ok so maybe *I* worded it wrong, either way this is from my MECP installer at work (Circuit City, Saginaw, MI)
"I hear a lot of people saying that in bridged configuration, the amp channels are "sharing the load". Wouldn't sharing the load make the load lighter for each channel, in effect making the amp "see" a higher impedance? Answer: Yes. That'* what "sharing the load" is. If you have one truck, producing 100 horsepower, towing a load that takes EXACTLY 100 horsepower to keep it moving, and you add an additional IDENTICAL truck to SHARE that load, the trucks each only have to produce 50HP, right? Do half the work, each, right? Answer: Again, yes. THAT is "sharing the load". An amplifier doing half the work would be equivalent to loading it with half the load, or twice the impedance, i.e. 8 ohms, vs. 4 ohms.
What actually happens when bridging an amplifier, is you are now putting TWICE THE VOLTAGE across the load, which will cause the load to pull more current, twice the current, to be exact. This makes the amp produce 4 times the power of a stereo load. The additional CURRENT demand (2X the stereo current demand) is why the amplifier "sees" twice the load, i.e. half the stereo impedance.
The load does not change, people are exactly correct in saying this. If you have (2) 4 ohm voice coils in parallel, that is a 2 ohm load - period. The amp is still loaded with 2 ohms whatever the configuration. ELECTRICALLY, due to the reasons described above, it "sees" a lower impedance across the terminals."
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