Industry & Product News
OBO Pro.2 Launches New Line of Full-Range Liquid Silicone Rubber Micro Speakers
OBO Pro.2's new full-range liquid silicone rubber (LSR) micro speakers are designed for next-generation earphones, wearables, and other electronic devices. These speakers feature a highly precise, customizable, and durable LSR speaker surround. OBO Pro.2's LSR know-how and complete micro speaker value chain allow for a precision product at a competitive price .    Read More
Loudspeaker Industry Sourcebook 2020. Now Available Online!
In the best annual tradition of the Loudspeaker Industry Sourcebook, the 2020 edition contains updated company listings and so much more. In this edition, readers will find several must-read articles from some of the finest industry leaders, interviews with audio professionals on trending industry topics, and our annual industry reports about the state of the industry. Now online!    Read More  
Successful Smart Speakers and Voice-Enabled Products Free Webinar - July 9
The recently launched Audio Product Education Institute (APEI) is promoting a free introductory webinar focused on Interactive Voice Products, intended to share real world experiences in voice integrated product development. APEI's first online event - July 9, 4:00PM - 6:00PM Eastern Daylight Time - is the first in a roadmap that will also address Supply Chain and Sourcing, Modeling and Measurement, Product Management, The Legal World, and Artificial Intelligence and Machine Learning .    Read More

Dirac and Klipsch Collaborate to Enhance the Next Generation of Headphone Audio Performance
Swedish sound pioneer Dirac and Klipsch, the famous consumer audio brand and a VOXX International company, are partnering to integrate Dirac's sound optimization software and latest digital audio solutions into Klipsch's upcoming generation of earphones. The partnership highlights the growing market trend for headphone manufacturers to increasingly leverage premium digital audio software to level-up their hardware performance .    Read More  

Eastman Introduces Tritan Renew Sustainable Material Using 50% Recycled Plastic
Global specialty plastics provider Eastman has introduced Tritan Renew, a new-generation Tritan copolyester that offers sustainability without compromise, providing the same durability, performance, and safety of the original Tritan formula but now with up to 50% recycled content derived from waste plastic. Eastman also confirms that it is actively working with electronics brands to develop earbuds, headphones, audio cases, and peripherals made from sustainable materials, including Tritan Renew .    Read More  

TDK Announces T3902 Lowest-Power PDM MEMS Microphone
TDK Corp. has introduced the InvenSense T3902, which the company touts as the world's lowest power Pulse Density Modulation (PDM) microphone for consumer devices. The new T3902 offers a high SNR of 64.5 dB, and high Acoustic Overload Point (AOP) of 120 dB in a very small package, optimized for mobile devices, wearables, headsets, TV remotes, and more, supporting far-field communications, enabling clear audio capture in loud conditions, and ideal for voice recognition .    Read More  

Resonado Announces Flat Core Speaker Licensing Partnership with Zylux
Audio technology startup Resonado just revealed its first major technology licensing partnership with original equipment and design manufacturing audio company, Zylux. Resonado's innovative and proprietary Flat Core Speaker (FCS) technology will be manufactured and initially incorporated into a range of Zylux designs within the soundbar category, with the expectation to expand into other Zylux produced audio products in the near future. This marks Resonado's first integration agreement for FCS technology .    Read More

JBL Announces New High-Definition Imaging High-End Speaker Series
Designed and engineered in JBL's engineering facility in Northridge, CA, the new JBL HDI Series features two floor-standing loudspeakers, a center channel speaker, a bookshelf model, and a powered subwoofer. The series is named after its patented High-Definition Imaging (HDI) waveguide, coupled with a family of patented compression drivers, and patented low- and mid-frequency transducers, allowing for powerful dynamics and accurate sound reproduction. Thoughtful, modern curved cabinets with quality finishes with magnetically attached grilles complete the designs .    Read More  

Guest Editorial
Mike Klasco

Servo-Control in Mainstream Audio
From Motional Feedback to the Bend-Sensor
Imagine a new class of speaker diaphragm position sensors that enable audio engineers to reduce distortion and extend bass response from studio monitors, soundbars, smart speakers, and even smartphone microspeakers. With the precision of laser displacement instrumentation, this sensor is located between a stationary component of the speaker and an appropriate moving part to provide an error correction reference signal back to the amplifier. Well, that sensor has already been developed.

