Update 12/10/23: While I was waiting for my proper 1mH crossover coils to arrive I made two quick hand wound inductors to see how it might differ from my initial test. The results were surprising! This coil doesn't quite match the specs of the type of chokes I believe Allan used but it's much closer in terms of inductance.

	This coil was wound using approx. 22 AWG enameled wire. I don't know how many turns it ended up being but it measured 0.82mH when by itself. As soon as I put it on the aluminum baseplate (with screw in center of the bobbin) the apparent inductance went up to 1.26mh. With the addition of the nut and washers it settled at 1.36mH. That adds up to an increase of 65%! Far more than I was expecting to see.
	While I was at it, I thought I'd figure out what the resonant frequency of my coil was using my DIY curve tracer. It occurs at about 65Hz, which is not too far off from the resonant frequency of a 12" guitar speaker, which can be anywhere between 55Hz & 75Hz. A "broken in" speaker will typically have a resonant frequency of 60-65Hz, while a new one will often be at about 75Hz. With two inductors in series the resonant frequency went down to about 50Hz.
	In order to do further testing I had to make a new aluminum baseplate that would hold two to three inductor coils approx. the same distance apart as in Allan's units. Since the 1mH inductor I ordered was taking a long time to arrive I just hand wound another one with a little smaller gage wire than the first one I made (approx. 24 AWG). I ended up with exactly 1mH. The DC resistance between the two coils of different gage wire aren't too dissimilar, but both are much higher than the coil I ordered. The series inductance between the two coils equaled the sum of the two individually. The inductance of the new 1mH coil I made went up roughly 50% when it was mounted to the baseplate. I will compare that to the one I ordered when it arrives. I am not sure that the results will be that much different from what I've done here.
	The main thing I wanted to do here is to see if there was any crosstalk (mutual inductance) between the two coils when mounted on an aluminum baseplate. There is indeed some crosstalk occuring between adjacent coils. The crosstalk occurring on the adjacent coil with no signal going thru it (top of o'scope screen) is about 25-30% of the amplitude of the coil with the signal from the function generator going thru it (bottom of o'scope screen).
	While I was at it I plotted the frequency response. Left side is amplitude of RMS voltage at the output of the two coils and the bottom is the frequencies. This was done by feeding the coils with a 1V RMS sine wave. It's fairly flat until around 1kHz, after which it steadily declines. I'm not sure how seven of these affects the overall frequency response, or if it would change the same way with a higher voltage and much more current than what my function generator can supply, but it does demonstrate the high frequency attentuation effect of the inductors in the circuit. This would filter out a lot of the nasty sounding stuff in the higher frequencies and make "the tone" sound smoother and perhaps more "mid-heavy".

Even though I have a fairly good idea of what the outcome will be, it will still be interesting to see how a proper perfectly manufactured 1mH inductor will compare to my two previous tests. Based on these tests I'm guessing the apparent inductance will be considerably more than my initial estimate of 20%. So, we can see that another factor in this simple yet surprisingly complex circuit is that the mutual inductance may also have some effect on the sound. In Allan's circuit the "chokes" are in rather close proximity to each other, which in ordinary circumstances would create crosstalk and it does here also. My testing has confirmed that the baseplate does not negate that effect. I am not sure how this affects things in the overall picture. It may just contribute more to the losses of the inductors, and/or it may also actually impart something to the sound that can not be achieved any other way.



Update 12/11/23: My proper air core inductors arrived today and I did some more measurements. Turns out that with these 200 watt 20 AWG 1.0mH inductors with a DC resistance of 0.73 ohms the apparent inductance goes up only about 20%, so I was actually right on target with my initial hunch. Or so I thought. It turns out in my theoretical clone that the apparent inductance actually measured 42% higher - double what I concluded from this simple test.

I investigated what happens when there are three in series. With three coils, the resonant frequency dropped to about 45 Hz. So, after conducting this series of experiments it turns out that the height of the coil, the wire gage and DC resistance have a significant effect on what happens with the inductance. Less turns with larger wire equals less losses due to the screws, washers and nuts. It's also likely that my imperfect hand wound coils are very inefficient compared to the perfectly wound air core inductor beyond.

In conclusion, I don't know that I can really make any concrete conclusions but I found this exercise to be very interesting. I learned a few things I did not know before, and with so many variables, it is still somewhat mysterious as to what actually happens inside these boxes that Allan designed and built. I can not determine that without actually having one in hand to test and measure. In any case, this device may be another legitimate Holdsworth secret sauce kind of thing. All things considered, I think The Harness is definitely responsible for some of Allan's best "tones", such as the ones on the Secrets album. Who knew The Harness had so many secrets?! I think I know enough now to build a functional unit, which I may do just for kicks. I will replicate the component layout that Allan used and get all the proper parts so I can replicate it as closely as possible.