Torrent Audio Mistral 12 DVC

**eyekode** · **04-04-08, 10:38 PM**

So after spending the time designing a sub to fit in my constrained space I figured out a way to get a few more inches of height. So I redesigned the sub. I also decided to do a modular design inspired by Zaph's sealed sub.

The idea is to allow replaceable front and rear baffles. This way I can try both a low Q sealed sub and a ported sub without building two boxes. I also can swap out drivers.

To make manufacturing easier I decided to build all 6 faces using 19.5x21" panels. This yields ~3.9 ft^3 without an internal brace. After adding a 4x17 precision port, bracing and driver I get ~3.6 ft^3 and a tune of ~21Hz. I plan on mounting the port only to the front baffle without additional internal support. But may have to add some internal brace that is not glued to the cabinet.

I have started cutting panels and hope to be listening to it next week. Thanks for all the help!

I have attached a cad drawing of the new design.

**Mike P.** · **04-04-08, 11:21 PM**

Keep us updated with some build pics.

**eyekode** · **04-25-08, 09:47 PM**

I finally got my build started. Wood is cut, most of the box is glued, all parts are here. Tomorrow I should finish up the baffle and back panel. I also picked up a Crown PS-400 for cheap to power it. Big passively cooled amp from yesteryear

.

I also ended up changing the plans a little bit. I decided having a modular box (removable front/back) was just too much effort

. So I am simply going to glue the front and back.

Here are my project start pictures:
http://photos.ganzhorn.org/album638

**jwh7399** · **04-26-08, 04:00 PM**

I see that the supervisor was on site from the start! I can't wait to see the build as it comes together and hear your opinion of the driver.

**eyekode** · **04-26-08, 09:27 PM**

Here are some pictures of the box: http://photos.ganzhorn.org/album644
The skeleton is put together and the front baffle is routed and glued into place. All that is left is the back panel and then I can have a listen. Simple design with just one window brace. Front baffle is 1.5" thick. Biscuits used on all butt joints.

This is the first time I worked with plywood instead of MDF. Love the lack of dust and the light weight. But it seems to be a more resonant structure. MDF feels much more "dead".

By the way this is going to go in the center bay of my salamander designs triple 30: http://salamanderdesigns.com/syn/syn...modelbase=sl30

**jwh7399** · **04-26-08, 09:38 PM**

Lookin' good!

Will the sub be built into the tv stand?

**eyekode** · **04-26-08, 09:43 PM**

Quote:

jwh7399 wrote:

Lookin' good!

Will the sub be built into the tv stand?

I built it to take up 2 shelf spaces. It will not be permanently attached. Just slid in. The shelves are removable in the salamander cabinets. If I can put together a half-way decent looking grill I think it will turn out really nice.

**eyekode** · **04-26-08, 09:49 PM**

By the way if anyone else builds with this sub re-measure the cut-out diameter. I think I cut exactly what the website said (11.25) and this doesn't seem to leave enough landing. Another .25" or so would have more of the driver's gasket on the baffle. And this in turn would allow the use of hurricane nuts. I am going to have to use drywall screws because there is not enough room.

<edit> and by "exactly" I mean I cut the hole 3/16th's too big (just remeasured). So scratch that, cut it as prescribed to 11.25

. I did get the counter sink for the driver exact...

**jwh7399** · **04-26-08, 09:49 PM**

That sounds very cool. It will have a real custom look.

I see that you decided to go with a larger amplifier. Will you need to use a high-pass filter so it doesn't bottom?

**eyekode** · **04-26-08, 10:04 PM**

Quote:

jwh7399 wrote:

That sounds very cool. It will have a real custom look.

I see that you decided to go with a larger amplifier. Will you need to use a high-pass filter so it doesn't bottom?

Really I have way too much amp for the port. Most people say that after ~18m/s port "chuffing" will become audible. This happens ~100w! I did splurge on the precision port so maybe I can push it a little louder. The thing flares out to a 7+" flange! My model says this will be 103db @20hz without room gain using only 100w. This should be plenty loud for me. So... what I am going to do with my other 500w? Eh, who knows

I picked up the amp for 80$ so no great loss.

**eyekode** · **04-26-08, 10:10 PM**

Oh... and you asked about a high-pass filter. My _guess_ is due to port compression and other losses I will never bottom out. With 100w it runs out of Xmax at ~12.5hz.

But I am also ramping up to build a sub-preamp. The crown PS-400 I bought needs a higher voltage then my receiver puts out on the subwoofer output. I also want to use a summing amplifier on the input so I can use the sub with my Tv's default speakers/sound as well. And if I am going to go to all that effort I might as well add a subsonic filter. Elliot Sound has been inspiring me

: http://sound.westhost.com/

**jwh7399** · **04-26-08, 10:13 PM**

For $80 you couldn't go wrong. You never know what the future will bring. You might use all of that power some day.

**jwh7399** · **04-26-08, 10:16 PM**

Wow, That's WAY over my head.

**mdrake** · **04-27-08, 12:07 AM**

Quote:

And if I am going to go to all that effort I might as well add a subsonic filter.

I could be wrong but I believe the Crown amps have a roll off at around 7hz-10hz.

Matt

**eyekode** · **04-27-08, 01:30 PM**

Quote:

mdrake wrote:

I could be wrong but I believe the Crown amps have a roll off at around 7hz-10hz.

Matt

I think many crown's do, but this is an old piece of gear. The spec's say it s +-.1db down to DC!. But looking at the repair manual it limits the output voltage at low frequency (starting at 10Hz). But it still lets a 30v swing at 8Hz and 10v at 2Hz.

**eyekode** · **04-29-08, 08:47 PM**

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.** · **04-30-08, 01:02 AM**

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

**eyekode** · **04-30-08, 07:55 PM**

Quote:

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

**eyekode** · **04-30-08, 10:34 PM**

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!

**eyekode** · **05-01-08, 09:19 PM**

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.** · **05-02-08, 07:37 AM**

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

**jwh7399** · **05-07-08, 08:21 PM**

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!

**eyekode** · **05-07-08, 10:13 PM**

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

.

**eyekode** · **05-07-08, 10:22 PM**

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.

Advertisement