Running Benchmark AHB2 in bridged mode and 4 Ohm Speaker

George I agree with you that with efficient low impedance speakers the OP may likely be better off with a single AHB2.

However it’s worth noting that unlike most power amps, the Benchmark AHB2 does not have increasing distortion into lower impedance loads. The bridged AHB2’s distortion is just as low as in stereo mode - the THX AAA circuit takes care of that - the quoted THD+N spec is the same for stereo/mono "at full rated output into any rated load". This has been corroborated by independent measurements. Note that Benchmark only provides power ratings for nominal 8 and 6 ohm loads in bridged mono.

In my case the bridged AHB2 amps do sound better than a single AHB2, but my ATC speakers are very different from the OP. The ATC’s are inefficient with high power handling (ATC recommends 75-300W) and have a nominal 8ohm rating with a minimum of 5.6ohms - pretty much the ideal application for the bridged AHB2.
Using the amps in mono mode also allows for much shorter speaker cables, which may also have contributed to my positive impressions vs a single stereo AHB2.

Having said the above, Benchmark have demoed with bridged AHB2’s on several occasions with nominal 4ohm rated speakers. So clearly they don’t see any issue. Here is a recent positive impression: 
https://parttimeaudiophile.com/2018/05/21/axpona-2018-benchmark-stays-smooth-with-martin-logan/

In my case the bridged AHB2 amps do sound better than a single AHB2, but my ATC speakers are very different from the OP.

Yes because your speakers need the extra watts, the OP’s don’t, and that’s what the discussion is all about.

I would lay money on it, that if your speakers didn’t need those extra watts, you’d be saying one stereo sounds better that two bridged, regardless of the cost saving.

Roger Modjeski (Ramtubes) a few posts back has also tried to say similar.


Cheers George

I would lay money on it, that if your speakers didn’t need those extra watts, you’d be saying one stereo sounds better that two bridged, regardless of the cost saving.

Perhaps.
But you did say that "distortion goes up" with bridged amps - however this is not the case with the AHB2 in bridged mono, nor into lower impedances in stereo mode for that matter. So in that respect it is a bit different to most conventional power amps.

You believe what you want, and I'll believe what I know for the OP's speakers, and that's what this thread is all about.

In general Bridged Amps
Pros=
More watts.

Cons=
Worse damping factor
Higher output impedance (has relevance to damping factor)
Lower stability (especially into low impedance's)
Current ability is reduced  (especially into low impedance's)
Higher distortion.

Cheers George 
 
 

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.

The manual states:
Output voltage: >80Vpp into any load
Output current: 29A peak into 1 ohm, both channels driven

 BTW 18 amps is not an impressive amount of current for modern amp of that size. Should be more like 40 amps. 

I presume you mean current compared to power output not physical size?
The AHB2 is very small and lightweight. IMO the power/current output  - not to mention almost non-existent distortion, super high SNR, efficiency, cool running and (most importantly) resulting purity of sound - are very impressive.
Other than bragging rights, I doubt 40A of current has any advantage in driving practical loudspeaker loads.