advertisement


Air core preferable to ferrite cored inductors ?

Chris

pfm Member
Given the choice, and having exactly the same values, do you think air core inductors might be preferable to ferrite cores for use in crossovers with the Seas mid bass driver on the WD25TEx ? Peter Comeau´s original design was for the ferrite cores but Jantzen wax foil air cores are available at the same value of 0.76H ? Needless to say, an educated guess would be far more useful than my own uneducated one.
 
Air cores are considerably larger for the same value as ferrite cores. So make sure you have room...

In theory a very large signal can saturate a ferrite core - in practice unlikely in a crossover...

I nearly forgot - air cores for the same value may have more copper (perhaps a lot) and so watch out for resistance values too....
 
Technically they are not air core as the wax is there but at audio it won't matter. Air cored is better in many ways but will usually need much more copper wire for same inductance so will often be higher resistance and this matters.
Use whatever the designer of the crossover recommends.
 
The resistance is the same too. These coils are on a wooden bobbin which I presume is electrically the same as air, no _
 
The resistance is the same too. These coils are on a wooden bobbin which I presume is electrically the same as air, no _

To be pedantic, no. But at audio it is so nothing to worry about. Having precisely the correct inductance and resistance is much more important than the "quality" of the inductor.
 
You need something to hold the windings still with all the magnetic forces anyway.
Getting dc resistance low with an air core is not easy as you need a lot of turns for inductance useful for a bass driver
 
If you want air cored inductors then buy your self an inductance meter off eBay and wind your own.

Regards

Henry
BadAss Magnetics Co
 
Henry, the mild-mannered inductor maker?

Foo-ey

;)




To be serious - there are some good inductor winding calculators out on the web that - for a target inductance, will calculate size, no. of turns, even total length of wire required. - of which - be prepared to buy lots - and as noted above - once done, you'll want to constrain the windings in some way.
In fact last time I pondered making my own such - it was worth just buying them in, becasue te margin over material cost & what free time I had was trivial.
 
Do coil calculators give accurate results? I remember a formula being taught at A level physics, which when I've used this in the past was no where near. I do remember someone on the 'net saying that from basic dimensions (former diameter and winding length) quoted length of wire rather than number of turns for a specific inductance and I found this was much closer, but can't for the life of me remember what site this was.
 
Do coil calculators give accurate results? I remember a formula being taught at A level physics, which when I've used this in the past was no where near.

Is that not simply down to neatness/tightness of winding? Think of a new coil of garden hose in a garden centre. Think of the coil size after you rewind it after first use.
 
I was hoping for a clear cut air core superiority recommendation to solve all my problems but alas it would seem it’s just a question of taste like so many things in audio. I’ll just have to accept that to my ears my cans are better than my speakers for certain things like bass snap.
 
Like most things, no simple answer. Similar to output transformers on valve gear, if the transformers are not properly designed or too small, saturation of the core occurs at low frequencies which produces distortion.
However as has already been said, to get the same inductance without a ferrite or laminated core, you need more windings and so more overall length of copper and therefore thicker copper to offset this so much larger and more expensive.
 
Henry, the mild-mannered inductor maker?

Foo-ey

;)




To be serious - there are some good inductor winding calculators out on the web that - for a target inductance, will calculate size, no. of turns, even total length of wire required. - of which - be prepared to buy lots - and as noted above - once done, you'll want to constrain the windings in some way.
In fact last time I pondered making my own such - it was worth just buying them in, becasue te margin over material cost & what free time I had was trivial.


I wanted the coils for an error correcting amplifier, so it was quite easy to build and measure them, approx 2uH, but measured so the resistor values in the bridge could be set accurately.
 
The inductance calculators vary considerably in accuracy but when winding coils you must actually measure them as in real life you will be very lucky indeed to get within 20% accuracy by any calculation method.
 


advertisement


Back
Top