4 ohms VS 8 ohms for MarkIV?

[petejt]

The Mesa/Boogie MarkIV has two options for connecting speakers- either one 8 ohm output, or connect to 8 ohm outputs which in the amp are wired parallel and thus become 4 ohms in the amp.

What actual sound difference is there between them?

 

[blackba]

The 8 ohm tap will use all the transformers windings on the output, the 4ohm will not. Typically the different impedance options will also be mixed with wiring differences in the cab, speaker could differences, etc, so its tough to just isolate down to just one factor like which tap you are using on the amp.

 

[fretout]

The difference in sound is that using into a lower ohm rating (on the amp) will sound darker.

One thing I like to do is plug in two speaker cables from the 4 ohm outputs on the amp into the stereo inputs on the Mesa cabs. In this scenario, it doesn't sound darker, but for whatever reason, it allows you to run a higher master volume, and it sounds thick!

In other words, this is how I'll run my rig sometimes, but instead of two cabs, I'll plug it into a single 4x12s stereo inputs...



And for reference...

 

[petejt]

Thanks for your responses guys. I think I'll stick with the 8 ohm tap.

I have tried the two 4ohm taps but I ran them at a 16 ohm mismatch (so I didn't get a clear idea of how its supposed to sound), which sounded okay-ish... I thought I liked it at first. But over time I'm not that keen on it so have wondered how it would work with correct impedance matching.

The cab I use with the MarkIV has two MC90 Black Shadow speakers, and a 200 watt EV speaker. There's another speaker but I'm gonna bypass it with some load resistors because I don't think it sounds as good. I reckon the EV sounds dark enough already.

 

[psychodave]

I like the mismatch most of the time...especially with Marshall type amps. Using a 16 ohm cab with an 8 ohm output changes (I believe if I'm remembering correctly) the negative feedback and makes the sound have a different midrange. It also changes the feel of the amp too. When I use Marshall cabs with boogie amps, I use a splitter box (2 into 1) and plug two cabinets into one side and go out with one into the 8 ohm tap ( or 4 for a safe mismatch). I did this because the boogies have only one 8 ohm tap and when using two 16 ohm cabs, one cab would be louder.

 

[petejt]

I like the mismatch most of the time...especially with Marshall type amps. Using a 16 ohm cab with an 8 ohm output changes (I believe if I'm remembering correctly) the negative feedback and makes the sound have a different midrange. It also changes the feel of the amp too. When I use Marshall cabs with boogie amps, I use a splitter box (2 into 1) and plug two cabinets into one side and go out with one into the 8 ohm tap ( or 4 for a safe mismatch). I did this because the boogies have only one 8 ohm tap and when using two 16 ohm cabs, one cab would be louder.

What sort of midrange? High mids? Central? Low? Stiffer feel? Looser? Tighter? More crunchy? Chuggy? Greasy?"