Long time ago i found out the hard way that i grossly underestimated the losses of a multilayer air cored coil operating a 50Hz. I calculate the losses using only Rdc instead of Rac as i should have done.
Why?
Because i foolishly assumed that since skindepth was much larger than the rectangular 6.85x4.85mm conductor-tube (with only 1.5mm wallthickness !!! ) i would not have to worry about Rac.
Big mistake, losses turned out to be about double of what i expected ased on Rdc.
Why? Proximity losses! Much, much higher than what i assumed (based on skin depth)!
THE COIL HAD 12 LAYERS wound on top of each other, approx. 60mm total thickness.
Now, those additional losses ment that the efficience of my 50Hz inductionheater was instead of nearly 70% only 50%.
If you wind a multilayer coil, NEVER underestimate PROXIMITY losses, as i did (unless you really want to filter out some higher frquencies by turning them into heat).
Nowdays it is so easy to calculate Rac at the frquencies of interest with a free online calculator.
My advice, do yourself a favor and make some calculations before you wind a multilayer coil with thick wire!
Rdc, is what it says, direct current resistance, but since you hardly cross over at dc it is Rac what really counts in performing as a shunt!
As to skin depth, it only applies for a SINGLE wire suspended in frée space!
Why?
Because i foolishly assumed that since skindepth was much larger than the rectangular 6.85x4.85mm conductor-tube (with only 1.5mm wallthickness !!! ) i would not have to worry about Rac.
Big mistake, losses turned out to be about double of what i expected ased on Rdc.
Why? Proximity losses! Much, much higher than what i assumed (based on skin depth)!
THE COIL HAD 12 LAYERS wound on top of each other, approx. 60mm total thickness.
Now, those additional losses ment that the efficience of my 50Hz inductionheater was instead of nearly 70% only 50%.
If you wind a multilayer coil, NEVER underestimate PROXIMITY losses, as i did (unless you really want to filter out some higher frquencies by turning them into heat).
Nowdays it is so easy to calculate Rac at the frquencies of interest with a free online calculator.
My advice, do yourself a favor and make some calculations before you wind a multilayer coil with thick wire!
Rdc, is what it says, direct current resistance, but since you hardly cross over at dc it is Rac what really counts in performing as a shunt!
As to skin depth, it only applies for a SINGLE wire suspended in frée space!
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While there's alot of science and intricate technical details surrounding the performance of inductors, I can tell you that most non-air cored coils sound awful, especially at higher power levels. The only non-air cored inductor I use is a laminated transformer coil with a massive core. I'd only use it in LF low pass circuits and make sure its from a reputable source. There are big differences in laminated core materials. The cheaper Chinese laminates sound awful despite looking almost identical to the higher end ones sold by Mundorf and Erse.
Regarding all other core materials available, anything made from sintered or powdered materials is garbage and should never be used in a critical application. They all add distortion and some saturate very early with little current. The black ferrite cores are by far the worst in this regard.
I started winding my own air core coils and haven't looked back. You can build any value you like, even ones with multiple taps for varying BSC and for running multiple woofers in a 2.5 way.
Regarding all other core materials available, anything made from sintered or powdered materials is garbage and should never be used in a critical application. They all add distortion and some saturate very early with little current. The black ferrite cores are by far the worst in this regard.
I started winding my own air core coils and haven't looked back. You can build any value you like, even ones with multiple taps for varying BSC and for running multiple woofers in a 2.5 way.
As rightly described there is a lot more going on in a coil of wire than just xl and dcr.coils in xovers opperate over wide bandwidths and the phyisical construction of the coil impacts its ability to act as inductance only. All coils will at some frequency end up reasonating due to the inherent distributed capacitance but we knew that.this is why audio manufactures make coils with differing construction so they function in their audio range effectively. Same with audio transformers.