Guerrilla Engineering:

the art of “run what you brung” technology.

History

This is a story about how I built a 1 x10” bass cabinet for my rig for no money. I was able to find enough materials from leftovers of former projects to assemble this project with no cash outlay.

This is a long story so prepare yourself.

Grab a beverage.

Smoke ‘em if ya got ‘em.

Here goes:

I’ve been building speaker cabinets for some time. I’ve built p.a. mid cabinets and monitor cabinets that held up and worked well for years. I’ve repaired my own gear and rebuilt several speaker cabinets. I come from a long line of do-it-yourselfers, and I’m willing to have a go at anything speaker related. I’ve never sold any of these pieces. I keep them around for when I get bored and get restless enough to get creative and actually build something.

I come by that honest.

My dad built three boats from drawings. He could improvise and come with up a solution for building just about anything he wanted with sweat and ingenuity.  He called it guerrilla engineering, and that idea has stuck with me ever since.

By taking what I had laying about my household for years and turning it into something useful, I made no trips to the store and made no online purchases which makes this the perfect Guerrilla Engineering project.

Here’s some background on me:

About 7 years ago, I got back into playing music. My 35 year career as a semi professional musician was culminated after a 7 year period of playing nightly to make a part time income while working full time at a day job. I played in a lot of bars and was an opening act at 1500 seat venues a few times. Just local stuff, but as it turned out, my musical ability was very profitable in a part time job kind of way.

I stayed busy doing one nighters and house gigs. My gear was lean and durable. Short of going on the road, my gear was put to a mighty test, and the pieces I needed most held up remarkably well. To be honest, my gear wasn’t always treated with the respect it deserved, but it held up under a lot of traveling sometimes under the worst circumstances. Finally, my kids were grown and on their own, and the need was no longer there for me to put in 80 hour workweeks. Suffering from severe burnout and near exhaustion, I stopped playing in bars for 7 years.

Those 7 years of storage weren’t kind to the old gear though. Early in my career, I had purchased a Sound City 4 x 10” guitar cabinet that I used for bass for many years. Though not built for bass, the cabinet was sturdy, dependable and got the job done until I could afford a Peavey 1 x 15” cabinet that I used for more than a decade.

Pictured here is the Sound City cabinet showing its years of wear and tear,

and on top of the 4 x 10” cabinet is the guerrilla engineered 19” rack I built when I wanted to employ an old Crown amp to drive the Sound City 4 x 10”.

 

When my band got back together 7 years ago, I wheeled out my old gear to play. Some of it worked okay, but when I got my trusty 4 x 10” cab out, it failed after about 15 minutes of playing. I decided not to attempt to repair the old components in the 4 x 10” but to replace them and rewire the cabinet.

So I found a set of four 10” 300watt bass speakers on clearance at an online store for $7.59ea. A year later, I rewired the cab with lamp cord and put the new speakers in. It didn’t work well with the Crown amp so I got rid of the amp and set the 4 x 10” cabinet aside for an additional 6 years.

Since that point, I’ve purchased a dozen or so cabinets.

I found a used NADY 18” sub cabinet for a great price.

I considered using it for bass in my rig at first, but wound up setting it aside for a few months. Then I got a call from a friend telling me about a large used p.a. system that was up for sale at a Guitar Center here in Cincinnati.

From among a wall full of stacked cabinets that made up this massive used p.a. , I purchased two of the matching 18” subwoofer cabinets for a great price. I spent a little extra and put proper speaker grills on the cabinets saving the flat steel mesh that had served as grills. The old subwoofers had vintage JBL 18” K-151 speaker drivers in them and I swapped one of the JBL speaker drivers with the speaker that was in the Nady 18” subwoofer cabinet.

I put wheels on the Nady subwoofer cabinet that was now loaded with the JBL 18”. I used it with a 1 x 15” Hartke cabinet with a Hartke HA5500 amp driving both.  It was an awesome sounding rig. I wrote a poem called “Guttural Thump” about that rig. It had plenty of low end and the aluminum cone of the Hartke 1 x 15” added attack and definition to the notes.

I thought I had found the perfect bass rig, but the Hartke and cabs were big and heavy and took a lot of work to move. Then I discovered that the d.i. didn’t work on the Hartke amp. I was surprised and disappointed that the Hartke head had such an unforgivable shortcoming. I’d felt a change was in order so I made a move.

For my next rig, I decided to up my game and change my approach altogether.

