Transformer Match vs. Speaker Impedance

I noticed years ago that my real Marshall Plexis sounded best to me when the amp was set at 8 ohms and I was using two 16 ohm cabs (for an 8 ohm load). How do I set the new speaker impedance to equal this?

I sometimes used the Plexi set to 16 ohms with one 16 ohm cabinet. How do I set the new speaker impedance to equal this?

I sometimes even set the Marshall to 4 ohms and used four 16 ohm cabs. How do I set the new speaker impedance to equal this?

I never mismatched the head and cab impedance for fear of damaging the amp, though this wouldn't be an issue with the Axe FXIII.
All of the above cases are matched, so leaving it at 1.000 would cover it.... 😎
 
I know the examples I gave were all matched, but Marshall Plexi's sound different at 4, 8, or 16 ohms. I think they sound best at 8 ohms. Eric Johnson likes the sound of his Marshall's best at 8 ohms also. Is there a way to emulate what impedance the amp is set to?
 
I know the examples I gave were all matched, but Marshall Plexi's sound different at 4, 8, or 16 ohms. I think they sound best at 8 ohms. Eric Johnson likes the sound of his Marshall's best at 8 ohms also. Is there a way to emulate what impedance the amp is set to?
Short of examining one of their transformers to get the exact turns ratio at each tap, to verify the actual load impedance in the primary side with each, to find any variation from the exact turns ratio needed for that tap's rated impedance to be 100% correct, I would not be able to tell you what to set the settings to.

An extra turn or two (or a turn or two short) on one of the secondary taps (say, to finish a turns layer rather than bring out an external lead in the middle of one because the wire is fat and would FUBAR the effort of getting subsequent layers to wind straight and true) can make a measureable difference on the plate load the tubes see, as that couple turns high or low is multiplied by the turns ratio.

TL;DR: I don't have the specifications and measurements on hand to be able to answer that specific question (,but I know a couple folks who probably do)....
 
I know the examples I gave were all matched, but Marshall Plexi's sound different at 4, 8, or 16 ohms. I think they sound best at 8 ohms. Eric Johnson likes the sound of his Marshall's best at 8 ohms also. Is there a way to emulate what impedance the amp is set to?
Turn it up a bit, turn it down a bit. Which sounds better? Use that.
 
So, you’re okay with the Ace Frehley approach, in this instance?
Unlike with real amps, you have no possibility of a mismatch hurting anything if it's too far off, and you have a knob to adjust in much finer increments than you could possibly come up with by hooking a bunch of cabs in series and/or parallel to get a mismatch of a particular amount.
 
I'm pretty sure (though I didn't look) that this is already in the Cliff Notes on Yek's wiki!
 
Why does 9.xx have these two separate controls?

Prior to 9.xx the "matching" was controlled by a single Transformer Match parameter. 9.xx introduces a new Speaker Impedance parameter. The distortion of a tube power amp is dependent upon the load presented to the power tubes. The overall sound, however, is also often dependent upon the voltage at the speaker since that voltage is fed back to the input.

The following examples illustrate the difference.
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