tractrix horn spreadsheet wanted please |
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_djk_
Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002 |
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"The reason why Geddes' doesn't like the BMS coaxes is because they have the xover frequency in the wrong place."
Where else could it be?
If yours is an accurate description of Geddes' objection to the BMS, it just makes me think less of him.
The real problem with the BMS is the abrupt transition from the 1" exit of the tweeter to....nothing. You have a 2" tube with the midrange, around a 1" tube with the treble (no transition). I know of no way to design a 2" entry horn to properly load the 1" portion of the BMS.
I sold my first pair, I may buy another pair to try on some Emilar horns with a block of 30PPI foam in the first expansion plane (a trick I saw first used by Meyer, probably 10 years or more before Geddes).
Dr. Bruce Edgar is of a similar opinion as regards the BMS, he thinks the same drivers on dedicated horns sound better.
Of course, the problem may simply be that we are too picky. The fellow I sold the first pair of BMS to likes them (although he still owes me money on them).
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djk
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Deadbeat
Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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It is nearly accurate . It's in his 'critical range' for CD. I've heard the BMS...they are nice, but the value en't there compared to their other models, imo. Here's the post:
Its at the crossover frequency. The wavefronts change in complex ways and the polar responses get pretty bad. This happens at a critical point in frequency for audibility. On a plane wave tube or on axis things are not so bad, but off axis the responses are not at all under control.
Personally, I would have thought it would be something along your lines to do with driver design details. Thanks.
I'm thinking of putting the celestion on a simple conical horn, bunging it, and ignoring the HF that I can't hear anyway. I'll ask celestion exactly how curvy their wavefronts are.
Geddes didn't think of foam, that's been used for yonks. He did however think of a novel explanation for using it, apart from the usual stuff.
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Away on extended leave.
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darkmatter
Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425 |
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p.s. ignore my earlier question about exit angles, i hadn't really thought it through at all before posting, DJK's post makes the question irrelevant |
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S DeXter
Young Croc Joined: 12 May 2008 Location: Moon Status: Offline Points: 1268 |
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You mentioned this before deadbeat,
As i recall the xover from mid to top is around 6.5kHz? Dont forget this is pretty high, the worst place to have it is about 800Hz-4kHz in my mind. This is where most of the intelligibility problems are. This is the range where the majority of vocal information is for example. Above that is just the 'tiss' part and the esses from vocals. My ATC SM75-150 mids at home cross over about 3.8kHz which is acceptable i dont see the problem.
The main problem as i see it as djk says with the poor start to the horn for the 1". Maybe this why Tannoy opted for the smaller exit coax?
Would the foam be a serious option? I take it you mean to fill part of the mid exit and form a proper exit for the 1".
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S DeXter
Young Croc Joined: 12 May 2008 Location: Moon Status: Offline Points: 1268 |
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I think what you loose in the 1" exit troubles, you gain in phase coherence and also size of enclosure due to sharing the horn. I thought the tannoys are exceptionally clear and pleasant to listen to esp. at very high volumes, something i cant say for alot of other cabs. |
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Deadbeat
Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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IMO, I like to have a low crossover point (around 1khz) and nothing upwards save in the ranges where I can't hear anyway.
Each to his own. The smaller the exit, the less HOM apparently. I still don't know why tannoy opted for a sharp end termination... |
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Away on extended leave.
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AndyWave
Registered User Joined: 30 March 2008 Location: Finland Status: Offline Points: 380 |
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Hi you all.
I must ring the bell for the bms 4594 coax mounted in OS waveguide with proper termination. No foam plugs are necessarily needed. My version is crossed to the 12"MB-horn at 535Hz 24dB LR. Passive x/o in the coax itself is around 6k7Hz 12LP/18HP. Also positive there is no need for massive EQing (like was in some EV xeq modules, cut mid 12dB or so and treble rises up to the level) I'm very pleased with the sound. Not so harsh as "usual" pa cabinets. I'd describe the sound being more like big HiFi system. No hf beaming problems. The tannoy systems use the 4592 model. May be god for extreme sound pressures for the sake of less distortion. Highest end will beam at lower freq. The phase plug helps a bit, because the nose is touching the driver exit. I must say the smooth high end is nice thing to have when listening some Jazz or Symphony orchestra. Or miking drum set with good condenser OHs or when audience says that they can hear the words or.... Andy |
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cesout
New Member Joined: 27 April 2009 Location: Florida Status: Offline Points: 1 |
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I have a worksheet (which is my modification of the one people all seem to use) which solves the X axis stretch problem. It does round, square, and rectangular mouth shapes and correct horn flare is maintained and seam lengths are all equal, for any aspect ratio. It will also give you edge cut angles to keep the seam contact area at a maximum with no exposed edge. I hope you will find it self explanatory and perhaps useful. How to actually set up for the cuts is another discussion. Lot's of ways to skin a cat. I like a real sharp knife. Sub millimeter accuracy may be attained with a 5 axis cnc router/mill for those so inclined.
You may find the worksheet here: Mileage may vary.
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Deadbeat
Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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Thanks a LOT.
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Away on extended leave.
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Paulo Duto
Registered User Joined: 06 January 2005 Location: Brazil Status: Offline Points: 123 |
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Hi!
Volvotreter's site has a calculator too.
Also his HT system has tractrix horns beside TH subs; enjoy it.
Regards, Edited by Paulo Duto - 28 April 2009 at 2:03pm |
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Paulo Duto
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biotec
Old Croc Joined: 07 June 2004 Location: United Kingdom Status: Offline Points: 2932 |
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project is back on. I now have a house in which to put the horns!
I have done some reading but am still unsure whether to go for a tractrix or OS horn. I would like people personal opinions on which they would choose under the following conditions:
1. Asssume that I will always be sitting bang on the axis of the left and right horns and so polar response less important.
2. I will be using the horns down to around 400Hz and would like to minimise the size of the horns. The house is in London and so I do not have the space for anything absurd.
3. The priority is reducing distortion; listening levels will be low for 90% of the time, at least until my 70 year old neighbours leave (this mortal dimension).
4. The horns will be used with a 1.4 or 1.5 inch BMS coaxial compression driver or similar high quality compression driver (not coaxial) from beyma, TAD or the like.
Many thanks,
Nick
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me so horny, me love you long throw.
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Deadbeat
Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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How about conical?
Anyway, your point 2 clinches it, tractrix if you're on axis. But then you have to ask yourself...Why sit on axis when you can sit off axis? Haha!
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Away on extended leave.
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