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Need advice on first DIY sub project (possibly isobarik) (1 Viewer)

Dustin B

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I was planning on two layers of 3/4" MDF. I will probably do that, but the problem is I have limited space. I can't fit a medium to large sonotub. I want the dimensions under 22" x 22" x 22", and I don't think it's possible to get 20hz at a decent volume out of a Shiva in a box smaller than that. From WinISD it would have to be isobaric to get the box small enough to satisfy me and that makes it iffy as to whether or not it would be worth it.
 

Dustin B

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So have I made myself look like an idiot yet. I just looked at the application white paper on the Shiva again. Why I didn't see it in Blake, or Craig's posts I don't know. The EBS design has specs I like, but is a couple inches taller than I would have liked (26" with legs).
So now that I've gotten my head out of thinking about an isobarik configuration (why I wanted to prove it was what I wanted I'm not sure, guess I just wanted to say I had an isobarik sub
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I guess I'll just have to wait for Craig's report on his comparison of the Shiva EBS to a Parardigm PW2200.
Has anyone mounted an AVA250 to the EBS design without building an extra little add on box for it? Will the modifications required to the braces and the slight reduction in volume (9.5" x 9.5" x (3.5" - 0.75")) make a significant impact on its performance (don't really want to add another little box for the plate amp).
Is there any reason the EBS design couldn't be run as a front firing sub with shorter legs? Would it perform as well?
The only thing that is bothering me is the numbers from WinISD when I plug the EBS stats into it. It says a 4" port that is just over 17" should be used instead of 12". And the gain and spl graphs don't have it's response quite as good as the specs in the white paper. And when I set the Pe value to 600 W the mach number is in the red, but when I set it to 250 W the mach number is in the green. Is this just the program in error? I know I'm paranoid, but with so many people using this program and it asking for a port that is 5" longer I have to wonder.
 

Hank Frankenberg

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Hang in there, Dustin. We all started with little knowledge. Your D-I-Y sub will be WELL worth your investigative and construction efforts. When you crank it up and watch the jaws drop, a silly grin will come over your face and you'll be very satisfied
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Craig LeBlanc

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Dustin,
Here's something from Dan Wiggins from Adire :
As far as the differences between the two vents, the 3" vent is good up to around 125W delivered, then you start to get some compression (this would be at SPL levels around 103-105 dB SPL, however). The 4" vent is good up to around
200W delivered, before compression starts to set in (SPL levels closer to 105-108 dB SPL).
So I don't think there would be any issues using the ava250 for power. When the preliminary testing was done on my EBS, we side fired it...and it worked pretty good! I'm tempted to leave it that way... cause it looks pretty mean when you're looking down the business end of a 12" driver and the port ! I propabaly won't have the box completely finished until after this weekend... then put some hours on the driver to break it in. After that's done, I will break out the SPL meter and see what she can do.
One quick note about the vented Shiva .pdf, go by the schematics instead of the written instructions for cutting the panels and braces. And if you have the 3" port, use the diameter from the schematics of the 85L box for the hole.
 
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Dustin:
I am mounting the AVA250 on the front side of the box (the side above the woofer). Dan Wiggins said that the 3 liters of space taken up by the amp will have little to no effect on the sub. If you need pictures or a drawing of where to cut for the amp, let me know. The cut also shouldn't affect the strenght of the braces.
Blake
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Jack Gilvey

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So have I made myself look like an idiot yet...
I do that quite often,Dustin, and it does get easier. Just hang in there.
To seriously answer your question: No.
As far as an isobaric configuration, the only advantage is reduced size. You need two drivers and twice the power to get the same performance as a single driver in an enclosure twice the size. As I mentioned, the port requirements are not reduced, so something like this must be resorted to to fit the port. I think it makes more sense for a sealed or PR sub, at least at the frequencies that these high-performance drivers allow our subs to be tuned to.
I would also recommend that you download Adire audio's version of LSPCad . It is definitely not as easy to use (initially) as WinISD, but is much more accurate as far as vent lengths, in-room response, and such, and will be a better learning tool. It's got the Adire drivers already loaded.
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Jack Gilvey

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And since it is a vented box, there wouldn't be a whole lot of internal pressure inside the chamber anyways. If I had gone with a sealed design, then I might have thought about using screws.
Actually, there's quite a bit of pressure in a vented box around its tuning frequency. In fact, at Fb, there's enough pressure created in a vented box to almost completely damp the motion of the woofer cone, which is a primary advantage of the reflex cab. Even slight leaks can compromise this damping, leading to premature bottoming/overexcursion of the driver.
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Dustin B

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Thanks for the encouragement guys.
Boris
Looks awesome, what did you use to finish it? The white paper says not to use batting, how much did you use and do you think it affected performance at all?
After more thought and looking, I'm liking the EBS box design from Adire with a Shiva more and more. It will either be earily april or may before I can get the time to build it. April will be easier since I have a really long break before I write finals that will make the hour drive to my parents and several days there to build it easier to handle.
Still, I just want more assurance an EBS shiva with a 4" port will match or beat a PW2200, so I'm waiting for that comparison Craig. I know I can count on you :P What should be a >= $300 savings over a PW2200 would certainly be worth my time.
 

Boris

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Jan 10, 2001
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Hi Dustin
I used a black gloss auto spray to finish it. Maybe a bad idea as I went through loads of cans. Well, you live and learn.
I lined the enclosure. The white paper talked about using Polyfill which is a stuffing thing.
Many DIY sites advised lining a ported alignment usually gives better results, so I did.
Stuffing (which is different) makes the enclosure seem bigger.
I'm sure somebody with more technical expertise can clarify and explain this.
Cheers
Boris
 

Andrew_Chan

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Aug 27, 2001
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What kind of glue is good in a way that I do not need clamps to force it to make it stick? Is there a specific glue? or any wood glue will do? is there a specific key word written on the bottle I'll have to look for?
 

Dustin B

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Mar 10, 2001
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Wow, how did this get drug back up. How my plans changed since march
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I was almost laughing out loud rereading what I posted in this thread. Makes me realize how much I learned about subs over the last several months. I'm certainly glad I built my big black tube Tempest and not an Isobaric Shiva
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If someone remembers this thread but didn't connect it to what I ended up doing, here's the link again:
http://ht.s5.com/Sonosub.html
Anyways, for your glue question Andrew, save contact cement, which wouldn't be the best choice for glueing a box together (I think carpenter's wood glue would be best), you'll have to either clamp or screw it along with glue.
Since you don't want to clamp I guess you'll have to use screws. What I find works best is to line up the pieces, and predrill them. Then put the glue on and screw the pieces back together. The screws will hold the wood while the glue dries and all will be good.
 

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