In this article, I will take you on a brief trip down the evolution of feedback speakers, before previewing SubVo's Bend-Sensor and Klara-T servo-control approach to feedback error correction in loudspeakers, promised for next week.

Most speaker engineers expect the amplifiers we use with our speakers to have a fraction of 1% distortion. On the other hand, our loudspeakers often have an order of magnitude more distortion than the amplifiers with which they are used, especially at their bottom-end. As to why speakers have more distortion, we could discuss the nonlinearities of the motor, the spider, and the surround... But instead of fixing each less-then-perfect aspect to achieve a linear transfer function, we could take a more elegant route - as is done with audio amplifiers to null out the nonlinearities of the transistors, caps, and so forth. 
The reason amplifiers have a fraction of a percent distortion, even the less inspired designs, is due to negative feedback correction. Negative feedback occurs when the output of a system is fed back to reduce the deviation of the output from the input. By returning an out-of-phase output signal back to the input, errors can significantly cancel.

The Infinity Servo Statik 18" subwoofer is shown with optional Coke can for reference.

The "Holy Grail" is to get all the components/factors within the feedback loop. A tube amp's "Achilles heel" was that the output transformer was not in the loop. I remember when Marantz (Sid Smith) managed to get the output transformer into the feedback loop and that was a big thing. Actually, the feedback signal was taken not from the secondary tied to the loudspeaker outputs, but from an extra pair of secondary windings. The output transformer contributed more distortion than the rest of the amplifier and today we all live better for the lack of interstage and output transformers.

But the biggest remaining challenge is with including the speaker in the feedback loop. Anyone who thinks feedback correction (servo-control) is a no-brainer to instantly fix poor speaker performance is in for more than a few surprises. Servo control definitely offers performance improvements not readily achieved by tweaking physical construction, but there are many new design rules with which to wrestle. Nevertheless, finding a robust stable sensor and the right positioning location can be game-changing (more about that later).

Yet perhaps what blocked making feedback speakers practical has been two-fold. One was that amplifier feedback loops are picky. To keep the "network" stable, an integrated solution is needed for fighting chance of a reliable design. While essentially all subwoofers today have the amp built-in, same for soundbars, smart speakers, and smartphones - all these "systems" are optimized and all variables predetermined by the design team before going into the shipping carton. But 20 years ago, the receiver was matched to the speakers in the retail store, the wire selection and wire run was also random. The unpredictable nature of separate components was confounded by servo-control - and integrated systems were just not popular in days gone by.

One of the first feedback network loudspeaker designs was introduced in 1965 by LWE, designed by geophysical engineer Louis W. Erath. Employing a back-EMF-based negative feedback network, enabled over-sized woofers to behave as if they were in a larger enclosure. The speakers were picky about what they connected to and were typically paired with McIntosh amplifiers but also worked well with many of the Japanese receivers of the day.
In 1968, Infinity, while still a start-up, launched its Servo-Statik 1 and created quite a splash in the audiophile world. The 18"woofer itself was built by Cerwin-Vega, facing downward from a 2' cubic enclosure, it uniquely boasted a sensing coil coincident with the main voice coil. The signal induced into the sensing coil was fed back to the bass amplifier to provide the "servo" correction. While dramatic, it wasn't a completely stable design and was eventually discontinued in 1972.

A Philips MFB speaker system, the MFB block diagram, and detail of the MFB woofer with sensor assembly are shown here

Motional Feedback (MFB) was introduced by then audio giant Philips in the early 1970s. There was a full series consisting of five models, starting with a 7" woofer + dome tweeter. The loudspeakers had built-in amplifiers and a feedback sensor on the woofer. As with the Infinity Servo-Statik, the sensor measured the output signal of the woofer and compared it to the amplifier input signal.

In 1978, AudioPro, a Swedish startup (still very much alive today) introduced its ACE Bass negative output impedance scheme.  In an audio system, the damping factor is the ratio of the impedance of the loudspeaker to the source impedance. The amplifier feedback contributes to the low-source impedance of the output stage. High feedback amplifiers have almost negligible source impedance - but imagine if you could have less than zero - then you could negate the voice coil characteristics and you could start with a clean slate. In this way, ACE Bass electronically synthesized the attributes of an "ideal speaker," or at least enabled the speaker designer to achieve virtual Thiele-Small parameters without some of the physical implications and compromises. The network is connected in series with the actual speaker and the voltage characteristics between the two are compared in real time. The difference is sent back to the amplifier as an inverse corrective voltage and fed into the input of the amplifiers negative feedback output stage.

