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How to make a Circular Waveguide: In pictures

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minaximal View Drop Down
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    Posted: 26 May 2010 at 7:30pm
#Re-uploaded, and added pics 21-01-15

1:  Obviously design your desired guide, any round horn or waveguide is possible (there are quite a few spreadsheats or horn response out there) and print out dimensions of the contour to scale. (this took some printer fiddling but possible)

I decided to go for a sort of Oblate spheroid waveguide inspired by Earl Geddes, but then went for a large roundover that is a bastardisation of a semi  Le'Cleach mouth roundover when placed in the final cab, with its round over continuation.

One thing of note, is it's best to find out the exit angle of the driver you want to use, so the waveguide starts at the correct flair rate, as this is a critical point to minimise any form of diffraction and refraction to cause higher order modes (HOM's) which also limits the top end, that's why some comp drivers don't like different horns.

Then cut rings of wood, glue and screw to a big stepped cone but slightly oversized of the final wanted dimensions.  If i did it again i would probably use mdf, as the ply wants to expand from the heat of resin catalyzation, and crack the gelcoat glaze of the mould.



All my rings had a central drill hole so they could be aligned and then put centrally on a lathe, i used my trusty angle grinder with sanding pad to get the steps out of the cone, bear in mind safety aspects!!



and then lots, and lots of sanding, working up in grit size to the finer grades.



i got a massive blister on my thumb pretty quickly..



Sexy ply, thats why i used ply.



Below you can see the scale printout of the contour on the right, (offer up frequently to keep on track) and the flange back ring and driver mounting back cup.  I made sure the wood was about 1mm smaller than finished to allow for the gelcoat, next time i think i'll give more to the gelcoat so it can be thicker with more layers.



I missed a few pics of the gel-coating, and then more sanding (wet and dry paper), and then polishing, to get as shiney as possible.



Then some waxing.. 12 coats 1 hour apart, but i wouldn't bother with that many next time.



More polishing and we can see the flange ring and back flange cup mounted (these also need the gel and waxing.





Now for the green pva release, it helps release the mould, i painted it and it really doesn't want to stick without spider webbing on the gel coat, the trick is to keep brushing until tacky, when it starts to stick, had to build up a few coats tho'.


For final production i cut each piece into a cone shape ready to lay up, each layer needed a few glass matt cones, they're a bit smaller below than i'd normally pre-cut, as it's quicker just to use larger cones of matting.



Another few steps missed, but i didn't want to use my phone camera when covered in gel-coat and fibreglass, this is a picture of the thinnish first layup on the mould with a thin gel-coat and then just a few messy layers of matt and resin to break-in the mould. (for actual production make sure all the fibres are wetted out and consolidated onto the form)



I actually found i had to make the back driver flange very thick, so it was strong enough to use a gear puller to get the guide off the mould, even so only angry frustration and a whack with a bit of 2"x2" got a few off. *edit - update, get wedges! see below.





The first one is a bit messy on the back, mainly due to not mixing enough resin with loose chopped strand, i stuck to using matting after the first pull. 


Larger forms can also be made, and also very satisfying! Tongue




And I cannot emphasize this enough, but BUY SOME WEDGES to lever the piece off the mould, when i first made this thread a few years ago i didn't use them, now my life is much happier.




After a little rinse off, of the pva, and sanding the edges, they can be slapped in a suitable cab.



A few needed a further light sand and polish where the mould had cracked its gel coat between the largest ply rings, (probably from heavy handed persuasion!) but most came out as shiney as they look, just a quick wax to protect the gelcoat.



These went into the shown reflex cabs, of which the whole design purpose of having the curves to minimise diffraction and HOM's went hand in hand to even off axis dispersion, ideally placed for room corners.





Here are some measurement of just the waveguide, after eq, we can see the amazing control off axis in the top range (beyond 20k), each line apart from the first, represents 7.5 degree off axis increments. So the purple line hovering around 100dB is 37.5 degrees off axis, and just before here we can see at around 35deg off axis (the -6dB point) it starts to loose control, albeit fairly evenly.. which is perfect as i wanted a 70deg guide.



The raw response (no smoothing) but waveguide compensation equalisation, i used a 1.86khz xo, to match the off axis response of the 12" and the guide was designed to be a 1k fc, a little lower than xo point, ideally it should be an octave lower, but for me this worked very well.



Job done.





Edited by minaximal - 21 January 2015 at 7:55pm
Subs + Barges = :)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 7:34pm
wooooahhhhh! Clap
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dougies Music Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 7:41pm
Man you have some skills
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 8:06pm
Ha, was looking at exactly this last night and going through the fiberglassing vids on youtubeSmile

Very nice work!

Your tip about making the back driver flange really thick is invaluable. Hadn't thought of that, I would've been seriously annoyed if I'd got to that point and realized I couldn't get it off!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 8:17pm
Originally posted by darkmatter darkmatter wrote:



Your tip about making the back driver flange really thick is invaluable. Hadn't thought of that, I would've been seriously annoyed if I'd got to that point and realized I couldn't get it off!


indeed!

you could always make the glass overlap the back flange rim, and lever inbetween the flange ring and mould.. should work to help.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saul Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 8:37pm
nice work Thumbs Up
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 8:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 9:22pm
Aye good plan.

My main worry with glassing my own horns is getting the interface between comp driver exit and the horn throat seamless - did you find this an issue at all? I'd even thought about getting a bit of metal machined for the throat section of the horn, dunno whether this would help things.

Think I'll start on an 8" horn before trying with comp drivers, might be a bit more forgiving.

Edited by darkmatter - 26 May 2010 at 9:23pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote login4 Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 9:30pm
 wow, they are sexy Clap good work
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minaximal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2010 at 9:40pm
aslong as the mould is accurate, and terminates exactly where the back cup would go, you should be alright, i had to sand a couple of the driver flanges flat a tiny bit just to get the fraction of a mm lip flat, but it worked better than i had expected.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 27 May 2010 at 1:30am
Very nice work there minaximal, how do you hold them into the cabs?

I did some tractrix flares last year,, when i made the mold i clamped all the discs with a length of threaded bar and a bolt and washer on each end, then mounted that bar in the lathe (ok bench drill but it worked),  The 1" washer at the throat end was really usefull to sand too, the throat fits the compressoin driver exit perfictly.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 27 May 2010 at 2:59am


love it.
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