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Karma-8 Build Thread

post #1 of 100
Thread Starter 
I just ordered a set of these and am very excited to get my feet wet with the waveguide speakers, just on a small scale. I wanted to see how these worked/performed before getting the Fusion-12 Tempests for LCR. I plan on using these Karma's for surrounds.

Instead of building standard rectangular boxes, I wanted to build them with 45's on the backside as these will be sitting sideways up in the corners of the room to save space. I'm pretty sure I figured the math out and got pretty dang close (see attached spreadsheet). The formula for the area of the triangles is =((A9*C9)/2)*B9 or basically base x depth divided by 2 for square inches x height for cubic inches. Should be correct if I remember my 8th grade Geometry right biggrin.gif I could have obviously made the airpsace exactly the same but I wanted to use standard imperial dimensions so its not exact. I think it'll be close enough though.

Any thoughts on my box, does the math look correct? Here's a picture of a similar box that is close enough (except the angles are not symmetrical but you get the idea):



I'll keep this updated as I get the speakers but wanted to at least get this started and get input on the basic design.

Thanks all for doing the legwork and making this all possible!

Scott

Karma-8 Box.xlsx 11k .xlsx file
post #2 of 100
Thread Starter 
Here's a picture of the excel file so it doesn't need to be downloaded.

Scott

post #3 of 100
I didn't check your math but I find it slightly easier to calculate the area of the large rectangle and then subtract the areas of the triangles. Ignore height if the same.

Assuming those are all internal dimensions...I get that you need to increase the depth of the box to about 9.25" and then whack the corners off.
post #4 of 100
Thread Starter 
Ahh that would have been a little easier! I appreciated the math challenge though biggrin.gif

Yes, those are all internal dimensions based on the drawing on the DIY Sound Group site for this speaker.

Scott
post #5 of 100
Those will be really cool!

You don't need to be super precise with the internal volume, as long as you get it between 0.5 and 0.8 cu ft you need not worry.
post #6 of 100
Thread Starter 
Quote:
Originally Posted by mtg90 View Post

Those will be really cool!

You don't need to be super precise with the internal volume, as long as you get it between 0.5 and 0.8 cu ft you need not worry.

Thanks! I appreciate all your work making them biggrin.gif

Good to know about the volume, I guess I'll be close enough! Does the math look correct?
post #7 of 100
Hang on don't start yet, Erich has the image for the EOS-8 box linked on the MTG-08 design. The enclosure for that one is larger since it uses a taller waveguide, 9.5"w x 19.5"h x 10.5"d external, 8"x18"x9" internal about 0.75 cuft.

That probably throws off all your calculations. redface.gif
post #8 of 100
This is the correct enclosure image for that design:
post #9 of 100
Thread Starter 
Oh wow that definitely is different! Cool thing about excel now that the formulas are figured out is I can just change values to fix it. I'll do that in the AM. I won't start on the cabs until the drivers and crossovers arrive.

I will definitely need help with the crossover as I've never built one before. Anyone have pics of these crossovers finished? I don't know how to translate a schematic into an actual crossover biggrin.gif

Scott
post #10 of 100
Only ones I know are mine and Gadkins in the original design thread on the DIY sound group forums: http://www.diysoundgroup.com/forum/index.php?topic=53.0
post #11 of 100
Thread Starter 
Quote:
Originally Posted by mtg90 View Post

Only ones I know are mine and Gadkins in the original design thread on the DIY sound group forums: http://www.diysoundgroup.com/forum/index.php?topic=53.0

Ok no problem, I'll check out the thread. I showed my wife yours last night and she thought they looked pretty cool.

I've revised the spreadsheet to reflect the CORRECT drawings (I should have realized they were different based on the baffle size included with the kit).

post #12 of 100
Just subscribed!
In my general purpose media area (family room), I am limited by the layout to a 5.1 system.
These might be just the ticket for my surrounds..
post #13 of 100
Thread Starter 
Quote:
Originally Posted by cuzed2 View Post

Just subscribed!
In my general purpose media area (family room), I am limited by the layout to a 5.1 system.
These might be just the ticket for my surrounds..

Exactly my thought. I MAY be able to get 7.1 in my area but we'll have to see once I get them built and up. I think having them small enough with the wide dispersion waveguide may be just the ticket for those of us who can't do a fully matched Tempest-12 system all around biggrin.gif

Scott
post #14 of 100
Skeeter, have you thought through all the joinery and clamping issues that there might be building a non-rectangular box? I ask because I've never built any cabinets, but if I did I would probably need some to be non-rectangular as well.

Fred

(subscribed!)
post #15 of 100
Thread Starter 
Fred,

I have thought about it definitely. I have a lot of clamps both standard and wraps and may resort to doing some tiny nails with the air gun if necessary. It may be a challenge but it'll be a fun one for sure!

