in ,

Oppo PM-1 Planar Magnetic headphones review (Part 3)

  • [Part 1 of this review can be read here, Part 2 here – Ed]

    Team Oz beat gang UK. When answers from the UK weren’t coming, John Darko got Sam Encel from Oppo’s Australian distributor involved. He supplied the following intel and this link to a video of the London launch from which I extrapolate below.

    “Weight reduction was on our mind from the very beginning. It’s one of the most important features to the user experience. One should feel as comfortable as possible. Hence we put a lot of work into identifying materials which would make the product lighter whilst maintaining high sound quality. The PM-1 project commenced in the first quarter of 2012 before KEF had their model. The final cosmetic similarity is mere coincidence. We had industrial designers from the UK lead our team to finalize cosmetics. Our factory for the headphone is in Manila/Philippines where we employ strategic teams for design, R&D, material sourcing, testing, production and QC. This includes many experts and consultants who oversee the operation. We are the first manufacturer to have moved the traditional planar-magnetic headphone onto a modern production line. Unlike equivalent product which is produced by hand, the advantages of automation are guaranteed reliability, consistency and stringent matching between both ear modules. We also invested in many test jigs and tools for production.”

    “The most important role during R&D was filled by our acoustics expert Igor Levitsky. He studied electro acoustics at the Technical University of Kiev in the Ukraine. For nine years Igor worked as first engineer, then project leader for an R&D firm developing planar ribbon speakers and headphones. By 1995 he had immigrated to the US before moving to Canada. From 1995–1999 he continued work on drivers based on planar-magnetic tech using new materials that had become available by the late 90s. Now he designed many speaker models and drivers exploiting those materials for Swans/Hi-Vi Research. Subsequently he worked as consultant for US companies like Bohlender-Graebener Radia in the consumer and SLS Audio in the pro markets. For them he further developed advanced planar-magnetic/ribbon driver tech and designed many speaker system for various apps including recording studios, live-sound reinforcement and high-end residential installs. He currently works with a US-based firm developing new speaker tech for the commercial cinema market supporting the new Dolby Atmos multi-channel format. By about 2006 he’d formed a small team of engineers and material scientists in Europe who resumed work on headphones developing the next generation of planar-magnetic drivers. As Igor would say, ’the Oppo PM-1 is the culmination of this 7-year long project.’ “

    3.1

    “The reason that dynamic drivers weren’t an option for us is Igor’s contention that the typical dome-shaped 20um-thick Mylar diaphragm driven from a small voice coil in a circular central patch suffers breakup modes to be mechanically unstable, nonlinear and prone to distortion. Its moving voice coil merely adds distortion. When companies develop premium products with dynamic driver tech, they must go to extraordinary lengths to achieve top results. Even so a dynamic driver will always have certain issues which cannot be solved. By contrast the planar-magnetic approach distributes the driving force evenly over the entire flat membrane. This enforces coherent movement of the diaphragm that’s in phase across the entire bandwidth. Depending on frequency, a dynamic driver will actually deform in the opposite direction to introduce various phase angles across its audible bandwidth. Our dual-coil planar-magnetic design incorporates proprietary corrugation to stabilize the membrane for uniform pistonic movement and to undermine breakup.”

    Igor added that “between 1991 and 1992 Sennheiser had tasked its engineers to develop a cost-no-object headphone whose sole goal was to be as good as humanly possible. The end result was the Orpheus electrostatic headphone which I believe is the best in the world. Every time I put it on it’s simply amazing. In short, Sennheiser’s best isn’t a dynamic but film driver. That should tell us something. Beyond distortion from mechanical membrane behavior, there’s distortion generated by the magnetic system of motor, voice coil and electro-dynamic forces. There’s variable inductance which produces nonlinear impedance; and intermodulation distortion. Variable inductive mode aka fluctuating impedance creates unpredictable interactions with the driving amplifier. Flat planar-magnetic membranes use flat conductors to eliminate inductive components in favor of a purely resistive load. The amp sees a stable resistance to ensure consistent sound quality i.e. a linear amplitude response.”

    3.2

    “Measurements we conducted during R&D included multi-tone signals which drive the device with multiple tones simultaneously to reveal intermodulation effects not captured by standard THD measurements. Here our planar-magnetic driver measures clearly better than even very good dynamic competitors. It doesn’t suffer their masking effects from additional noise components. The PM-1 produces measurably lower IMD. As a result one can listen far louder without suffering the sharp bright distortion which dynamic drivers generate at the same levels.”

    “Compared to planar models from Fostex, HifiMan and Audeze all of which we have carefully measured, the PM-1 has the far more linear response. Another important difference is the consistency between left and right drivers. This affects the accuracy of soundstaging and imaging. It is particularly vital in the upper midrange where human hearing is most sensitive. Any discrepancies between channels there have bad consequences. At Oppo we’re very intolerant of channel mismatches during QC. We measure each pad and driver and only matched pairs make it into production. At our price a customer has the right to expect perfectly consistent performance.”