I really liked the sound I was able to achieve in the store with a 2 x 12” Mesa Venture combo.  The 600 watt Mesa M Pulse amp was already an upgrade from the 500 watt Hartke amp and the 12” speakers in the combo have a great voice for bass.  Like the Hartke head, the M Pulse is a mosfet configuration meaning that a tube powered preamp signal is amplified by a powerful solid state amplifier section. The result is that the warm tube signal from the preamp is faithfully reproduced and boosted by the clean ss amp. Most working bassists prefer this type of amp because they deliver great tone and a powerful signal but weigh about half as much as an all tube head. 

The M Pulse amp has a parametric equalizer which was tough for an old guy like me to understand at first, but as time went by I began to appreciate the subtle but effective e.q. and the versatility and power at my disposal.  I really liked the sound of the amp, but I felt held down by the 2 x 12” combo.

After two years of working with the Venture Combo, I concluded that I wasn’t content with some of the limitations the 2 x 12” cab seems to experience. I missed the sub-harmonics that a larger speaker can produce in a bass signal. At the same time I like a smaller speaker driver with good response to help bring out the signal attack and properly reproduce the upper end of the bass spectrum.  The horn driver in the 2 x 12” cabinet isn’t useful to me either. I like good crisp top end, but small horn drivers and piezos only bring out string noise when I play. Another theory I have about tweeters in bass cabinets is that the manufacturer can cut corners on the speaker drivers and use less efficient speakers (i.e. less costly) for their applications.  I may come back to the 2 x 12” combo in the future, but for now the 2 x 12” Mesa cabinet is hooked up to my 20 watt practice amp in my study.

I began to explore my options for a rig. I looked at what I had available in terms of speaker cabinets. I still had the operational 1 x 18” Nady/JBL subwoofer on wheels, and the old non-operational 4 x 10” Sound City cabinet with newer speakers and upgraded wiring. I had enough to experiment with so I put a plan into action.

I separated the M Pulse amp from the combo after a long telephone conversation with a customer service representative at Mesa. The Mesa service rep informed me that the M Pulse in the Venture combo was not rack mountable.  He thought I could use it by just removing it from the combo. He claimed that the M Pulse is “built like a tank” and would hold up outside the combo if I didn’t do anything foolish like drop it down a set of stairs or something.

I wasn’t happy with the “tank” M Pulse chassis once it was unprotected by the slot in the combo. I called Mesa again to see if they made a carrying case or something for the Venture’s M Pulse. The same rep confirmed that they had nothing to help me.

So I took the old guerrilla engineered rack I’d made years before for the Crown amp and modified it to accept the M Pulse amp. The M Pulse is held into the cabinet frame of the Venture combo by four vertical bolts that slide down from the top all the way through the chassis to bolt to the bottom plate of the amp. I fastened the M Pulse to the Guerrilla rack in the same way.

Then I got out my old 4 x 10” cabinet and began to listen to the speaker drivers individually. I found the best sounding driver and hooked it up by itself but left it mounted with the other 3 speakers in the 4 x 10” cabinet. I took both cabinets to our practice space. The rig sounded great.

Used with the 18” JBL, the single 10” gave me the top end that the big speaker didn’t reproduce well. One of the main aspects apparent when I changed from electric bass guitar to electric upright was that I didn’t have to adjust settings or volume on my amp like I did with the 2 x 12”.

That’s when I made up my mind to begin Guerrilla Engineering a 1 x 10” speaker cabinet to pair with the 1 x 18” cabinet.

The Art of run what you brung:

The best thing about Guerrilla Engineering is that I don’t spend a cent to build these projects. Half of the challenge is to make do with what you have on hand. Granted I have a lot of years on most of you so my collection of miscellaneous lumber and hardware is probably more extensive than many.

The rack and speaker box are built entirely of items that I had lying around my house, garage and barn. Everything in these pieces were left over from a previous project or removed from a discard. A lot of the hardware I used has been transported in several household moving days, some are more than two decades old, and so this project is eco-friendly too.

Also I wanted to use as little material as possible. I measured a couple pieces of gear and determined that the outer dimensions of the cabinet would be 16” x 16” x 22”. After some calculation on paper, I determined that a 48” x 48” piece of plywood could suffice for the project.

I studied the major brands’ 1 x 10” bass enclosures and noticed that all but one were rear ported. I’ve never liked tweeters for bass so my cab wasn’t going to get one (though most 1 x 10” enclosures I saw had one.)

