Many Benchmark customers are using their AHB2 power amplifiers with REL subwoofers. This application note shows how to connect one or two AHB2 amplifiers to one or two REL subwoofers using the speaker outputs on the back of the AHB2 amplifiers.
The MODE switch in the lower right-hand corner sets the AHB2 to stereo or mono mode. In stereo mode, the outputs of the AHB2 are conventional unbalanced outputs. In mono mode, the output of the ABH2 is balanced.
The two red binding posts (1+ and 2+) on the AHB2 are driven by the amplifier outputs. The black terminals (1- and 2-) are the ground returns for each of the two channels. We will use one of these speaker ground returns as a connection point for the REL ground wire. Notice that the SpeakON connectors provide access to the same set of outputs. In stereo mode, the left speaker is connected between 1+ and 1- using the binding posts or the SpeakON connectors. The right speaker is connected between 2+ and 2-.
Notice that the 1+ post is labeled M+ and the 2+ post is labeled M-. These are the outputs for mono operation. The speaker is connected between M+ and M- using either the binding posts or the SpeakON connectors. In mono mode, M- is an inverted version of M+.
REL supplies a cable with yellow, red and black wires that connect to the speaker output terminals on a power amplifier. The SpeakON connector plugs into the back of the REL subwoofer. The yellow and red wires deliver speaker-level inputs to the REL, but draw no power from the amplifier. The black wire is a signal ground reference for the speaker inputs. The yellow and red inputs are summed together in the REL. This summing allows the input of a left and right channel which will be summed to a single subwoofer. The yellow, red and black spade terminals will need to be connected to the binding posts on the back of the AHB2 power amplifier. We recommend connecting your speakers to the SpeakON connectors on the back of the AHB2 while reserving the binding posts for the REL cable.
Please read these instructions carefully because the yellow, red and black connection assignments will vary according to one of the following system configurations:
Caution: Never connect the REL BLACK wire to a RED binding post on the AHB2. This will short the output of the AHB2 ground and put it into protection mode. It could also damage the REL subwoofer.
Adjust the level of the REL subwoofer by turning the control on the back of the unit.
At Benchmark, listening is the final exam that determines if a design passes from engineering to production. When all of the measurements show that a product is working flawlessly, we spend time listening for issues that may not have shown up on the test station. If we hear something, we go back and figure out how to measure what we heard. We then add this test to our arsenal of measurements.
Benchmark's listening room is equipped with a variety of signal sources, amplifiers and loudspeakers, including the selection of nearfield monitors shown in the photo. It is also equipped with ABX switch boxes that can be used to switch sources while the music is playing.
Benchmark's lab is equipped with Audio Precision test stations that include the top-of-the-line APx555 and the older AP2722 and AP2522. We don't just use these test stations for R&D - every product must pass a full set of tests on one of our Audio Precision test stations before it ships from our factory in Syracuse, NY.
Paul Seydor of The Absolute Sound interviews John Siau, VP and chief designer at Benchmark Media Systems. The interview accompanies Paul's review of the LA4 in the December, 2020 issue of TAS.
"At Benchmark, listening is the final exam that determines if a design passes from engineering to production. But since listening tests are never perfect, it’s essential we develop measurements for each artifact we identify in a listening test. An APx555 test set has far more resolution than human hearing, but it has no intelligence. We have to tell it exactly what to measure and how to measure it. When we hear something we cannot measure, we are not doing the right measurements. If we just listen, redesign, then repeat, we may arrive at a solution that just masks the artifact with another less-objectionable artifact. But if we focus on eliminating every artifact that we can measure, we can quickly converge on a solution that approaches sonic transparency. If we can measure an artifact, we don't try to determine if it’s low enough to be inaudible, we simply try to eliminate it."
- John Siau
Myth - "Damping Factor Isn't Much of a Factor"
Myth - "A Damping Factor of 10 is High Enough"
Myth - "All Amplifiers Have a High-Enough Damping Factor"
These myths seem to trace back to a well-know paper written by Dick Pierce. His analysis shows that a damping factor of 10 is virtually indistinguishable from a damping factor of 10,000 when it comes to damping the motion of a loudspeaker cone. This analysis has been examined and repeated in many more recent articles, such as a well-written post on Audiofrog.com by Andy Wehmeyer. Articles such as these are often cited as evidence that amplifier damping factor doesn't matter. The mathematical analyses are correct, but the conclusions are incomplete and misleading!