When you bridge an amp it effectively sees the speaker's load impedance as half of what it is, and accordingly demands twice the current draw. So for example when driving a 4 ohm speaker with a bridged amp, the amp sees it as a 2 ohm load and has to deliver twice the current as it would with a 4 ohm speaker being driven in stereo mode. This results in many amps performing at a lower level when operating in bridged mode, but you do gain a significant amount of power and headroom so there are typically trade-offs. A lot depends on how well the amp's power supply is built, and whether the amp is truly optimized for bridged operation or if it's just implemented as a selling feature without regard to potential compromises. Luxman for example puts a lot of thought into their design and flexibility to run in bridged mode without compromise of sonic quality, but it still cannot drive as low an impedance load in bridged mode as it can in stereo mode. Hope this helps!
Like I previously stated there are trade-offs involved, and ultimately power limitations have to do with power supply design/regulation as well as current capacity of the output devices. As you pointed out with the Esoteric amp running in bridged mode you get 4 times the power output compared to stereo mode, but it isn't rated to handle that into a load below 8 ohms since then maximum current will be the limiting factor. You are clearly more limited in speaker choices when running a bridged amp, but some amps like Luxman and Accuphase can still handle an impedance of 4 ohms or even lower when bridged. Alternately you can design a non-bridged amplifier which will have different capacities, likely not as much power but with more current headroom to handle the requirements (additional current draw) of lower impedance speakers. There is not one way which is universally best, it comes down to specific system matching to optimize an amplifier's ability to most effectively drive a particular speaker. You can't always predict it by the specs either although they can provide some insight into potential mismatches. Some don't care for the sound of bridged amplifier designs, but I've found that it really depends on the specific implementation of a particular design and proper load matching.
High current capacity can be indicated by amps that "double down", which means doubling their output power each time the load impedance is halved as you go down into 4, 2, or even 1 ohm loads. There are quite a few that double into 4 ohms, but fewer that can do it again into 2 or 1 ohms. If you're looking at higher power amps then the max power into really low impedances (like 2 or 1 ohm loads) can limit out due to available power of the incoming AC which may be either a 15A or 20A circuit. Amps like most Luxman and Accuphase are rated down to 1 ohms (in unbridged mode) but they get pretty expensive, and not all speakers require such power reserves and low impedance drive capacities so they can be considered overkill. Any amp is going to sound better when running well within its power ratings and not near its rated capacity. Another thing to keep in mind is that we're talking about solid state amps without output transformers here. Tube amps generally use output transformers (other than OTLs) and some solid state amps do as well like McIntosh, which will not increase power output into lower impedance loads.
I'm a pretty big guy but getting older and can relate regarding the weight of the M-900u... I had to use a dolly to move the amp which arrived strapped to a pallet, and then had to get help to unpack and move it into place on my rack. :lol: I'm sure you'll enjoy it, be sure to let us know how it goes!
opcorn:
