DIY Lightweight Composite Cab Build II - ZL1263, 3-way

[zac2944]

I've been using my first composite cab, the ZL210, for about a year now with much success. My arms and back thank me every time I choose the 23lb ZL210 over some of my other much heavier cabs, and my ears are rewarded by satisfying full bass. Despite all the things I like about that cab I have decided I must build again. Here's why:

• For some gigs the ZL210 is louder than I need and I could get away with a smaller/quieter cab.
  
• For other gigs the ZL210 is not enough, and being 4ohms I can't add another one without out making an amp change (which I'm not interested in).
  
• The geek inside of me really wants to build with the Eminence Kappalite 3012LF.
  
• I learned a lot with my first build and want to incorporate some new ideas into a better second build.

So with those motivations I've set out to design and build two, 3-way, 12" bass cabs; the ZL1263.

For this design I wanted to go with two slightly smaller and lighter 8 ohm cabs than the one 4 ohm ZL210. It turns out the ZL1263s are only a little bit smaller than the ZL210 and I haven't been able to weigh them yet, but they should be just a little less than the 210. The size and weight of the cab is dictated by the driver selection and box/tuning design; not much I can do there.

I chose the Eminence 3012LF woofer, Alpha-6A midrange, and CTS1005 tweeter for my design. In many ways my design is similar to the fEarful 12-6 Greenboy has so generously designed for us. The 3012LF and Alpha-6A will be crossed over using a stock Eminence 800Hz crossover, and the piezo tweeter gets wired in to the mid with a switch and a few capacitors to attenuate the level. I built a test bed and spent some time with the Alpha-6A and various piezo/cap combinations until I found one I liked best. The Alpha covers about 80% of the high end I like to hear in my bass tone, and the piezo handles the other 20% (sparkle, if you will). I know many people don't like piezos, and that's fine with me. For my application and tastes they work fine. IMHO, a really fancy tweeter is not fully taken advantage of in a 3-way bass cab design with such a nice midrange. In a studio monitor or PA main it might be a different story, but that's not what I'm looking to do here.

Here's a quick peak at where I'm going with this. I'll be back to post more after a coffee break and a trip to the hardware store for some 10-32 button head cap screws.

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(sorry for the link, can't do photobucket from work anymore)

 

[gerryjazzman]

Hey Zac, looks like this is going to be a very interesting design. Between yours and Greenboy's designs, I think there is more useful innovation in cabinet designs here on TB than there seems to be in most of the commercial offerings. Subscribed.

EDIT: I take it that is a rear duct port behind the midrange enclosure?

 

[zac2944]

Hey Zac, looks like this is going to be a very interesting design. Between yours and Greenboy's designs, I think there is more useful innovation in cabinet designs here on TB than there seems to be in most of the commercial offerings. Subscribed.

EDIT: I take it that is a rear duct port behind the midrange enclosure?

There is a round port on the back side. It is a 3.3125 ID tube. It is actually located behind, and concentric with, the tweeter. The midrange enclosure would not leave enough clearance to locate the port behind the mid, and I didn't want the port directly behind the woofer.

 

[zac2944]

There we go. FWIW, If you right click and "Copy Image Location" from Google/Picasa web albums and put a

around the link you can embed images. You learn something new every day.

So, back to the ZL1263.

Why are hex socket cap screws so damn hard to find? I mean, they are only the sweetest type of hardware you could use? My local ACE hardware is the only place around with any selection and even theirs is limited. I wanted to mount everything with socket head cap screws, but getting the right sizes can be tough. Once you get into lengths greater than 1" they can be very tough to locate and expensive. I ordered most online, but inevitably I spec'd some incorrectly.

Each cab uses 39 cap screws and T-nuts for all the mounting. You can't just run a wood screw into a foam/epoxy/glass/carbon sandwich and expect it to hold. You need to use T-nuts and machine screws.

This means precisely locating 39 holes, drilling, then bonding the T-nuts in place. I bond in the T-nuts with 2 part epoxy cement (think JB Weld), and temporarily mount the items (speakers, dish, port, etc.) in place while the bond is setting up. This ensures proper alignment. I neglected these steps last time around and ended up wasting a lot of time reworking the T-nut because they were either misaligned or didn't bond well and spun out when trying to tighten down on them. Not fun work considering once you bond the baffle in place (or the back as I did last time) you have limited your access to these T-nuts. I will NOT make that mistake again. So, 39 T-nuts per cab were painstakingly bonded in place.

 

[zac2944]

Since most of the basics of composite sandwich construction were covered in my first thread, I'll skip this here and just get right into it. Anyone interested in learning more can read through the first thread linked above.

Once I had my design worked out on paper, the first thing to start working on was building the foam cores. Here are a few of the foam panels after being cut.

