Magnepan MG-12 Crossover upgrade

[gootee]

So NOW I have to try to decide what to do.

Is it worth switching to a foil air core coil for the crossover's bass circuit, even if its DCR is HIGHER than that of the stock coil?

A lower DCR is said to make the bass better or louder and have better bass slam. So why did this guy at the link below report the bass going lower and having more slam when using a foil air core coil that has a DCR spec of 0.669 Ohms versus the 0.36 Ohms of the metal core stock coil that he replaced?

Does using a better 50 uF bass cap perhaps have a lot more effect than people might think? Or is there some other benefit that the foil air core provides that could account for it? Or is it something else that he did?

Here is the link: magnapan3

Here is the schematic of the the stock MG12 crossover: http://www.integracoustics.com/MUG/M...ver/mg12xo.jpg

Here are the current stock coil and most of the foil air core coil choices that I could find:

Stock 2.8 mH (nominal), not foil, not air core, 0.36 Ohms (meas) DCR

Alpha Core Goertz 2.7 mH, 14ga foil, air core, 0.370 Ohms DCR, $49.75
https://www.madisound.com/store/prod...products_id=41

ERSE FoilQ 2.70 mH, 12ga, air core, 0.365 Ohms DCR, $73.30 https://www.madisound.com/store/prod...oducts_id=8850

ERSE FoilQ 2.70 mH, 14ga foil, air core, 0.441 Ohms DCR, $42.25 https://www.madisound.com/store/prod...oducts_id=8907

ERSE FoilQ 2.70 mH, 16ga foil, air core, 0.669 Ohms DCR, $33.50 https://www.madisound.com/store/prod...oducts_id=8759

Alpha Core Goertz 2.7 mH, 16ga foil, air core, 0.583 Ohms DCR, $36.25

Those all seem to have a DCR that is higher than the stock crossover coil.

BUT, from the following link, Alpha-Core Goertz Inductors , it is clear that if Goertz would offer a 12ga foil coil value of 2.7 or 2.8 mH, then it would have to have between 0.202 and 0.304 Ohms DCR, and would probably be closer to the 0.202 than the 0.304, since those are the values for their 12ga 2.0 mH and their 3.9 mH coils. The Goertz website seems to be acting strangely, right now. But maybe they would custom wind some coils.

[gootee]

Since this is for a bass coil, maybe it's time to look at a large-gauge wire-wound air core coil.

Has anyone tried winding their own?

I wonder if using laquered copper tubing might work better than solid wire.

It looks like it's time for some coil inductance and DCR calculations.

[gootee]

Wow, copper magnet wire is expensive:

Magnet Wire - $7.34

But it looks like a little less than 5 lbs (250 feet or about 76 meters) of 12 AWG wire would make two 2.8 mH air core coils, each with a DCR of 0.18 Ohms, for a wire cost of about $50 each, plus shipping.

The length needed and thus the DCR will vary depending on the coil's dimensions. I used the calculator at Pronine Electronics Design - Multilayer Air Core Inductor Calculator to play around with the dimensions. Note that you need to adjust the coil "length" parameter so that you get a whole number of turns per layer (i.e. with no fractional part). And, if you bought a 250-foot roll of 12 AWG wire (5 lbs), you would need each coil to be made with less than 125 feet of the wire.

Using 8 turns per layer of 12 AWG (0.66133 inch width) would make a narrow, tall 2.8 mH coil. It looks like 6 to 8 turns per layer uses less wire than fewer or more turns per layer, at least with the small inner diameters that I tried.

If the inside diameter was 0.5 inch, then the 8-turn-per-layer coil would have 188 turns (23.5 layers) and a 4.47-inch outside diameter, with 115.76 feet of wire and a DC resistance of 0.18 Ohm.

If the inside diameter was 1.0 inch, then the 8-turn-per-layer coil would have 172 turns (21.5 layers) and a 4.64-inch outside diameter, with 120.98 feet of wire and a DC resistance of 0.19 Ohm.

I tried calculating a Brooks Coil configuration for it, too, but for 2.8 mH with 12 AWG wire it turned out to be 13 turns per layer for 13 layers (170 turns) with a width of 1.075 inches and an inner diameter of 2.15 inches and outer diameter of 4.47 inches, giving a wire length of 139.43 feet and a DCR of 0.22 Ohms. So that wouldn't be as good, in terms of DCR and wire length, and two of them couldn't be made from a 250-foot roll of 12 AWG wire. (Interestingly, maybe, the outer diameter is the same as for the first 8-turn-per-layer example, above.)

Or maybe I was doing something incorrectly. And even if I wasn't, there may be other configurations that are better.

Cheers,

Tom

[gootee]

Here's some MUCH CHEAPER magnet wire:

cPath_9 | Applied Magnets : Magnet Wire & Magnet Wire Spools - discount wholesale prices.

And it's factory-wound spools instead of rewound.

[gootee]

Here is a somewhat-more-general thread that I started, about some possible pitfalls when trying to upgrade crossover components:

Crossover Component Upgrade Pitfalls?