psychodave":3tukxe2q said:
The different ohm selector is using different windings on the output transformer.
Assuming the output transformer isn't faulty on one tap somehow (and the transformers aren't smaller/"lower headroom"), I don't think this would make the difference since it's actually not much of a difference overall.
Using different output transformer windings (8 ohm versus 16 ohm) may have a slight difference in the sound, but not nearly as much as other factors (and unless the amp is blasting full-out for volume, you might not notice much difference if any).
Trying to test for the difference in the sound of using different output transformer windings (8 ohm versus 16 ohm) alone is actually quite tricky since there are other more significant variables to consider.
Even if the speakers are "the same" model but made as different impedance versions (for instance a Vintage 30 8-ohm speaker versus a Vintage 30 16-ohm speaker), they have different properties due to how they're made differently for those different impedances. Here are some things which differ in speakers of "the same design" but different impedances:
-resonant frequency
-frequency range
-inductance
-sensitivity
Even if those things aren't very different from speaker to speaker, add them all up and you'll find an "8-ohm version" of speaker X sounds different from a "16-ohm version" of speaker X. Given that you have to match impedance to the amp to hear how each speaker actually sounds (mismatch of impedance to the amp means a really noticeable change in the sound and response, so you can't do that), you can't really just properly A/B a single 8-ohm version of "speaker X" with a single 16-ohm speaker of "speaker X" using the same output transformer winding because of that.
Then there's the matter of how the inductance plays into it, which is often overlooked. Simply wiring a 4x12 cab as parallel-series versus series-parallel makes a noticeable difference because of the difference in combined inductances (due to how they're combined differently in series versus parallel). Some consider it a make-or-break difference, just one wire different (sometimes I do too, depending on the cabinet and/or speakers). That's using the exact same speakers, and keeping the impedance the same in the same cabinet. So "16 ohms" can even sound "different from 16 ohms" in the same 4x12.
Now consider that wiring different cabs differently in general--series versus parallel--can have an even more noticeable effect than that. So if one cab has two speakers wired in series and the other has two speakers wired in parallel (or a 4x12 cabinet has four speakers in series-parallel compared to a 2x12 wired in series or parallel), it's a bigger difference than you'd hear wiring a 4x12 as parallel-series versus series-parallel.
And if the speakers are different models in general, we can put that at the top of the list of suspects in this case (although I don't think that's what the OP meant).
scottosan:
What you hear "when the amp cleans up" might be related to the specific speaker cabinet having an effect on feedback your guitar is picking up, due to different frequencies the cabinet is projecting. If you notice this difference at low volumes though, I wouldn't suspect this much.
Also: you mention "chimey top end" as part of this. Maybe what you consider "better at cleaning up" is hearing more of that "chimey top end" and less about the speakers really "cleaning up"? It wouldn't be the first time someone associated that aspect of the sound with "a clean tone" (I notice people are more forgiving about a higher gain amp's limited ability to "clean up with the guitar's volume" if there's chimey top end in the sound). That aspect of the sound could be due to the speakers and their differences I mentioned, as well as the cabinet design (differences in resonance due to different wood and more/less of it, different bracing in the cabinet, how tightly it's sealed, if there's damping material inside).
