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Old 20th January 2013, 08:10 PM   #121
Hentai is offline Hentai  Romania
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Quote:
Originally Posted by JMFahey View Post
So in a wayyou took the "easy" path
You just built a "dedicated magnetizer" and made it part of the speaker.
Yes, I have assembled motors with already magnetized PM and it is a pain to precisely align it. This way, it could be done but to no real value. For DIY especially tho, field coil is the way.

Thank you for posting about magnetizers. Before starting this project i looked after information and couldn't find any and then i looked after field coil information and couldn't find much on these either. You are right, magnetizers are a dangerous things.

Would sure like to hear more about the 30" speaker and your current works.
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Old 20th January 2013, 08:19 PM   #122
Hentai is offline Hentai  Romania
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Originally Posted by Dave Zan View Post
Earlier in this thread "Linesource" showed a simulation with more than 2 tesla field where the elimination of the pole-piece was actually the key. Not a practical structure as shown but of interest. Pity he never followed up.
Yes, i didn't quite get that design, lets hope he will join in again.
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Old 21st January 2013, 03:31 AM   #123
JMFahey is offline JMFahey  Argentina
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Well, all work on those monsters was lost long ago. (around '82/'84 or thereabouts)
My personal contribution was designing the fieldcoil and the PSU.
All done with paper, pencil, graphs and calculators
No computers (original PCs had *just* appeared, with whopping 128KB of memory, no hard disk and only 1 or 2 360KB floppies), so no software and even less simulation.
And Gauss could not be measured directly, for lack of proper sensors.
So measurement was tedious total flux (in maxwells) measuring with a scanning coil which fed an Op Amp integrator, and dividing said flux by gap area.
The first idea was that these would sell like hot cakes.
It didn't happen, so second best was to *rent* them to dance clubs to provide "thump".
Fine, but their checks bounced.
Combine that with fired employees suing , banks trying to collect loans, etc. , and you'll have a pale idea of what a mess it was.
I was happy to leave without personal debt and having signed no contracts.
Oh well.

But the Bass was gut-wrenching

As of today I just make perfectly standard Guitar and Bass speakers (think Jensen/Celestion/Eminence) for my own commercial use; I also supply small custom builders and export a little to neighbouring Countries.
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Old 21st January 2013, 07:41 AM   #124
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I always assumed that the Aura NeoRadial had to be assembled with the magnet already at full force, so a similar requirement for a reversed pole structure didn't seem too impractical. Now you have made me wonder if I was correct.
Thanks for the information from real, practical experience. Sorry it did not turn out better.

Best wishes
David
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Old 21st January 2013, 01:15 PM   #125
JMFahey is offline JMFahey  Argentina
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Just checked the Aura Radials.
Yes, in that case, it *has* to be magnetized "outside".
But because of the 90º magnetic angle, it's not that difficult to mount it in the iron structure, I imagine a "guide tube" to lower it straight, centered, into its place so magnetic force sort of self-equalizes.
Sometimes I have to re-glue shifted ferrite rings, obviously magnetized, and it is murder because pull force is axial, and the iron disks are exactly in the path.
Talk about nicked fingers and cursing!!!
Worst is that you have to work in a hurry, because epoxy is already applied and curing fast
As of the commercial aspects, the only way of avoiding failure is not trying
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Old 21st January 2013, 06:14 PM   #126
Hentai is offline Hentai  Romania
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Success comes if you try enough times and i like that you are still in the audio field. Even now there are people seeking that 30" EV.

What was the efficiency of that unit?
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Old 21st January 2013, 06:58 PM   #127
JMFahey is offline JMFahey  Argentina
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Quote:
Success comes if you try enough times and i like that you are still in the audio field. Even now there are people seeking that 30" EV.
Oh, I have tried so often and so many times that I have been continuously successful on something for the last 43 years or so.
Paid houses, cars, factory, machines, trips, etc., everything out of my successful products.
And sank a lot of money on bad moves too.
Never betting everything on a single card.
Never ever worked for anybody or got/needed a salary since I was 16 , always living from building and selling Electronic products.
The balance was always positive , although many times not wide enough.
Now and then old friends/colleagues visit my shop, to drink a few "mates" Click the image to open in full size. and chat about the old times ... and it's sad to see that most of them gave up, and "bought a job", be it a Taxi, a 24/7 convenience store , a cellphone/hot dog/ice cream shop or a small restaurant or Hotel.
Al dream about "grabbing the soldering iron " again.
One good principle was letting go something when it became unsalvegeable.
Trying to fill a "black hole" is MUCH worse than trying something else.
And yes, that speaker was more than "inspired" in the EV, but with much larger VC (100 mm/4") which forced us to use a field coil.
It also had much higher power handling, about 200/250W RMS which at the moment was groundbreaking.
Roundwire VC on an anodized aluminum former.

