Equipment

Oppo Digital PM-1 measurements can be found by clicking this link.

September 2014

Oppo Digital is best known in North America as a manufacturer of high-quality DVD and Blu-ray players. In fact, many reviewers will suggest that consumers interested in disc players start, and usually end, their search with a model from Oppo. And in 2014, Oppo entered the thriving personal-audio arena with a DAC-headphone amplifier, the HA-1 ($1199 USD), and two headphone models: the PM-2 ($699) and the subject of this review, the PM-1 ($1099).

Description

Like the very well-regarded models from Audeze and HiFiMAN, Oppo’s PM models are planar-magnetic designs. As in dynamic loudspeakers, the drivers in dynamic headphones consist of a conical or dome-shaped diaphragm with a coil of wire affixed to it, this assembly sitting in front of a permanent magnet. Current passing through the coil induces a magnetic force that interacts with the magnet to drive the coil and diaphragm back and forth. In a planar-magnetic driver, a conductive path is bonded directly to a thin membrane, which is placed in a field generated by multiple permanent magnets, usually placed on both sides of the diaphragm. Current along the conductive path again creates magnetic flux to move the diaphragm. All else being equal, the lower mass of the planar-magnetic diaphragm will let it respond more quickly and accurately than a dynamic driver. Driving the planar-magnetic diaphragm over its entire area also reduces breakup modes, improves phase coherence, and reduces distortion. The diaphragms of planar magnetics also tend to be larger than those found in dynamic headphones, which means they will move more air for a given displacement. The PM-1s’ oval diaphragms each measure 85 x 69mm, giving them a radiating area nearly four times that of a 40mm circular diaphragm, and 15% larger than that of the Audeze headphones.

Although Oppo is new to headphones, Igor Levitsky, the PM-1s’ chief designer, has considerable experience in designing planar drivers for high-end loudspeakers. It’s therefore no surprise that the drivers in the Oppos have some design elements that set them apart from those found in other planar-magnetic headphones. The spiraling conductive path is printed on both sides of the PM-1s’ seven-layer diaphragms, effectively doubling the number of turns and thereby increasing sensitivity. Rather than using an array of bar magnets, the PM-1s’ drivers employ concentric ring magnets that have been vertically polarized -- i.e., north and south are on opposite faces.

Most unusual is that a plate in front of the driver forces all of the air to pass through a relatively small area at the center. This arrangement increases compression at low frequencies, and provides some acoustic loading for the diaphragm that combines with the controlled air leakage through the earpads to make the PM-1s relatively insensitive to the quality of seal against the listener's head. There is also a plate behind the diaphragm with radial cutouts to balance the acoustic load. Finally, a significant amount of damping material behind the driver is intended to minimize reflections back through the diaphragm.

The PM-1s are exceptionally attractive headphones. The color scheme is black and silver, with the slim oval earcups mounted in wide aluminum bands that allow them a fair degree of tilt in the vertical plane. Attachment to the lambskin-wrapped, stainless-steel headband is by way of reassuringly sturdy-looking, chromed-metal hardware that allows the earcups to swivel flat for placement on a desk, or transport in the included denim carrying bag. Originally, the PM-1s shipped with two sets of earpads: one set covered in extremely supple, perforated lambskin, the other in high-quality velour. The current package includes a second set of lambskin pads that are said to slightly increase the treble response, but these weren’t available in time for the review. The soft earpads and headband, wide degree of adjustability, and 395gm mass -- about one-third less than the Audeze LCD-Xes -- make the PM-1s among the most comfortable headphones I’ve experienced.

Two connecting cables are included. There is a heavy, fabric-covered, Ohno Continuous Casting (OCC) cable for home use that is 10’ long and terminated with a 1/4” plug. The portable cable is much thinner, rubber coated, only 3’ long, terminated with a 1/8” stereo plug, and has no microphone or remote control. The cables connect to each earcup by way of 2.5mm monaural plugs, the plug housing providing a firm friction fit with the recessed jacks. Balanced cables are also available, for $129/2m and $139/3m. In an added touch of luxury, the PM-1s are delivered in a highly polished wooden presentation-and-storage box with custom cutouts for the headphones and cables. Oppo also shipped me their thoroughly modern-looking, dedicated stand ($79), which includes cable management in its base.

