Running Benchmark AHB2 in bridged mode and 4 Ohm Speaker

@geek101 

Now I just have to decide if I need to buy two amps or just live with one. Does bridging bump up the 18A per channel limit or keep it the same. Non bridged amp can send 18A per channel so I am guessing bridged version can put more than 18A to a single channel. How do I calculate this number?.

The output current is not increased in bridging, it stays the same, only the voltage doubles so the power quadruples. The amp now thinks its driving  half the resistance so a 4 ohm speaker looks like 2 ohms. 2 ohms x 18 amps will voltage clip at 39 volts and thats peak not RMS. This is now lower than you would clip had you NOT bridged the amplifier.   :(   An amplifier of this power would likely have about 60 volt rails and would provide those 60 volts to the point where 18 amps became the limit at around 3 ohms.

 Now you are paying more to get less. Seems no one has yet to point out this little problem. I expect some disagreemet with this calculation so lets chat about it.

I read the specs, the amp is not rated to drive a 4 ohm load bridged let alone when the 4 ohms dips. 

With 18 amps of current be happy. The amp is rated down to 3 ohms and will happily drive 2 ohms, but don't bridge it. If you want two amps then use them as bi amps. At least you have a chance of some sonic advantage. If you are smart, filter the inputs so the woofer channel doesnt see the highs and the tweeter channel doesnt see the lows. Just a simple RC at the input.

Hitting a few more posts lightly.

They promote bridging so they can sell you two amplifiers obviously. 

Why do we need all this power?

They promote bridging so they can sell you two amplifiers obviously.

geek101 OP seeing I gave many other cons and hardly any pros, glad someone else said this, I held off that one, good one Roger now I don’t have to bring it up.

Cheers George

According to Benchmark the amp in bridged mono  the maximum unclipped output voltage is 45.5 Vrms (64.4V peak) into a 4 Ohm load. 

georgehifi, my question was in the form of yes/no.  I can only interpret your non-response as "no, I have no direct experience with the amps in bridged mode".  This dosen't mean that your speculations are not correct.

According to Benchmark the amp in bridged mono the maximum unclipped output voltage is 45.5 Vrms (64.4V peak) into a 4 Ohm load.

I would expect it to be higher. If the rails are 60 volts then the peak volts should approach 120, say 100 Volts with losses,  but the current won't support that as 25 amps are needed. BTW 18 amps is not an impressive amount of current for modern amp of that size. Should be more like 40 amps. The Mitsubishi Docking Amp of 1978 delivered 60 amps, I measured it!

Something is a little off here and the more I here the more I wouldnt want to bridge this amplifier. I have nothing against bridging in general and have made bridged amps.

The reason we bridge amplifiers is when WE DO NOT have a low impedance load. We bridge to get voltage not current. We bridge to get some juice into 8 ohms. When we have 4 ohms we dont bridge. 

Where are the italics around here? All caps is my best substitute. :)