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Old 11th July 2012, 07:36 AM   #1
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Question Crossover inductors in series ,question.

I am building a new speaker to replace my Volt 2208/ Home monitor.
The new design will be three way and I am trying to use up some existing
high grade inductors.
So to make up my 3mh units I am considering the 1.8 air cored and the 1.2
ferrite cored in series.
Having read all the supposed disadvantages of iron cored units,
My question , Is their a theoretical difference in which way around these should be placed in series?
Does it matter higher first or aircore first?
It is going to be biwired.
I am aware that they should be 20cm apart and at 90 degree angle to each other to
avoid crosstalk.
Any theories and explanations as to why?.
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Old 11th July 2012, 07:48 AM   #2
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AFAIK when a current runs into an inductor, a magnetic filed comes up. this virtual magnet is sensitive to frequency changes and will vary with frequency changes going to speaker so the magnetic field direction will change according to the frequency change for example 1000hz/seconds, considering this the magnetic field keeps changing with the frequency all the time. the magnetic field is a bit lazy with a direct relation to the inductance value, so when the frequency is change the magnetic field of previous freq. is still there and will fight back with new signals and the magnetic field will nullify the new frequency to a certain amount so some of the frequencies pass through and some will get blocked... this is how an inductor works (Thank God I don't have to explain heart surgery in English )
so I think an inductor should be there to do the filtering job. maybe two in series won't create that much of magnetic field needed to do the freakin' job

Last edited by ARIYAHOOR; 11th July 2012 at 07:51 AM.
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Old 11th July 2012, 08:44 AM   #3
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Hi and thanks for reply.
The reason for asking was because I remember reading somewhere about the backwards effect of ferrite core in inductors, so long ago I forgotten the theory.
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Old 11th July 2012, 10:17 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

You'll get the worst aspects of both inductor types.

The high resistance of the air core and the "distortion" of the iron core.

FWIW order does not matter.

rgds, sreten.
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Old 11th July 2012, 11:02 AM   #5
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Originally Posted by sreten View Post
Hi,

You'll get the worst aspects of both inductor types.

The high resistance of the air core and the "distortion" of the iron core.

FWIW order does not matter.

rgds, sreten.
I want pose a question
I want to know how can be estimate the saturation deadline of an iron core inductor? you know we can increase inductance of a for example 1mH air core inductor by putting a very small screw inside of it and it will show for example 1.1 mH... you know what I'm talking about... I think saturation and distortion depend on the mass of the iron we use and also the inductance. we can wind iron core but less than expected and then add more turns so I think it would take turn for less distortion and so we can obtain a balance between Iron core (less resistance) and air core (less distortion)... aint we?
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Old 11th July 2012, 11:30 AM   #6
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as part of my job i test electrical machines, and a common task is the saturation curve. From my working knowledge i would run a similar test. This is what i would do. Get a variable ac supply, take a curve of V against I, working from 1.3 times inductor current rating down to 10% rating or lower. For a real valid test, winding temp would need to be monitored also. Then the Z, this is found from the trace and plotted. Temp compensation should be employed to correct for winding heating effect. The resultant corrected plot will be linear to the point of saturation. However, ferrite cored inductors whose typical use is in SMPS supplies are rated at a level where minimal or no saturation occurs, or they would fail to fulfill their purpose. A revealing question to ask yourself is: what current peak would i expect? Decide an answer,0hen pick an inductor whose current rating exceeds that level. Then you can be fairly sure that saturation will not occur. I have used 10amp ferrites with no issue whatsoever, 3amp rated arent so good. I reckon that the core diameter and wire gauge and number of turns is very relevant though. Scale core dia to inductance. Im using 2mm wire on a 1.5 inch ferrite. Monacor 'high power' at 2.2mH. Works well. The 0.6mm 3/4inch lower power monacor ferrite in 2.2mH is ok, UNTIL you add another L in series, even just 0.22mH makes it saturate wildly. Going for 10amp rating MINIMUM will work well. Even doing this hysteresis is still present, but it is a comprimise between DCR and size and saturation as sreten was inferring. Use 1 coil if possible, be it air or ferrite cored.
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Old 11th July 2012, 12:51 PM   #7
DavidL is offline DavidL  United States
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Laminated iron core inductors are less prone to saturation than ferrite cored.
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Old 11th July 2012, 01:09 PM   #8
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Laminated iron core inductors are less prone to saturation than ferrite cored.
really? Not alot to pick between them, in comparison to no core at all. Silicon steel lammed cores saturate rather alot in my scope of experience. Air cored is better, but either DCR or expense may be a problem, as Sreten stated. The trade off is a high current iron or ferrite core. For 3mH a transformer could be used. By taking OCC and SCC curves saturation can be found. In this way, using 1 winding, you could 'tune' the secondary Rload, and experiment. An inductor of this type could be very low in saturation and distortion, and likely still cheaper than the equivalent air core
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Old 11th July 2012, 01:51 PM   #9
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Laminated iron core inductors are less prone to saturation than ferrite cored.
I'm in with that idea
laminated cored ones are better
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Old 11th July 2012, 08:32 PM   #10
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Having read all the supposed disadvantages of iron cored units,
Are you going to use them at their max. power?
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