Oppo specifies the PM-1s’ input sensitivity as 102dB/mW. That’s about in line with other portable headphones, and 8-12dB more sensitive than most other planar-magnetic models. The PM-1s’ maximum input power is 500mW, and they can handle short pulses up to 2W. The impedance is specified as a purely resistive 32 ohms, which should result in no modification of frequency response with differing output impedance between sources. Oppo claims a frequency response of 10Hz-50kHz, but that is a free-field response for the driver, rather than what will be measured at the ear.

Sound

The tonal balance of the PM-1s was unapologetically warm, with a subdued top octave that was never harsh or aggressive. Violins, as in the Philadelphia Orchestra’s recording of Prokofiev’s Symphony No.4 conducted by Vladimir Jurowski (24-bit/88.2kHz FLAC, Philadelphia Orchestra/HDtracks), were lush and silky, never steely or strident. Brass instruments were more burnished than brilliant, but the trombones’ entrance in the first movement still had a satisfying amount of blat. Even though instrumental timbres weren’t quite what I hear in real life, I was never in any doubt as to what instrument or instruments I was hearing, and the PM-1s still delivered a wide range of tonal color from each.

A warm tilt is often complimentary to the human voice, and that was very much the case here. Voices through the PM-1s sounded natural, with just a little extra glow and saturation. In the recording of J.S. Bach’s Cantata BWV 211, “Schweigt stille, plaudert nicht” -- aka the “Coffee Cantata” -- by Masaaki Suzuki and the Bach Collegium Japan (16/44.1 FLAC, BIS/e-classical), the Oppos did an excellent job of reproducing the timbre of Carolyn Sampson’s light, pure, sweet soprano, and of rendering her diction easily intelligible without making it too crisp or sibilant. At the other end of the vocal range, Stephan Schreckenberger’s bass in the same recording was deep, full, and resonant, with no obscuring chestiness.

Turning to some examples of close-miked voices, as are found on essentially all non-classical recordings, the PM-1s captured the range of Eva Cassidy’s singing styles -- from achingly vulnerable to belted blues -- on her Live at Blues Alley (CD, Blix Street G2-10046). The technical quality of this recording isn’t up to its artistic merits, but the Oppos sufficiently tamed the extra sibilance to make the album even more enjoyable. In “Bird on the Wire,” from his live album Songs from the Road (16/44.1 FLAC, Columbia), Leonard Cohen’s voice was big, bassy, and full of grit and gravel.

Incredibly, the PM-1s’ warm, forgiving character didn’t sacrifice texture and detail. With Tori Amos’s exceptionally well-recorded Night of Hunters (24/88.2 FLAC, Deutsche Grammophon/HDtracks), the Oppos illuminated the whole spectrum of Amos’s voice, from throaty through open to somewhat nasal. They also communicated the scrape of the bows in the string accompaniment, and the buzz of the various woodwinds’ reeds. Listening to Menahem Pressler’s Tales from Vienna: Schubert, Mozart, and Beethoven (24/96 FLAC, La Dolce Volta/e-classical), I could easily hear the metallic buzz of the piano’s strings in its lower registers, as if I were standing right next to Pressler as he played. The PM-1s also preserved the incidental sounds picked up in live recordings -- e.g., in the Philadelphia Orchestra performance, chair creaks and turned pages from the orchestra, and coughs from the audience. Equally clear was the sound of a coffee cup being lifted from a saucer, then replaced, before the final reprise of “Ei! wie schmeckt der kaffee süsse” (Ah! how sweet the coffee tastes) in the “Coffee Cantata.”

Planar-magnetic headphones have a reputation for powerful, extended bass, and the PM-1s didn’t disappoint. John Robinson’s kick drum in “Lose Yourself to Dance,” from Daft Punk’s Random Access Memories (24/88.2 FLAC, Édition Studio Masters Columbia), threw a punch with a lot of weight behind it. I also felt the percussive wave from Bernard Purdie’s kick drum in Bucky Pizzarelli’s Swing Live (24/96 FLAC, Chesky/HDtracks), but it was appropriately lighter and looser than the one in “Lose Yourself to Dance.” Going bigger, in the Prokofiev symphony, the PM-1s delivered the subterranean rumble of bass-drum rolls, and drew marked distinctions in pitch, tone, and scale between single strokes on the bass drum and timpani.