    “The PM-1 also uses what presently is the only planar-magnetic double-sided diaphragm. We worked hard on increasing sensitivity without raising weight. This was critical. We wanted customers to use our headphones with an iPod or iPhone as devices they already own and love. What’s the appeal of advanced technology if you can’t use it with what you’ve already got? We also paid a lot of attention to the design of the ear cushions to stabilize their acoustical performance regardless of different head anatomies or even wearers of glasses without applying undue pressure.”

    3.3

     “Quality control includes cross measurements for various forms of distortion and even clamping pressure. Each headband is stretched and its ear cups are rotated 20’000 times by machine to insure structural integrity, then twisted 5’000 times to check for environmental stresses. Rather than foam we use natural latex for the pads and cushions because Latex is free of synthetic chemicals to act hypoallergenic. It also keeps your ears cooler during long sessions. The perforations in the hand-selected lambskin aid cooling and also play an acoustic role. We even designed our own 6.3mm plug. The included alternate velour pads are thinner and also sound a bit different. Optional accessories not included in the stock PM-1 shipment are the headphone stand we showed in London and a Neutrik-terminated balanced wiring harness. The forthcoming more affordable PM-2 model will reduce cost by replacing the lambskin parts with synthetic leather; certain difficult-to-manufacture aluminum parts with plastic; the OCC cable with OFC; and eliminate the wooden presentation box and velour pads.”

    About the HP-1, Oppo’s presenters said that it improves over the output stage in their BDP-105/105D player which already drives efficient headphones very well but was never designed to support certain popular inefficient designs. One design goal for the HA-1 was to be an uncompromising headphone amp capable of driving the most challenging loads, hence its fully balanced circuit. Based on requests they’ve even included a home-theater bypass function and trigger ports.”

    To extricate the core message for PM-2 fence sitters, the only meaningful difference to the ears is the cable. Those so inclined could roll their own or hit up an aftermarket supplier of their choice and end up with a PM-1 on sonics if not price.

    Listening impressions next

    Associated equipment

    • System1: Quad-core 27” iMac (256GB SSD, 2TB hard drive, 16GB RAM) with PureMusic 1.89g in 176.4kHz NOS upsampler and memory play modes, SOtM 2-box battery-powered super-clock USB bridge, Metrum Hex, April Music Stello HP100MkII, Questyle CMA800R
    • System2 : 160GB Apple iPod Classic (AIFF), Pro-Ject iPod dock, RWA-modified Astell&Kern AK100 (ALAC), Aqua Hifi La Voce DAC, Bakoon AMP-12R, AURALiC Gemini 2000
    • System3: Windows 7 64-bit HP Z230 work station with JPlay’s alternate version, Spotify Premium (320kbps streaming), Qobuz Hifi (FLAC streaming), Aura Note V2
    • Headphones for all systems: Audeze LCD-2, LCD-XC; HifiMan HE-500, HE-6; beyerdynamic T5p recabled by ALO; MrSpeakers Alpha Dog; Sennheiser HD800 recabled by ALO
    • Cables: Light Harmonic LightSpeed USB cable, KingRex uArt double-header red, Zu Event power cords and interconnects, Vibex Three 11R power conditioner, Furutech eTP6 power bar

    Audition music

    • Mercan Dede “Su”, “800″, “Dünya”
    • Adnan Joubran “Borders Behind”
    • Sœur Marie Keyrouz “Méditations d’Orient
    • iLenKa “iLenKa“
    • Joana Jiménez “Joana Jiménez“
    • Tord Gustavsen Quartet “Extended Circle”
    • Rodolfo Mederos & Miguel Poveda “Diálogos”
    • Karim Baggili “Kali City“
    • Aytac Dogan “Deva”
    • Angelo Debarre & Marius Apostol “Gipsy Unity“
    • Sabine Meyer Bläserensemble “Antonin Dvorak’s Serenade in D-minor op.44”

     

    Further information:  Oppo UK | OPPO Digital | Oppo Digital Australia

    Written by Srajan Ebaen

    Srajan is the owner and publisher of 6moons. He used to play clarinet at the conservatory. Later he worked in audio retail, then marketing for three different hifi manufacturers. Writing about hifi and music came next, then launching his own mag. Today he lives with his wife Ivette and Nori and Chai the Bengal cats in a very small village on Ireland’s west coast, between the holy mountain Croagh Patrick and the Atlantic ocean of Clew Bay in County Mayo’s Westport area. Srajan derives his income from the ad revenues of 6moons but contributes to Darko.Audio pro bono.

    Blu-ray audio with the Essence HDACC (Part 2 – 192kHz)

    Fujiya Avic Spring 2014 (Part 1 – It’s a headphone festival)