I have been thinking about winding up some field coils too .
the iron parts should be fairly simple to machine.
But I have been looking for some drivers with magnets that could be removed without destroying the whole works, most seem to be spot welded then glued . A bolted on magnet would be preffered.
Have even toyed with the idea of building a complete unit, basket and all but that would be fairly ambitious.
the iron parts should be fairly simple to machine.
But I have been looking for some drivers with magnets that could be removed without destroying the whole works, most seem to be spot welded then glued . A bolted on magnet would be preffered.
Have even toyed with the idea of building a complete unit, basket and all but that would be fairly ambitious.
I'm selling my crappy broken down car so might get some OB's made with the extra
cash ill have on payday, the car $$$ has to pay bills
I still find myself wondering what a field coil speaker sounds like since
I have never hered one, I hered there a sweet sounding speaker like alnico but ill stick to alnico or neo for now, can't even
get close to affording a modern field coil but if I find some used ones and got the cash ill take them home. I find all kinds of
vintage radio/stereo stuff at yard sales and flea markets.
Sorry if the formatting didn't work rite, cellphone post....
cash ill have on payday, the car $$$ has to pay bills
I still find myself wondering what a field coil speaker sounds like sinceI have never hered one, I hered there a sweet sounding speaker like alnico but ill stick to alnico or neo for now, can't even
get close to affording a modern field coil but if I find some used ones and got the cash ill take them home. I find all kinds of
vintage radio/stereo stuff at yard sales and flea markets.
Sorry if the formatting didn't work rite, cellphone post....
You mean barkhausen noise generated in ferrite magnets? Or something else?
Something of a controversial subject - I have not heard demonstrable evidence that it is an issue, but I have only heard a limited number of Alnico and field coils. My system is partially Alnico as you know, but I am not sure I can hear a significant difference. My last system was all Alnico, but this set up clobbers it.. So I don't know, perhaps I don't know what to listen for.
Alnico has one disadvantage over ferrite and that is the magnet weakens appreciably over time to maybe as little as half the original flux density over some number of decades. This of course significantly affects the performance of the motor. My Alnico driver mid horns were remagged just before I got them, so hopefully I will not have to send them out to be remagged for quite some time to come.
I read a little on barkhausen noise. I used to own some jbl speakers with alnico mags, never heard rice crispys in my tune LOL.
As for the loss in the magnetic strength, you could always line them up with the earths field. So it could act like a keeper LOL.
Don't know how well it would work, but it would be an interesting experiment.
Still the idea of field coils to me is just coil LOL. Give you something else to tweak.
Nick
I might be wrong so don't quote me on this lol
But from what i have read it's not just time that gradually demagnetises Alnico magnets, but the power fed to the voicecoil. With low power there won't be much effect (probably good with tweeters like the old Wharfedale Gold Super 3") but with woofers the signal has a much greater effect & as you mentioned the flux density can drop quite significantly & in a short period of time (depending on power level).
I might be wrong so don't quote me on this lol
I've heard the same, my understanding is that with the power levels commonly available for domestic use in the day this was not a particular issue. Of course it might not have been noticeable in the short term. A lot of these drivers of course have now lived well beyond their original design lifetimes - a tribute to their construction quality, and it is becoming somewhat common to get them remagnetized at some point.
I might be wrong so don't quote me on this lol
From what I remember,
Alnico is *less* likely to suffer Gauss losses due to thermal stress.. up to a rather high temp. At some point however, when it does loose it, it losses it permanently (until re-magnetized). Contrasted with your common ceramic ferrite versions that quickly loose Gauss at relatively low temp., but NOT permanently.
Alnico is also *less* likely to demagnetize over time UNLESS, it's in the presence of another magnetic field, and/or it suffers mechanical shock. (..and presumably under both conditions it's something of a "fly-weight" when compared to most other magnetic material.) Of course the higher the Gauss, the higher the chance to demagnetize over time.. so perhaps that's why it's gotten a bad rep. in this particular instance.
this is what I remember.
I repeatedly read that Alnico is among the best at holding it's flux, until I read this Forum.
Are you referring to the higher grade Alnico V or the lessor alnico alloys?
Iam stiil looking for some inexpensive speakers that I can remove the magnets from to experiment with field coils . so far have only been succesfull at destruction, whatever they glue those suckers on with is tough!
So will probably ens up making some baskets up similar to some that Atelier Rulit has done . I have a bridgport mill and a lathe so not a problem, just finding the time.
Iam stiil looking for some inexpensive speakers that I can remove the magnets from to experiment with field coils . so far have only been succesfull at destruction, whatever they glue those suckers on with is tough!
So will probably ens up making some baskets up similar to some that Atelier Rulit has done . I have a bridgport mill and a lathe so not a problem, just finding the time.
I worked for a company that designed and manufactured speaker drivers amongst other things, and that is where I first heard this allegation. The problem seems to be overstated and of greater concern in applications where the Alnico is exposed to very strong external magnetic fields. I would think that this would not be a big issue in domestic environments given the amount of time in use and the average levels involved.
Here is a useful link on the magnetic properties of Alnico and how it is processed to achieve it: Alnico - Wikipedia, the free encyclopedia It does hint at some of the issues here, but is a bit vague..
Here is some more information that makes some interesting comments about retention of magnetism in the presence of external magnetic fields amongst other things: Magnetsales.com Actually lots of other interesting information here as well.
I've had old Alnico JBL drivers that have not been remagnetized that seem to work fine and I also have ones that have been recently remagnetized and they also work fine.
