Anikun's Auto Tuba Build

[anikun07]

Today I began working on my Auto Tuba. I ordered the 8" Dayton subwoofer listed in the instructions and it's scheduled to arrive on Tuesday. Last night, I printed the instructions for the standard Auto Tuba and wrote out a lumber list to see how much I would need. I calculated that a singe 4' x 8' sheet would be perfect. Today I pulled out a sheet of 1/2" Arauco Ply and got to work. I used a circular saw to rip the sheet into thirds (16" on center) then proceeded to cut the sides out and panels 1 and 2. After cutting out the access hole in side one and marking up the panel placement lines, I pieced together panels 1 and 2 to make sure I cut the beveled edges in the right direction. After checking and re-checking several times, I made the cuts and was happy with the results. I also experimented with holding a small block of Arauco Ply on end to draw the width of the panels. The directions show 1/2" panel depths, but since the lumber should be 15/32" (right?) I figured the panels might line up a little better than when I did my THT.

Here's my Side 1 with the the hole cut out and the lines drawn on it. In the instructions the routed flush mount panel cover is done at the end. Is it possible this might be easier if done in the beginning? I will probably not go through the trouble of that type of cover, but it sounds like it would look pretty nice when it's done.



Here's panel 1 curing.

[miked]

I also use a piece of scrap BB to draw panel lines. It's quicker than marking out 1/2" on one end and 1/2" on the other end and connecting the lines.

We have similar workspaces. I also have the HF dust collector and I built a Thein separator for it. Great thing, that separator is.

Build's looking good so far. You've built a THT already, so this will be much easier for you since you're already familar with the pitfalls of building these cabs.

[anikun07]

Yep, the THT wasn't too bad at all and I'm happy to be building something again. You can't really see the separator in the picture, but you can see the hoses arching in and out of it. I love it! I just wish my second set of HF hoses were identical to my first set. They seem a little tighter and are way more flexible. The flexibility is nice, but the seem a lot less heavy duty. I can't wait 'til my sub arrives so I can trace it and continue onward. I decided to make the cab width 15" so all the panels are being cut to 14". Since this will be going in my '97 Corolla, what would be the recommended location, back seat or trunk? I've never had a sub in a car before - except for a little passive one I had a long time ago that sat perfect on the little raised hump between rear passenger seats on the floor. I don't remember what speakers are in the car, I installed them a really long time ago. I think the rears are some Kenwoods, maybe 5.25"(?) and the fronts had to be replaced at some point and I think Pioneers were put in - whatever OEM size was, probably 4". Is there something better that can be had at a cheap price to match the quality of the AT? I think the cost of each pair was probably around $70.

[miked]

Oh, you haven't lived until you've had a subwoofer in the car. What will you power it with? I'd put it in the trunk.

[anikun07]

A while back I asked what would be recommended and there's one sold at Walmart for about $55 (I saw it on Amazon.com for $50 - gotta love Prime shipping). Let me see if I can find it..I think it's the Dual XPE2700, 2-channel bridgeable to single channel up to 400W. I still have to figure out if it's better to have my cheap Sony Xplode head unit do the crossover or put it in-line with the rear speakers. I think the head unit says it does crossover at 160 or 180 Hz.

[miked]

Any head unit that has a subwoofer pre-out should have a lower xover than 160Hz. That is way too high for a sub, especially in a car. Does the amp in question have a built in xover? It should. 400W will be plenty for your Autotuba.

[anikun07]

The Sony HU has high and low pass filters from 80Hz to 160Hz in 20Hz intervals. The amp has a high or low pass filter that can be disabled depending on the installation configuration. I think I will only run RCA cables for a low-level input to the amp to only power the AT. Otherwise the amp manual says I need to disable the crossover and use passive in order to send a signal to both the speakers and the sub. Any thoughts on adding an in-dash power switch to the amp so I can turn it on and off whenever I want? Is 80Hz standard for car audio crossover, too?