The Velodyne DD-18 driver is shown with an accelerometer. (Image courtesy

David Hall founded Velodyne in 1983 as an audio company specializing in servo-controlled transducers. Back then, I had just moved to California and Velodyne was my consulting company's first client. Hall wanted to develop a full-range 8" servo speaker, essentially a next generation of the Philips design. My contribution was to suggest we pivot to a servo-subwoofer and use it only in its piston range (up to a few hundred Hertz). I wanted to avoid getting bogged down with wideband feedback and the problematic aspects of cone breakup. At my previous company, we had developed a low distortion 18" woofer. We used a 3" voice coil but undercut the pole piece down to 2.5". For the Velodyne ULD-18, we bonded a piezo sensor to the voice coil collar. And many other "secret" refinements were developed at Velodyne, which enabled "high gain feedback" - about 20 dB, which then buys almost that much distortion reduction. We found that stable operation was best achieved by limiting our feedback loop to a fraction of the otherwise usable bandwidth. But there were many tweaks and tricks used to get a bit more performance and stability.

In 1989, I began work with Yamaha in Japan on the Yamaha Active Servo Technology (YST). The efforts involved many similarities but also some differences with MFB and ACE Bass. Developed to expand low-frequency reproduction, it involved two technologies. One was the Air Woofer (port) and the other was Negative Impedance Drive, which drives the speaker to cancel the impedance of the voice coil so the apparent impedance of the speaker is zero. The former was performed by a speaker, and the latter by an amplifier. Thirty years later, Active Servo Technology continues to be a cornerstone of Yamaha's audio products.

This Yamaha YST-SW012 8" subwoofer is already using Advanced YST II and QD-Bass Subwoofer technologies.

Next week, we will take a close look at the subVo servo-pickup bend-sensor, a unique screen-printed sensor that changes in resistance when bent. It is durable, has a long stable life, and is inexpensive to produce in mass quantities. SubVo's KlaraT is a proprietary DSP algorithm that controls the feedback loop, offers over-excursion protection, and eliminates end-of-line calibration routines required with other feedback techniques. The Klara-T self-calibration also compensates for degradation of the loudspeaker (surround/spider wear and tear and magnet sensitivity losses) over time and any change in the loudspeaker's environment.

Sound Control
Progress on Calculating Edge Effect of Acoustical Absorption
By  Richard Honeycutt
For his monthly acoustics column, Richard Honeycutt wrote an important article exploring new methods to calculate the edge effect of acoustical absorption and the research behind these methods. The research focuses on the recognized fact that rooms in which Reverberation Time (RT) is important, requiring the application of acoustical treatment such as absorptive wall panels, seem to achieve better results when the absorptive material is applied only to parts of each wall, in contrast to applying panels that cover entire walls. This implies that the same area of absorption can have more or less effect in reducing reverberation, depending upon the physical shape. Although the Sabine and other statistical RT equations do not predict such an effect, experience has shown it to occur. The physical reasons behind this apparent anomaly are often lumped into the category of "edge effect." This article was originally published in audioXpress, December 2017 .    Read the Full Article Now Available Here
Voice Coil  Test Bench
The 18NDLX Imperium Woofer from Fane
By  Vance Dickason
In this Test Bench article, Vance Dickason receives the latest 18NDXL Imperium, a very high power handling 18" low-frequency woofer from British brand Fane. Designed by this revitalized company with a rich history, the 18NDXL Imperium includes uses as a bass driver in multi-way systems or as a dedicated woofer in bass reflex or horn-loaded designs. The feature set for the 18NDXL is like most high-performance pro sound drivers, rather substantial. The 18NDXL uses a proprietary eight-spoke cast-aluminum frame incorporating eight 40 mm x 10 mm rectangular vent holes in the area below the spider mounting shelf for enhanced voice coil cooling. This series of cooling vents allows air to move past the voice coil and across the front side of the neodymium motor assembly. Motor parts, such as the return cup and rear heatsink plate are coated with a black heat-emissive coating for improved cooling, with the cooling additionally enhanced by a 63 mm flared pole vent. In addition to the convection cooling enhancements, the 18NDXL also has an aluminum core heatsink, which further wicks heat from the voice coil assembly. Factory-rated power handling for this driver is 1200 W AES and 2400 W program. This article was originally published in Voice Coil, April 2020 .    Read the Full Article Now Available Here

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