I just want to weigh in with my opinion on the whole steel core vs air core business.
I don’t think there is any debate that adding a metallic core to a coil of wire provides an opportunity for that core to saturate. I think the question in speaker design is whether the core will saturate sufficiently to cause an audible detriment in practical use. To this question, I think that the answer is “no” with the right kind of inductor.
steel laminate inductors saturate at much higher levels and have lower levels of distortion when they do start to saturate. More importantantly, the saturation is based on a certain current point. It doesn’t just saturate once it’s powered up or over time. Once sufficient current is passed through, it begins to saturate. Most speaker inductors have a core saturation point that is actually above the wire current limit. The exception are those cheap little 20 gauge or smaller types with cheaper powder ferrite cores.
the Erse superQ steel laminate inductors are rated at 500 watts. They won’t actually saturate until after that point and what happens is that the inductance drops slightly. Not enough to make a big difference. A slight amount of harmonic and Intermodulation distortion is also created. At the same time, at more than 500 watts, the woofer is also distorting as smoke comes out.
on the other hand, fixing that problem with an air core would mean accepting a substantial loss of sensitivity and addition of series dc resistance and loss of power handling in the inductor, or an inductor that would be way more expensive. In my speakers the SuperQ inductors were ~$20 each. I have 2 in each speaker. I have three speakers. That is $120 in inductors for the three speakers. The DC resistance is something like .16 ohms each. .32 for the pair.
now if we go to a 14 gauge air core, price is $60 each, the size is about 4 times larger, DCr is .4 each, about .8 for the pair, power handling is about the same. This upgrade then is $360 vs the original $120. That’s a lot of money. And I would pay it if I thought it made a difference but I don’t.
in the place where it might make a difference. A very high powered pro audio speaker, we still see metallic core inductors primarily used.
my opinion is that whatever audible benefit they might have is being outweighed by their detriment. Not all metallic core inductors of course, but once you start getting into values greater than 1mh, good metallic core inductors become attractive. You usually don’t want to add a lot of excess series resistance in your speaker, it kills needed sensitivity and wastes precious power as heat. It also kills the amplifier damping factor (many Class D amplifiers have very low damping factors to begin with, some class AB designs aren’t so hot either.)