I remembered a 4’ x 4’ piece of ¾” plywood in the loft of the barn.  

How would I go about achieving the desired outer dimensions? I took the plywood out of the loft and began to draw out cutting lines. Then I had to go back refigure and correct to create cuts necessary for a 16” x 16” x 22” enclosure by taking into consideration the thickness of the plywood and determining how the outer boards were going to go together.

I had to think in 3D. How many sides to a box? Six sides to this box but you needed access to the interior for assembly and service. That would all be achieved by first building the 5 sided box that would comprise the resonance chamber. Obviously you want to construct something that’s stout and relatively indestructible, but sound quality is at risk here as well. Most enclosures I’ve seen let the top and bottom boards serve as caps for the back and side boards. I determined to take another path. I used the back board to cap the top and bottom board and the 16” x 16” end pieces to cap the three larger boards. The speaker baffle would be a board that slid into the 5 sided box from the front to form the sixth side of the enclosure. After several attempts at drafting, sufficient modification to the original design had been made to cut the board into sections.

 

I helped a neighbor get his older project car running, and in return he afforded me ten minutes on his table saw. I cut the pieces and brought them home for assembly. I stacked the outer pieces where they would go to make sure that they fit together.

Not having a handle on hand, I designed a handle into the back that would also serve as a rear sound port. Then I went looking for screws to hold the cabinet together.  The reason I wanted screws was because my dad was a firm believer that screws were not only the most economical method to hold wood together, they are the method least likely to give way under stress. I’ve seen some videos of modern music company factory tours and the cabinet makers nail cabinets together using glue and caulking to seal the cabinet.

I believe in a tighter fit than that. The Guerrilla cabinet isn’t perfect, but it’s really tight, and screwed together to stay that way.

Many of my wood and metal screws had been extracted from previous projects or were spare parts for one small appliance or another. They’re the kind of hardware I didn’t use for one reason or another but look at and see something that could come in handy one day. My screw collection is mostly kept out in the garage by the workbench in jelly jars. None of the screws match, in fact, some are flat head and some Phillips head. Some are wood screws, some are metal, some are drywall screws, but after a couple of hours of searching tool boxes and my tool bench, I’d gathered enough stray screws of correct length to construct the cabinet I had in mind.

First things first, I constructed the five sided box and put spacers and reinforcements in place. I made all of the reinforcements and spacers from the same piece of plywood that I’d cut the sides and back from. I used my electric drill for 3/64” pilot holes for each screw and my portable drill for a screw driver.

A dozen design adjustments later, I got the cabinet together and began to plan for the speaker installation. I recessed the speaker baffle to accommodate a grill.

I took one of the leftover grills once used on the big 18” subwoofers, cut it down with metal shears and built a frame for it out of scraps from the original plywood board. I put washers on 16 screws to hold the mesh firmly to the frame.

I cut the speaker hole in the baffle with a jig saw making sure not to cut too much off of the board and trimming where I needed to. I used a hole saw to cut the hole for the connector and mounted a piece of flat sheet metal to the inside. Then I spray painted the baffle, the grill and the exterior of the 5 sides with black engine paint.

I dug around in some old boxes and found a few packages of speaker mounting screw kits I’d purchased almost a decade ago. In the final stages of construction, I mounted the speaker onto the baffle with the speaker mounting screws and used one of the same speaker screw kits to mount the grill over the driver.

Here it is assembled and ready to test.

The Guerrilla Engineered rack and the 1 x 10” cabinet aren’t pretty—they’re beautiful.

Introducing the frankenrig.

Mesa M Pulse amp head mounted in a Guerrilla Engineering rack on top of a Guerrilla Engineering 1 x 10” cab and the 1 x 18” JBL/Nady frankencab.

Tone Report

Like most 1 x 10” bass cabs, the Guerrilla cab is somewhat limited in what it can do for bass. The factory made 1 x 10” and 1 x 12” cabs I’ve tried have all “rattled” when they got to a couple of the lower notes on the E string. Using the parametric eq on the M Pulse amp head, I dialed out a couple of “rattling” resonant frequencies in the 1 x 10” and it performed well by itself though it was a little thin when I pushed the volume. The thinness was remedied when I plugged in the 1 x 18”. Suddenly my frankenrig was transformed into a huge bass love fest. Giant warm tones and tons of low end with little effort. I’m going to use this rig for awhile—at least until I get bored and try something else.