Benchmark AHB2 Amplifier

The Alon IV and the bit later V are among the best sounding dynamic speakers--based on repeated dealer auditions--I never owned. Of roughly the same vintage, the Aerial 10T is another one I found to sound great at dealers but never owned. I was never so taken with later models from Alon/Nola or Aerial.

If you have not already, experiment with tri-wiring the Alons with the Benchmark AHB2 amps in mono bridged mode. You might get yet-better sound.

In the years since its introduction, some, while acknowledging its matchless specs in terms of low noise and distortion combined with remarkable power output given its small and light form factor, have criticized the Benchmark AHB2's sonics by saying it is lacking in macro dynamic swings. I hear this, but I hear it differently and hear it as a plus for the Benchmark. The Benchmarks lack the overblown-sounding midbass of some other amps which can provide a sense of greater dynamic power. It also lacks the ultimate degree of "splash" on large transients which some interpret as a dynamic limitation. I think this "splash" is actually caused by a blast of slightly distorted sound in the higher frequencies. The Benchmark is ever precise, controlled, and clean, clean, clean, which amounts to "beautiful" sound in my book. Likewise, the Benchmark midbass is fully ample and certainly not lean in any way, just more controlled and defined/less distorted. This "uncovers" the Benchmark's lower bass, revealing more detail, definition, and power in the bottom two octaves.
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Click to expand...

One very useful tweak of the Benchmark AHB2 Amp sound, which I think can ameliorate any objections to its sonic presentation is the use of AV Room Service Electronic Vibration Protectors ('EVPs) in place of the amp's stock feet. Why this simple change has a more profound effect on the Benchmark's sonics in my system than on other electronics, I do not know, but there it is. I suggest trying this if you have any reservations about the sound of the Benchmark amp (in my case, a pair of them, run in bridged mono mode).

Remove the two stock rear feet using a #2 Phillips or Pozidriv screwdriver. Replace them with 2-inch square HD (High Density) EVPs. Place them in the rear corners just inboard of the black casing--at the rear corners of and on the silvery bottom plate, in other words. Then center a third 2-inch square HD EVP along the front edge of the silvery bottom plate, just inboard of the front panel. There is no need to remove the two front stock feet of the amp.

That's it. Now see what you think of the sound. Many aspects of the sonic presentation seem yet better in my system, including dynamic headroom and dynamic swings. This is despite the fact that I was already using separate Bright Star Audio Little Rock isolating platforms beneath each amp.

The amps actually seem to be yet more unlimited in their power reserves with this tweak. Using the amps without this tweak with the Watkins Generation 4 speakers (as opposed to the Graham LS8/1s) I was occasionally aware of a bit of high-frequency transient crunch at high SPLs. When I heard this, I would just turn down the volume a notch and this problem would vanish. At first I thought this was just due to dynamic limitations of these rather-small Watkins speakers. But with this tweak, this problem vanished and the speakers play as loud as I want on any material without any apparent "crunch." The apparent frequency response with the Watkins speakers further smooths out when supported by EVPs, the stage expands in all directions, images are yet more focused, the bass further extends and warms a bit.

Unfortunately, this tweak is not as inexpensive as it used to be. When I purchased my EVPs, they were only $40 each. Now they are $119 each. Still, for owners of one or two of these amps, I regard using the EVPs as capable of producing a significant sonic improvement.

Shawnf's question appears to me to be about how to bi-amp speakers with two Benchmark AHB2 amps. The Benchmark manual says:

"The 1&2 OUT NL4 jack can also be used for biamp applications. Use this jack with a four-pole cable to connect both output channels to the high and low drivers in a biamped 2-way speaker. "

Make sure that the SpeakOn connectors you have are the NL4 four-pole variety rather than the NL2. Then the speaker cable you use can be one which is capable of internally providing bi-wired or bi-amped connections. The Canare 4S-11 Benchmark used for its speaker cables is one such cable. While the Benchmark cable page only lists speaker cables with NL4 to NL4 connections, I'm sure Benchmark could provide you with cables terminated with an NL4 SpeakOn at the amp end and two sets of locking bananas at the other end. These cables could then be used for bi-amp or bi-wire connections.

Alternatively, you could use both the SpeakOn and binding post connections of each of two Benchmark amps to bi-amp your speakers.

Kal may well be correct that neither bi-amp nor bridged operation of the Benchmark amps is "necessary" for your speakers. In my experience with these amps, however, bridged operation usually sounds better in that it provides more headroom with at least equally excellent specs and sonics. That greater headroom translates to yet cleaner, more dynamically alive sound at louder SPLs. Of course, if you listen at SPLs which rarely exceed 80 dB or so and don't listen to much orchestral/choral power music, electronic music, or hard rock, you won't need the extra power with any reasonably sensitive speakers.

I have never tried bi-amping with my two Benchmark AHB2's.