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SEAS, a well-known manufacturer of high-quality loudspeakers, selected the Benchmark AHB2 as a key component for use in testing loudspeakers. They created an innovative test system that measures loudspeaker motor strength and moving mass with higher accuracy than previous methods. This new measurement system was documented in the December 2017 Journal of the Audio Engineering Society.
According to the AES paper, the SEAS team selected the Benchmark AHB2 for the following reasons:
"A Benchmark AHB2 amplifier is used, which has excellent signal-to-noise ratio and bandwidth, low output impedance, and is suitable for laboratory use (with advanced overload protection)."
In late 2016, SEAS contacted Benchmark about the possibility of using the AHB2 power amplifier in a laboratory environment. They needed an amplifier with exceptionally wide bandwidth, low noise, low output impedance, low distortion, and bulletproof overload protection.
The AHB2 offers a solution that is more than 15 dB quieter than other top-quality high-end amplifiers. Distortion is virtually non-existent, even when heavily loaded with low impedances. The -3 dB bandwidth extends from 0.1 Hz to 200 kHz with an exceptionally flat response. The extended bandwidth provides the precise phase response that their application requires. Last but not least, the FPGA-based protection system in the AHB2 provides the robust protection necessary in a laboratory environment.
One independent test lab had this to say about the AHB2:
"I measured less distortion and noise in the AHB2 than in any other of the many power amps I've measured over the years.”
-Bascom King, BHK Labs
The protection system monitors:
The protection system controls the following:
The audio path in the AHB2 is an entirely linear design. It uses a parallel structure that includes a class-AB amplifier and a class-A feed-forward correction amplifier. The class-AB amplifier operates inside of class-H tracking rails that are also fully linear. The tracking rails provide efficiency that approaches that of a class-D amplifier while entirely avoiding the noise and distortion produced by class-D designs.
The important difference between the AHB2 and class-D amplifiers is that the AHB2 does not produce switching noise. Class-D amplifiers are measured with brick-wall AES17 filters that ignore the switching noise above 20 kHz or 40 kHz. Tweeters can demodulate this ultrasonic noise and fold it into the audible band.
Class-D amplifier switching noise can create problems in a loudspeaker measurement system. More importantly, this ultrasonic noise may become audible when it is demodulated by the non-linearities that occur in all loudspeakers. This potential source of distortion may detract from our musical enjoyment. Class-D amplifiers are compact and cheap, but are not necessarily a good choice for a high-end Hi-Fi system.
Class-D amplifiers are not as clean as some specifications seem to imply. It is important to understand that AES17 distortion and SNR measurements use a brick-wall filter (shown at left) to ignore the noise produced by class-D amplifiers. This noise may make class-D amplifiers unsuitable for some measurement systems.
The AHB2 was designed to outperform all competing power amplifiers in terms of noise and distortion. It achieves these design goals and sets benchmarks in these key performance parameters. The result is an amplifier with unrivaled transparency.
Our goal was to create the ultimate amplifier for the enjoyment of music. It is nice to know that the AHB2 is also being used to test new and improved loudspeakers!
"An Added-Mass Measurement Technique for Transducer Parameter Estimation", Jeff Candy and Claus Futtrup, Journal of the Audio Engineering Society Vol. 65, No. 12, December 2017 (C 2017) DOI: https://doi.org/10.17743/jaes.2017.0040
"The AHB2 - A Radical Approach to Audio Power Amplification", John Siau, Benchmark Application Notes: https://benchmarkmedia.com/blogs/application_notes/14680625-the-ahb2-a-radical-approach-to-audio-power-amplification
"Optional Filters S-AES17 Low Pass Filter", Audio Precision: http://www.audiotech.com.tw/AES17%20Filter.htm
If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:
Use Benchmark's online audio calculators to find answers!
For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.
This application note provides interactive examples that help to answer the questions listed above.
We have added an "Audio Calculators" section to our webpage. Click "Calculators" on the top menu to see more like these:
Secrets contributor Sumit Chawla recently caught up with Benchmark’s VP and Chief Designer, John Siau to get a little more in-depth on several subjects.
Q: "Benchmark is one of the few companies that publishes an extensive set of measurements, but you also balance that with subjective testing. Can you talk about the equipment, the listening room, and the process for subjective testing?"
Q: "Was there ever a time where you learned something from a subjective test that was not captured by measurements?"
Q: "You conducted some listening tests to determine whether distortion in the “First Watt” was audible. What test material did you use for this, and what did you find?"
Q: "The AHB2 amplifier incorporates THX Audio Achromatic Amplifier technology. When and how did the partnership with THX come about?"
Q: "Linear power supplies have been and remain quite popular in high-end devices. You favor switch-mode power supplies. When and why did you make this switch?"
... and more!
