From Micro to Pro and High-End Speakers in Voice Coil May 2021

In this edition’s Voice Coil Spotlight article, Andrew Taylor (Klippel GmbH) explains how to do Comprehensive Transducer Testing in 24 Minutes. As a way to illustrate how the latest Klippel Multi-Scanning Workbench solution allows measurements across several domains (acoustical, mechanical, electrical, and magnetic) while working from non-anechoic environments, the author uses a practical characterization of balanced mode radiator (BMR) loudspeakers, which require a more complex approach when compared to conventional cone-based woofers or dome-tweeters. This is primarily caused by the long measurement time associated with assessing full vertical and horizontal directivity, which the article shows, can be achieved in a short time, saving money and space by dispensing with the need for a large baffle and anechoic room.

Next, Mike Klasco (Menlo Scientific) wrote a new article about Plastic Film Diaphragms and the use of PEEK High-Performance Film Diaphragms and Cones for Headphones and Speakers. Having worked as a consultant for multiple material science companies involved in research for the loudspeaker industry, Klasco is in a position to share real-world knowledge about the use of these plastic-based formulas in the most critical component for sound quality, which is the diaphragm. The article takes a closer look at Polyetherether Ketone (PEEK) and comparisons with the PEI (polyetherimide) or polyethylene naphthalate (PEN) developments, and even standard PET formulas that dominate most cheap earphone and headphone diaphragm applications. The article also references key product implementation and the latest knowledge directly sourced from vendors and patent holders, such as DuPont, Teijin, and Victrex.

To add to the valuable information combined in this single issue of Voice Coil, Mike Klasco and Nora Wong (Menlo Scientific) compiled two updated directories of cutting-edge components, starting with an updated list of MEMS Speaker Vendors for 2021. After five years have passed since the first directory on MEMS speaker vendors, Mike Klasco shares that the technology is now ripe for market adoption: ”For the first time I can really say that some of these devices are really shipping, and not just pre-production beta prototypes.” To complement the topic, this edition also includes an updated directory of Microspeaker Vendors for Mobile Electronics, covering all available topologies, but limited to companies supplying microspeakers for smartphone and laptop applications.

In this month’s Acoustic Patents column, James Croft (Croft Acoustical) reviews a recent patent with wide-ranging implications in the loudspeaker industry. Titled “Speaker with Dual Diffuser,” US Patent 10812912 was granted in October 2020 to Mikhail Dinaburg (Plano, TX) on behalf of his own company Dinaburg Technology Corp., registered in Canada. The improved loudspeaker patent includes 16 claims and 8 drawings, detailing a speaker where the diaphragm has an inner portion (active portion) and an outer portion (stabilizing portion), both typically ring-shaped. The interaction between the magnets causing a symbiotic movement between both portions, where they “move relative to each other as sound is produced so that a relatively constant volume of air is displaced on either side of the diaphragm thus minimizing acoustic distortion.

In his review, Croft alludes to all the possible comparisons with prior art and similar concepts, including existing active patents, and he explores the merits and promises of the current invention, which are now in the hands of the inventor. As he writes, “the curious theoretical notions along with the questionable associated benefits belie that fact that the invention, if realized with the correct parameters, is a useful device that should provide high performance in a practical package.”

And to the eagerly anticipated Voice Coil Test Bench section, in this May edition Vance Dickason characterizes a new 1.4” Pro Sound Compression Driver from Eighteen Sound. Now operating as a separate division of B&C Speakers (together with Ciare) since the acquisition in 2017 from the Landi Renzo Group, Eighteen Sound sent one of its latest 1.4” compression driver designs, the NSD1424BTN, that for the measurements was combined with the Eighteen Sound XT1464 elliptical-shaped 60°x50° horn used previously here.

Designed for use with 1.4” throat horns, the ultra-compact Eighteen Sound NSD1424BTN compression driver is driven by a 62mm (2.4”) diameter edge-wound voice coil wound with aluminum wire on a non-conducting Nomex former with a proprietary treatment. This assembly drives the proprietary True Pistonic Motion (TPM) Tin (nitrate compound)-coated titanium diaphragm, and also incorporates a proprietary phase plug design (3P) that has short openings and a high flare rate to reduce distortion and improve mid-range detail. Other features include a computer-optimized neodymium multiple magnet motor structure, a copper pole piece shorting ring, a continuous power handling of 140W with a 70W nominal power handling rating, and 1.2kHz recommended crossover frequency (with a minimum 12dB/octave high-pass network).

The second driver in this edition’s Test Bench is a high-end dome tweeter from Kartesian, a French home audio/pro OEM new to the pages of Voice Coil. Kartesian was founded in 2011 and is located near Strasbourg, France, where it produces an impressive lineup of drivers — all featuring some equally impressive proprietary cone, suspension, and motor design technologies. The company sent Voice Coil a 28mm soft dome tweeter, the Twt28_vMS. Features include a proprietary Nylon-coated cloth type diaphragm and surround, a 28mm diameter CCAW voice coil wound on a vented aluminum former, dual N48H neodymium magnets fitted to a low-carbon-content steel motor structure, an extruded polyester damped pole piece venting into a stamped aluminum back enclosure, as well as a shaped enclosure below the suspension. The rear and suspension enclosures are acoustically linked and tuned to about 670Hz. Other features include 92.5dB 2.83V/1m sensitivity, an aluminum faceplate, and nominal 6Ω impedance.

Finally, in this month’s Industry Watch, Vance Dickason pays tribute to Dr. Bruce Edgar (1942-2021), a respected contributing editor to Speaker Builder magazine (one of the predecessor publications to Voice Coil’s sister magazine, audioXpress). Among the many articles he wrote for Speaker Builder in 1980s, the most noted focused on his specialty — bass horns and Tractrix horns, and his work continues to be frequently cited to this day.

The May 2021 edition of Voice Coil is available for download and already in the mail to print subscribers. Subscribers can go to - www.gotomyvcoil.com - to download this issue.

Remember, Voice Coil is available in print and download for all registered subscribers, free for industry professionals. To qualify for a free subscription to Voice Coil, or renew your subscription, go to: audioxpress.com/page/Voice-Coil-Subscriber-Services.html

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