Tubifex pt.2: materials and construction tips

Tubifex

The Repository->DIY->Tubifex pt. 2 (materials and construction tips)

Materials

Aside from the normal drivers and crossovers, here are the materials you will need to construct a pair of Tubifex:

(x1) 10-foot length of 6" dia PVC pipe

(x2) 14" length of 4" dia PVC pipe

(x4) 4" length of 1.5 dia PVC pipe

(x1) 2'x4' sheet of MDF (aka "Handypanel"). Needs to be 1/2" or thicker.

(x12+) #10 machine screws and machine screw nuts

(x24+) metal washers for above machine screws

(x1) tube of adhesive. (Household Goop or Gorilla Glue. Some epoxies will work as well)

(x1) egg crate mattress pad from Wal Mart (avoid that thin crap from Target. If you don't like Wal Mart, then open-cell acoustic foam will work)

(few handfulls) Polyfil or acoustistuf

6" diameter PVC is pretty standard stuff, and any local plumbing supply place should carry it. The 4" and 1.5" diameter PVC is available at your local hardware store, and if they're feeling nice they may even cut it for you if you don't want the whole 10 foot length. The machine screws are used to bolt the tubes together. More on them later.

Cutting MDF Pieces

The first bit is easy. You need some spacer strips to go between the tubes. These will be 1" tall and probably 8" long. If you have a table saw, you can do all four spacer strips in about 10 seconds. Put them off to the side for now.

Now for the most tedious part of the whole project: cutting the endcaps. If you want to do a neat and tidy job and flush-mount the drivers, you'll be doing a lot of circle routing. You don't think about it, but for each endcap, you have to do twice the amount of circle cutting you would for a normal speaker--in my case even more.

You see, I decided that I wanted a bit of "fit" to the endcaps, so I created a rabbeted edge around each of them. I thought this would allow for more glue contact, and also keep less glue from seeping out the joint. It would also let me dry-fit the endcaps in case I decided to change directions with driver choice. In theory, all this requires is a 1/4" rabbet around the edge of each endcap. In reality, it means even more routing in addition to the ridiculous initial amount.

For me, the process went like this:

1. I drilled the pilot hole in a piece of stock, and routed a 1/4" recess on the back (I don't own any rabbet bits, because it seems kind of pointless when you have a circle jig)

2. I flipped the stock over and routed the full width of the cutout.

Repeat steps 1 and 2 twelve times and this is what I'd made:

3. I attached the endcap discs to a piece of scrap wood using a few brad nails (easy to remove when finished. Supposedly,double-sided carpet tape or hot melt glue are good for this sort of thing as well.)

4. With the discs on the scrap wood, it made it fairly steady and safe to route the driver recesses.

I repeated this step 4x for the woofers, 2x for the tweeters, and 4x for the 1.5" PVC vents, and this is what I'd made (vent endcaps not shown):

Here's a side view so you can see the excessive amount of routing that went into each one.

NOTE: If you don't care to flush-mount the drivers or do the rabbet around the edge to "fit" into the pipe, this whole process will go much faster. With a steady hand, you could do it with a jig saw.

Cutting Large PVC Pipes

The challenge with the 4" and 6" PVC is that it's so large that traditional PVC cutting methods won't work. It's too big to use a miter saw or table saw. A hack saw will work, but takes a very long time. I suggest using a jig saw, it lets you be pretty accurate, and goes surprisingly fast. Here's how I did it...

I used a long piece of flexible plastic (specifically, an old strip of vertical blinds) wrapped around the tube to mark a square line with a sharpie pen. Then I started the cut with a sawzall, and then carefully drove a jig saw around the tube, following the line, rotating the pipe every 30 degrees or so. The edges aren't perfect, but they're not terrible; I'd wager I'm within 1/8" of true all the way around. Polyurethane Glue or Goop would easily swell to fill a gap that size when the endcaps are attached.

Note, the short tubes shown in the picture are 6" PVC; in reality you want yours to be 4" PVC.

This picture was taken while building an earlier version of the Tubifex. Sorry for the confusion

Cutting the small PVC (the 1.5" dia stuff) into 4" lengths is very easy. You can use almost any old saw you have around. Try your best to keep the edge square and true. If you're off a bit, you'll probably still be OK; the glue will expand to fill the void when we get to gluing everything together.

Drilling the Alignment Holes

The key to holding and aligning the tubes together are the bolts that go through each PVC pipe, through the spacer strip, and into the adjacent pipe. Drilling the holes for the bolts in precisely the right places on the tubes and spacers is crucial to getting the speakers to stand up straight and hold together solidly. But how does one accurately drill holes on exactly the same spot on opposite sides of a large tube? I gave this puzzle quite a bit of thought, and the solution is quite simple and requires no investment in more tools.

Step #1: Take your 1"x8" spacer strips of MDF and pre-drill them so that the #10 machine screws just fit through with as little "wiggle" as possible. 2 bolts is adequate to hold the tubes together, since the glue will do most of the holding in the end. You will need at least 1 or 2 additional holes to run wires through as well.

Step #2: Take a sheet of newspaper and wrap it around the tube (make sure the corners of your newspaper are square). If you look in the photo, the left edges of the newspaper are lined up, which means that the top of the page (above where it says "Legal Notices") is now perfectly parallel to the pipe. Trace that line along the top of the page onto the pipe using a pencil, and also mark the upper-left corner (you'll notice a little "tick" just next to the upper-left corner of my page). If your hand is not very steady, hold your 1x8 spacer strip against the top edge of the paper and trace onto the pipe.

Step #3: Hold the pre-drilled strip against the line you just traced, and insert your drill into the pre-drilled holes, and use them to guide the drill into the pipe. For added measure, I put a machine screw in each hole right after I drilled it to make sure the strip stayed in place as I drilled the remaining holes. At this point, I also decided to label the MDF strips and tubes and mark which side of which strip touched which holes on which pipe. In the picture below, you can see that I have drilled the two holes on the right side of the strip, and have inserted machines screws into the holes to keep things steady as I drilled the final, leftmost. (Please ignore the big red stripe on the pipe. It came from the plumbing supply like that and has no meaning to our build.)

4. Do a test-fit of the pipes to make sure your efforts worked correctly. Use your #10 machine screws, and some washers under the screw head and the nut. Don't glue anything yet, just hand-tighten a bit. (Note: it was while doing this dry-fit that I decided I like the look of the smaller mid tube better.)

So what about the base? Well, get creative. Mike V (with his Totally Tubulars) took a few pieces of leftover small diameter PVC and made a support out of them. Mine were actually just a square of MDF with a circle cut out of the middle; which I then cut diagonally into 4 pieces. Another solution would be to simply do one more spacer strip, and then bolt the speaker into some sort of heavy plank. Heck, you could put eyebolts into the top of it and fly the speakers from the ceiling, as one Parts Express board member did.

Putting it All Together

Once you have done a dry-fit you can thread all your wires through the holes, and glue everything up. (It's probably a wise idea to thread the wires before you glue up; you never know if excess glue will seep into your holes and plug them up.) Then you can mount the drivers and crossover, plug 'em in, and enjoy some very high fidelity sound.

Completed Builds

As you can see, the Tubifex are not necessarily the easiest speakers to build. But that doesn't mean there aren't some DIYers who are up to the task.

[Time] went all out on his build. Veneer wrap all around, and custom-made braces. So many little details, and you can read about it here.

Showing no fear, [WJJR] built the Tubifex as his first DIY speakers, and pretty much nailed it.

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