bridging an amp

The only benefit is to quadruple output power (49% louder).  Not every amp can be bridged (some are already bridged), but assuming you can, the main problem would be power supply that has to deliver 2x power (it has to be designed for that). Read amp’s user guide. If they don’t mention bridging - don’t do it. In addition output stage has to deliver 2x current. Your 4 ohm speaker will draw as much current as 2 ohm speaker would without bridging. My 6 ohm speakers have benign impedance dip to about 3.6 ohm, but bridged amp would have to be able to deliver current equivalent to driving 1.8 ohm and many amps would have problem with it. Amplifier’s output impedance doubles (two outputs in series). For some amps that have very low output impedance, like class D, it won’t make much difference, but for others it might affect the sound. In addition you need to invert phase of one channel. My amp, designed for bridging, has switch for that. You also need additional amplifier, to play stereo (2x cost). You could use this money to get better, more efficient speakers or better amp. That’s like additional loss of quality. I would consider getting 3dB more efficient speakers. It would give you equivalent of 2x power (22% louder). It won’t be as much as 4x power (49% louder), but it might be enough. Also, bridging amp likely won’t fully quadruple power.

g_nakamoto
what are the pros and cons of bridging an amplifier?

Bridging amp raises the wattage quite a bit, but that’s where the advantages end.

1: Distortion goes up,
2: Output impedance is higher (damping factor lower), which means bass is not as controlled.
3: The ability to drive below low impedance’s takes a hit.
4: The amp becomes more unstable..

The only thing you gain is more wattage into easy loads, your far better off getting the right amp to start with, otherwise you could end up with a powerfull P.A. amp. 

Cheers George

my son has a mcintosh mc7300 and mc2002 that he want's to bridge. is that ok with these amplifiers?

Tell him if he wants more watts, to sell them, and get the correct amps with the wattage he wants in a normal stereo amp/s. And to forget about bridging!

Cheers George