The Ron Apple Memorial Bass Cabinet

This is a bass cabinet I customized for a friend. I didn’t do the paint job—it was already painted when I got my mitts on it.

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This cab started life in the 1980’s as a Peavey 115.

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Typical Peavey gear, nothing fancy but it got the job done.  One 15″ driver in a vented cab.  The cab was a mix of plywood and particle board, tolexed, with one 1/4″ jack and one strap handle on top.

I don’t know how many times this cab changed hands, but I do know that in the ’80’s it belonged to Ron Apple, who played bass in the Bohemians.  The Bohemians nearly comprised the entire music scene in Novato at that time (approx ’83-’84) and they were a great inspiration to a lot of us who had dreams of making music.  They played lots of local venues–San Marin High School, the Novato theater, various rec. centers.  They had a great jangly melodic sound that with sixties pop and psychedelic influences.  They had a dedicated tambourine player, Joey Kosdrosky.  Imagine having the balls to get up there and play tambourine and do your own weird style of dance.  They did their own thing their own way, that’s what inspired me.

Anyway, the current owner of this cab is Pat “the Rat” Powers, AKA Pat Riot, AKA Ned Zapariah.  The cab had seen many years of use and abuse in his previous bands, most notably RETOX, whose name is still painted on the cab.  When he brought it to me the speaker was shredded and the grille was long gone.

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Before

 

Modeling the Kappa 15LFA in WinISD
Modeling the Kappa 15LFA in WinISD

The original plan was to just slap a new 15″ driver in there, maybe tune the box a bit, and hand it back to Pat.  Thing is, the only 15 I had on hand was a Kappa 15LFA, which wouldn’t be well suited to Pat’s playing style, which is definitely “lead bass” in the mode of Flea or Adam Clayton.  He’s not content to hold down the root and fill out the low end.  He needs to cut through the mix.

As it happened, I’d already been noodling the idea of a 15/6 cab with the Kappa as the low and an Alphalite 6A CBMR for the mid.  I’d arrived at that idea simply because the Alphalite was relatively affordable (compared to, say, an 18Sound mid) and its sensitivity matched that of the Kappa, at about 99 dB 1w/1m.  The cab I’d been modelling in WinISD was about 2.8 cubic feet.

When I measured the volume of the old Peavey it was right at 3 cubic feet before subtracting for the driver, port, etc.  So basically I’d just been handed the right size cab for the project I’d been envisioning.

Modeling a crossover in LTSpice

So I had a box, it already had a hole for the 15 and a 6″ port about 7″ deep, which WinISD told me was pretty close to what I’d want.  But I needed to design a crossover, which I’d never done before.  So I got on TalkBass and started a thread, which wound up being crucial.  I got tons of good info, got PMs from experienced guys offering advice, and got turned on to BoxSim, which I wound up using to simulate the box & crossover.  I also learned how to simulate a crossover in LTSpice.  The trick was to model the speaker as an inductor, assigning it a series resistance of approximately what you’d expect at the crossover frequency and an inductance straight off the Thiele-Small parameters for the driver.

BoxSim turned out to be the most helpful for getting ballpark values for the crossover.  It lets you input all of your box and driver parameters, then simulated the crossover taking into account the effects of the box tuning, baffle step, etc.  It will even optimize the crossover for you, adjusting whichever component values you allow it to adjust.  I based my initial crossover design partly on BoxSim’s optimization, partly on advice from an experienced builder on TalkBass.

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some bracing
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Oops, cut the wrong hole and had to glue the cutout back in. Guess that’s where I’ll mount the memorial plaque.
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Once I’d ordered the crossover parts and 6″ driver, I set to work on the cabinet.  There was very little bracing, so I added some—spine and girdle bracing, as well as a couple of runners from the bottom of the baffle up to the girdle brace, on either side of the 15″ hole.  All the bracing I added was 3/4″ poplar stock from Home Depot, glued in with PL Premium construction adhesive and tacked into place with a brad nailer.  I also cut holes for some inset handles I had lying around from a previous project.  The stock single top strap was definitely inadequate.

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Final crossover

Once I got my parts I built the crossover on a scrap of 1/4″ ply, installed that and the 6″ driver and put the whole thing together to try it out.  I’d been warned about the Alphalite’s impedance spike around 500hz, and I’d thought I had crossed over high enough to avoid it, but no dice.  Farty noises from the 6 with any loud midrange-y notes.  Back to the drawing board.  BoxSim told me that I needed a bigger cap and smaller inductor on the HF driver.  I dug out an crossover from an old, failed project and found to my surprise that the parts I had on hand looked like they world work pretty well.  In fact, I couldn’t sim anything much better.  So I rebuilt with the new (old) parts and blammo!  Good sound!

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BoxSim frequency plot

I finished up by shortening the port a bit, which brought the box tuning up to about 48hz.  I also added some fiberglass batting (the cab as it came to me had no stuffing, unless you count the random garbage floating around inside [punk rock!]).  I tacked on some grille supports (hardware store moulding and weatherstripping), cut the grille material (screen door kick guard, OSH, $10) to size and screwed it on.  The memorial plaque I made from some leftover mild steel sheet using a cheap set of alphanumeric punches.

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