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Weekly Newsletter for the Audio Industry and Audio Product Developers
Product Design | Audio Electronics | Acoustics | DIY | Audio Innovations
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How to Get Alexa-Enabled Devices AVS Certified | Getting AVS certified for your Alexa built-in integrations is no trivial task. Amazon expects OEMs to follow specific processes when building and testing their devices including Acoustics, Security, Music, Functional, and User Experience. David Berol, Director of the Authorized Test Labs for Alexa at Silicon Valley Pioneer Surfaceink, shares his insights on what you need to know about getting your Alexa-enable devices through AVS Certification process. Read More | |
Creative Technology Launches LE Audio Ready Wireless Headphones | Creative Technology released its all-new range of Creative Zen Hybrid Pro wireless headphones and their accompanying bundles, the Creative Zen Hybrid Pro Classic and Creative Zen Hybrid Pro SXFI. Equipped with nifty features such as Hybrid Active Noise Cancellation (ANC) and Ambient Mode, a powerful 40mm Neodymium driver, and an impressive battery life of up to 100 hours, these latest headphones are also Bluetooth LE Audio Ready, thanks to the latest Airoha LE Audio (Mediatek) platform. Read More | |
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New Peak Amplification Product Line Presented at CEDIA Expo 2023 | Elytone Electronic the Taiwan-based producer of high-quality, custom audio solutions and magnetic components, has launched a new line of high-power, high-performance amplification products under its new division, Peak Amplification. The new Flexible Line consists of a series of amplifier modules and separate power supplies to support a wide variety of configurations for different consumer electronic and residential integration product applications. Read More | |
Sonical Partners with IDUN audio for Embedded Dynamic Spatial Audio | Sonical, the Headphone 3.0 pioneer based in San Mateo, CA, and IDUN audio, the leading-edge startup from Copenhagen, Denmark, specializing in dynamic spatial audio for headphones, have formalized a strategic partnership. The two companies have been cooperating since 2022, and IDUN audio was part of the Sonical CES 2023 demos, with its dynamic spatial audio software running on Sonical's headphone operating system CosmOS - enabling unsurpassed spatialization with fast head tracking. Read More | |
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Apple Updates AirPods Pro (2nd generation) with USB-C and Upcoming Lossless Wireless Audio Protocol | As expected, on September 12, Apple announced the new iPhone 15 series models, which now all have USB-C connectors (but only use USB3). More importantly, Apple introduced new AirPods Pro (2nd generation) with USB-C charging capabilities and anticipated new audio experiences to all AirPods Pro models with iOS 17 updates. Between the lines there was an announcement about an upcoming "groundbreaking wireless audio protocol" supporting lossless audio. Read More | |
Audio Pioneer xMEMS Promotes Seminar Series: xMEMS Live – China 2023 | Semiconductor pioneer xMEMS Labs announced the launch of xMEMS Live – China 2023, a two-day seminar aimed at demonstrating the company's technology for Chinese consumer tech and audio brands through product demos, keynotes and in-depth tech-talk presentations. The seminars will take place September 18 at the Renaissance Caohejing Hotel in Shanghai, and on September 20 at the Westin Nanshan in Shenzhen. The seminars signal xMEMS' significant expansion throughout Asia, North America, and Europe. Read More | |
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Bang & Olufsen Introduces Beolab 8 at CEDIA Expo 2023 | The new Bang & Olufsen Beolab 8 compact speaker was the highlight of the company's booth at CEDIA Expo 2023 in Denver, CO. Anticipating the official launch in October 2023, the new Beolab 8 was showcased at the residential integration trade show as "the embodiment of versatility that shines on its own, sings in any setup and performs wherever you place it." Available in distinct finishes and with a wide range of installation accessories for different use cases, this speaker promises to be a real popular model. Read More | |
B&C Speakers Finalizes Eminence Acquisition in the US and China | B&C Speakers, one of the leading loudspeaker manufacturers for professional audio applications, based in Florence, Italy, announced that it has acquired 100% of Kentucky-based Eminence Speaker, LLC, the manufacturer of professional audio and guitar amplification loudspeakers, and its manufacturing facilities in Dongguan, China. According to B&C Speakers' CEO Lorenzo Coppini, this acquisition will strengthen the company's global reach, while "creating an opportunity to relaunch and enhance an iconic American brand." Read More | |
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Lyngdorf Audio Launches MXA-8400 High-Performance Power Amplifier With Purifi Technology | It was one of the highlights of CEDIA Expo 2023. The launch of the Lyngdorf MXA-8400 8-channel amplifier introduces an extraordinarily powerful, power-efficient, and ultra-linear multichannel amplifier, incorporating Purifi Eigentakt technology and delivering 8 x 400 watt. The MXA-8400 also features the new, highly efficient Lyngdorf PowerPerfect power supply with Channel Balancing Technology and integrated mains power decoupling and filtering, to set new benchmarks in audio quality, measured performance, and reliability. Read More | |
Sonos Introduces Significantly Improved Move 2 Portable Speaker | Sonos debuted Move 2, the next generation of its original Move portable speaker, now with a dual tweeter design that delivers a more spacious stereo image, improved WiFi and Bluetooth connectivity, and new touch controls. But the improved Move 2 also features an expanded battery life for up to 24 hours, a new Wireless Charging Base (included), plus new USB-C Line in and USB-C device charging, which expands its possibilities considerably. The Move 2 is rated IP56 for dust and water resistance, making it perfect for outdoor use. Read More | |
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Editor's Desk
Jan Didden
(Technical Editor)
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Audio Myths: Feedback Re-Entrant Distortion
Should We Worry?