After cutting I bonded them in place with some epoxy filler.

Sorry about the low quality pics. I only had my phone that day for pictures.

 

[zac2944]

Before I began building the 1263, I built a small test cab. I built it to test out a few manufacturing techniques I had been thinking about, and also to act as a test cab for the Alpha-6A. It is a funky little cab, but the whole round corners idea didn't cary over to the 1263. It was a learning experience.

BTW, the 1263 WILL be done in matching white Duratex. Gotta pimp the cab.

 

[gil_mor]

Loved your first build thread, this is going to be sweet (I hope)

 

[kaiser_sosea]

Excellent, subscribed!

 

[ettsn]

I've spent entirely too much time today reading all 500 posts on your other thread, so I'm stoked to be following this build.

'scribed.

 

[zac2944]

With the core material all bonded I next shaped the corner radii. I did this freehand with just some 60-200 grit sandpaper. Came out pretty nice.

 

[zac2944]

I also filleted the inner corners with filled epoxy.

Here's both cores finished.

 

[zac2944]

Once the cores were finished it was on to cutting and prepping the reinforcement (fiberglass, carbon).

After cutting the reinforcement I laid up glass on the inside of the cabs,

and then the outside.

 

[zac2944]

For the baffles I used a slightly different method for the layup. I laid the pieces up on glass so that the glass acted like a mold surface. Before laying up I applied 3-4 coats of Meguiar's Mirror Glaze mold release wax to the glass to prevent any sticking to the mold.

 

[zac2944]

Here's another shot of the glassed cabs.

Here's a look at the carbon baffles.

Oooo. Let's see some more of that sweet carbon fiber.

 

[zac2944]

Now its time for some cutting. To trim up the baffles I used a rotary tool in a similar fashion to how veneers are trimmed.

Here's a closer look.

Since the cores were cut to size, the rotary tool just follows the edge of the core making a clean cut to the carbon. I tape up the edge of the core and the tip of the cutting tool with a little masking tape so that the core doesn't get damaged.

Here are the trimmed out baffles; super stiff and super lightweight. I put masking tape over the carbon fiber on the face so that it won't get scratched up during the rest of the build.

 

[zac2944]

With the layup work done it was time to make the cutouts for the drivers, ports, dishes, etc. This work can be a bit tedious, but careful measuring and cutting is crucial.

Here's the marked cuts on the back for the control dish and port tube.

For the round cuts, the circle cutter tool that came with my Dremel worked very well.

For straight cuts I used a straight edge as a guide.

Testing to see that everything fits.

Like a glove.

 

[zac2944]

Here's a cab with cutouts.

And here's the baffles with cutouts.

 

[zac2944]

With the cutouts done I moved on to the mid enclosure.

You might also notice in the pictures that I sealed any exposed foam core. It might be tough to see. Unfortunately I didn't get any good pics of this. What I did was use a hot knife (like a large soldering iron) to melt the core down just a bit. Maybe 1/16". Then I filled in this area with a super tough filled epoxy mixture containing milled glass fibers (nasty stuff, never breath this stuff in). This filler protects the core and forms a strong bond between the inner and outer skins.

Another thing you'll notice are the bonded T-nuts.

I can't stress this enough - these things need to be bonded well. If they come loose after the baffle is bonded in place they are a PITA to fix. Unfortunately, these T-nuts weren't made specifically for composites. They were made to be welded in place. I roughen each one with sand paper before bonding to ensure a good bond. I also roughen the bond area on the fiberglass. It takes for ever to do these things. There are some really high end fasteners systems specifically made for composites which are much easier to use. They come with super strong 3M adhesive (like double sided tape) and quickly and securely bond. However, they are too expensive to this build.

 

[zac2944]

With all the T-muts in place, and the mid enclosure finished, I next glued in the dampening foam. I used a foam mattress topper I got at Target for $9. I got three cabs out of this one $9 pad. Don't waste your money on that expensive stuff they sell at PartsExpress and other audio stores.

This 581 foam glue I found is the best I have ever used for mounting foam. I tried 3M 77 spray in the past, but is never worked that well with the foam and composite. This stuff was great.

Here's the foamed up cabs.

 

[zac2944]

After glueing in the foam it was time to bond the baffles in place. To do this I first sanded all mating surfaces, then ran a large bead of filled epoxy around the mating area. After mating the baffles to the cabs I ran a large fillet of filled epoxy around the exposed mating edges to secure the baffles in place. Doing the fillet on the inside is tough because you have to reach inside. It doesn't need to be pretty, just secure. I do it with a gloved finger.

Once the bond was ready to go I clamped everything do while the epoxy was setting.

Here you can see the fillet. Notice that I cut away a bit of the masking tape on the face of the baffle so that the fillet would bond to the carbon fiber and not the tape.