Ohms question for you guys..

[metalmaniac93]

I know.... its been discussed to death.

Ive always used a 4x12, but now I am getting a Randall RD110 to go with my RD45 head just for band practice

Is the rule of thumb this.. Match the ohms on cab with head ??

if the cab has 4.. then set it to 4 on the head? if 8, set to 8 on head and etc ?

The 110 cab is rated at 30 watts.. If my head is 45watts, then I will only have a total output of 30 watts ?
That's is more that needed for practice, I've jammed with 22 watts and it was easily loud enough..

Any help would be appreciated guys !

You are correct all everything you said. That is the general rule of thumb.

 

[rupe]

I know.... its been discussed to death.

Ive always used a 4x12, but now I am getting a Randall RD110 to go with my RD45 head just for band practice

Is the rule of thumb this.. Match the ohms on cab with head ??

if the cab has 4.. then set it to 4 on the head? if 8, set to 8 on head and etc ?

The 110 cab is rated at 30 watts.. If my head is 45watts, then I will only have a total output of 30 watts ?
That's is more that needed for practice, I've jammed with 22 watts and it was easily loud enough..

Any help would be appreciated guys !

You are correct all everything you said. That is the general rule of thumb.

Not quite. As long as you are only using one cab then yes, you should match the ohms on your speaker output to the cab. If you mismatch, you should always do so with the cab having the higher resistance...unless your amp was built for it, never use a cab with a lower ohm rating than your amp is set at.

As for the 30 watt cab, no, it doesn't mean that is what your output is limited to...it means that's what the speaker can handle. If you run your amp wide open into that cab, you'll blow your speaker. Ideally, you want a cab rated for approx twice your amp's output although it ultimately depends on the speakers, amp, and how high you turn up your volume.

 

[metalmaniac93]

Thanks guys. I just found this from Mesa..

And thanks for the tip on the speaker thing. That's kind of what I was thinking but no the part of running the amp full out and blowing the cab

Usually, I will run the amp at 5 for practice.. which is way loud enough anyway, so that should be fine for the speaker I guess since its not full out?

I do not run any of my cabs via a mismatched load even using the safe mismatch range of the cab being higher than the amp. Just do not want to take any chances with my amps. Plus this is for MESA amps and not all amps are alike in this respect so you might want to contact Randall on this issue.

 

[rupe]

The chart is from Mesa but it's a safe mismatch for whatever you have when done that way.
If you run your amp on 5, you should be ok for the most part, but there's always a chance of a power spike of sorts depending on how hard you play. If it were me, I would worry about it, but just know that there's a possibility of an issue.

 

[blackba]

I would add another 30Watt cab, so your total cab power would be 60Watt. Than it would be less likely for your 45Watt head to blow the speakers.

I like to have my speakers rated for at least 20% more than my amp can put out, to give some margin. A 45Watt tube amp can put out in excess of 45Watts in most cases, hence a 60Watt cab (or two 30Watt cabs) is what I would recommend.