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Old 11th January 2013, 01:35 PM   #371
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by hajj View Post
I already have an interesting resonator profile that should fit this application well, so if you feel like doing some mods to your enclosure, let me know
Yes, I am working on optimizing the enclosure from the ground up - so whatever mods that can improve things should be considered.
Thanks.
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Old 11th January 2013, 02:37 PM   #372
hajj is offline hajj  Lebanon
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The helmholtz sizing I have right now is for the full sized 70cm cornu, I'll need to resize it for the smaller sized versions as these have a higher cutoff point, and thus accordingly need a different resonator to match the cutoff frequency.
If you send me the horn characteristics of the smaller cornucopya you have (throat size, mouth size, length) I should be able to recalculate.

Last edited by hajj; 11th January 2013 at 02:46 PM.
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Old 11th January 2013, 03:27 PM   #373
xrk971 is offline xrk971  United States
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Hajj,

I am still in the midst of designing the next one, but it will probably be based on what I call the "True Cornu Function": 24 inches x 3.5 inches deep with the mouth size spanning the entire perimeter for an area of 24x3.5x4 in^2=336 in^2 or 2167 cm^2. The throat will be 31.3 cm^2. The driver chamber will have an area of 148 cm^2 and a volume of 1312 cm^3. The horn lengths will be 104 cm (Long path) and 49 cm (Short path) with a bifurcation. The path plan is attached.

If you can, please post the info on the resonator for the 70 cm case because many folks are interested in that size.

Thanks.

Xrk971
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Old 11th January 2013, 06:05 PM   #374
xrk971 is offline xrk971  United States
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Default Presenting the "Puck"

Cal Weldon had this idea for a speaker that represented one of the favorite activities of our good neighbors' up North. He called it the 'Puck' of course. Here is a True Cornu spiral horn in the shape of a disc with 6 channels. 3 of the channels are 1.26 meters long and 3 are 0.85 meters long. It can be made between 4 to 5 inches deep for use with your favorite 4 to 5 inch driver. The overall diameter of 27 inches. Since this is a true Cornu spiral with narrow channels and a small throat (32 cm^2), there will be some driver chamber compression effects. You may want to select a high efficiency driver with a more powerful motor and short stoke (think Fostex). Note that the horn mouth occupies the entire circumference of the speaker which has an area of about 2735 cm^2 for a 5 in deep cabinet to give an expansion ratio of 85!
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Old 11th January 2013, 06:16 PM   #375
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My goodness you certainly don't puck around do you?

Who's going to be the first to try that I wonder? Looks rather involved in and around the centre chamber, no?

You know X, that's a far cry from what I had in mind all those years ago. Since I was thinking it would be made from plywood, I was thinking something like this:
Or a more recent idea I could make from foam called the 'Daisy'.
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File Type: jpg daisy puck.jpg (63.3 KB, 428 views)
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Old 11th January 2013, 06:41 PM   #376
xrk971 is offline xrk971  United States
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Cal,
How deep is the Daisy? Looks like fun, one only has so much foam core boards though...
For the six channel Puck, you may want to use a thinner material for the channels near the middle. So that as you say, you don't want to puck around with how difficult it will be to hot melt those narrow passages. I am thinking something like stiff carboard (like the high quality stuff used to make mattes for framing) no foam near the middle.
Regards,
X
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Old 11th January 2013, 07:17 PM   #377
Fenris is offline Fenris  United States
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xrk,

Do your drawings and calculations in MathCad take into account the thickness of the foam in making the spirals?

Quote:
Originally Posted by xrk971 View Post
Cal Weldon had this idea for a speaker that represented one of the favorite activities of our good neighbors' up North. He called it the 'Puck' of course. Here is a True Cornu spiral horn in the shape of a disc with 6 channels.
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Old 11th January 2013, 08:22 PM   #378
xrk971 is offline xrk971  United States
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Fenris,
No, the channel thickness is not accounted for. I am taking a closer look at horn design theory and the relationship between driver chamber volume & throat vs the upper cut-off frequency. I am seeing that having a too small of a throat will impact bass output. I will have to incorporate this into these spirals and its relation to the depth.
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Old 12th January 2013, 02:07 AM   #379
Fenris is offline Fenris  United States
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Quote:
Originally Posted by xrk971 View Post
Fenris,
No, the channel thickness is not accounted for. I am taking a closer look at horn design theory and the relationship between driver chamber volume & throat vs the upper cut-off frequency. I am seeing that having a too small of a throat will impact bass output. I will have to incorporate this into these spirals and its relation to the depth.
The added thickness will change the geometry. 3/16" isn't much of a difference at the 24" opening, but it's a huge difference with a 3/4" wide passage. The dimensions will no longer be an exponential horn Each "lap" around that the spiral does adds that much to the overall size. Plus it subtracts linearly from the cross-sectional area at each point.
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Old 12th January 2013, 02:51 AM   #380
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Fenris View Post
The added thickness will change the geometry. 3/16" isn't much of a difference at the 24" opening, but it's a huge difference with a 3/4" wide passage. The dimensions will no longer be an exponential horn Each "lap" around that the spiral does adds that much to the overall size. Plus it subtracts linearly from the cross-sectional area at each point.
You are right about the thickness being more important towards the middle where the spacing is smaller. It is easy enough to put a thickness offset into the Mathcad equations used to generate the spirals. I am more concerned about having too narrow a throat right now with the true Cornu function. I may have to accelerate the spiral to get wider spacing towards the middle.
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