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Old 8th September 2008, 02:58 AM   #1
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Default CNC Routing Big Fun Horn

I would interested to get feedback on this project.

I'm trying some designs out using CNC routing. Having built the Medallion horn using 'traditional' wood working methods, I decided I needed an easier build....hence CNC.

My plan is to build the horn in slices, using 32mm high density chipboard or MDF. The internal horn path will be coated in a hard resin to minimise sound absorption in the wood.

I also plan to offer the horns for sale via flat packing them. The assembly will be very straight forward, as the horn internals will fit together on 2 or 3 dowels, ensuring 100% alignment. Even the external panels will be aligned this way. There will be no screwing, only gluing. Real wood veneered external MDF panels will be used, or plain MDF for painting. Optional hardwood or ply can be arranged.

In looking at the design, what tweaks would you recommend? I've essentially taken the exact measurements of the BFH and rounded out the entire horn path. There are no straight lines in the internal section at all.

On the drawing, you can see a small line breaking the horn on the left hand side. As the routing procedure will cause a lot of waste, the horn will be made in two section. The line indicates where the break will occur. I'll then turn that lower section up towards the larger section, which will cut the waste down by 50%.

Being able to tweak the size of the compression chamber, I can build the horns to suit different drivers - eg Lowther DX series, or even something like the Fostex 206E. Basically, I want to build speakers that mean people can have access to a quality unit, at an affordable price.

Thoughts/feedback appreciated.

Andrew. Sydney.
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Old 8th September 2008, 03:33 AM   #2
spacies is offline spacies  New Zealand
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Hi,

Good idea. I am not sure how you would get the flat packs to the USA, UK etc because of costs but throughout OZ should be ok. Possibly an option for overseas users would be to offer to buy the plans to take to their local CNC shop? I know you want to make a couple of dollars but I can't see the shipping thing working IMO.

Since its all going to be joined why use 50mm material? Surely 18mm would be cheaper overall? Or were you thinking less bits to stick together would outweigh that?

Look forward to whats others say.
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Old 8th September 2008, 06:21 AM   #3
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Spacies, thanks.

Yes - there's no plan to ship overseas...however I have given some thought to the CAD plans being made available online. In this regard, I would also offer 'custom' plans whereby a speaker plan will be tailored to suit a particular driver. This process is relatively easy as I would simply size the compression chamber and throat to suit. Then upload the revised CAD file on the net for that customer

On thicknesses, I'n not sure where you got 50mm from. The individual 'slices' will be 32 mm, with the outer panels in 25mm. A 17mm venerred MDF panel can be applied to this subject to what the buyer wants.

Regards
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Old 8th September 2008, 06:57 AM   #4
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Hi atilsley

A couple of points occurred to me....

1. if I understand correctly that you will supply flatpack in sections/slices, wouldn't the flatpack be the same size as the finished cab, or am I misunderstanding?

2. Wouldn't it be possible to supply templates from your CNC rig, to cater for all the guys with router capability??

just a couple of thoughts, I'm not really a horn devotee but your post did intrigue me..

Regards

Ed
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Old 8th September 2008, 07:08 AM   #5
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Vitalstates

1. Because of the very large horn mouth of the Big Fun Horn, I will break the routed sections into two. This will cut down on wastage by 50%, plus make the transport easier. Remember, this is a large speaker, and I don't expect to promote it greatly....it's more one for my own use. However, I wish to get to a proof of concept for alternate designs - eg the public domain designs by Lowther etc. A flatpack acousta 115, for example, would be very easy to ship and assemble.

http://www.lowther.com.hk/acousta.htm

2. Yes - I plan to put up the designs on the web, but I'd like to recoup some of my set-up costs. I don't do the actual CAD drawings, so I have to fund that aspect.

On another point - while my passion is horns, the CNC routing enables me to construct all sorts of cabinets. For example, I've been playing around with a design that incorporates a 'standard' bass unit with curved sides and exceptional internal bracing, with a Lowther driver housed in a separate cabinet on top taking care of 200Hz and above. The top cabinet would feature the same curved sides, just a smaller profile. The bass unit would be active with adj cross-over, thus making this type of application very easy for valve lovers to hook up their amps.

Regards
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Old 8th September 2008, 07:10 AM   #6
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Oh, one other thing on flatpacks.

I just built our new kitchen from Ikea. We aqcuired 59 individual flat packs! The tallest being 2.0m. All delviered on one shipment.
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Old 8th September 2008, 09:33 PM   #7
spacies is offline spacies  New Zealand
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I don't know where I got 50mm from either? Heh.

I have a CNC router as well but the version of the program I use doesn't allow the import/export of .dxf files. The later versions do but the upgrade is $$$$$

I hope this works out for you and would love to see some progress shots.
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Old 12th September 2008, 02:30 PM   #8
marekst is offline marekst  Poland
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Hi Andrew,
You wrote about “your” BFH:
“There are no straight lines in the internal section at all”

Actually you can draw infinitive number of straight lines on internal section - from one side wall to the other. Not to mention that side walls are totally flat and parallel.
Anyway, what made you believe that a spiral horn is better than a horn with straight sections connected by rounded turns? Look at two Carfrae horns – the good one has two straight or almost straight sections.

Have fun plying a pro but don’t quit your day time job yet…

Marek Stojek
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Old 13th September 2008, 11:31 AM   #9
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Marek, not quite sure whether you're having a go at me or not...this is just a fun hobby for me....but enables me to create great horn speakers for people using a modern easy build process.

I was using nonparallel walls to take the best use of CNC routing. I understand straight lines are ok....but I just wanted to play with the design a little. Plus, there's a theoretical issue re standing waves which my approach minimises.

I have Jim's permission to market the Carfrae LBH, so I'll be using the CNC routing to its fullest in this design.

Any tweaks you'd suggest?

Cheers.
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Old 13th September 2008, 03:31 PM   #10
marekst is offline marekst  Poland
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I learned geometry a long time ago in Polish so sometimes I have a problem understanding.

“I was using nonparallel walls…”

A horn with a rectangle as its cross section has 4 walls. I believe the designs you are trying to improve (LBH, BFH, Hedlund) have 2 parallel (side) walls. Is that right? Are you planning to change that or are you just rounding the corners of the other two walls which are already not parallel?
The walls of Big Carfare Horn are not parallel although it has a rectangular cross section and one can draw straight lines on the horn walls.

“Any tweaks you’d suggest?”

Not exactly a tweak but if you want a good horn ask your neighbor the Azura dude if he has anything left over.

Good luck.
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