# Solid Core Inductors
**URL:** https://discourse.midwestaudio.club/t/solid-core-inductors/203
**Category:** General
**Tags:** passive-xover
**Created:** [October 12, 2025, 2:00pm UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203 "2025-10-12T14:00:47Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@RobertH3](https://discourse.midwestaudio.club/u/RobertH3)
#### Post date: [October 12, 2025, 2:00pm UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/1 "2025-10-12T14:00:47Z")
Thought I would share this. It is interesting and measurable.
This is from the **“Transformer and Inductor Design Handbook”** by Col. William T. McLyman. He designed transformers for Mariner and other spacecraft. Good news: he did all of the calculus for you. Bad news: it still requires “very” careful reading and formula figuring. The text is available on the web as a free PDF but is a basic scan. The book is much more useful than the scan and highly recommended if you are interested in electromagnetics. I got into this while building high voltage power supplies and Tesla Coils.
Here are some BH Loops for Solid core materials. First, an air-core inductor has a permeability of 1. In other words, they have a 1:1 ratio of B/H. This is why they’re desirable - _they are linear._ Limits are power handling and DC resistance.
Here is an Air Core BH loop.
There is no such thing as a perfectly linear solid core inductor, but some are more linear than others. Both non-linearity and Remanent Flux (tendency to “want” to stay magnetized after current is applied) affect all solid core inductors.
Below is a bar-core (Silicon-Steel) inductor. The pic below doesn’t account for the much-reduced permeability of a bar core. The Air Gap is essentially equal to the length of the core. This shears the curve way to the right and makes the straight portions of the curve more diagonal. It gives more of a linear area at the expense of a little efficiency.
If you push enough current through it, you increase H to the point that it starts to work in the non-linear area of the curve. Distortion. Silicon steel also has a tendency to hold “Remanent” Flux. This is what separates the 2 portions of the loop. It takes time for the core to switch from positive-going to negative-going.
Effect of an Air Gap on a BH Loop
Next is a Ferrite Inductor. These have a very high frequency response at an expense. They can run in the hundreds of Khz but aren’t very linear. They can also be inefficient at low frequencies. Not audio grade IMHO. Good for high voltage / high frequency stuff!
Next is an Iron Powder Core, or P-Core. Again, the BH loop will be shifted to the right and will increase the Linear region. Note the gentle “knee” of the curve into saturation.
Here’s the most interesting one to me. This is a Kool-Mu, or “Sendust” core. It has the least Remanent Flux (almost none) and is quite linear. It also has the same gentle saturation characteristic of the powder core. Again, the curve will be rotated to the right by the large Air Gap.
Based on all of the above, I would choose either a Bar-Core or P-Core. A Kool-Mu Powder core, properly designed, would be a nice option too.
Cheers / Robert
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### Author:  [@RobertH3](https://discourse.midwestaudio.club/u/RobertH3)
#### Post date: [October 13, 2025, 3:17pm UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/3 "2025-10-13T15:17:32Z")
Of course! That is absolutely required.
A waaayyy back, Wolf did a cap comparison at one of the DIY’s and there were audible differences.
That’s why I let the cheaper caps go and went to poly.
Cheers / Robert
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### Author:  [@raddon](https://discourse.midwestaudio.club/u/raddon)
#### Post date: [October 14, 2025, 3:05am UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/5 "2025-10-14T03:05:59Z")
I thought that I had seen a detailed test of air core versus solid core inductors in Audioxpress, but I can’t find it now.
[mtg designs inductor tests](https://www.mtg-designs.com/tips-tricks-tests/inductor-testing) - has some basic tests. Some of the findings are that the HD % varies with mH value and power level and is mostly odd order.
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### Author:  [@JasonP](https://discourse.midwestaudio.club/u/JasonP)
#### Post date: [October 14, 2025, 3:36am UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/6 "2025-10-14T03:36:49Z")
HiFi compass did some testing on solid core inductors here:
[https://hificompass.com/en/projects/experiment/test-couple-iron-core-inductors](https://hificompass.com/en/projects/experiment/test-couple-iron-core-inductors)
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### Author:  [@Wolf](https://discourse.midwestaudio.club/u/Wolf)
#### Post date: [October 14, 2025, 7:59am UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/7 "2025-10-14T07:59:16Z")
Craig and Nick tested some coils not too long ago as well.
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### Author:  [@RobertH3](https://discourse.midwestaudio.club/u/RobertH3)
#### Post date: [October 14, 2025, 12:14pm UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/8 "2025-10-14T12:14:23Z")
The above was for information purposes - sometimes you need a low-DCR coil. It’s not a must-do. Low-crossing 3-ways can run into the above woofer DCR issue. The F8 3-way did.
Nice Hi-Fi Compass article - it covers measurements well, but to reet’s point, there should be listening tests, too. AE Lambda’s are high power and low distortion, so it was a good test. I couldn’t find the Craig/Nick study but would like to read it.
The cap test didn’t get me buying Clarity’s or other super-high price caps, just the standard Film and Foil polys like Jule and Dayton sell. The difference between these and the cheaper caps with different compositions was audible at the DIY.
The rather entertaining reason I got into the design book is in the link below.
> **[DC Tesla Coil design](https://www.richieburnett.co.uk/dcreschg.html)**
>
> Tesla Coil design, construction, operation and measurement information
The circuit uses a switching power supply approach without semiconductor switches to charge the primary LC circuit. I did all the calcs and the circuit I made required a _ **4-Henry** _ high voltage coil!!! I never made one but did successfully design the coil. Lol - a bar wouldn’t work for this, it required a C or E coil and a large winding window.
Cheers / Robert
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### Author:  [@raddon](https://discourse.midwestaudio.club/u/raddon)
#### Post date: [March 25, 2026, 8:35pm UTC](https://discourse.midwestaudio.club/t/solid-core-inductors/203/9 "2026-03-25T20:35:26Z")
For those who are interested in digging into inductor saturation an distortion vs signal level, Practical Electronics mag has articles Feb/March 2026 for a high powered LCR tester than can output up to 30A to DUT. Not real clear, though, on what the output screen displays.
> **[February 2026 – Practical Electronics](https://www.electronpublishing.com/product/february-2026/)**
>
> Practical Electronics hobby constructor magazine
