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Old 25th March 2008, 04:53 AM   #11
jkeny is offline jkeny  Ireland
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Found it Brett, thanks & here's the thread:
http://audioheritage.org/vbulletin/s...ghlight=spiral

He uses a pipe with spiral steps - I was thinking of using the angular steps with the sonic fins - easier to build!
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Old 25th March 2008, 09:47 AM   #12
Pano is offline Pano  United States
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Great find on the Lansing site.

To think, spiral horns with a 15" dirver! Crazy, man, crazy.

Hey - wonder how well it would work with a 15" coaxial?
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Old 26th March 2008, 10:20 PM   #13
jkeny is offline jkeny  Ireland
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Ok, I think I'll go for a 3D spiral version of the MLTL cabinets recommended for the JX92S drivers. WoodturnerFran is doing all the hard stuff for me i.e. the cabinet build, otherwise I wouldn't attempt to take this on.

As this is new ground & I have no idea about speaker building I need some experts to help in guiding me towards the most likely design to succeed with the Jordans.

My reason for going this route is to try to minimise the profile of the MLTL (mainly baffle width & height) while preserving the good bass response of this design, so I thought something like the Helix-AG150 cabinets shown here (about half way down page) http://www3.ocn.ne.jp/~hanbei/eng-angular.html

These are for the Fostex's 12 cm FE126E with low Qts (0.25) with a front port. Here's the spec
Full-range FE126E (Fostex)
Height 800 mm (except base)
Width 150 mm (except base)
Depth 180 mm (except base)
Air chamber volume; V 2.9 liters
Rotation number of spiral; n 5
Rotation number of sonic fins 6
Max length of sound passage; L 280 cm
Cross sectional area of throat; S 37 sq. cm

Now I know the JX92S are 14.4cm and total Q (is this Qts?) of 0.4 but and here are some measures for other designs including MLTL:
GM's original MLTL CSA = 30.0407 with a total volume = 932.46332

This trapezoidial version has a CSA = 30.04187 and a total volume = 932.4996

The CSA is cross sectional area, I presume. What is the significance of the rest? How should I optimise these figures for the JX92S?

Consider this a new DIYA speaker project which I will detail along the way with pics & the end result will be tested against Fran's Fonkens & Fonken tuned Towers & his Quad ESLs
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Old 26th March 2008, 10:40 PM   #14
jkeny is offline jkeny  Ireland
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One other thing I'd like members opinion on is something I brought up on another thread about some other non-standard ideas:
- screwing on the back of the cabinets rather than glue & screw.
- using thin walls for the cabinets

I know this mightn't be the widely agreed build method but the Rogers LS3/5As cabinets with screwed backs were the ones favoured by the BBC research dept and are considered to sound the best in a major shootout of all the flavours of LS3/5As. It's offered now by Sterling Reference as the thin walled reference cabinets so as well as screwed backs they have thinner cabinet walls than usual http://www.stoneaudio.co.uk/

The theory being, IIRC, that it acts as some sort of lossy baffle, helping to reduce some resonances. I'll look for the reference & post the link here.

Does this have any applicability here?
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Old 27th March 2008, 10:13 AM   #15
jkeny is offline jkeny  Ireland
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Anybody interested?
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Old 27th March 2008, 10:54 AM   #16
Pano is offline Pano  United States
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The Helix-AG150 seems like a good choice. Guess you'll have to try it and see.

As for screwed on backs, I've seen that mostly on pro gear, where you need to get inside the case from time to time.

And for thin walls, ask Planet 10, he knows all about them.
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Old 27th March 2008, 11:55 PM   #17
jkeny is offline jkeny  Ireland
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What I'm hoping for feedback on is:
- What are these the two important measures that I should try to match to i.e CSA = 30 & Total vol = 932.4996 (932.5)
- How does the Max length of sound passage effect these measures, if any effect?
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Old 28th March 2008, 12:32 AM   #18
mightym is offline mightym  United States
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- screwing on the back of the cabinets rather than glue & screw.
- using thin walls for the cabinets

If you are building the spiral horn cabinets as described, IMO you wouldn't want the back to be removable, you would not be able to get to anything back there except the binding posts.

Seems more reasonable to me to screw on the front, then if stuffing is required you'll be able to get in.

I think you''ll still want to gasket the removable panel, regardless, to seal it when closed.

As to using thinwall material on the balance of the cabinet, just how thin? seems to me that where you'd use 3/4" front, back , top, and bottom. You could get away with 1/2" on the sides where all the spiral parts are glued as these would stiffen them up considerably.

That said, I am a noob, and IMHO advice is usually worth just exactly what you pay for it.

JB
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Old 28th March 2008, 12:57 AM   #19
mightym is offline mightym  United States
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oops, I didn't go look at the referenced cabinet until after I put my foot in my mouth.

He shows 15mm ( that's pretty close to 5/8" in imperial, which right or wrong is how I'm wired to think....)

I think I'd stay with that as a minimum.

If I was to build that cabinet, I believe I would use 3/4" anyway ( maintaining inner dimensions ).

JB
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Old 7th April 2008, 06:27 PM   #20
Colin is offline Colin  United Kingdom
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Default Thin wall cabinets

I wouldn't mix the classic BBC thin-wall cabinet technique with something like a horn or TL. The technique seems to work best on sealed and reflex enclosures. There's also some good info on this technique on the Harbeth site. They continue to use this technique in their modern, post-BBC designs.

PMC use heavier wall techniques in their studio and broadcast TLs.

FWIW, I'd have thought the 31" MLTL designed by GM would lend itself quite well to a folded, compact TL.
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