Build log: a pair of AutoTubas - Page 2

On 11/6, I cut the excess material off the end of panel 6. I used my Eurekazone track butted up against a couple of clamps to guide the circular saw. It was pretty easy to set up by eyeballing the blade against the edges at both ends. The cuts were simple and it turned out great -- ready for sanding.



I installed the drivers. I found this cool little ratchet at Home Depot that made it really easy to tighten all the fasteners, and it even came with the 5/32" hex socket bit that I needed. You could use a 1/4" socket wrench to hold a screwdriver bit in a similar manner, but this little specialized ratchet is really small, light and easy to work with. Fortunately, all the fasteners went in smoothly and none of the Hurricane nuts spun.





To test them out, I connected a Dayton DTA-100 amp that I had in another system, and fed it the sub channel from my garage stereo. I don't have the access covers on yet, which I think makes the response a little strange. But they make a bunch of bass, and I don't hear any motorboat sounds that would indicate internal leaks. Yay!



After playing around with coupling the subs a little, I painted the edges of the recess holes and the backs and edges of the access panels. I plan to paint the outside surfaces of the subs with white Duratex, but I used some plain exterior paint+primer for the inside of the horn and the edges / insides of the access panel.



That all took 2h19m, bringing the total time spent to 28h55m.

-Max

Congrats on getting yours bumping (if only a little), Andreas. Are you planning to use an EQ?

I've been moving slowly (as usual), but I'm getting close to being finished. I'll post some more detailed log posts with pics soon.

I've been researching my amp options, and I pulled the trigger today. I decided to get an amp that will do 300w@8ohms stereo, so that I can use it to drive my THTLP and be power-handling limited, rather than amp limited (like I think I am with the Behringer A500). I also like the idea of getting one of these new 10-pound amps that all the companies are making, so that it is easy to move around and won't add much cargo weight when I drag it to Burning Man. Here are the candidates I identified with those specs:

* Peavey IPR1600: Proven output, but more expensive than the Behringer, and I'm not sure the Peavey brand warrants the price premium.

* QSC GX300: Good connectivity, price, and reputation. But it weighs 30 lbs, so didn't quite meet my selection criteria. It also has a loud fan, and the only crossover feature is a fixed 100Hz crossover.

* Behringer iNuke 3000 DSP: The DSP model is only $50 more (street price) than the one without DSP, so I was considering that version. The DSP stuff has a nice UI, would be useful for running a 2-way speaker or setting a high-pass to protect a sub, and I like that I could do that without having additional boxes or wires in the system. But it requires Windows, I only have one old XP laptop that I hate using, and I can always use MiniDSP boxes instead. It also has a loud fan, which could be improved via DIY, though it is a hassle + additional expense, and the end result seems not as good as an amp that controls its fan more intelligently. It also has limited connections (XLR in, Speakon out), which, though I have no functional concerns about, would require me to purchase adapters and would be more of a hassle to deal with in the field.

* Crown XLS 1500: Good connectivity (RCA/TRS/XLR in, Speakon/TS/Posts out), good reputation. Quiet fan, from the factory! Sounds like it has some circuitry that works well when running it off a generator. Has an adjustable crossover (50Hz-3KHz) that might be useful someday. The Crown does not have the DSP flexibility that the Behringer has, but it also doesn't require any adapters or fan mods, so it ends up being cheaper than the Behringer. On the downside, it has less input sensitivity than the Behringer, so it might be harder to drive, but I don't expect any problems.

Conclusion: I ordered the Crown XLS 1500. It won out slightly over the iNuke DSP since I can just hook it up without fan mods or adapters. And maybe it will be more reliable / less quirky since it is a Crown amp.

-Max

On Nov 11, I spent 3h12m sanding, flush cutting some edges with a router, doing a 3/16" roundover on all the edges with a router, and then applied some Bondo.



Without sanding, but after inspecting (and turning) the subs, I ended up applying Bondo twice more that day. The additional Bondo and some cleanup time took 38m, and bringing the grand total time spent to 32h45m by the end of the day.

