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Old 2nd November 2012, 07:54 PM   #11
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Quote:
Originally Posted by ▀art West-VL. View Post
Totally different picture :
That looks more like what I'd expect. If you could post a pic of the impedance also, showing the two peaks of a br box, it could be helpful for a comparison.
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Old 2nd November 2012, 09:41 PM   #12
Prj57 is offline Prj57  Bulgaria
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Ok, I may have screwed up with the software

There's an option that says "include vent resonance peaks in all relevant graphs" In the previous graphs this option was ON. I am still trying to figure out some of the options, so I am still learning...

Now, with this option OFF, this is how the graphs look and the resulted frequencies:

Type: Vented Box
Shape: Prism, square
Vb = 87455 cu.cm
Fb = 28.46 Hz
QL = 6.582
F3 = 25.44 Hz
Fill = normal
No. of Vents = 1
Vent shape = rectangle
Vent ends = one flush
Hv = 382 mm
Wv = 32 mm
Lv = 452 mm
QLv = 7

If things are really that bad I think I will have to start over. I think I ll double check with WinISD
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File Type: jpg new settings 1.jpg (247.8 KB, 53 views)
File Type: jpg new settings 2.jpg (179.8 KB, 48 views)
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Old 2nd November 2012, 09:59 PM   #13
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by duanebrow View Post
I don't like MDF for braces, I suggest plywood as it is stiffer. (MDF will work, you just need to use a bigger piece.)
Sorry duanebrow, internal braces have exactly the same pressure on both sides!
In other words, braces don't flex by themselves.
The only panels in an enclosure that will suffer from flexing are panels that have an unequal pressure between the two sides.
For basreflex enclosures that are usually the panels facing the outside and the basreflex tunnel.
For this reason braces can be made of less stiff (cheaper) materials.
When made out of the same material the thickness of the braces can less if the attachment points are enforced/supported.

Click the image to open in full size.

Last edited by Djim; 2nd November 2012 at 10:07 PM.
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Old 2nd November 2012, 11:40 PM   #14
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Quote:
Originally Posted by duanebrow View Post
... If you could post a pic of the impedance also, showing the two peaks of a br box, it could be helpful for a comparison.
Good thing you asked for it, I don't like the looks of the impedance response. I was under the impression that both peaks should be equal for optimum performance┐
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Old 3rd November 2012, 03:25 AM   #15
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Quote:
Originally Posted by Djim View Post
Sorry duanebrow, internal braces have exactly the same pressure on both sides!
In other words, braces don't flex by themselves.
The only panels in an enclosure that will suffer from flexing are panels that have an unequal pressure between the two sides.
For basreflex enclosures that are usually the panels facing the outside and the basreflex tunnel.
For this reason braces can be made of less stiff (cheaper) materials.
When made out of the same material the thickness of the braces can less if the attachment points are enforced/supported.

Click the image to open in full size.
I agree with you, for a brace like you have pictured. And it is just my preference to use Plywood when I can. When I wrote my post, I was thinking about "cross bracing" (for lack of a better term). Lets go back to what flexes on a box. The corners can't flex because they are attached to another panel. So the most flexing in a box will be the center of the largest panel. By simply running a brace from the center of the panel to the opposing panel all flexing in the center of the panel can be stopped. In this case the brace can flex if it is not strong enough to withstand the pressure exerted on it by the sides. Both braced panels now flex as much as one 1/4 of the size. By using more of these braces on the panels the results greatly increase. The law of diminishing returns applies of course.
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Old 4th November 2012, 08:10 PM   #16
Prj57 is offline Prj57  Bulgaria
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OK guys, there's been an update! I managed to somehow explain to my friend that there's a difference between sub for car audio and for home audio! I was showing him some examples and by at one point after I showed him the Eminance Lab 12 he stopped me and said "You convinced me, I ordered it already" !

So now I am pretty excited, since I never thought I would be able to get this speaker here in this country and is not something I have the loose change for to experiment! I've taken an interest in the bracing discussion earlier, I have some updated designs. I would like to hear opinions about the design... talking about the braces. The box with the Lab 12 will be the same as last time, 100.3 liters total, tuned to 28Hz, single slot 42w x 382h x 500-520l mm. I plugged the numbers both in Bass Box and WinISD and the results are almost identical! Pretty flat response but will have to make a steep high-pass at around 25Hz to protect the sub. I have no idea about crossovers, I am willing to try and make one, but have no idea where and how to start. But that for later on.... I am more interested in the bracing as I want to finish the design so I can take the dimensions and cut the MDF.

I am not sure wheter or not I am going to be able to find or use different material for bracing. So far the cost of the whole thing went more than double with the new driver! I think I can find plywood but can't really count on it. So far I figured I reinforce the box with something similar to what Djim proposed, however with some minor modifications. If I'm limited to 19mm MDF, I provide for 2 extra panels to be used as braces inside. They will reinforce the back, port wall and side of the box. The panels will be glued then bolted from the sides, bottom and top part. In my view this will reduce flex to a minimum without making the insides too crowded

The base support is also from 19mm MDF so basically brace and brace support will be 1/1 panel thickness both! Would that be a problem? Also, please advise if the current brace design isn't an overkill?
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File Type: jpg Lab 12 @ 28Hz w_brace 1.jpg (201.6 KB, 15 views)
File Type: jpg Lab 12 @ 28Hz w_brace 2.jpg (212.3 KB, 18 views)
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Old 4th November 2012, 09:12 PM   #17
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MDF is fine, don't worry about other material.
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Old 4th November 2012, 10:21 PM   #18
Djim is offline Djim  Netherlands
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Hi Prj57,

Just make the brace cut-outs a little smaller. Also extend the centre of the braces towards the front baffle and your braces are okay.


Click the image to open in full size.


You can cross brace every panel to increase stiffness even further... (blue brace)

Click the image to open in full size.

Last edited by Djim; 4th November 2012 at 10:44 PM.
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Old 4th November 2012, 10:45 PM   #19
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The 45's at the sides of the front baffle are just using up airspace. Since the corners are basically a brace. You don't need to use any type of mechanical fasteners on the braces, the glue is stronger than anything else in the box. And MDF likes to split when anything is driven into the end grain. Lots of clamps and glue and you are all set.

It looks fine in the drawing, but make sure that you have clearance for the drivers vent.

Btw, Lab 12 drivers are very nice. Is he getting one of the new 4 ohm versions? I know a guy that got two of them before they were released. Seems very pleased with them.
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Old 4th November 2012, 11:51 PM   #20
Djim is offline Djim  Netherlands
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Click the image to open in full size.

(including the end-flaring of the reflex-port)
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