[miked]

Your HU should have a switched amp turn-on lead. Usually, it is blue in color and sometimes has a tag on it that says "T.O." You'll have to pull the HU out of the dash to get it at, obviously. Check your owner's manual (you can find it online if you no longer have yours) to ensure your HU has a TO lead before pulling it out of the dash. The power amp's "power connections" will have three screws. Two large ones labeled "+" and "-" and a smaller screw labeled "Turn on" or "Head unit" or "switched 12v."

I can help you more as you progress. I was a car audio nut from about 1990 until 2006-ish. I had small hatchback cars with no trunk b/c the stereo occupied it. Then I had a 4-door car with no trunk; same reason. Then I had a big old SUV with no "Utility" left b/c the entire back was a stereo. All that's gone now as I have a family and need to haul stuff. I still have a small system in the SUV. It takes up about 1.5 square feet of space. A single 12" mounted in a small, sealed box. Small 4-channel amp bolted on the back. Channels 1&2 go to the components I have in the doors up front. Channels 3&4 are bridged to the sub. The amp has variable crossovers, so it works really well. It looks ugly b/c I just threw it in there. I don't show the truck anymore nor compete so all it has to do is work.

[Radian]

The AT works best when the mouth is fired at the rear of the trunk space (with the cab orientated front to back), or with the mouth firing into either rear-most corner of the trunk space (with the cab orientated side to side).

Use the low pass on the outboard amp (not the HU) to avoid the pitfall of cascading filters.

When it's all said and done, the AT typically favors a low-pass filter set point between 40-60 Hz to yield a crossover region between 90-100Hz.

[anikun07]

I wonder if I have more than 32" of trunk space fore and aft.

[Tom Smit]

+1 to what the other guys were saying.

If you want to switch out your other drivers, these Silver Flutes or these have been suggested. Tweets are still needed, possibly these ones.

[anikun07]

Tonight I worked on the next panel (3) so it's ready to be pieced and glued after I have panel 2 done tomorrow. Since my table saw can't cut angles greater that 45* and I didn't want to sand 11* after making the cut, I decided to try a slightly different approach. I created an 11* "ramp" to angle the panel so it would cut at the needed angle. I think trigonometry was my friend tonight is solving the height needed at the distance of the end of my saw sled. It's a little hard to explain, so here's a picture of a board cut to the proper height to sit at the end of the sled. I used the other part of the 11* cut to create 90* complementary angles and hold the ramp in place on the sled.




Then I put my board to the end of the edge of the saw blade and angled the blade to 45*. In the picture, I think the saw is still set to 11*.



Then I got a pretty good looking angle. I had to put a lot of downward pressure on the panel in order to hold it flad because it was warped. Probably not the safest method, but luckily the "ramp" didn't slip out from underneath. I probably should have put a screw or two through the panel into the "ramp."



If you decide to try this method BE VERY CAREFUL. It is much safer to follow the instructions in the guide and I am not responsible for any accidents someone might have in copying what I did (<--**DISCLAIMER**)

[Bill Fitzmaurice]

The idea is good, the implementation, not quite there. The key to safety is that everything is well secured. Screw the ramp to the panel jig, and screw the panel to the ramp. A more sophisticated ramp would be better as well. It's a good enough idea that I'll refine it and add it to the panel jig plans.

[anikun07]

Thanks, Bill! My first jog didn't work as well, I had the panel braced at 90* to the saw but for some reason was thinking a right angle was 100* and put the saw at 44* instead of 34* Yeah, I Know - AMATEUR HOUR! But that's why I cut the panel a little bit long, and it was perfectly salvageable with a difference approach.

[anikun07]

The 8" driver came today, so I was able to complete panels 2, 3, and 4.

Here's the 8" Dayton Audio subwoofer.


Here's a side view of the panels glued into place and curing.


Here's a top-down view looking into the horn.


It took a few passes with the jigsaw to clear the opening big enough that I don't think the baffle is going to be in the way of the surround. Does the AT only get one brace, unlike the THT? I have't got Sketchup on this computer at the moment. The instructions just say panel, and it is quite a bit smaller than the THT, so that's what I expect. I'm definitely looking forward to hearing this play in my car.