100 watt amp, 40 and 60 watt cabs

[Phil M]

I have a 100 watt MV head. When I run two 8 ohm 2x12 cabs with it, I plug both cabs into the back of the head and switch the head to 4 ohms. This is per advice here and from the manufacturer.

I used to run a 120 watt cab and a 60 watt cab. My understanding is that it's safe to do this with a 100 watt head because each cab is getting half the power.

But, what about a 40 watt 2x12 G12M Greenback cab plus a 60 watt cab? There's a bit of wattage mismatch with the 40 watt cab. It is probably worth noting that with this particular head (Splawn) it's hard to get the master above 9:00-10:00 even live with drums.

[GCDEF]

Obviously, you'd be potentially running 50 watts ore more into your 40 watt cab. I wouldn't do it.

[Phil M]

That's kind of what I thought too (seems obvious, LOL!). Maybe I'll stick with the 30 watt Budda head when using that cab.

What if I mixed up the speakers with the ones in my other cab (V30 and G12H30)? All are 16 ohms, so what if I did:

20 watt G12M + 30 watt G12H30 = ________ watts and an 8 ohm output

20 watt G12M + 60 watt V30 = _______ watts and an 8 ohm output

Can someone fill in the blanks?

[FrankieSixxxgun]

Just because you have 100 watts and two cabinets does not mean that you're splitting wattage evenly 50/50. Efficiency of the speaker, impedance of each speaker, etc... come into play. You'll probably be okay with the 40 watt cab if you don't crank up to 10. Otherwise it might blow.

[Phil M]

Thanks Frankie. I checked out that page, love that band! Got more stuff?

Can anyone help me with the "fill in the blanks" above?

[Phil M]

If I took one 20 watt G12M Greenback out, and put in a 60 watt V30, what would the wattage capability of the cab be?

16 ohm G12M + 16 ohm V30, wired for 8 ohms at the cab = how many watts?

I like the way this cab sounds with my 30 watt Budda, I'm just trying to find a way to use it with my Splawn too (as one of two cabs).

[rockon1]

Originally Posted by Phil M

If I took one 20 watt G12M Greenback out, and put in a 60 watt V30, what would the wattage capability of the cab be?

16 ohm G12M + 16 ohm V30, wired for 8 ohms at the cab = how many watts?

I like the way this cab sounds with my 30 watt Budda, I'm just trying to find a way to use it with my Splawn too (as one of two cabs).

40 watts or twice the lowest wattage speaker. Bob

[rockon1]

Originally Posted by FrankieSixxxgun

Just because you have 100 watts and two cabinets does not mean that you're splitting wattage evenly 50/50. Efficiency of the speaker, impedance of each speaker, etc... come into play. You'll probably be okay with the 40 watt cab if you don't crank up to 10. Otherwise it might blow.

Speaker efficiency doesnt come into play. If both cabs are the same impedance the power will be divided equally. Bob

[Phil M]

Hey, Bob, thanks. Both posts were very helpful. I always wondered why my V30 + G12H30 cab was 60 watts and you've explained. That's also obviously why my two 20 watt G12M is 40 watts.

So putting in a V30 won't get me there and I still can't really use the Splawn with this cab. No worries. I've been digging this Budda more than the Splawn lately anyway and it's plenty loud for anywhere I'd play.

[rockon1]

There are instances where the power will be divided unequally. For example- An 8 ohm and 16 ohm wired in parallel. The 8 ohm will get 2/3's the power. The impedance will be 5.33 ohms.

In series with an 8 and 16 ohm speaker the 16 ohm will get 2/3's the power and the impedance will be 24 ohms however this impedance isnt very practical. HTH Bob

[Phil M]

I don't know about anyone else, but I've found these posts informative. Thanks, Bob.

Phil

[Hacksaw]

Originally Posted by Phil M

Hey, Bob, thanks. Both posts were very helpful. I always wondered why my V30 + G12H30 cab was 60 watts and you've explained. That's also obviously why my two 20 watt G12M is 40 watts.

So putting in a V30 won't get me there and I still can't really use the Splawn with this cab. No worries. I've been digging this Budda more than the Splawn lately anyway and it's plenty loud for anywhere I'd play.

Phil, You can put the splawn in half power mode. (dont forget to half your impedence) with a 60 watt cab fairly safe. are you really cranking the amp?

I know I used a 100 watt marshall cranked through 4x12 greenbacks, yea, blew a few.. over the years. LOL but if your not cranking it way up you can get away with it. at least I have.

[Phil M]

Originally Posted by Rik

Phil, You can put the splawn in half power mode. (dont forget to half your impedence) with a 60 watt cab fairly safe. are you really cranking the amp?

This is what I was driving at in the first post--even at band volumes I can't get the master above 9:00-10:00. In the past I have often run the QR on half power with an 60 watt Avatar cab with no problems.

Originally Posted by Rik

I know I used a 100 watt marshall cranked through 4x12 greenbacks, yea, blew a few.. over the years. LOL but if your not cranking it way up you can get away with it. at least I have.

I am more concerned with the 40 watt greenback cab even though I'm not really cranking the master up. I will just keep the Splawn away from that one unless I'm at half power and bedroom volumes.

[GCDEF]

Originally Posted by FrankieSixxxgun

Just because you have 100 watts and two cabinets does not mean that you're splitting wattage evenly 50/50. Efficiency of the speaker, impedance of each speaker, etc... come into play. You'll probably be okay with the 40 watt cab if you don't crank up to 10. Otherwise it might blow.

Impedance determines how the power is split. Nothing else.

Also, you can't know for sure how much power you're putting out by the position of your master volume. Making any assumptions that just because your master is on 5 or whatever that you're only outputting a certain amount of power is foolhardy.