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by John Siau January 26, 2018 4 min read
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 (link in references).
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
by Benchmark Media Systems June 06, 2023 2 min read
At the 2023 AXPONA show in Chicago, I had the opportunity to see and hear the Hill Plasmatronics tweeter. I also had the great pleasure of meeting Dr. Alan Hill, the physicist who invented this unique device.
The plasma driver has no moving parts and no diaphragm. Sound is emitted directly from the thermal expansion and contraction of an electrically sustained plasma. The plasma is generated within a stream of helium gas. In the demonstration, there was a large helium tank on the floor with a sufficient supply for several hours of listening.
by John Siau June 02, 2023 2 min read
I asked ChatGPT to review the Benchmark AHB2, and I was shocked at the results!
It turns out that ChatGPT wrote a review by gleaning information from the many publicly available reviews of the AHB2. I recognized phases and sequences of words that had appeared in prior reviews, and yet the text was new, original, and well written. The ChatGPT review seemed to summarize the collective impressions of the reviewers without directly quoting any particular reviewer.
It should be possible to ask ChatGPT to write a review on any well-known product and the result will be an AI-generated review that reflects the collective opinions of many human reviewers.
These AI-generated reviews may be more useful than traditional search results!
If I am not mistaken, ChatGPT seems to have golden ears!
Here is my dialog with ChatGPT:
John Siau:
Write a review of the Benchmark AHB2 complete with listening impressions.
ChatGPT:
Title: Unleashing Sonic Purity: A Review of the Benchmark AHB2 Amplifier
Introduction: The Benchmark AHB2 amplifier has gained a reputation for its exceptional audio performance and unwavering dedication to sonic purity. In this review, we delve into the heart of this powerhouse amplifier, exploring its features, design, and most importantly, the listening impressions it evokes...
by Benchmark Media Systems May 30, 2023 7 min read
Today, Benchmark's John Siau and OpenAI's ChatGPT had a conversation about star-quad cables. It turns out that ChatGPT got quite a few things wrong, but learned quickly when these errors were pointed out by John Siau.
ChatGPT is quick to recognize mistakes, and quick to provide detailed corrections. In each of the first few corrections, additional errors were made. As each of these were pointed out, ChatGPT began to provide accurate information.
Here is my conversation with ChatGPT:
John Siau:
How do star-quad cables reject interference?
ChatGPT:
Star-quad cables are designed to provide improved rejection of ...