How to make a Circular Waveguide: In pictures |
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minaximal
Old Croc Joined: 26 September 2004 Location: United Kingdom Status: Offline Points: 1780 |
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Posted: 26 May 2010 at 7:30pm |
#Re-uploaded, and added pics 21-01-15 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! 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 |
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Jake_Fielder
Old Croc Joined: 08 October 2007 Status: Offline Points: 4231 |
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wooooahhhhh!
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Dougies Music
Young Croc Joined: 02 September 2005 Location: London Status: Offline Points: 1102 |
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Man you have some skills
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darkmatter
Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425 |
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Ha, was looking at exactly this last night and going through the fiberglassing vids on youtube
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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minaximal
Old Croc Joined: 26 September 2004 Location: United Kingdom Status: Offline Points: 1780 |
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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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Saul
Old Croc Joined: 15 June 2007 Status: Offline Points: 5912 |
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nice work
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bitzo
Registered User Joined: 20 November 2007 Location: Italy Status: Offline Points: 977 |
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chapeau
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darkmatter
Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425 |
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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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login4
Old Croc Joined: 03 April 2006 Location: Wales Status: Offline Points: 1552 |
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wow, they are sexy good work
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CELTIC SUBSONIC SOUND SYSTEMS
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minaximal
Old Croc Joined: 26 September 2004 Location: United Kingdom Status: Offline Points: 1780 |
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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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Timebomb
Old Croc Joined: 11 October 2004 Location: Lancaster Status: Offline Points: 2716 |
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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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James Secker facebook.com/soundgearuk
James@soundgear.co.uk www.soundgear.co.uk |
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cravings
Old Croc Joined: 30 January 2007 Location: Ireland Status: Offline Points: 7441 |
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love it. |
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