#1
This is a fairly crazy question but here goes:

I have a marshall VS100 Valvestate combo, it has a minimum of 4 ohms to speakers, with two speaker output holes. The combo has one speaker, its a Celestion Gold back series 100Watts, 8 ohms. I have another speaker spare, it is some crappy "Ross Systems" 160watt 4 ohms speaker.

Could i plug this spare speaker into the other speaker output on my marshall, thus making it 6 ohms?

Please no comments on how shit it will sound, i know this
- Duvmunch
- Jackson RR24
- Marshall VS100 + Marshall 1960A Cab
#2
Its best to keep your impedances the same, not just for sound, as you already know, but for the safety of your amp. This could cause your amp to go belly up on you, and a VS is a horrible amp to wreck. They sound so gooood :P.

Also, underpowering on the wattage can seriously damage things as well (the theory goes anyway). The ross would draw more power and both speakers would run cold. Ewww. If you ever decided to play with a little overdrive or distortion your speakers would crap out on you.
#3
how would an 8ohm and a 4 ohm speaker be able to equal 6 ohms?

in series, you would have 12 ohms...
in parallel you would have 1/8 + 1/4 = 1/8 + 2/8 = 3/8r = (8/3) ohms
unless my math is messed up
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