Quote:
What was the efficiency of that unit?
Never measured it.
Technology-of-the-day mandated Brüel&Kjäer equipment inside an anechoic chamber.
A BIG one at that.
As I said, no easy simulation way back then ... but it could hold its own and integrate with 15" PA woofers which now we know were around 95/96dB efficient, so it must have been close to that.
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Old 21st January 2013, 07:39 PM   #128
Hentai is offline Hentai  Romania
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Originally Posted by JMFahey View Post
Never betting everything on a single card.
Couldn't agree more.

Thanks for sharing your thoughts, very helpful for a youngster like me.
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Old 22nd January 2013, 07:37 PM   #129
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Hi, Hentai
Wonderful work! I would be interested to know your critical opinions of the driver you have made here: an impression, if you will. You know, strengths and weaknesses, what you like and dislike about the sound of them, and the like.
Also, I would be entirely grateful if you would be kind enough to post a bibliography of sorts. I also am interested in making my own field coil (and with paper cones) but information is seemingly impossible to come by. When info is found, it is broken fragments of disconnected gibberish: nothing comprehensive, no "Bibles of the craft[s]".
There was once a sight where more than several persons were involved in such craft, but I can not find it anymore.
The first request, of a first impression, I am asking of you. The second request, a list of 'must reads' I am asking of everyone who has it to offer here.
I hope this isn't to be considered a hijacking of the thread, but I must say, I can't think of a better place for it. I wwould really like to read what you have studied in the process of originating this really Beautiful work. ciao
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Old 26th January 2013, 04:39 PM   #130
Hentai is offline Hentai  Romania
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Hello nottolkien,

Thank you for your words.
My impressions, hmm i stayed away from that as i tried to keep it things objective as ofc i cannot show how it sounds on a forum but since you asked...
The best thing this speaker does is dynamics and is something i always crave for in sound. I belive it is one of the most important characteristics that gets you closer to the "live" sound. When i play Pink Floyd "More Blues" and Nick Mason hits that snare drum like there's no tomorrow i get goose bumps, it just bites you. Aphrodite's Child "The Four Horsemen" disables gravity field, the sound is full, tons of impact. Another thing i enjoy is the midrange, it really captures the meat of the instrument. I like Japanese music and that Japanese flute sounds really good. Van Morrison "Stranded", Archie Shepp "Thrill is gone", New American Orchestra's take on Vangelis' "Blade Runner Blues", Hugh Masekela "Stimela" and Mike Figgis "Leaving Las Vegas" sounded thin and unconvincing in the midrange on most 6.5"-8" reflex systems. Mine plays it with a great tonal balance and low distortion at low or loud levels.

It lacks a certain precission in timbre as of yet, even if keeping balance in tone. I've been working on designing the cone, a new cone that will bring me closer to a certain neutrality. On the upper midrange there are some rather abrupt changes in response (4-5 dBs but over a short frequency range) and anything abrupt is not good.

Another aspect that one should consider is that this driver should be horn loaded. OB is a choice but i found lower current through field coil to achieve higher Qts muddies the sound, easily noticeable from songs with rather busy and lots of instruments, they all get lost in a cloud somewhere. So horn loading is the way to go. Now, to some, this might be a weakness, to some it might be a strength.

For classical music the high frequency extension and sound might please many. I had some friends, lovers of classical genre and no one felt the need of supertweeter, in fact they disliked it when it was added but i do admit it might not have been the best implementation. For blues/rock/jazz i think a ST is a good addition.

To compile a bibliography is a pretty difficult and time consuming task. I've been interested in designing drivers for many years. The work on this project started in december 2011. In my research i found so little about the design of drivers themselves unlike the tons of info on loudspeaker design. So basically you need to return to physics and work it up from there. Very useful is modeling and analogies to electrical circuitry. You can take the whole electro-mechano-acoustical assembly and model it as an electrical circuit and then run analisys just like normal filters. It helps to see transfer function of the system and model it to suite what you desire.

The first recommendation would be my bible: Acoustics by Leo Beranek. Something less technical but offering some interesting information and insights is High Performance Loudspeakers by Martin Colloms.

Papers published by manufacturers like JBL,EV or from people like Don Keele offer good information as well. Studying market drivers that are close to what you have in mind will provide perhaps more information than anything else though.

In closing my comments, some pics of the frame parts:

Click the image to open in full size.
Click the image to open in full size.
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