From TalkBass Wiki
My cab has been built by a local furniture hobbyist... (I encourage you to ask around and find someone in your area). Once he has finished the woodwork, I'll do all the finishing, electronics and outfitting. What this project is not: A bargain build. I know that this CAN be done on the cheap. I wanted it to be done correctly and without compromise. In the end, it will cost somewhere between a nice production cab and a boutique build.
The first set of pictures have been provided by the builder, hereto known as "Andy", since that's his name. He supposedly will be posting HIS take on the build on his own online space including commentary. I'll be happy to post that link when and if it comes to me.
1/2" Baltic Birch (cabinet grade) ply, all dadoes are 1/8". All measurements are within 1/32". You can see that the build starts with one side, the front baffle, shelf and the top bracing unit. The top bracing piece (including mid-chamber bottom) are all one piece of wood. The other pieces of bracing are individual.
Three sides...done. Additional side has been added, all but the lower bracing is in place. The pieces are glued in place, Brads are used as a secondary fastener, but I'm not sure how much they actually add to the structure. The only screws that are used are in the back, and that's so I can get in and do what I need to, to go over the seams and prep the interior once in my hands. Andy doesn't use any metal fasteners, and prefers traditional joinery.
The box together without top and bottom. The back is fitted but not attached. The final cab came to me with all screw holes in the back drilled and counter sunk along with pocket-drilled holes so there are no screws in from the top. There are screws and drill holes in the bottom, where they won't show.
Next up: pictures of the build I took earlier today once getting the cab home:
Pieces and parts:
Speakers:
15” Speaker: Eminence 3015LF: [1]
6” Speaker: 18 Sound 4ND410: [2]
Look around before buying. I got my 15” for around 135+ 5 dollars shipping, and the 6” came for 135 shipping included. Like deals should be fairly easy to come by. While there has been plenty of talk of substituting cheaper speakers, I haven’t found a good argument to skimp. You’re building this cab for a reason, so why not do it right.
Some words about electronics:
CROSSOVER:
I've chosen the Eminence PXB2-800 for the crossover. Its an 8ohm unit, and I chose the 800 as my crossover point because as most of my sound is lows with some serious roll off on the highs, I want as much of the signal through the 15 with the 6 providing the upper reaches as needed. For me it means that the 15 will probably do about 85% of the heavy lifting. Not knowing ANYTHING about the real tech behind how the crossover works, I've done some research and basically even with two 8ohm speakers because of how the signal is split between speakers, and since impedance is not a static figure but variable changes with the wavelength of the sound produced, the amp will still see an 8ohm load. This way I can add a second cab (probably a fEarful 15 sub) at some time as needed.
PDF for Eminence PXB series crossovers: [3]
L-Pad:
For those like me doing this for the first time, this is a “loss pad” or an attenuator. You can certainly purchase one that’s a an adjustable pot, but I was just looking to balance the two speakers. The 18 Sound 6” is more sensitive than the 3015LF, so its suggested to “pad” it back by 3db.
My L-pad is 3.5 db, because the values for the two resistor components were a lot neater at 3.5db rather than 3. For others like me, doing this for the first time the L-pad is two resistors, one in series with the speaker, one in parallel. Of course, there’s a pile of sites that have L-pad calculators, but I like the Weber site: [4]
There are also a pile of different sites that have resistor series/parallel calculators to help figure out what resistor values will work best. (What helped me as a noob was to recognize that speakers are resistive devices too, so if you can figure out how impedance works with your cabs in series or parallel, you’ve got it down). Because the R1(Series) value is 2.65 ohms, running 3x8ohm resistors in parallel works perfectly. The R2 (parallel) resistor should be 16.12, so 2x8 ohm resistors in series does the job. Charlie Escher pointed out that 3.5db works out very neatly, and I appreciate his help!
Resistors: 5x 8ohm 50 watt non-inductive. Mouser and Parts Connexion both had good viable parts, the ones from Parts Connexion came out slightly cheaper:
Part# HUNT-016-68515 8.0R / MRC50
Vishay 8 ohm 50w non-inductive resistor
Wire: My wire is 16 gauge 100% copper. Mine came from an automotive store, but only because I couldn’t find any 16 gauge at any local electronics places and I didn’t want to have to mail order for wire. 18 would probably work as well, I notice that my Berg cab has wiring much smaller than 18 and its never given a problem. Larger than 16, and you’re probably going to have trouble soldering some connections.
Here’s my L-pad, done and ready for installation:
-green in lower left is the positive from the crossover.
-green in top center is the positive to the 6” speaker.
-red in the lower right is to the ground.
Further L-pad notes: Keep in mind that resistors work by creating heat, so space them appropriately for the fact that your array may see up to a couple hundred watts. If you're concerned, it's been noted in the 3rd fEarful thread that you can mount your components on an aluminum plate as a heat sink or probably easier, use a few washers under the components to create some air flow. Of course, don't use any sound deadening material over the L-pad or crossover.
Both crossover and L-pad will be mounted on the 'shelf created by the port. Greenboy has suggested that the upper reaches of the cab would be a good place for mounting (the back of the mid-chamber, etc.) as it wouuld shorten wire runs from the input jack plate. I've instead, gone against this good advice because I want to have access to these parts for future 'in case of's. Mine will be divided, with L-pad on the left of the shelf, below the mid-chamber (I'll wire it up through the holes in the bracing with zip ties to keep the wiring solidly in place), and the crossover will be mounted to the right side of the shelf. This will allow me to use some batting on the shelf, directly below the speaker.
back to Fearful™ 12/6 & 15/6