Scott
post #16 of 100
FWIW, the better way to go about this is to match base areas, then multiply it by the height.........so with the design's base area = 8*9 = 72"^2 and one triangle's area = [2*3]/2 = 3"^2 and the others = [3*3]/2 = 4.5"^2, then to find the new depth we add them and divide it by the base = [72+3+4.5]/8 = 9.9375" [9-15/16"]

To verify: 8*9.9375*19.5 = 1550.25"^3 - [3*19.5 = 58.5"^3] - [4.5*19.5 = 87.75"^3] = 1404"^3

GM
post #17 of 100
GPM, didn't that change the baffle size? (is that not a problem?)
post #18 of 100
Thread Starter 
I realized I'd made an error in figuring the volume of the triangles and only had one accounted for in the design, oops! So I've recalculated and was able to adjust the depth slightly of the main box to compensate and came up with a perfect match biggrin.gif



GPM I'm not following your math on this part: "one triangle's area = [2*3]/2 = 3"^2 and the others = [3*3]/2 = 4.5"^2" Why are they different? I want each triangle to be identical so the 45 degree cuts are more simple.

Scott
post #19 of 100
Quote:
Originally Posted by HopefulFred View Post

GPM, didn't that change the baffle size? (is that not a problem?)

No, only the depth increases to offset the net Vb loss due to whacking off the back corners.

Changing the baffle perimeter can change the baffle step's corner frequency point, which in turn ideally requires changing any BSC filter design, but it generally requires a significant difference to be audible.

GM
post #20 of 100
Quote:
Originally Posted by skeeter99 View Post

GPM I'm not following your math on this part: "one triangle's area = [2*3]/2 = 3"^2 and the others = [3*3]/2 = 4.5"^2" Why are they different? I want each triangle to be identical so the 45 degree cuts are more simple.

Scott

Looking at the picture in your first post, the speakers have unequal triangles, so interpreted your 2" x 3" and 3" x 3" to reflect this. If you want them equal, then just multiply the two side dimensions and don't divide by 2.

The new depth then is 72+[3*3 = 9] = 81/8 = 10.125" [ 10-1/8"]

GM
post #21 of 100
Thread Starter 
Quote:
Originally Posted by GPM View Post

Looking at the picture in your first post, the speakers have unequal triangles, so interpreted your 2" x 3" and 3" x 3" to reflect this. If you want them equal, then just multiply the two side dimensions and don't divide by 2.

The new depth then is 72+[3*3 = 9] = 81/8 = 10.125" [ 10-1/8"]

GM

Well if you'd read my second paragraph of my first post you'd know I wanted them equal and the pic was only for general reference biggrin.gif I'm joking around of course but I did say that. I want them to be the same so they're 45's and about as simple a bid as you can get without it being all a rectangle.

Scott
post #22 of 100
Nope, was just scanning threads to see any pics since I have precious little time these days to devote to this hobby and noticed your request to check your math, which at a glance left something to be desired IME and the listing of three different base dims 'fit' with the picture's image.

GM
post #23 of 100
Thread Starter 
I was just bustin your chops, it's all good.
post #24 of 100
Thread Starter 
Package just arrived! I'll echo everyone's statements that these were VERY well packed! Everything arrived perfectly. I'm really amazed at the quality of the horn, its very nice looking. I had fairly low expectations as I bought the least costly kit but to say I'm impressed at the quality is an understatement. I can't wait for this weekend so I can now try to figure out how to build a crossover AND get the box built!

Question, what kind/amount of stuffing should I do? Maybe I missed it somewhere but I don't see it discussed. I also haven't been fully unpacked the box so if its in there please disregard biggrin.gif

Scott
post #25 of 100
Line it with 1-2" of decent dampening material, poly batting, fiberglass, recycled denim insulation, acoustic foam etc.. Make sure you leave a clear path around the back of the woofer to the ports as well.
post #26 of 100
Thread Starter 
Cool thanks for the tip, that should be pretty easy. I'm reading through the threat on DIY Sound Group Forum again and ran across your crossover pics which will help for sure. I may actually try to tackle the crossovers tonight so I can take pics and get review from you all confused.gif

Scott
post #27 of 100
You won't be tackling the crossovers tonight because you have 2 inductors that were shipped separately because Parts Express was out of stock. But they are in route.

The lower prices on the site don't translate into lower quality gear. That just happens to be the price based on the actual cost of the parts added up.

By the way, that package took a lot longer than normal to reach you. Or at least it seems like it. I guess you are pretty far away.
post #28 of 100
Thread Starter 
Ah crud! Do you know which inductors? I haven't looked through the parts extensively yet. I may just go buy some more.

I totally get it about the price, it was just a happy surprise smile.gif

4 days is right to get to me from where you are. I used to work for a national distributor and 4 days was always how long it took to get to the west coast from your area. No worries at all.

Oh, and thanks for the binding posts! I totally forgot to order them so I appreciate it!

Scott
post #29 of 100
Thread Starter 
Started laying out the crossover, found out its the 2.5mh iron core. Crud. You have tracking on mine Erich?
post #30 of 100
Thread Starter 
Ugh realized I made another box calc error. Had the internal dims for the base and depth but external for height. Easy change down to 18" internal but still, irritating.

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