up mids of the 3012HO. It should be able to fatten up the 3012HO's nicely while those drivers should keep the STM900 low end tight.
2. I read that an inductor tuned at about 2kHz could be used to attenuate that pronounced 2.5 kHz peak to smooth the upper mids out (Bergantino AE212). I checked this out with the Eminence 3012HO frequency response and it looked like it should work.
3. I wanted to test an "umbrella" bracing configuration which should prove quite strong and minimize cabinet vibration.
Most sensible players looking for this sound would just contact Alex and order a Barefaced Super Twelve T but I enjoy the design and build process. For me this is a proof-of-concept build to put my speculation to the test. I considered a number of layouts and port configurations and then Jim Bergantino came out with the HD212. The symmetry and balance of this layout just struck me. It provided a compact format which would work well with my somewhat large HF waveguide and the triangular ports can be sized to the recommended dimensions. Here is the layout:
I used WinISD alpha and Eminence Designer to evaluate the size and tuning for this box. WinISD has better graphics but I have more confidence in Eminence Designer's porting recommendations. It also has features that WinISD doesn't such as driver volume, the effect of cabinet insulation, and recommended port size at X-max to avoid chuffing. Together these provide a capable, low cost DIY toolset.
From similar cabs on the market and WinISD models, an internal volume (Vb
) between 3.3 and 3.4 cu-ft seemed to optimize low end response and excursion limited power. I've seen several 50 Hz tuning recommendations for the 3012HO but I figured Fb would be close to the large vented cabinet design on the Eminence website. After accounting for drivers, handles, port volume, and bracing the net internal volume came out to 3.37 cu-ft. Eminence Designer recommended a tuning frequency (Fb) of 53.0 Hz with 43.7 sq-in of port area to avoid chuffing. To make the dimensions easier to work with I ended up at 53.5 Hz. This moved the -10dB point up from 42.8 to 44.4 Hz, but lowered the -3dB point from 77.0 to 69.0 Hz and increased displacement limited max power from 601.8 to 647.9 watts versus the 50 Hz tuning. I liked what I saw and moved forward. Combining the WinISD response up to about 400 Hz with the Eminence website 3012HO response data and adding a -6dB/octave (1st order filter) at 2.0 kHz generated the following:
Along with attenuating that 2.5 kHz peak this filter provides another benefit by lowering the crossover frequency by about 800 Hz. Crossing over at around 2.8 kHz should eliminate that upper mid/low treble hole often present with 212's crossed around 4.0kHz and provide a smoother mid/high transition.
I like the high frequency extension a 2-way system provides but detest the harshness of a cheap tweeter. The JBL HPTF-99 is a very nice 90x90 deg short throw HF waveguide I had left over from my nEarful 15/6/1 builds which is good for crossovers down to 2.5 kHz. This is a good match with a quality 1" HF driver like the Selenium D202Ti. This handles 60 watts rms with a 106 dB/watt sensitivity and very even response between 3 to 10 kHz. I'm not a crossover designer but knew what I was looking for so I contacted Ralf Patterson who provided an outstanding crossover for my 1212/66 build. He has done several 3012HO crossovers and confirmed that a 1st order low pass around 2.0 kHz should work as expected. Drivers and crossover - the heart of the cab ($570):
I was thinking about trying a composite build but didn't want to struggle through the learning curve so I decided on 12mm Oukume marine ply (aka Joubert) which worked out well with my 1212/66 build. This is high quality, high priced 9-ply wood with a good strength to weight ratio. It added $90 to the cost versus birch or Auraco but is lighter than either and stronger than the Auraco. Here is the cut sheet. Some of the final dimensions were adjusted for the wood's actual thickness of 7/16".
This first construction shot provides a view of the internal bracing. Large holes for drivers, handles, and the jack plate are reinforced with double-thickness ply. This adds strength without too much extra weight and works well with Recex screw mounting which I much prefer to tee nuts. PL Premium and a nail gun with 1.25" finishing nails provide solid construction and don't require a large number of clamps.
Here are front and rear shots of the unfinished cabinet. Holes were filled before sanding and edges were rounded to 1/2" radius. Cutouts and small housings were added for casters. The umbrella bracing is a set of six 45 degree angle braces 10.75" on the long side which tie adjacent side and back panels together. Two braces are provided for each side and one each for top and bottom panels along with a laminated front to back center brace which serves as the umbrella handle. The spline braces provide rigidity of their own and distribute the load of these angle braces over a larger area. I've never had vibration issues before with cabs but this is very solid. The weight of the empty cab at this point is 25.0 lbs.
Three coats of roll-on Duratex were used to finish the cab. Corners, handles, casters, feet, and open-cell polyurethane foam batting were then installed. Cabinet weight is now 30.3 lbs.
The crossover was mounted on the lower tri-port shelf and the jack cup fitted with two speakon connectors and a 100 watt 8-ohm mono L-pad for HF horn adjustment. One speakon was wired to the crossover input for 2-way operation and the other wired directly to the woofers for 1-way operation. This cab can't be in the middle of a daisy chain. Only one jack at a time can be in service. I'll be using the 2-way most of the time but thought full range to the twelves would add flexibility. All wiring is 14 or 16-gauge twisted pair. Finally, the drivers were mounted. Weight at this point is 55 lbs, same as the Berg AE212.
The 28"H x 21"W x 15"D size is easy to move around. Here are front and rear views of the finished cab:
Now it's time to check this little beast out.