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Old 16th March 2010, 02:23 AM   #1
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Default field coil vs. pm???

Im kinda new here, been lurking off an on thru the years, finnaly decided to take the plunge and make an account, I have been a stereo nut for years and thinking about some diy speakers, I definately want full range, every x-over I have had just kills my music, doesn't matter if it's Bach or Marilyn Manson, if theres a crossover, its dead, however every full range speaker I have tried has been lively and musical, even the cheap dual cones from wally world sound better than my pioneer or JBL "multi element screech boxes" however my current KLH speakers with 4" dual cones sound just incredible! those are so good I even use them on my keyboards the piano is wonderful thru them. I want to know if there is any sound quality differences or advantages to using field coils. I have never used them but have been doing a lot of reading about them and I am very intrigued by the technology. What has been your experiences with field coils vs permanent magnets? I want to build me some OB's with large full ranges, shouldn't be too hard considering my crappy woodworking skills. I am already well studied on full range drivers, I am just curious about these mysterious field coil drivers, there isn't a whole lot of info out there on them. what info I do find just makes me more curious. I know they were used in a lot of OLD radios, and now they seem to be making a come back in the hi-fi world. I am also a musician and looking for anything to create new sounds. my musical tastes are mainly classical music and goth/darkwave/death rock and metal. most of the time I just listen to classical and compose/arrange some too. I play pretty much anything with a keyboard on it.

any good sources of CHEAP tube amps or tube amp kits would be appreciated too. time to kick the transistor habit too.. LOL
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Old 16th March 2010, 04:19 AM   #2
ScottG is offline ScottG  United States
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No one has really looked into why some prefer field coils. One *thought* is that back emf has less effect on magnetic field integrity and therefor is more accurate under normal operation.

As to the sound - that depends *far* more on the driver than just the motor itself when comparing identical motor parameters.

The fact is that there aren't that many field-coils available, and all are generally much more expensive than *most* other (somewhat) similar offerings. In fact, I don't know of *any* cheap field-coil full range drivers.

Perhaps the Supravox 165EXC is the least expensive driver (..at around 700 US each).

Despite this (the very knowledgeable) Thorsten has heard permanent magnet versions from Supravox AND the field-coils, and believes the field-coils are in another "league", and others have only confirmed their happiness (..usually regarding the use of the more expensive 215 EXC.)

There are a few cheap tube amps, and even a few cheap tube kits.. NONE that are particularly good IMO.

One decent *design* that is relatively in-expensive is:
New 2A3

An amplifier that compared well to that designer's 845 SE tube amp is from this Co. though not tube, but isn't terribly costly:
NewClassD Amplifiers
2008 - Class D Amplifier comparasion test
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Last edited by ScottG; 16th March 2010 at 04:26 AM.
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Old 16th March 2010, 05:06 AM   #3
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that tube amp looks interesting and am thinking of that one seriously, but I will never use a class D amp, have tried them, killed all reception on my ham radio, cant have that. however the class D amps I used were dirt cheap, so probably badly filtered switching circuits. I just moved so none of my radios are set up, just my receiver, FR speakers and keyboard. probably wont set up the ham radio anyway, apartment = no antennas . The class D amps I did use had a sound very close to a tube amp, I just might try one if I can find a GOOD one that has addressed the RFI issue. the last one I had even killed my FM tuner, the locals didn't even get thru that mess but CD's did sound AMAZING!! That info on the field coils is all I was able to find on the net, I have got an itch to try some but the few I have found are rediculasly expensive. I found some info about being able to adjust the q and sensitivity with a field coil for musician applications. that's got me realy itchin to try some. I wonder if making my own would be a possibility???? I know enough about speakers and acoustics that it probably wouldn't be too hard to build my own driver from scratch. or at least modify one. Building an amp, thats no problem, I have built a few in the past, even ham radios.. from scratch.

Well ill be back tomorrow, probably with a few OB questiunes, im starting to fade, its time for bed..

good night!

P.S. those class D amps are TINY!!! I cant see how it's possible to get hundreds of watts out of those without frying them??? those numbers cant be right??? if they are, that's shocking. mine was bigger than that and a measly lil 10w.. and it did run HOT. Thats got me looking into class D amplifiers now.. I know practically nothing about them, But I can build old school anolog..LOL
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Old 16th March 2010, 12:28 PM   #4
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You may also want to do some reading about Alnico speakers. I will leave the search
for you but it seems that speakers built with Alnico magnets sound better like field
coil speakers sound better. It is too bad that Alnico and field coils are so expensive.
It's so much cheaper to use a 40oz ceramic magnet than an oz or two of Alnico.
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Old 16th March 2010, 01:23 PM   #5
AndrewT is offline AndrewT  Scotland
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Yes, Tannoy moved it's dual concentric range over to ceramic magnet.
A couple of years ago the dearest driver used in the horn has reverted to Alnico for improved sound.
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Old 16th March 2010, 06:16 PM   #6
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Ok I tried this from my phone but that didn't work.... opera mini and bolt (phone browsers) both suck at forums... I hate the blackberry browser because its soooooo slow... painfully slow.

Back on topic, I have used alnico speakers in the past and loved them, its amazing how big a difference changing the magnet metal can make. my experiance with both alnico and neodymium is that they are much fuller and open than the usual ceramic magnets. Im still trying to figure out why, its just a magnet??? they do the same thing: concentrate all there magnetic energy to the coil gap. I no longer have my old alnico's I had to sell them to survive since I had been in a bad relationship and was kicked out to the street, all my hifi stuff went bye bye. I cried over the tube amps I built.. Now things are better and im getting back into hifi currently with some cheap but surprisingly good full range speakers, and a low end pioneer receiver from a yard sale. I WILL get another pair of alnico full ranges if it kills me.. maybe even neodymium.. Why are alnico magnets so expensive?

Im going to check out ebay for some more of those vintage goodmans FR's...

I'm also going to try to find some old 6x9 dual cone car speakers for some OB experiments since there cheap and basically made for OB then if I want to go that route I'll get something better, thinking maybe 2 per baffle wired in series to get 8 ohms so my receiver don't fuss or burn.

anybody used these:
Kenwood - KFC-6950S
or
Pioneer USA - TS-694P - 6

How is the mid range on those? treble harsh or smooth? I had some OLD kenwoods simular to those about 12 yrs ago and they were very good in a sealed box, never tried them OB so I wonder if those new ones are an improvement or a step back. I have never used any pioneer car speakers for anything so dont know a lot about them, but the paper cones on the pioneer might be a plus over the hard heavy rigid poly cones on the kenwood for bringing out some detail.

Any other recomendations for just cheap OB experiments? I dont want to put a lot of money into it unless I know for sure I want to stick with OB.
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Old 16th March 2010, 06:38 PM   #7
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Quote:
Originally Posted by Fr34k5h0w View Post
Why are alnico magnets so expensive?
One word - Cobalt. It's not exactly the most common material & is nowadays incredibly expensive i believe.

Interesting thread so far
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Old 16th March 2010, 07:04 PM   #8
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Cobalt... that explains it... LOL
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Old 20th March 2010, 01:10 AM   #9
nhuwar is offline nhuwar  United States
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Cobalt isn't why it's o pricey. It's the nickel. One thing I heard aboust as to why alnico sounds better is the higher flux density produced by it.



Nick

Last edited by nhuwar; 20th March 2010 at 01:13 AM.
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Old 20th March 2010, 01:55 AM   #10
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It isn't just flux density there are other things that come into play. One
of them being Barkhausen noise. I won't even begin to describe that
I will just let you do a Google.
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