But great bass isn’t only about scale. The PM-1s gave equal weight to each note of Ray Brown’s bass lines in the Oscar Peterson Trio’s Night Train (24/96 FLAC, Verve/HDtracks), and let them decay naturally without ever running into each other. They even sorted out the myriad notes in Rimsky-Korsakov’s Flight of the Bumblebee, in Ödön Rácz’s performance of the work on his Double Bass Fantasy (16/44.1 FLAC, Gramola/e-classical). Most impressive was the PM-1s’ ability to discriminate between multiple bass instruments playing simultaneously. For example, the kick drum is used to accent the electric bass in many of the tracks on Random Access Memories, and the PM-1s let me hear the specific combination of those instruments rather than indistinguishable low-bass events. Similarly, in orchestral recordings, the Oppos kept the notes of the double basses, bass drum, and timpani separate from their reverberations in the hall.

Finally, the PM-1s’ accomplishments in preserving textures, small details, and the microdynamic shadings that are part and parcel of musical expression were matched by their capacity to play staggeringly loud without any sense of strain. The combination of the two meant that the PM-1s handled with aplomb the wide dynamic ranges of classical recordings. Further, when the volume was up and the material was dense -- as in the finale of Respighi’s Pines of Rome, played by the Minnesota Orchestra under the direction of Eiji Oue (24/88.2 FLAC, Reference/HDtracks); or in “Layla,” from Derek and the Dominos’ Layla and Other Assorted Love Songs (SACD/CD, Polydor B0003640-36) -- the PM-1s never got compressed or confused.

Comparison

A few months ago, I positively reviewed the Audeze LCD-X headphones ($1699). The Audezes are constructed from a robust combination of anodized aluminum and steel. While I appreciate their sturdy build quality, the LCD-Xes are much bulkier and heavier than the PM-1s; they’re really appropriate only for listening while calmly seated, and even then, the weight becomes noticeable in long listening sessions. The Audezes come in a rigid case that’s great for transport, but the Oppos’ fold-flat design allows them to be easily slipped into a large laptop bag or a carry-on suitcase. Both headphones have first-rate finish quality, but I find the Oppos the more attractive design. One compromise that was made to permit the PM-1s’ slimness was the use of 2.5mm plugs to connect the cables, whereas the LCD-Xes have locking mini-XLRs, which will yield a secure connection no matter how many hundreds of times you swap cables. Since the Audezes are intended only for stationary use, no shorter, 1/8”-terminated cord is provided. Instead, the LCD-Xes’ package includes two 10’ cables: one terminated with the standard 1/4” plug, the other with a four-pin balanced connection.

Although Audeze specifies the LCD-Xes at 96dB/mW, Brent Butterworth’s measurements, which accompanied my review, showed a sensitivity of 101.5dB. The difference in impedance means that the LCD-Xes will actually play about 1dB louder than the PM-1s at a given volume setting. I got adequate volume driving either with my fifth-generation iPod Touch, but both headphones gave a more dynamic performance when plugged into my Grace Design m902 headphone amplifier-DAC.

Though the LCD-Xes, like the PM-1s, are reticent in the top octave, their stronger mid-treble makes them more neutrally balanced than the Oppos. Massed violins are a little more astringent through the Audezes, the brass section a little more brassy, and right-hand piano parts have more sparkle. Voices, and other midrange instruments, were similarly balanced through both transducers, with just a little extra warmth through the PM-1s. Some might consider the LCD-Xes’ midrange slightly withdrawn, but that’s fully in keeping with their overall sound -- more on that anon.

The LCD-Xes’ bass extends deeper than that of the PM-1s, and couples better with the eardrums. That made the experience of Massive Attack’s Heligoland (CD, Virgin 5099960946621) more akin to what I hear when listening through my main audio system with my REL subwoofer -- I felt more enveloped by the throbbing bass synthesizer. The bass-drum thwack that opens Benjamin Britain’s Sinfonia da Requiem, from Michael Stern and the Kansas City Symphony’s Britten’s Orchestra (24/88.2 FLAC, Reference/HDtracks), was startlingly physical through both pairs of headphones, but the drum sounded even bigger through the Audezes. However, as I noted in my review, the LCD-Xes couldn’t keep up when there was a lot going on down low; fast runs in the double basses blended together, bass-drum rolls were more homogenized, and reverb trails weren’t as clear as they could have been. The PM-1s did a much better job of keeping the low bass tidy and precise.

