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Old 25th January 2013, 03:54 AM   #471
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Default 12 inch driver spiral horn

So I pushed and shuffed enlarged copies of the puck around until i managed to hand draw my new design for the 12 inch RCA driver.
Size is still about 33 by 39 inches, but to help the math I used 84cm by 100cm.
In this drawing all six horns have their throat in the circle of the speaker opening and I made the size 2cm wide. The horn guides will be 11cm tall, but I build this in two layers to get 22cm by 2cm horn throats.
I did the math starting with the Sd of 490cm square (27cm diameter).
Chamber volume will be 10.8 Liter
Total throat area is 2cm x 22cm x6 = 264cm square.
Upper cut off frequency works out to 133Hz - which I like, because from using these drivers in a Voight pipe I know only much lower frequencies were missing.
Horn length are h1 with 1.73m, h2 with 1.38m, h3 with 1.35m, h4 with 1.06m,
h5 with 1.01m and h6 with 1.23m
So now I need to get another sheet of ply for the second layer.
Yes I agree chazdrumzalot this will be huge, but given the location on the wall below the window and covered with a nice fabric it will nearly disapper :-) and thank you for your input, I did work it in.
Lots of thanks to our untiring coach xrk971 who makes a lot possible.
Below are to pics which really should be one of my design using the "Puck" posted by xrk971. My paper was to big for the scanner, so anyone who wants to use it now needs to make two copies and tape them together right.
I think this design could be made smaller for 8 inch and 10 inch drivers if someone wants to get into uncharted areas. My best estimate for listening reports is two weeks from now (or3). (if I can't do this picture posting right, please visit my album)
Great tread this

Click the image to open in full size.

Click the image to open in full size.
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Old 25th January 2013, 04:16 AM   #472
kambule is offline kambule  Hong Kong
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Default sealing up the last put-on-panel

I have an idea of sealing up the last put-on-panel properly :

- put the guides on the front panel (speaker mountings should have been properly prepared) using
hot melt gun, or anything good mentioned by other members. Nearly all projects so far put the
guides on the rear panel first.
- cut the 3/16 inch slots for the guides on the rear panel.
- With the guides facing up and the front panel facing the table, press the slots of the rear panel
on to the guides such that the guides just pop out of the rear panel surface (cant remember
the proper word). Use whatever glue or even hot-gun to stick ( and seal) the guides to the
rear panel. (This will look horrible if slots cut and sealing is done on front panel, oh
might be artistic).

Note the width of the guide should be wider by the thickness of the panel, for example
20 incher channels 2.8 inch deep and panel 3/16inch thick, the width of the guides should
be 2.8 + 3/16 inch.

This way will ensure the sealing is proper for the last put-on panel.

Any comment ??

Last edited by kambule; 25th January 2013 at 04:25 AM. Reason: forget to say the the guides and panels use the foam core board is 3/16 inch
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Old 25th January 2013, 06:35 AM   #473
xrk971 is online now xrk971  United States
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Cutting the slots for the channels (or guides as you call them) will be a major hassle. In addition to being difficult to do in foam even, it weakens the rear panel. In wood it will require a router and a jig or very steady hands. Sort of defeats the point of the easy to make foam core spiral. The way to ensure a good seal is to do a good job in cutting the channels so that they have a uniform width. When this is done, the glue has no trouble sealing. It's good that you are trying to come up with a good way to seal, as a leak in the channel will render the horn useless at generating bass. Segmenting the back and gluing sections at a time is another way.
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Old 25th January 2013, 07:54 AM   #474
kambule is offline kambule  Hong Kong
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Not sure about the strength. The width of the slot does not need to be exact as the glue will seal up the imperfect gaps. I guess less time in cutting slots than trying to putting the glue on the right place. Apart from time spent, using this method I will be very sure the slot is sealed while in other methods there is still a question mark.

After sealing, sticking another board onto it might help strengthen the structure.
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Old 25th January 2013, 09:31 PM   #475
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xrk,

LR = living room
as opposed to the systems in family room, kitchen, office & bed room

Cheers, Jim
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Old 26th January 2013, 01:11 AM   #476
xrk971 is online now xrk971  United States
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Glowglass,
Those are great looking plans you have. Thanks for sharing the scans. I think the plans would be very suitable for a smaller driver simply by making only a single layer spiral. Probably an 8 inch driver. 2 cm x 12.5 cm deep x 6 = 150 cm squared for 5 in deep channel. Cutoff high freq about 220 Hz. This opens the flood gate for anyone wishing to try a 8 inch full range like a BG20, a bofu, Fostex, Betsy, ...
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Old 26th January 2013, 03:24 AM   #477
xrk971 is online now xrk971  United States
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Default 20 inch plan with custom channels

Quote:
Originally Posted by kambule View Post
Your work and contribution are very impressive. I plan to build a 20 inch speaker with Vifa TC9FD. Noting that you have changed the throat width, would you mind to share a print of your 20 inch plan ?? I hope to get a successfuly reproduction. Thank you in advance.

By the way I have also gone through the other 100+ pages Foam Board thread and cant find your 20 inch plan as well. I only find the original sebastian and planet10 plans.
As requested, here is a photo of my original 20 inch plan with internal corners and a larger throat. The grid is 1 inch scale.
Attached Images
File Type: jpg 20-inch-cornu.JPG (468.3 KB, 323 views)
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Old 26th January 2013, 08:30 AM   #478
kambule is offline kambule  Hong Kong
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Default xrk, thank you

you are a good man
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Old 26th January 2013, 12:46 PM   #479
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I'll second that!
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Old 26th January 2013, 07:22 PM   #480
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Great to see all the progress while I was away in the deep woods of some tropical island with no internet. New guys onboard, a PM or two asking advice and, and, and...

and nothing, just like to see the enthusiasm.
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