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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 4:32 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 150
Here is an interesting video about gluing foam together. The winner is Glidden Gripper.

https://www.youtube.com/watch?v=rnOegaOKu38

ray


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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 4:39 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 259
Roscoe Primrose wrote:
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


I thought I might use a cabinet file after I have all the parts completed, to turn that abrupt change into a smooth transition with a little freehand modifiction of the relevant pieces.

If I can assemble the cabinet without gluing it together, I might just leave that alone to see what happens, and only try to fix it if I have to. (True DIY Fashion!)


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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 4:49 pm 
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Joined: January 15th, 2015, 7:19 am
Posts: 608
Location: Baltimore MD
I do not think you have to glue the slabs together. I do think you need to seal the face (edge) that forms the horn.


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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 5:59 pm 
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Joined: April 20th, 2014, 5:21 pm
Posts: 233
We built a variety of backhorns for 8" drivers, up to 4x 8" in one horn, using that stacked plywood technique.

The speakers are super heavy mofos! Something to consider for pro applications, if you are thinking of moving these around.

Also, unless you use very high grade ply, you will end up with a rough surface on the flare thanks to voids.
MDF might be better in this respect, but then they will be even heavier!

I have a pr of these drivers if you are interested...BOSE!!! No highs, no lowzzzz...

4 x 3 inch cones per driver, shooting into a combiner/manifold with a 3x9 rectangular orifice.

These are out of high end Bose pro stuff. Look like an ideal doodad for a project like this.

https://www.ebay.com/itm/BOSE-VEE-4-MID ... rmvSB=true

Let me know if you want to check them out.


Last edited by J-ROB on December 13th, 2017, 6:27 pm, edited 1 time in total.

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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 6:23 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 259
Pelliott321 wrote:
I do not think you have to glue the slabs together. I do think you need to seal the face (edge) that forms the horn.


The face needs to be reflective of High frequencies, right?


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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 6:36 pm 
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Joined: April 20th, 2014, 5:21 pm
Posts: 233
No, the flare near the mouth it does not need to be reflective. It was standard practice in many horns to put linen or other absorptive material in that part of the horn that will reflect at the listener.

Check out Western Electric 15A, 22A, 16A. Stock horns will still have the linen "bib" that they used.

i believe that the purpose of this was to catch reflections from the horns mouth back toward the driver. in a snail horn such as this, reflections will bounce off of the part of the flare that you can see and re-radiate.

We used leather in a resin backhorn mouth for this purpose, which helped a lot.

On the other hand, in the high compression area of the horn, i.e. near the driver, it pays to have as smooth a surface as possible. Diffraction in this area is not a good thing.

I question the little wiggle you put in the throat in this region. Iirregularities here are potential sources of distortion and wacky irregularities in the throat impedance.


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 Post subject: Re: CNC Speaker Design
PostPosted: December 13th, 2017, 7:05 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 259
chris1973 wrote:
Roscoe Primrose wrote:
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


Yes, I recognise too, that in that place, if some bad behavior occurs, it's only going to be magnified by the rest of the horn.

It's one part of the design that I can only mitigate, but I can't actually get around.


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 Post subject: Re: CNC Speaker Design
PostPosted: December 15th, 2017, 5:11 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 259
brombo wrote:
Suggestion. Print out drawing full size (printer software can print out full size on multiple sheets of paper with alignment marking). Glue printout to high density fiberboard. Cut out and use for template with jigsaw (cut off line) and sand to line (bench top oscillating sander best for this). Use hand router with guides to cut actual pattern in wood. I have all the wood working tools to loan to you if you can to come to Silver Spring to pick them up.


Thanks! This was my backup idea, when the CNC people I talked to, (mostly at sign companies) told me a sheet of plywood was going to cost me $200???

I appreciate the offer of tools too, but I don't exactly have a shortage of tools to accomplish it myself!

Because of the intensive labor, and because it's just an experiment, I think I'm going to hold out until I can do it CNC.

I have also made several revisions to the design since the post, and I figure by the time I actually get around to cutting some wood, there will be several more changes.

Chris


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 Post subject: Re: CNC Speaker Design
PostPosted: December 15th, 2017, 5:35 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 259
I question the little wiggle you put in the throat in this region. Iirregularities here are potential sources of distortion and wacky irregularities in the throat impedance.[/quote]

I kind of figured that this was not too big of a violation, because most folded horn designs I have seen, fire directly into a right angle throat.

I was hoping a little bit of straight on throat section, with a radius turn into the horn would be a little improvement over that.


Last edited by chris1973 on December 16th, 2017, 5:13 pm, edited 1 time in total.

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 Post subject: Re: CNC Speaker Design
PostPosted: December 15th, 2017, 5:59 pm 
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Joined: July 8th, 2016, 4:34 pm
Posts: 208
You might see if there is any software that can simulate your horn -

http://educypedia.karadimov.info/electr ... peaker.htm


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