Fundamentals of Headphone Electroacoustic Measurements
This 26-page application note discusses these challenges, headphone types, measurement standards, headphone acoustics, acoustic test fixtures required for measuring headphones, and the practical aspects of headphone measurements. An overview of the key electroacoustic measurements used to characterize the audio quality of headphones and earphones is also provided. Click here to download the free white paper.   Read More

Intel Announces New Development Kit for Far-Field Alexa-Enabled Products
Intel has announced the Intel Speech Enabling Developer Kit, designed for manufacturers and developers to quickly bring new Alexa-enabled products to market. This kit is the first audio front-end solution that combines far-field voice processing and "Alexa" wake word detection on a single chip. It is based on a new digital signal processor (DSP) architecture from Intel that enables high-quality voice capture in acoustically challenging environments.   Read More

AverLAB Audio Analyzer by Avermetrics is Now Shipping
An innovator in audio and electronic production test systems since 2011, Avermetrics has begun shipments of its new AverLAB portable audio analyzer, opening a completely new application segment for the company. AverLAB is the first audio analyzer to natively support both Mac and Windows computers and, at just $3,000, it offers a level of features and performance that was previously only attainable at triple the price.   Read More

New Synaptics and NXP Alexa Development Kit Available at Arrow Electronics
NXP has teamed up with Arrow Electronics, Synaptics, and Amazon to develop the Synaptics AudioSmart 2-Mic and NXP Pico i.MX7Dual Development Kit for Amazon Alexa Voice Service (AVS). This newly available development kit is one of the first to be qualified with a production-ready system-on-chip (SoC), a voice processor, and the AVS Device SDK. It enables device makers to quickly and cost-effectively integrate Alexa into a fully functioning prototype and then take that work into design for manufacturing and production.    Read More

Recording Academy Producers & Engineers Wing Publishes New and Updated Recommendations for Recording Deliverables and Hi-Res Music Production
Reflecting its ongoing mission to educate and offer technical guidelines, the Recording Academy Producers & Engineers Wing has officially published a new paper titled "Recommendations for Hi-Resolution Music Production," and an updated version of its historically influential "Recommendations for Delivery of Recorded Music Projects."The P&E Wing has created these new documents to help increase efficiency and transparency in the production process.   Read More

Burning Amp 2017 Will Be The Biggest and Best Ever! 
Burning Amp, the event for people interested in making or learning about do-it-yourself audio equipment, auditioning equipment made by others, and attending talks concerning various audio topics, will return November 12, 2017 to San Francisco, CA. It is not necessary to bring components to show in order to attend Burning Amp, but admission is free for those who do. So, this is a great opportunity for those wanting to show something they've made to be auditioned or admired! Read More

Acoustic Geometry Launches Pro Room Packs Acoustic Solutions
Acoustic Geometry announced the launch of Pro Room Packs, a unique grouping of acoustical products aimed at the professional audio market. Delivering professional-level acoustical performance at four cost-saving price points, these new product packages include Fabric-Wrapped Panels, Ceiling Clouds (absorbers), Curve Diffusors, CornerSorbers, and all the mounting hardware - providing convenient and well-balanced room treatment solutions for studios and high-end audio rooms.   Read More

Mike Klasco

Guest Editorial

The Tip of the Spear in Graphene Speaker Development

Paraphrasing from Wikipedia, Graphene is a form (allotrope is the more precise technical term) of carbon in a two-dimensional, one atom thick film. Graphene is the basic structural element of other carbon variants (allotropes), including graphite, charcoal, and carbon nanotubes. Graphene is hailed as a wonder material that should be intriguing for speaker engineers - strong, light, electrically and thermally conductive. It is more than 200 times stronger than high strength (high carbon) steel.
Graphene efficiently conducts heat and electricity, and carbon materials typically have good acoustical properties. It was originally observed using electron microscopes in 1962 and characterized in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester. This work resulted in their Nobel Prize in Physics in 2010 "for groundbreaking experiments regarding the two-dimensional material graphene."

An earlier prototype speaker membrane formed from a Graphene Composite Material (graphene-Q) from ORA Sound. For an introduction to speaker drivers using graphene read the article by Robert-Eric Gaskell, found in the Loudspeaker Industry Sourcebook 2017 edition.

So how is graphene used in headphones and speakers, and why does it matter? The first audio products to be commercialized with some form of graphene are from ORA Sound . An early-stage start-up, based in Montréal, QB, ORA has devised a graphene oxide-based composite material for speaker diaphragms. Dubbed grapheneQ, its low density and high stiffness enable potentially higher output drivers.
Readers interested in graphene should check out the cover story in the April 2017 issue of Voice Coil, and also the article "Graphene Composites for Improved Sound Quality and Increased Efficiency in Portable Devices" by Robert-Eric Gaskell, that was published in the Loudspeaker Industry Sourcebook 2017 edition, which you can read here: ORA was conceived at the engineering labs of McGill University, in Canada. Gaskell headed research into how the properties of graphene oxide could be tuned to create the conditions for high-quality sound.
Shortly after producing the first prototype audio transducer based on graphene oxide technology, Gaskell joined TandemLaunch, an incubator for university research and assembled the ORA Sound team. If ORA was going to succeed where other commercial endeavors of graphene had failed, it would have to put manufacturability at the forefront. Turning to Northwestern University, ORA found the research of Prof. SonBinh Nguyen who had a way to manufacture graphene sheets in a simple process that could be easily scaled to production quantities. Then, the focus was on tuning grapheneQ into high-performance diaphragm material for audio.

