running mark iv into a split mesa cab

[factorevif]

Hey guys, I have a Mark IV and a 4x12 mesa recto cab as my main rig. Due to overbearing loudness of two all-tube half stacks and a bass rig in my band, I have been wanting to split my mesa cab and run my mark iv to two speakers on the mesa cab. On the back of the mesa cab, it has an 8 ohm input for the regular, 4 speaker operation, but it has two more jacks that allows you to only use the left of right 2 speakers of the cab at a time. Each of these inputs are labels as 4 ohm.

My Mark IV has 1 8 ohm and 2 4 ohm outputs on the back to connect to cabinets, would it be safe to run a line from the 8 ohm jack of the amp into the 4 ohm jack of the cab or should I run the line from the 4 ohm jack from the amp to the 4 ohm jack on the cab. I know that running 4 ohm to 4 ohm is the safest bet, but in general, when is it safe to mismatch cab/amp loads: When the amp ohm load is more or less than the cab ohm load?

 

[ryjan]

Run it in the 4ohm jack of your amp. Safe mismatches are when the impedance of the cab is higher than the amps input. Example; 16ohm cab to 8ohm jack, 8ohm cab to 4ohm jack. Its in your owners manual.

 

[tony777]

Safe mismatch or not, I don't think you will get anywhere you want with splitting the cab, just lower the output volume a bit. If you use one of the 4 output jacks at the mark IV into one of the 4 ohm input at the cab, you will get the effect you ask for, but it doesn't turn down the volume, it only sounds tinner than using all the speakers.

 

[babow2]

Actually, switching the same amp between 4 ohm and 8ohm load won't create any noticable volume change. volume and hearing are logarithmic, not linear. It takes 10 times the power to double the perceived volume. So, a 100 watt amp will sound twice as loud as a 10 watt amp (all things being equal). So, actually there isn't signifcant volume difference between 50 and 100 watts (all things being equal). So, changing your resistance will help a little. The best thing to do is increase the resistance (higher ohms0 to reduce the volume.

In fact, running into 4 ohms will be louder, all things being equal, than running into 8ohms. 4 ohms is less resistance, which means more signal going to the speakers. Think of it like a faucet (only the numbers work in reverse). The lower the resistance/ohms, the more open the valve it, allowing more water to run through the line. Increase the resistance by closing the valve, to reduce the flow.

So, if you want to reduce the volume, increase the resistance. An attenuator, which can knock a lot of decibels off is a good way to go. yes, it affects tone, but that is why the knobs on the amp actually move. Change your settings to adjust for the perceived tone shifts due to volume change.

 

[factorevif]

Thanks for the help guys!