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CNC Speaker Design
http://dcaudiodiy.com/phpBB3/viewtopic.php?f=4&t=942		 Page 2 of 6
Author:  Cogito [ December 13th, 2017, 12:41 pm ]
Post subject:  Re: CNC Speaker Design
chris1973 wrote:

Also, would any of the other horn guys have any comments about whether there are any glaringly wrong problems with my horn profile?

The horn will accomodate a 10" woofer, and it will have a slotted trhoat about 1" by 7.5".

I'm assuming it will be a relatively long throw horn for pro audio use. I'm going to test it in my listening room, but I don't really have any intentions of keeping it there.


What type of a horn is this? How does the front view look like?

The throat area is 7.5 sq. in. where as the 10" driver cone area is 78.5 sql inches. Thats little over 10:1 compression. Roscoe's SLOBS are only 3:1 compression. That lob sided compression will create a havoc on the driver. You will see huge distortions.

What are the reviews of this horn?
Author:  brombo [ December 13th, 2017, 12:42 pm ]
Post subject:  Re: CNC Speaker Design
So Chris1973 what is it? Is the width of the horn constant?
Author:  tomp [ December 13th, 2017, 12:47 pm ]
Post subject:  Re: CNC Speaker Design
It's a tough call whether to do it with a CNC router or using templates for each layer and cutting out with a jig saw or router. Shashi is correct that the shape will change in both directions. You will also have the problem with registration of the individual layers. For my eggs I cut 18 sections with a router and used 4 1/8" holes in each piece that held sections of 1/8" dowel as registration pins when I glued the pieces together. That was a total pain and you still have to shape the rough edges by hand. I'll never do that again. If you could afford it I would go with the router. In either case you may wind up with a shape that does not give you the results you expect.

Tom

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Author:  Pelliott321 [ December 13th, 2017, 1:07 pm ]
Post subject:  Re: CNC Speaker Design
If that is the case then I would prototype out of ridged foam. Very cheap stuff, can cut with knife or even drywall saw.
4X8 ft sheet is $20 at HD. the cut edge can be sealed with just latex paint after shaping.
Author:  tomp [ December 13th, 2017, 2:56 pm ]
Post subject:  Re: CNC Speaker Design
As long as you are only doing the foam core process for shape that will work. However, it will be useless for sound evaluation. Someone did that with a strange horn design at the MWAF Speaker Design Competition this year and it was the worst sounding thing I have heard. Here is a photo. There were lots of other things wrong but the foam core construction did not help. In past years there were other horns made out of foam and they never sounded good.

Tom

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Author:  Pelliott321 [ December 13th, 2017, 3:38 pm ]
Post subject:  Re: CNC Speaker Design
the foam has to be sealed. This will work if done right.
Author:  chris1973 [ December 13th, 2017, 4:13 pm ]
Post subject:  Re: CNC Speaker Design
What are the reviews of this horn?[/quote]

This is my design. It's completely experimental, but I did read that I could go a small as 5 sqin. for a 10" driver.

I'll look up some compression ratio info, and see if I find any agreement with this claim.
Author:  chris1973 [ December 13th, 2017, 4:26 pm ]
Post subject:  Re: CNC Speaker Design
brombo wrote:
So Chris1973 what is it? Is the width of the horn constant?


The width is mostly constant, except for right at the throat.

The drawing hasn't been edited. The actual image in the drawing will constist of 10 layers with the throat opening throught the baffle to the front of the driver, which will be 7.5" x the 1" throat opening you can see in the dwg. Then on either side there will be 3 more layers of almost identical profile with the throat section across the baffle sealed. This creates the slot boundary on either side of the 7.5 inches.

I'll post the other image if you need it to visualize.

So at only one location, right near the beginning of the throat, the width of the horn does change from 7.5" to 12".

On the outside of the 16 layers, is two solid panels on either side that enclose the horn. 20 layers width altogether= 15" finished width.
Author:  Roscoe Primrose [ December 13th, 2017, 4:29 pm ]
Post subject:  Re: CNC Speaker Design
chris1973 wrote:
So at only one location, right near the beginning of the throat, the width of the horn does change from 7.5" to 12".


:character-oldtimer: Sudden changes in width like that can create all manner of problems....

Roscoe
Author:  chris1973 [ December 13th, 2017, 4:31 pm ]
Post subject:  Re: CNC Speaker Design
tomp wrote:
It's a tough call whether to do it with a CNC router or using templates for each layer and cutting out with a jig saw or router. Shashi is correct that the shape will change in both directions. You will also have the problem with registration of the individual layers. For my eggs I cut 18 sections with a router and used 4 1/8" holes in each piece that held sections of 1/8" dowel as registration pins when I glued the pieces together. That was a total pain and you still have to shape the rough edges by hand. I'll never do that again. If you could afford it I would go with the router. In either case you may wind up with a shape that does not give you the results you expect.

Tom


For the most part the horn will not be expanding in any other directions than you see in the drawing, so all the layers should stack up perfectly flush.

I'm going to run threaded rods all the way through the fourteen holes, and I think I'm going to try to not glue the layers together. Nut's on the outside will hold everything together.
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