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As the title of this thread is field coil v.s. alnico, it would be nice to hear a little more about field coils.
One of the properties I find attractive is the ability to adjust the field strength thereby changing the drivers characteristics.
Besides they are cool looking too
Can't comment on the sound - never heard one
One of the properties I find attractive is the ability to adjust the field strength thereby changing the drivers characteristics.
Besides they are cool looking too
Can't comment on the sound - never heard one
As the title of this thread is field coil v.s. alnico, it would be nice to hear a little more about field coils.
One of the properties I find attractive is the ability to adjust the field strength thereby changing the drivers characteristics.
Besides they are cool looking too
Can't comment on the sound - never heard one
I've always wanted to experiment with field strength in field coils but have not been able to persuade anyone of the few I know who own some to try some simple experiments. I assume as it affects BL amongst other things that at some level perhaps extreme that the differences would be audible.
Eventually I will try to identify some reasonably priced drivers that I can convert with parts within my ability to machine. Seems like that might be a project for next winter.
I have heard RCA theater field coils most recently, (woofers and horn tweeters) and a few WE tweeters as well. They sound good, but I can't really say based on my limited experience that they sound any better than a comparable quality Alnico or even ferrite magnet type.
I have never heard field coils in a hi-fi set up, but since you are a keyboard player I have a little experience. I used to own a 1940's Hammond M-2 organ and it had a 12" Jensen field coil driven by a push pull 6v6 amplifier. I also had friends that were into hammond organs so I had access to about 10 different models from B-3/ Leslie combos to A-100, M2, M3, C2, C3 ect. Everyone agreed that my M-2 had the most pure sound and the best growl when driven into clipping. Mine was the only Hammond with a field coil speaker. We also made many recordings on Ampex 351 tape machines and guess which recordings made your jaw drop on the floor, yep when we close mic'd that field coil.
That speaker was similar to this one:
Hammond Organ Speaker Jensen F12NS 8Ohm Field Coil - eBay (item 290355984849 end time Apr-01-10 07:52:59 PDT)
Also the one field coil and all the alnico drivers I have taken apart have had TINY voice coil gaps which would need a much more skilled person to assemble without voice coil rub. In contrast I have taken apart many ceramic/cobalt drivers that have had Grand Canyons for voice coil gaps which doesn't even make sense to me other than to have sloppy assembly and not have to worry about voice coil rub.
One last thing, I just noticed there is a guy converting Altec permanent magnet drivers to field coils on ebay for big bucks. Here:
Permanent Magnet to Field Coil Conversion Altec 288 B C - eBay (item 290412361082 end time Apr-10-10 06:16:13 PDT)
Better start winding those coils
That speaker was similar to this one:
Hammond Organ Speaker Jensen F12NS 8Ohm Field Coil - eBay (item 290355984849 end time Apr-01-10 07:52:59 PDT)
Also the one field coil and all the alnico drivers I have taken apart have had TINY voice coil gaps which would need a much more skilled person to assemble without voice coil rub. In contrast I have taken apart many ceramic/cobalt drivers that have had Grand Canyons for voice coil gaps which doesn't even make sense to me other than to have sloppy assembly and not have to worry about voice coil rub.
One last thing, I just noticed there is a guy converting Altec permanent magnet drivers to field coils on ebay for big bucks. Here:
Permanent Magnet to Field Coil Conversion Altec 288 B C - eBay (item 290412361082 end time Apr-10-10 06:16:13 PDT)
Better start winding those coils
the poster asked about pioneer car speakers.
to answer your question, you got things backwards.
Their studio/home speakers are paper on the high end but for car use the PP coaxial cones are far superior. ive got a set of 5 inch and a set of 6x9's. setting the magnet on my desk and standing over them even with the inverse reflections being present at the ear and being reflected into the cone the audio quality is amazing.precise isnt the word i would use for open baffle... its more along the lines of vivid. most of the time i listen to lacuna coil and moray eel (both are in your alley of music). typically lacuna's voice dominates my kenwood 3ways and my headphones but when i use these speakers i can hear the music under here voice so it sounds like an actual performance instead of her standing there singing it while some speakers quitely play background music behind her.
to answer your question, you got things backwards.
Their studio/home speakers are paper on the high end but for car use the PP coaxial cones are far superior. ive got a set of 5 inch and a set of 6x9's. setting the magnet on my desk and standing over them even with the inverse reflections being present at the ear and being reflected into the cone the audio quality is amazing.precise isnt the word i would use for open baffle... its more along the lines of vivid. most of the time i listen to lacuna coil and moray eel (both are in your alley of music). typically lacuna's voice dominates my kenwood 3ways and my headphones but when i use these speakers i can hear the music under here voice so it sounds like an actual performance instead of her standing there singing it while some speakers quitely play background music behind her.
Is this a mis-post? Doesn't seem to have anything to do with the topic we've been discussing..
Is this a mis-post? Doesn't seem to have anything to do with the topic we've been discussing..
I think it was meant for another thread.
The biggest practical advantage is the ability to adjust T/S parameters. This allows you to also alter the overall design (..like perhaps enclosure volume).
A disadvantage is the increase in heat to power the magnet. Practically speaking it means that there will be a limit on the voltage/current to power the magnet and an overall a limit to the driver via thermal compression.
Theoretically magnetic field integrity can be more stable under normal operation (..as I mentioned originally). It's even possible that the field can be more "uniform" - depending on the quality of the plates and pole piece (..and in particular the lack of carbon content).
What it would take to build an *actual* full-range driver (without correction)? That's well beyond the bounds of simply differences in motor type.
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