On 11/15, I sanded the cabinets into a paint-ready state using my trusty random orbital sander and 80 grit discs. I have learned over the years that continuing to sand with a worn-out disc is a waste of time, so my tip here is to buy extra sanding discs and don't be afraid to change them as soon as you feel like it isn't cutting. I went through maybe 3-5 discs on these subs. I'm not going for perfection, so I only used 80 grit, and did not get 100% smooth surfaces. Another lesson here might be that it isn't worth buying cheap plywood. I used some cheap stuff here and the surface has some bad areas. I could fill it all with Bondo, but I decided not to. Then I cleaned up all the dust. Well, some of the dust.

I drilled and countersunk the holes for the access panel screws. To make sure all the holes were equidistant from the edge of the panel, I clamped a guide on my drill press:



I also drilled the holes into the flanges on the sub, using the drilled access panel as a positioning guide, and then finally drilled out the holes in the access panel a bit so that the screws would grip the flange more than the access panel. That last step is probably unnecessary as long as you press the access panel down when installing the screws.

I am using some terminal cups that Erich sent me when I bought some (still unused) MFW-15 woofers. Thanks Erich! I used a hole saw in the drill press to cut the ~2" hole for those. I am painting the sub white, so I got some flat head #9 x 1.5" "hinge screws" from Lowes with the heads painted white. I also got some little black #6 x 5/8" flat head screws for installing the terminal cups from Lowes. I was surprised that Lowes had both, but I appreciate the convenience of being able to find them locally.





And then I applied the first coat of white Duratex, that I had left over from my Econowave SR speakers.



That took 4 hours in total, bringing the grand total to 36h45m.
Edited by maxcooper - 11/23/12 at 9:38pm

I spent 1h11m total on 11/20 - 11/22 applying three more coats of Duratex. I turned the sub once between each coat, so the sides all have 3 coats total, and 4 coats on the back. I put 3 coats on the access panel outer surface, too. I had previously painted the backs, sides, and flanges of the access panels with normal (non-Duratex) white paint+primer, which is the same stuff I used on the inside of the horn.

On 11/22, I installed the terminal cups and soldered the wires. I had some 3/4" wide black foam weatherstripping left over from my THTLP build, so I tried using that for the access cover. However, when I started screwing down the access panel, the weatherstripping proved to be too thick. It would have been excellent if I had made the flange a little deeper, but I really did not leave much room. I ripped the weatherstripping off the flange, and did my best to scrape it away. That stuff really sticks well, and there was still a lot of residue left, but I figured it would not be a problem. Finally I used some highly compressible gray foam 1/2"-wide weatherstrip I had left over from the handles on my Econowave SR build. That stuff does not stick nearly as well as the black foam weatherstrip, but it worked out fine. The lesson learned here is to make sure you recess your flange enough for the good black foam weatherstrip -- it seems better if it will fit.

Here's a pic of the access panel after installation:



And well, that's it! With 2h32m spent on 11/22, the final total comes in at 40h28m to build my two AutoTuba subs. It may be the slowest AutoTuba build ever, but I like putzing around in the garage and playing with tools. And I'm running out of space for the projects I have already built, so I don't want to be too prolific out there.

Last night I hooked them up to my new Crown XLS-1500 amp for testing. The Crown amp worked out nicely -- easy to hookup to a home stereo with RCA inputs and binding post outputs. I replaced the Behringer A500 that I was using to power my THTLP, and ran the THTLP off one channel and the two AutoTubas off the second channel in parallel. I used a y-cable to feed both channels. The fan in the amp turns very slowly and is virtually inaudible, even after running it hard for a while -- no mods required for home use. In hindsight, however, the iNuke3000DSP might be a better option -- the fan mod looks easy enough and doesn't seem like it would lead to thermal shutdown under practical loads, and it would be nice to have the DSP features, even though you need a Windows computer to program it. Hmm... I am tempted to pickup an iNuke via Guitar Center's Black Friday sale.

I haven't really had an opportunity to give the AutoTubas a fair audition, since my system is EQed for the THTLP (Anti-mode 8033 box + Audyssey XT in the receiver). But they work and make bass, with no weird sounds (that would indicate interior air leaks) or access panel air leaks. My unfair, uncontrolled impression is that the AutoTubas seem to have really good "chest hitting" impact, but the deeper extension of the THTLP is very noticeable, even with music. I have been listening to bass-heavy music, though. I think the additional power of the new amp has helped the THTLP performance, too.



(I still need to touch up a few spots inside the horn with white paint, after sanding off some Bondo. And maybe paint the glue squeeze-out, too. But I'm calling these "done".)