So last night I was working on a pedal mod (where I could toggle back between "original" and modded sound) when I started thinking about this Marshall 4x12 cabinet that I traded for a while back. It's my first 4x12 with switchable impedance. Up to last night I have been playing it exclusively at 4 ohms. I decided to perform an unscientific comparison of 4 ohms vs 16 ohms sound differences using my Marshall JMP 2203. As I didn't have an assistant to switch both the amp's and the cab's settings between 4 and 16 ohms, I left the amp and guitar settings alone and tried to always return to listen from the same spot that I marked on the floor. Here's what I found... The sound between the two settings was "almost" identical but I noticed some differences. It seemed that the sound with the amp running at 4 ohms into the 4 ohm cab input was just a tad louder/ more powerful and slightly more defined with a smidge more lows and highs. Running the amp at 16 ohms into the 16 ohm input sounded very similar but the signal was a little more smeared with a very slight decrease in the lows and highs and just a touch less presence / power. For lack of a better descriptive term, I would describe the sound as "rounder" at the 16 ohm setting and "bolder" on 4 ohms. But I must emphasize again that these differences were very slight. The closest comparison I can draw is that it was like a very high quality copy of a photograph where the edges become just a little softer. This was not a bad thing at all and I might start running the amp at 16 ohms for live use. I went back and forth several times to try to confirm what my initial impressions were and each time I reached the same conclusion. I was wondering if it was simply due to the differences in the output transformer taps or is there some physics at play. IDK. Either way, I thought I would share my findings and wondered if others have found the same thing.