Scanning electron micrograph (SEM) of the laminar nano-structure of Graphene Oxide paper at 100 µm resolution and 5 µm resolution. "The beauty of Graphene Oxide is that it is inexpensive to work with and it can easily be formed into different shapes such as cones and domes for standard woofers and tweeters." states Xavier Cauchy, co-founder of ORA.

The team made its graphene oxide by reducing graphene and then adding a proprietary blend of cross linkers to create the composite. The intrinsically high tan delta means that it requires less damping mass (especially at low frequencies) than commercial devices to prevent unwanted spurious breakup response characteristics. Less damping at lower frequencies also means that the bass and treble response are both extended, which ideally results in faster transient response and quicker settling times. grapheneQ is very stiff and distorts very little thanks to its high Young's Modulus of up to 130 GPa. This allows sound waves to travel quickly through the material, pushing diaphragm "break-up" to beyond audio frequencies where they are more easily damped. The material has a high thermal conductivity, which enables design for enhanced heat dumping from the voice coil and out from the diaphragm using various techniques. Specifically, the voice coil bobbin can be thermally conductive or in a microspeaker or a headphone driver, a bobbinless coil can be bonded (using thermally conductive adhesive) directly to the diaphragm.
The ORA researchers hope that grapheneQ will become a standard material for loudspeaker membranes in the future. Up to now they have a very successful Kickstarter crowdfunding program for a headphone, which should be shipping earlier 2018, and are establishing an OEM program for their diaphragm technology.
But graphene's promise is that not only can it be used as an additive for speaker diaphragms in traditional moving coil, magnetic dynamic speakers such as ORA is doing, but also theoretically as a speaker itself. In 2012 at the Lawrence Berkeley National Labs at the University (LBNL) of California, Berkeley, Dr. Alex Zettl and Dr. Qin Zhou were researching graphene for audio applications. About a year later a proof-of-concept graphene earphone was demonstrated, consisting of a graphene diaphragm sandwiched between electrodes to create the electrical field.

In 2016 GraphAudio licensed the graphene audio work and patents from The Lawrence Berkeley National Labs at UC Berkeley. GraphAudio's goal is to develop a new generation of graphene-based microspeaker transducers with high sensitivity and ultra-low distortion. The picture shows a comparison of an 8 mm Dynamic Speaker and 8 mm GraphAudio Gen1 Transducer.

Now the LBNL technology has been licensed by GraphAudio to be developed into commercialized audio products. In a future edition of the Audio Voice we will discuss GraphAudio's progress in graphene mics, earphones, and speakers in more detail. Graphene has been hailed for years as one of the miracles in material science. For the audio industry, it's already a very promising alternative for established transducer technologies.


From The Vault
T-reg: A High-Voltage Regulator for Tube Amps
By Jan Didden
Tube amplifiers can benefit from regulated and stabilized power supplies, especially sensitive preamplifier stages, but also (single-ended) power amps. But traditional high-voltage regulators add several extra tubes, complexity, and power losses, while good performance is not easy to obtain. This article describes a novel design that is very simple yet offers excellent performance. Output voltage is fully adjustable with a single resistor without any compromises in performance. The idea for this project came to me when I was working on a broken 1970s Lambda 250 V lab power supply. After spending a few hours on it, I found the problem: a defective voltage regulator IC, a 14-pin Lambda FBT-00031. Tech support at Lambda kindly provided a single spec sheet for the chip. It took several weeks for someone on the Internet to identify the chip as a re-branded Motorola MC1466L (see Figure 1), which was obsolete, of course. The concept of my circuit is a high-voltage regulator, but I'd like to avoid as much as possible relatively rare and expensive high-voltage devices and parts. That's why there is a separate low-voltage supply, floating on top of the high-voltage output. This low-voltage supply, powered from the rectified pass tube heater, runs the reference and control circuits, which can be low-voltage. This type of regulator consists of the same modules. There is always a reference voltage and an error amplifier that compares the reference voltage to (a sample of) the output voltage. The error amplifier then drives the pass element to control the output. This article was originally published in audioXpress, April 2009.   Read the Full Article Now Available Here

Voice  Coil Test Bench
Celestion CDX1-1447 1" Compression Driver with H1-7050 "No Bell" 70° × 50° Horn 
By Vance Dickason
These Test Bench samples came from UK pro sound OEM Celestion. I received the CDX1-1447 1" ferrite motor compression driver coupled with Celestion's recently released H1-7050 "No Bell" 70° × 50° horn. Features for the CDX1-1447 include a one piece polyimide diaphragm and surround, with an exit (throat) diameter of 25.4 mm (1.0"). The polyimide diaphragm is coupled to a 35 mm (1.4") diameter voice coil wound with copper-clad aluminum wire (CCAW). Other features include an injection-molded body, a 35 WRMS AES-rated power handling (70 W maximum), a minimum crossover of 2.2 kHz (using a second-order network), a ferrite ring magnet motor, and solderable terminals. As with all Celestion's compression drivers, the CDX1-1447 was designed using FEA CAD software to optimize both the magnetic and the acoustic systems. The horn supplied with the CDX1-1447 was a new and rather innovative design. The H1-7050 "No Bell" is a cast-aluminum exponential flare-type horn with a 70° × 50° radiation pattern. The "No Bell" part refers to the general bell ringing character of cast-aluminum horns when you "ping" them with your finger. In order to dampen this parasitic ringing, Celestion has cut out (well, molded out) a horizontal section on either side of the 1" exit and filled it with elastomer side panels to make the horn more acoustically inert. After giving the H1-7050 the traditional "ping" test, I found the elastomer panels function quite effectively. This article was originally published in Voice Coil, March 2017.   Read the Full Article Online

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