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Old 22nd November 2011, 11:59 AM   #241
DrDyna is online now DrDyna  United States
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Air core coils typically have a little more DCR which doesn't make too much difference in parallel / hpf filters but in series / lpf there may be some loss of sensitivity.

Here's an old thread on the subject, info still applies.

Air core vs Iron core
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Old 22nd November 2011, 12:25 PM   #242
Starre is offline Starre  Sweden
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Thanks bbggg and DrDyna, I will check that thread. Observe I meant a non-ferrite core, in that thread DrDyna they discuss ferrite core vs air core. Before chosing my 2.5mH coil I ead it was a good alternative to the air core coil since it is cheaper but still good. I know it sounds good in my speakers but I wonder what it really is, "non-ferrite core coil". It got some kind of core material, is it steel pulver or something like that ?

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Old 22nd November 2011, 02:13 PM   #243
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Quote:
Originally Posted by Starre View Post
Thanks bbggg and DrDyna, I will check that thread. Observe I meant a non-ferrite core, in that thread DrDyna they discuss ferrite core vs air core. Before chosing my 2.5mH coil I ead it was a good alternative to the air core coil since it is cheaper but still good. I know it sounds good in my speakers but I wonder what it really is, "non-ferrite core coil". It got some kind of core material, is it steel pulver or something like that ?
Permite maybe, does it look like this one?

Jantzen 4.7mH 15 AWG P-Core Inductor 255-116
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Old 22nd November 2011, 02:40 PM   #244
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Yes it is that type of coil, "Permite", is it the general opinion it is a good coil?
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Old 22nd November 2011, 02:44 PM   #245
DrDyna is online now DrDyna  United States
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Quote:
Originally Posted by Starre View Post
Yes it is that type of coil, "Permite", is it the general opinion it is a good coil?
I haven't personally used them, but there are some respectable speaker designs that do, such as these:

Jenzen CA
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Old 22nd November 2011, 02:52 PM   #246
Starre is offline Starre  Sweden
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Yes I have seen that, one of the reasons I bought them for my speakers, they had a reasonable price too.
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Old 22nd November 2011, 03:26 PM   #247
bbggg is offline bbggg  United States
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It's all rather straightforward to comprehend, if explained well.

An armature in a coil gets magnetized by the magnetic field created by current flow in the coil. What then happens is that gazillions of magnetic crystals in the armature get into alignment with the external field, whereas their alignment was haphazard before. The generating current is alternating and, after peaking, it dies down again. This allows the crystals to return to their haphazard status quo ante. Ideally they are back to where they were before current ever flowed. Except they are not, there is always a small percentage of crystals that do not snap back into their previous random orientation. They stay roughly aligned to the field that existed a while ago. As current reverses, they start to align with the new field (which is the opposite of the old field) and in a short while about half of them are out of order, their field cancelling the field of the other half. The field in the armature is then zero, but the current in the coil is not.
This whole charade is repeated with every current cycle. Ideally, if one were to graph armature magnetisation versus field intensity, they should get a straight line passing through zero. In reality the phenomenon roughly described above warps this straight line into two S-shaped curves, one going up, one going down, and they are offset from each other as well.
Click the image to open in full size.
This is called magnetic hysteresis. It means that, when subjected to a changing external magnetic field, armatures respond lazily and they also need some persuasion to do so. This hysteretic curve not being straight, means that there is distortion in the waveform as it is "reflected" on the curve. The offset between the up and down parts of the curve means that there is asymmetry in the resultant output. Asymmetry means even order distortion by definition. In practice the bulk of this even order distortion is proved to be 2nd harmonic.
2nd HD can be very nice. Has anyone noticed how composers use it? They double violins with flutes and flutes with piccolos. As long as they all play unison, it works. Strings thrum and sparkle at the same time. It's magic. The magic of unison, i.e. the magic of even order harmonic distortion. Hint: it's false.

Armatures can support much higher magnetic intensities than air or wood, for example, but there is only so much they can do before they saturate. This happens when all their crystals are in total alignment with the field. From that point upwards, there is no more magnetism to be had from the armature. It "clips" so to speak. This is odd order harmonic distortion by definition, and it's predominantly 3rd harmonic.
3rd HD can be very exciting. It adds whack. Drummers play more forcefully, as though they are on speed, ehm, as though they were on speed, cue statute of limitations blah, blah, blah, and since drummers on drugs is a whole other issue, I'll leave it at that. Anyhow it can be very exciting to listen to. Hint: it's false.

To minimize these phenomena, the two S curves need to be as flat as possible, or at least to have a reasonably straight part, and to be offset from each other in the least amount possible. The closer an armature approaches this ideal behavior, the smaller the distortion it can generate.
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Old 22nd November 2011, 06:19 PM   #248
Starre is offline Starre  Sweden
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Ok bbggg, that explains the advantage with an air coil, the question is how much difference in sound quality it means when listening. Thanks for the explanation .
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Old 22nd November 2011, 10:38 PM   #249
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There is no single answer to this. One has to measure a fully assembled speaker for distortion. There are many sources of nonlinearity in a speaker, and coil armature is unlikely to be the principal one in most cases.
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Old 23rd November 2011, 06:28 AM   #250
Starre is offline Starre  Sweden
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That is good to know, I think my next build will probably have all air core just in case, too bad copper is expensive .
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