Torrent Audio Mistral 12 DVC

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So I finally glued on the back baffle and trimmed all the edges using a flush trim router bit. I also cut the hole for the terminal box. All that is left is some poly and to bolt the thing together.

Some things to remember:
Saws have tear-out. Don't cut too close to a finished edge with a circular saw! I did this trying to cut down on the amount of material I had to remove from my 1.5" baffle (to flush trim it to the box).

Double check before you cut. Duh right? And I know this one, really... but I found a new variant of it tonight. I was trying to figure out how to route a nice rectangle in exactly the spot I wanted for my terminal box. I thought about simply clamping a straight edge for each side. I thought about using a template guide and some scrap. I thought about where exactly to put the box... maybe a little offset from the port? In the end I did it very simple by drawing the cut-out in place and routing it with a plunge router without any guide. But do you know what I forgot to think about?... What side should I put the terminal box on. I somehow managed to get so wrapped up in how to cut the cut-out that I ended up cutting the rectangle on the top of the cabinet. Sweet!!! I am glad nobody knows my real name on this board... .

[Mike P.]

We all have our moments at one time or another. How are you going to fix it, glue on another top piece?

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Mike P. wrote:

We all have our moments at one time or another. How are you going to fix it, glue on another top piece?

I am just going to live with it . The sub is going to fit into my entertainment cabinet and the center channel is going on top of it. So I don't think the terminal box will be too obvious from the front. Oh well

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Tonight I bolted it together for a test run. I brought it in the living room and put the driver, port and terminal box in. The box looks huge. It makes my entertainment center look small. In fact my wife thought there was no way it would fit in the center bay. Turns out I did measure that correctly it fits just right. And having terminals on the top of the cabinet may have been a blessing in disguise. It means I can push it all the way against the wall which in turn will let the front of the (yet to be created) grill even with the front of the entertainment cabinet.

I have not equalized and only set the level roughly with an SPL meeter. But initial impressions are good.

I ran some test signals through it and 90+db @20hz was absolutely silent but my pant legs were flappin . Couldn't crank it any further for fear of waking the house. I will let it blast tomorrow!

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I tested it some more tonight. I think it is ready to rock. I cranked it up but honestly cannot judge the sq above 90db @20hz. At first I thought I was hearing chuffing or some bad box resonance. Turns out it was the closet door rattling . By 98db everything else in the room is shaking (windows, blinds, stuff on tables etc) so SQ really doesn't matter. However at 100db 20hz I still cannot make-out 40hz (first order harminic), so the driver must be at least reasonable.

Just have to sand/stain it and make a grill. I have heard nightmare stories about staining birch, but the grain looks so good I cannot bear to paint it. I bought an ebony stain and will try it out on some scrap first.

Here are some pictures:
http://photos.ganzhorn.org/album645

[Mike P.]

Nice work on the cabinet, it looks great with the birch grain. Good luck with the staining process.

[jwh7399]

That looks excellent! I'm excited to see how the staining goes. I'm very happy to hear that it seems to be a descent driver.

What modelling software do you use? I'm thinking maybe a 170w @ 8ohm PE plate amp but don't know what the best volume/port size would be.

Very nice job on the sub!

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I used WinISD. It predicts that 170w will make the air velocity 28m/s in a 4" port. It also says it will be 105db @ 20Hz. Most people say 18m/s is the onset of "chuffing" (port noise). When I get the sub put back together I will run 170w through it to see if I can hear the port noise. I will have to do it outside though because inside all I will be hearing is the room .

This driver models really well in a reasonably sized box. The problem comes in when considering the port. To get a 4" port in there you need a pretty big box (for me that was ~4cu for a 17" port). But as I mentioned a 4" port really doesn't do justice to the driver (according to WinISD). You could get more port volume with a slot as in my first design in this thread. But I backed off and used a 4" precision port because it was easier and accomplishes (in modeling) my goal of 100db at 20hz (which only is ~50w) at an air velocity of only ~16m/s.

For staining I used a simple oil based ebony stain (which they tell you NOT to do with Birch). It looked great on a test strip. But the first coat on the cabinet didn't go so hot. It streaked a little on the vertical sides. The top looked perfect though. Note I don't mean runs, I mean streaks from the brush. I sanded it again and put another coat on it tonight. This one looks much better. I don't think I had enough light on it last night to really judge my coverage. This is the first time I have stained anything so you will have to look elsewhere for expert advice .

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I took another look at the model and it would take 3 3" ports of 27.5" to keep air velocity under 18m/s with 150w. In the same sized external volume box it shrinks the internal volume by .25 cu compared to the single 4" port. This still has a great FR curve to it. But I have no idea where you would place 3 3" ports on the front baffle! And you would have to bend the ports probably.

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It is really hard to take pictures that show a finish. So I uploaded a quick video to youtube

This is before the polyurethane coat. I did one coat of poly tonight and plan a second one tomorrow night. So far I am pretty happy with the finish. Not perfect, but pretty nice.

Note to self: make sure to remove all stray glue before staining. I have one streak and a small spot on the cabinet where the stain didn't take as well. I assume this is because I failed to sand off all of the glue.

YouTube - Mistral DVC subwoofer enclosure