A bit of blurb I found on another forum in relation to solid state amps:
Most solid state power amps and a small amount of amp heads are “stereo” containing 2 separate power amp sections. This allows you to connect more cabinets to the amp, and of course gives you more wattage. Most of these stereo amps can be run in “bridged mode”. This connects the two amplifiers together and requires you to hit a switch when the amp is off, and to hook up your speaker cable differently, (usually by connecting a banana jack to the positive terminal of both 5 way output jacks on the back of the amp. When running in bridged mode each amp “sees” ½ of the total impedance of the cabinets connected to it. Therefore, an amp rated at 4 ohms minimum per side that will put out 300 watts into 4 ohms per side can only be safely bridged into an 8 ohm load, and will put out 600 watts into the 8 ohm cabinet. Most amplifiers only safely power a minimum of 4 ohm loads, however, more and more amplifiers have been produced that handle 2 ohm minimum loads, which is good news for us, as we can run a good number of cabinets in different combinations. As a last point, you may have noticed that the ratings for our “typical amplifier didn’t double each time the impedance of the load was cut in half. Why not? Well, in a perfect world, an amplifier that put out 200 watts into 8 ohms would put out 400 watts into 4 ohms and 800 watts into 2 ohms. In the real world, other consideration, (such as thermal limits), limit the actual number of watts an amplifier will safely produce at a given impedance.
OK, so, this pretty much explains my current situation - I run an Ampeg SVT-4 PRO, which has the following output power ratings:
1600 Watts Mono-Bridged @ 4 Ohms (1200 Watts Continuous)
1200 Watts Mono-Bridged @ 8 Ohms (900 Watts Continuous)
2 x 900 Watts @ 2 Ohms (600 Watts Continuous)
2 x 625 Watts @ 4 Ohms (490 Watts Continuous)
2 x 350 Watts @ 8 Ohms (300 Watts Continuous)
I currently run it in to a single Ampeg 8x10 running @ 4ohms through the single mono-bridged output, whice gives me the maximum output I can get with the amp, which is great.
However, I'm looking at "downgrading" and getting two new cabs to replace the single 8x10 and its too damn heavy.
Looking at getting a 4x10 @ 4ohms (EDEN D410XST) and a 1x18 at 8ohms (EDEN D118XL). I'll be running them in stereo mode in order to take advantage of my crossover control.
Am I right in my calculations here:
Total cab impedance: (4/2)+(8/2) = 6ohms
Total "visible" impedance to the amp in stereo mode: 6/2 = 3ohms
So the mimimum load on the head would be 3ohms, which puts me between 625W and 900W output per side?
The EDEN D118XL is 500W output, and the EDEN D410XST is 1000W output. Does this mean that the D118XL will be overloaded? Or will the wattage be added together too? I don't know how this bit works - I'm afraid one of the bi-amps will blow the D118XL?