air / core inductor question - Page 1
Forum section: electronics / projects

author: ttx450
author_rank: Regular Contributor
timestamp: May 09, 2021, 11:14:03 pm
content: I recently, made a inductor for a speaker crossover repair. One inductor had a air core - tweeter, the other the one had a ferric magnetizable rod - mid.how does the increase magnetism effect the inductor response in a crossover compared to a air core with less magnetism ?

author: TimNJ
author_rank: Super Contributor
timestamp: May 10, 2021, 01:14:09 am
content: Air core inductors cannot be saturated, so they cannot introduce saturation-related distortion.A magnetic core like ferrite or iron powder can handle a finite amount of magnetic flux before the inductor stops behaving like an inductor...and starts looking more like a short circuit. Given a sine wave stimulus, the resulting current through the inductor will no longer look like a sine wave. There will be some "hooks" or peaks.The major benefit of magnetic core inductors is that they can be made much smaller and can use less turns of wire to accomplish the same inductance as an air core inductor. But, the peak current handling capability needs to be known and accounted for during the design. If not properly designed, or used on a system with a very high peak current demand, the THD will increase.Another benefit ofclosedmagnetic cores like toroids or or shaped ferrite cores in POT/PQ/RM style, is that they have very little leakage flux, meaning the magnetic field is contained to the inductor. A rod core or an air core inductor is an open magnetic circuit, and the flux lines (theoretically) extend out to infinity. So, in close quarters, closed magnetic cores may let you smoosh things together more closely without interference.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 10, 2021, 04:46:36 pm
content: The inductance values needed for the lower part of a speaker crossover can be rather large. It saves money if the manufacturer can use an iron core, rather than the huge number of turns of expensive copper wire needed to get the same value in an air core. The iron core inductor, with a reasonable wire gage, will likely have a lower DC resistance and higher Q than the air core version. Hopefully one would account for the differences when doing the original speaker design. It's not just a matter of matching the inductance. Yes, Tim beat me to a lot of this!

author: Gyro
author_rank: Super Contributor
timestamp: May 10, 2021, 08:29:18 pm
content: Better quality speakers - BBC designed monitors, Tannoy monitors etc. tended to use gapped laminated iron cored inductors (Ok, some were autotransformers) in favour of Ferrite. Whether this was due to lower magnetic field interaction, minimising winding resistance against ferrite rod, or lower distortion, I'm not sure.

author: ttx450
author_rank: Regular Contributor
timestamp: May 10, 2021, 09:40:00 pm
content: thanks everyone.. helps with the understanding. trying to understand how they work.when I redone a inductor I was able to get the inductance, Q, and resistance close. little challenging winding the coil, one adds more to the other value, or takes away from the other value. give and take, got it close. thks