I am curious about the output power curve for impedance loads between 2-4ohms. The data sheet provides a spec for each amp configuration at 2ohms and at 4ohms, but I am curious about what happens for Bridge, and I-share modes between 2-4ohms. Where is the point where I-share becomes more efficient than Bridge? Are the power curves symmetrical? Do you have any guidelines for choosing the mode for loads in this range? A triple-stack MA12EX wired in parallel produces a load around 2.5ohms. Is this best handled by the I-share mode?
This is a great question. I hope that over time we will develop and post some app notes around this topic to create clear guidelines.
For now I would say it this way:
A good conservative answer is that if you need 500W or greater (and for the three MA12EX's you probably want around 900W of amplifier rated power), you should use i-share below 4 Ohms and v-bridge for loads above 4 Ohms.
At the nominal 2.7 Ohms of three MA12EX's in parallel you will get about 940W out in i-share mode, definitely more than with a single mono channel or with a bridged pair. So we definitely recommend i-share mode for maximum power for that case.
So to summarize:
Recommended: 2 to 4 Ohms: i-share >4 Ohms: v-bridge
The question is actually more complex than what I just said above between three and four Ohms, mainly because we build some margin into our power specification for driving highly resonant loads like bass boxes. Most amplifier manufacturers allow some margin in their specifications for this, the amount varies from manufacturer to manufacturer. So the point where bridging delivers more power than i-share is actually someplace between 3 and 4 Ohms, depending on how much inductance is in your load.
If you measure the power into a purely resistive load, then the crossover point where v-bridge delivers more power than i-bridge is around 3 Ohms:
In that case we could say this:
2 to 3 Ohms: i-share 3-4 Ohms: i-share (recommended) or possibly v-bridge in cases where the load is not too inductive, like mid or high-f drivers >4 Ohms: v-bridge
I hope that helps. I'm not sure I answered your question about the curves being symmetrical, maybe you can explain more to help me understand what you mean by that if you still have questions.
Bill, Thank you. That is good information. I was already wondering about the various types of loads and the fact that the impedance curve of some loudspeakers varies dramatically across the frequency spectrum. These are good guidelines for now. Thanks.