Q:

Query - Running two ampeg 8ohm cabs with different Wattages

Now I've tried to get my head around ohms etc and I thiiiiiiink i understand but I want to double check because I'm feeling pretty thick today and getting in a muddle.
I have a markbass TTE500. It's 500W at 4ohms/ 300W at 8ohms. I am borrowing an ampeg 4x10 SVT which is 500W at 8ohms for my upcoming tour. I would like to add an ampeg B-115E to this which is 200W at 8ohms. Will I be able to safely drive these cabs with my amp to their potential? I'm wondering if the 1x15 might be driven too hard. 
Any wisdom or suggestions appreciated!

A:

Looks like the safest assumption (since I can't find details on the Markbass site or the manual) is that the two speakON outputs on the TTE500 are wired in parallel.
What that means is that when you plug a separate 8 Ohm cabinet into both of the TTE500 speakON outs, you are presenting a total 4 Ohm load to the amp. That means the amp's rated output will be 500 Watts, although it's not clear whether that's peak or RMS. It could be RMS.
Now your total dissipation (again, probably RMS) between the two cabinets is 700 Watts, which is good, but the problem is that the power will be essentially divided evenly between the two cabs. That means if you run the amp full out, each cab will be asked to dissipate 250 Watts (approximately) and that could overdrive the B-115E.
You could look for a 1x15 with higher power capacity, you could use only the 4x10 SVT, or you could hook it up the way you plan to and just keep the amp fairly quiet. If you need a rig to be reliable for a whole tour, I personally wouldn't risk it.

