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Air Core Inductors


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#1 Deang

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Posted 12 November 2013 - 08:09 PM

Okay, so I get this phone call from the University of Utah. The accent is a little thick and I'm really tired. He informs me that he has a background in audio, and is curious as to why I don't use air core inductors in my low pass sections. Red flags start going up, because well, I'm the guy that can hear the difference between capacitors but now have to blurt out that I can't hear the difference between coil types (if inductance and DCR are kept the same). He insists there is a difference and that it's quite easy to measure. I'm having some trouble understanding him, but there is an air (ha ha) of competency to his speech. The only thing I can think of that might be applicable is in the area of hysteresis. So, even though I don't think the bigger horn loudspeakers come within a light year of experiencing this problem, I realize I might actually be wrong.

I start thinking that if this guys thinks this way, then others probably think this way too. This brings us to the question of using something you don't think makes a difference, but you do it because someone else might. So, to cover my backside, I decide to ask Mark Cooper of Universal Transformer if he might be interested in winding up a 2.5mH air core for me in 14AWG. It won't win a beauty contest, but these guys don't mess around when it comes to winding stuff. Alright, it's ugly, but it's tight and varnish impregnated/dipped. I specified the peculiar shape -- the conventional method takes up too much geography on the board.

Comments?

Attached Thumbnails

  • UT_2.5mH_Air_Core1.JPG
  • UT_2.5mH_Air_Core2.JPG

Edited by DeanG, 12 November 2013 - 08:10 PM.


#2 Wingfield

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Posted 12 November 2013 - 08:25 PM

Only a question......did you hear a difference?



#3 Deang

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Posted 12 November 2013 - 08:35 PM

I only have one at this point. They are waiting for me to decide if I like what they sent me. As for what I hear, I am jaded. I've made my mind up about certain things a long time ago and this creates problems. Last year I adopted the idea of letting others evaluate for me. Some are like me (opinionated), and some are relatively new to the concept of critical listening. It's been fun and educational.



#4 djk

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Posted 12 November 2013 - 09:29 PM

excellence17.jpg



#5 djk

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Posted 12 November 2013 - 09:32 PM

M6 laminations on inductors for $130,000 Wilson Audio loudspeaker system.



#6 muel

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Posted 12 November 2013 - 09:35 PM

Yep, it's ugly. With that surgical tape wrap I'd be afraid it would sound sterile. :wacko:

Kidding aside... is there much of a cost difference? What "easy" measurements was he proposing?

I admit that the big air core windings look cool but the bottom line is the sound.



#7 Deang

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Posted 12 November 2013 - 10:07 PM

Not helpful Dennis, not even a little bit -- all we know is what we've always known, that Wilson is ripping people off in the worst kind of way. Man, you were supposed to blow me away with at least a paragraph of something I couldn't understand.

Cost difference is 40% more than the normal coils I get from them. Compared to what others are charging for their air cores of this size, a pretty big cost savings.

It's not surgical tape. I'm not sure what it is. I think it's something special. Probably costs more than the copper they used to wind the coil. I kind of like the thing. Man I hate admitting that -- I don't do ugly. Maybe I should shove it into some kind of cool looking canister. I'll call it "The Space Coil".


Edited by DeanG, 12 November 2013 - 10:16 PM.


#8 boom3

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Posted 13 November 2013 - 10:22 AM

maybe he is talking abot magnetostrictive effects? I am under the impression that if you have a coil of adequate wire size (i.e. low DCR) and it is wound properly, and you are not using it near it's wattage rating, that magnetostrictive effecst are negligable.

Plaese let us know what angle this guy is working...



#9 mach-1

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Posted 13 November 2013 - 10:48 AM

I took me ten minutes each to wind 2.5 mh 14 gage air core inductors. They sound the same IMHO as the # 2133 Klipsch inductor. They both have the same approximate DCR.

I notice that the really old Klipsch crossovers 500/5000 cps use large fine (small) wire air cores. Really big spools of magnet wire.