The biggest difference between these two headphones had to do with their reproductions of space. The PM-1s imaged much like typical headphones, while the LCD-Xes create a bigger soundscape that exists somewhat outside the head. With studio productions, the LCD-Xes’ soundstage was spread slightly larger, and pushed toward the front of my cranium. With distantly miked classical recordings, I felt more that I was in the audience, with the orchestra out in front of me -- whereas the same recordings through the PM-1s placed me at the conductor’s podium. Through the LCD-Xes, the hardanger fiddle in the Norwegian Soloists’ Choir’s White Night: Impressions of Norwegian Folk Music, conducted by Grete Pedersen (24/88.2 FLAC, BIS/e-classical), was placed slightly in front of me, with the choir spread out significantly behind it. Both fiddle and choir were much closer through the PM-1s, and the relationship between them was less explicit.

Consistent with the closer perspective, the PM-1s presented more instrumental and vocal texture than the LCD-Xes. With White Night, the attack of each note and the scrape of the bow against the fiddle’s strings were more evident. With Night of Hunters, I heard every last breath and movement of lips and tongue, as if Tori Amos were singing directly into my ear. These details were slightly obscured by the LCD-Xes.

I also compared the Oppo PM-1s to the HiFiMAN HE-500 headphones ($699). At 89dB/mW, the HE-500s’ sensitivity is considerably lower than that of the other two models. As a result, the HiFiMAN headphones demand a real headphone amp in order to come to life. Even then, the HE-500s don’t give as dynamic a performance as either the PM-1s or the LCD-Xes. Still, the HiFiMANs’ overall balance is commendably neutral. Their bass doesn’t reach as low as the Oppos’ or the Audezes’, but it’s controlled and well damped. The HE-500s’ soundstage isn’t projected much outside of the head, but their sound is somewhat more spacious than the Oppos’. Where the HE-500s give up the most ground to their higher-priced competition is in low-level detail and overall naturalness. While the HE-500s remain a solid value, the Oppo PM-1s belong to a higher class.

Conclusions

Oppo Digital’s first headphone model proves itself a strong competitor in the very demanding premium-headphone segment. The PM-1s’ warm balance pairs wonderfully with voices, offers enough extension to capture the essence of all manner of instruments, and grants an enjoyable listening experience with almost any recording. Their bass reaches authoritatively into the bottom octave and can deliver a firm punch, but always remains clear and controlled. They are comfortable playing extremely loudly, but can also resolve tiny details at lower volumes, transmitting the nuances that most audiophiles crave. The PM-1s would be worth considering on the basis of their sound alone.

Where Oppo has really demonstrated leadership is in the area of ergonomics and styling. The size and shape of other high-end headphones is clearly a secondary concern to their designers, while Oppo has fit excellent performance into a pair of headphones that are both attractive and portable. Their soft, lightweight padding makes the PM-1s exceptionally comfortable for wearing all day long. Adding in the first-rate materials and luxurious presentation, the PM-1s seem well worth their asking price.

. . . S. Andrea Sundaram
andreas@soundstagenetwork.com

Associated Equipment

• Headphones -- Audeze LCD-X, HiFiMAN HE-500
• Headphone amplifier -- Grace Design m902
• Digital sources -- Grace Design m902, Ayre Acoustics C-5xe^MP, Mel Audio Rechav, Apple iPod Touch (fifth generation)
• Computer -- Custom laptop running Windows Vista, Realtek HD audio ALC 272, with coaxial digital output running foobar2000
• Interconnects -- DH Labs Revelation, QED Silver Spiral
• Power conditioner -- Equi=Tech Son of Q

Oppo Digital PM-1 Headphones
Price: $1099 USD.
Warranty: Three years, limited; one year, earpads and headband leather.

Oppo Digital, Inc.
2629B Terminal Blvd.
Mountain View, CA 94043
Phone: (650) 961-1118

E-mail: service@oppodigital.com
Website: www.oppodigital.com