Fostex T50RP part2: General analysis

Disclaimer: Measurement has been carried out with a single positional placement, as it is the only spot of which an acoustic seal is successfully obtained.

Continued from part1: Aesthetics

The internal design of an isodynamic headphone can be described as a vibrating system consisting a patternized conductive membrane on top of a magnetic system, with magnetic rods configured to push each other apart on a yoke. With a magnetic flux generated at the magnets, the membrane, which is situated perpendicular to the magnetic flux, is driven as current runs through. Carl A. Poldy, the mastermind behind the development of AKG K1000, describes the working principle of an isodynamic driver in detail on Loudspeaker and Headphone Handbook written by John Borwick:

"...The resultant magnetic field at the membrane is in the plane of the membrane and perpendicular to the current in the conductors...The pattern of the conducting layer, which resembles a printed circuit, is arranged so that the whole membrane is driven in phase. In order to increase the total force, each conductor is divided into a number of tracks which are mechanically in parallel but electrically in series..."

As its conducting layer is enlarged to fortify the driving force, the surface area of the membrane increases as well, lowering the mechanical constraint of the driver itself. And rises the greatest technological advantage of an isodynamic driver:

"..The flat response down to the lowest frequencies is a natural result of the relatively low mechanical impedance of the membrane, and requires no special effort on the part of the acoustics engineer. Even the effect of leaks under the cushion has no dramatic influence on the response..."

With its low acoustic impedance, an isodynamic driver is more lenient when it comes down to linearity under load than an electrodynamic driver.

Released in 2002, Fostex T50RP is an orthodynamic headphone too, but it is implemented with the manufacturer's proprietary RP (regulated phase) technology, employeeing "a copper foil etched polyimide film to provide resistance to high level input peaks of up to 3000mW combined with a neodynium magnet for high sensitivity and excellent transient handling", according to the manufacturer.

The RP technology, which is comprehensively described in 特開２００２－１４２２８９, essentially addresses two fundamental limitations of the conventional design.

1. Poor damping characteristic of the membrane

2. Deviation with the driving direction of the vibration system

Fostex solves the former issue by forming a conductive membrane on top of a vibration damping layer, and removes unnecessary oscillation of the vibration system. For the latter, by patternizing the conductors in zig-zag, the driving direction of the membrane is equally distributed, hence lowering the distortion along.

And the result is quite promising. While the high-frequency artifacts are effectively removed, the mechanical resonance is shifted slightly upward.

Sony MDR-1R: "The ONE"

Released in October 2012, Sony MDR-1R bears the number "1" in its model name, which indicates the manufacturer's current reference sound signature. Starting from the classical MDR-1, the naming has been passed on to Q010-MDR1. As Sony's new reference model, 角田直隆-san, who is in charge of acoustic design & the mastermind behind the development of E888, D777, and Q010, implements the HD driver and the BRC(beat response control), which is perhaps the most intriguing feature of 1R.

"特に低域の使い方に違いがあり、80から90年代にかけては100Hzにピークがあったものが現在のエレクトロニカなどの音楽では30～40Hzにピークが来るのです。このベースの音色をきちんと再生できないと音楽そのもののバランスも崩してしまう。これまで手本としてきたMDR-CD900STよりもさらに下の帯域にピークがあるので、音の設計に関してもだいぶ考えを改めなければとそこで気付いたんですね。" http://www.sony.jp/headphone/special/park/products_m1/tech1.html

Conventionally, Sony's target frequency of interest has always been at 100 Hz, as that is where the majority of low frequency contents have been located with traditional music. However, the time's changed: In order to accommodate the current music industry's demand of low frequency reproduction at as low as  30 - 40 Hz, 角田-san develops a special damping system.

"さらに低域再生という点ではハウジング上に設けたポート（通気孔）によって低域の過渡特性を改善させるビートレスポンスコントロール（Beat Response Control）を導入しました。振動板の動作を最適化することで30～40Hzのリズム感も改善され、立ち上がりや立下り特性も向上しています。" http://www.sony.jp/headphone/special/park/products_m1/tech1.html

By optimizing the air compliance within the housing using two rear vents and a frontal resistive opening, a great damping over the driver's transient has been accomplished, according to the manufacturer.

Westone 2

Disclaimer: Yet again, Inks generously let me borrow his pair for analysis. I owe him greatly.

Measurement has been carried out with a pair of smallest Westone STAR sleeves, which are green-coded.

Released in 2009 along with UM3X, ES3X, and Westone 1, Westone 2 is a dual-driver IEM featuring the manufacturer's 50 years long experience in IEM industry. Designed for personal listening, this IEM is highly unnoticed by headphone users, despite the manufacturer's claim of "ultra-accurate ... the most dynamic sound available in a universal fit earphone".

Beyerdynamic DT 1350

Disclaimer: This headphone is owned by Inks, who is indeed the greatest contributor of this blog.

Along with full-sized T-series models, Beyerdynamic DT 1350 is also a part of Beyerdynamic's proprietary Tesla-driver technology implemented line up. Although it is a portable supraaural design, the manufacturer emphasizes the headphone's professional monitoring quality sound.

The goal of Tesla-driver is to achieve 1 Tesla, or 1 weber, which is according to the BIPM, producing an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second. In other words, Beyerdynamic is trying to accomplish very high electroacoustic efficiency by increasing the magnetic power of the driver. According to Mario Gebhardt, Head of Development for audio products at beyerdynamic,

"In beyerdynamic headphones, “Tesla” stands for our latest system technology that is distinguished by a very powerful magnetic drive and clean reproduction with a low degree of total harmonic distortion ... With the Tesla principle, the magnet is mounted as a ring encircling the coil and this enables us to divert more energy to the membrane, which is where it is required."

Beyerdynamic's German patent, DE102009038593, indicates that the technology is comprised of a big annular "neodymium-iron-boron" magnet 120, which is situated at the outer rim of the voice coil, holding a base plate 110 and a cover plate 130, creating a massive magnetic system altogether, much bigger than that of any conventional dynamic transducer designs.

Moreover, the diaphragm 140 is made of a dual-layer compound foil, allowing "high inner damping of partial oscillations despite its low weight and contributes to the transparent, finely defined, and distortion-free sound".

In contrast to Sennheiser's ring-driver patent, DE102007005620, of which the magnet is situated in the inner rim of the overhung voice coil, Tesla-driver technology has fewer components(lower production cost), a larger magnet(greater efficiency), and an underhung voice coil(emphasis in the bass quality). And these fundamental differences clearly distinguish the unique design goals the two German manufacturers are embracing, and ultimately, reveal Beyerdynamic's technical advantage over its arch-competitor.

EURI's accuracy compared to other conventional dummyheads [UPDATED]

Few weeks ago, I found out a gunk of glue residue was found to be melting inside the head. While Cleaning up the equipments, accuracy of the head has been modified, yet again. 

Novodio iHX: Yet another IEM from Widing?

Disclaimer: This pair is owned by James too!

Better known as a portable version of Widing ME-10EX, iHX is the very first IEM from the french company, Novodio. Compared to the original ME-10EX, Novodio iHX, which was released in January 2012, is of higher sensitivity and lower impedance. And most importantly it is way cheaper, priced at 39,90 €.

Perhaps the most distinguished feature of iHX is the proprietary 3D sound stage technology. Just like how a human HRTF works in a loudspeaker environment, a bit of signal from each channel is mixed into one another in order to create a natural stereophonic sound image, according to the manufacturer. In other words, they implemented an analog version of crossfeed into iHX. Since this kind of pseudo 3D simulation is usually realized by a DSP process, their approach is absolutely brilliant, only if the claim turns out to be real.