The larger wire could handle more power, Klipsch told me the stock 2133 is good to 100 vollts

Pix of my air cores....chris Cost = free :) left over spools of wire on jobsite and time (it was fun)


Edited by christopher frank, 13 November 2013 - 10:52 AM.


#10 CECAA850

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Posted 13 November 2013 - 10:57 AM

Did you use audiophile grade tie straps?



#11 mach-1

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Posted 13 November 2013 - 11:08 AM

Well - I didn't factor in the ties. They are from Grote. WWW.GROTE.COM #83-6021. 11 3/4 inch long and 50 lbs tensile strength. Grade = good to go!!

Also free from job site. :) chris


Edited by christopher frank, 13 November 2013 - 03:08 PM.


#12 Deang

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Posted 13 November 2013 - 11:15 AM

That's wild. Where did I get the idea that you had to use magnet wire?

Boom3, that's just it, I'm not exactly sure what he was trying to tell me. I probably should have listened more and talked less -- I do remember something about the effects from more power at lower frequencies.



#13 mach-1

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Posted 13 November 2013 - 11:21 AM

Above home brew air core inductor in a DIY Type "A" crossover. Bob Crites 3654 autoformer - ERSE 13 and 2 uf caps. chris



#14 Deang

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Posted 13 November 2013 - 03:34 PM

Man, some people are just terrified of spending money. :)

ruh-oh, why kind of screw is that?



#15 mach-1

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Posted 13 November 2013 - 03:44 PM

The screw holding the coil is stainless steel, the black plate is painted plywood. Cost me about $50 each to build. :) chris

[about the cost of used "E" types on eBay, but with the values needed for my project and all "new" parts]


Edited by christopher frank, 13 November 2013 - 08:40 PM.


#16 babadono

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Posted 13 November 2013 - 04:58 PM

Christopher,

What driver is that on thet horn? Is that the PRV D250Ph?

sorry for diverging off the thread topic....................

Eric



#17 mach-1

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Posted 13 November 2013 - 05:13 PM

:) The driver is a Selenium D250-X, the horn is Electro Voice 8HD. It is an 8 ohm driver, so the "A" design with 13 uf and tap 4 gives approx 800 cps crossover. Thanks for the interest... chris



#18 canyonman

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Posted 13 November 2013 - 07:32 PM

This is not an apples to apples example but, the way it was put to me was. Use bigger air core wire instead of smaller iron core or magnet wire and you get a much better bottom end because of the low DCR... The example was if you have a motor with 600 horse power and you have a 2inch exhaust system you don't get all the power, if you have a 4inch exhaust system well things move much more freely and you get alot more power!!!



#19 UH1dg337

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Posted 13 November 2013 - 07:41 PM

I took me ten minutes each to wind 2.5 mh 14 gage air core inductors. They sound the same IMHO as the # 2133 Klipsch inductor. They both have the same approximate DCR.

I notice that the really old Klipsch crossovers 500/5000 cps use large fine (small) wire air cores. Really big spools of magnet wire.

The larger wire could handle more power, Klipsch told me the stock 2133 is good to 100 vollts

Pix of my air cores....chris Cost = free :) left over spools of wire on jobsite and time (it was fun)

How did you measure their values?

I was under the impression that the magnet wire allows less wire to be used because the windings are closer making a stronger field.



#20 Don Richard

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Posted 13 November 2013 - 08:42 PM

This is not an apples to apples example but, the way it was put to me was. Use bigger air core wire instead of smaller iron core or magnet wire and you get a much better bottom end because of the low DCR... The example was if you have a motor with 600 horse power and you have a 2inch exhaust system you don't get all the power, if you have a 4inch exhaust system well things move much more freely and you get alot more power!!!

The iron core allows fewer turns for the same inductance. With less and/or smaller wire the DCR of an iron core inductor is often lower than an air core inductor with larger wire.

Changing an inductor to one with a lower DCR changes the Q of the inductor, which changes the filter characteristics. It's not the lower resistance allowing more power to flow, its the hump in low frequency response that results from changing the damping of the filter that you are hearing.