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There are many aspects of negative feedback in audio that are the subject of continued discussion. We’ve previously examined a few of those (see The Audio Voice newsletter 434); in this installment I’d like to address re-entrant distortion.
The idea is that, since negative feedback sends some of the distorted output signal back to the input, this already-distorted signal would only get more distorted by going through the nonlinear amplifier, over and over again. As an example, say that amp has 2nd harmonic distortion, sending that again through the amplifier would generate 2nd harmonic from the original second harmonic which is the 4th harmonic of the fundamental. So you’d get distortions-of-distortions, greatly increasing the number of spectral components in the signal. But, as so often, it’s more subtle.
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Much of the current dispute can be traced back to an article by the great Peter Baxandall [1] which contained Figure 1. In 1978, Baxandall noted that negative feedback around strong nonlinearities creates distortion components that weren't previously there. In his Figure 1 measurements, the feedback increases along the X-axis, from right to left. The curves show, from top to bottom, the fundamental and the harmonics levels, and you see that initially the 3rd and higher harmonics increase in level with increasing feedback. Only when you get past a certain point, say 15dB negative feedback, do the harmonics decrease monotonically to a low level with high feedback. So, based on this, the conclusion would be: if you use feedback, use lots of it, stay away from ‘moderate’ feedback [2]. | |
Figure 1: Harmonic distortion as function of feedback for the simple circuit of Figure 2. | |
But this isn’t the whole story; this is a very rudimentary circuit that would never be used in audio, on itself. See Figure 2. A single FET stage with no source degeneration, probably the most distorting circuit you can come up with; Baxandall’s circuit has about 10% THD. It is a great circuit to demonstrate the mechanisms involved. But as often happens, this started to lead its own life and to the mantra – negative feedback causes re-entrant distortion and therefore is BAD. | |
Figure 2: Simple test circuit for harmonic distortion measurement. | |
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But let us look at a more common situation where we would have a complete amplifier that would not be so strongly nonlinear to begin with, and would have lower harmonic components. Let’s see what we get when we wrap feedback around it. Bob Cordell has done exactly that for us, and his results are documented in Figure 3, below. He uses the term ‘spectral growth distortion’. [3].
Here the feedback increases from left to right. It is clear that in this situation, any increase in feedback decreases the distortion, starting at 0dB feedback. There are some wrinkles in some of the curves, but the trend is clear. Again, for lowest distortion, use as much feedback as you can get away with, stability-wise.
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Figure 3: Harmonic distortion as function of feedback for a complete power amplifier. [3] | |
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The Verdict
Re-entrant or spectral growth distortion does exist, but it only manifests itself with low feedback factors in very nonlinear circuits. Its effect is absent in all but the most non-linear amplifiers, and even in those cases it can be negated by using sufficient negative feedback. The worst thing you can do is take, say, a tube amplifier with 5% distortion and wrap 10dB of feedback around it. Chances are it will not sound very good.
Comments and contributions always welcome.
techeditor@audioxpress.com
[1] P. J. Baxandall, "Audio Power Amplifier Design," Wireless World, December 1978, Part 5, Negative feedback and non-linear distortion.
[2] B. Putzeys, "The F-word, or, why there is no such thing as too much feedback," Linear Audio Volume 1, 2011, https://linearaudio.net/sites/linearaudio.net/files/volume1bp.pdf
[3] B. Cordell, Designing Audio Power Amplifiers, Routledge, ISBN 1138555444, 2nd Ed. Figure 24.5, page 504. https://www.cordellaudio.com/
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The Live-Edge Dipoles
By Perry Marshall
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For the speaker builders, Perry Marshall details everything there is to know about his beautiful Live-Edge Dipoles project. A design that was inspired by two slabs of birch the author brought home, allowing him to finally bring to fruition his idea to build these dipoles. In the detailed DIY project, Marshall reveals all the specifics of the driver choices, radiation pattern, and crossovers, while explaining the effects of the obtained radiation pattern and how the speakers behave in practice. This article was originally published in audioXpress, January 2021. Read the Full Article Now Available Here
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The TW29BNWG Beryllium Dome and Waveguide from the SB Acoustics Satori Line
By Vance Dickason
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This Test Bench characterizes the SB Acoustics TW29BNWG beryllium dome and waveguide from the brand's prestigious Satori line. As Vance Dickason underlines, Voice Coil has characterized several of these SB Acoustics tweeters, including ferrite and neodymium motor models with beryllium, cloth and TeXtreme TPCD domes. All these Satori transducers are developed by former Danish Vifa/Scan-Speak engineers Ulrik Schmidt and Frank Nielsen at Danesian Audio. The new high-end 29mm beryllium diaphragm neodymium dome, the Satori TW29BNWG, incorporates a 170mm (6.7") diameter aluminum waveguide, an 8mm wide coated cloth surround, a 29mm (1.14") beryllium diaphragm, dual copper caps on the T-shaped pole piece, dual balanced compression chambers, non-reflective optimally damped rear cavity, and CCAW round voice coil wire. A great evolution of the Satori TW29BN tweeter. This article was originally published in Voice Coil, June 2023. Read the Full Article Now Available Here
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