TH-18 Flat to 35hz! (Xoc1's design) - Page 91 - diyAudio
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Old 14th September 2012, 06:40 PM   #901
ODougbo is offline ODougbo  United States
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Default Foam

I was thinking this would be a good way to make the box extra solid; and won't add weight. Fill the triangles up with poly foam - one $5 can should do the job.
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Old 14th September 2012, 06:43 PM   #902
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Default cone correction

Hi Djim,
I went back to the start of conversations on cone corrections at post 484,and read it all again.
So is the triangle shape the preferred way to go ?
I can still make that change so I am going to fit braces and other touch ups before I close the box ,
The drawings look like the tip of the triangle needs to be at the baffle level,and the side pieces create a slot ,I could not glue these pieces just use screws and use them to tune it ,then glue it in and make it permanent,LOL.
I am not in a hurry to finish ,I hope to make them the best I can ,I wish I was smarter with speaker science,lol
Thanks for your help!
NS
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Old 14th September 2012, 07:24 PM   #903
Djim is offline Djim  Netherlands
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Hi noSmoking,

Martin (Xoc1) seems to be working on a new design for the Xoc1-TH18 with cone correction. It wouldn't surprise me if that would lead to a new internal structure.
I am not sure but it looks like you already have made some sheet cuts so changing to a new internal lay-out will be difficult (or you need to spend some extra on new sheets).

For Crescendo I suggested something that really follows the structure of the cone. This is probably not necessary as the main goal of cone correction is to correct the position of the pressure zone (there where the horn-path is most narrow) towards the centre of the driver or towards the position as in the sim. For the strongest drivers it doesn't matter so it is best positioned as the sim suggests but for less capable drivers I believe it is best positioned above the centre of the driver.

A more simplistic way to do that is shown in the picture. The "stub" is going from one side to the other, so it expands of the entire width of the cab. As you can see it is just a little out of the centre of the driver (somewhere between 0.5 to 1.5cm). I suggest to use at least two braces in the "stub" cavity. You can also make the whole stub from one solid piece to increase stiffness (but is more heavy of course).

Like ODougbo already said, don't forget to fill up your cavities....

Click the image to open in full size.

Last edited by Djim; 14th September 2012 at 07:44 PM.
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Old 14th September 2012, 11:10 PM   #904
NEO Dan is offline NEO Dan  United States
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Is there any performance benefit in doing this?
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Dan
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Old 14th September 2012, 11:21 PM   #905
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Default ! a good idea

Quote:
Originally Posted by ODougbo View Post
I was thinking this would be a good way to make the box extra solid; and won't add weight. Fill the triangles up with poly foam - one $5 can should do the job.
I was hoping I had made my last trip to the depo,,,,,,LOL. But that's a good Idea!
Ns
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Old 14th September 2012, 11:30 PM   #906
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by NEO Dan View Post
Is there any performance benefit in doing this?
This should give a similar results to Crescendo's findings.
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Old 14th September 2012, 11:32 PM   #907
Xoc1 is offline Xoc1  United Kingdom
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Hi All
The Tour of Britain Cycle Race comes to our town tomorrow, and a I have a gig in town so I have been busy rebuilding and configuring my PA rig.

I was given some dimensions for a B&C SW115 so I used that to model a cross sectional area. I used a 422mm cutout in a 18mm baffle.
I can slice the model at different points and measure the cross section.
I found that 2cm wide slices were adequate.
This is a screengrab of the cone and baffle volume at the speaker mid point.
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Old 14th September 2012, 11:34 PM   #908
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Hi Djim,
Looks like a good way to do this,Thanks for taking the time to draw it out,I know you built a set of these ,did you use this stub also ? Did you see a difference ,and how low was your useable freq?
Thanks,
NS
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Old 14th September 2012, 11:41 PM   #909
Xoc1 is offline Xoc1  United Kingdom
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I sliced the model in 2cm increments and put the results into a spreadsheet.
The area is then divided by the internal width of the TH18 cab and an equivalent depth dimension calculated.
The amazing thing is how constant the midddle section of the cone area is.
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Old 14th September 2012, 11:43 PM   #910
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Hi Xoc1,
Thanks for the pic,
Would you give me your opinion on the cone stub PLEASE. I am after bottom end not the top maybe will cross at around a 100hz ,I have a dcx2496 so I can adjust till it sounds best.
NS
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