Introduction
I recently participated in the OPPO PM-1 loaner program -- many thanks to Chris and the folks at OPPO for providing this wonderful opportunity! I was able to demo the PM-1 headphones at home and at work for the past week, and it was a great experience.
I'll forego a long introduction to these headphones -- if you're reading this review, you probably already know that the PM-1 is OPPO's current flagship headphone and represents their unique take on planar magnetic technology in an open-back design. The PM-1 departs from the other planar magnetics on the market in many ways, and I'll do my best to explore those things that make the PM-1 a unique product in this review.
Design and Build Quality
Removing the PM-1 from their packaging, the first thing that strikes you is the outstanding level of build quality. It's immediately obvious that these headphones are built to the highest standards, using premium leather, metal, and plastic materials. The headband is wrapped in lambskin leather and is nicely padded on the underside. The adjuster mechanisms and ear cup swivels are made from a polished metal, and the ear cup gimbals are of brushed aluminum. The ear cups themselves are crafted from high-quality plastics with polished metal trim rings and metal screens on the back. The ear pads are either made from the same lambskin leather as the headband, or from a soft, microfiber velour. To say that these headphones set the standards for build quality would be an understatement -- they are head and shoulders above most other headphones I have used. The only headphones that I can think of that may be able to compete in build quality are the Sony MDR-R10 and the Stax SR-009, both of which are many times the price of the PM-1. Other manufacturers could certainly learn a thing or two from OPPO's example.
The design of the PM-1 is very well-conceived, both aesthetically and functionally. The headphones have a simple understated and elegant look, and they sit unobtrusively on the head, especially when compared to headphones with suspension-type headbands such as the newer HiFiMANs or AKGs. The adjuster mechanisms operate smoothly and adjust with a reassuringly tactile click. The swivels and gimbal joints rotate smoothly and silently without any slack or slop. The detachable cable is two-sided and plugs into the headphones via a pair of mono 2.5mm plugs. I usually find the 2.5mm plugs to be an inferior option when compared to the Sennheiser HD800 connectors, which are the gold standard in my opinion, but the PM-1's connectors are particularly well-implemented. They seat into the ear cups firmly, and there is a small rubber boot at the base of the plug that fits into a recess in the ear cups to provide some additional insertion friction and strain relief.
Also very much worthy of note is the attachment system for the ear pads. The ear pads have four small posts on their base, and these posts slide securely into four rubber grommets in the ear cup. This design, very similar to the way in which many speaker grilles are attached to speakers, is by far the best ear pad attachment system I have ever used. Ear pad changes are extremely easy and can be done in a matter of seconds. Bravo!
The PM-1 is an open-back headphone, and it sounds like an open-back headphone, but interestingly it doesn't leak very much sound to the surrounding environment. I was able to listen to the PM-1 at significantly louder volumes than my K701 at work without disturbing my coworkers. It's a very neat trick that I definitely appreciated.
All considered, the PM-1 gets perfect marks from me for design and build quality. The care that was taken in creating these headphones is self-evident in every facet of their look and function.
Accessories
The PM-1 comes with a veritable plethora of accessories. For carrying and storage, there is a beautiful wooden box (though for ease of shipping, this was not included in the loaner program, so I did not get a chance to see it for myself), as well as a zippered selvedge denim carrying case. The denim carrying case is lined with a soft velour and the headphones fit snugly inside. There is even a small velour flap that sits in between the two ear cups to prevent the aluminum gimbals from scratching against each other during transit -- smart! The only minor downside to the denim case is that the cable must be detached from the headphones for them to fit.
There are two cables included in the package as well -- a three-meter, fabric jacketed cable intended for home use, and a one-meter small rubbery cable for portable use. Like the headphones, the larger cable is built very nicely, with custom metal plugs on both ends and a matching metal splitter at the Y. The smaller cable, though perfectly functional, falls short of all the other accessories in terms of build quality -- it's a little bit thin and it tends to suffer from a memory effect, so when you coil the cable to fit it in the case, it retains some of that coiled shape during use. Just a minor annoyance.
Finally, the PM-1 is packaged with three sets of ear pads: the original lambskin leather pads, alternate lambskin leather pads, and velour pads. All of these pads alter the sound of the headphones, and with the super-easy-to-use attachment system, it is a simple matter to swap pads to find the pair that best suits your sonic preferences (more on this below). The pads are all very well-made, with nice-feeling leather or velour covering a compliant, springy latex foam cushion sitting atop a solid plastic frame.
Compared to many competitors, the PM-1 is very well-accessorized and comes with almost everything you could possibly need. The only other thing I can think of that could be included is a balanced cable, but this would certainly raise the price unnecessarily for those users who don't need it. For this reason, OPPO offers a couple of different balanced cable options that can be purchased separately. Once again, my hat is off to OPPO!
Comfort
I was originally concerned about comfort with the PM-1, but I am happy to report that these concerns turned out to be mostly non-factors. The rectangular opening of the ear pads is somewhat small, but my medium-large ears fit inside without any trouble, albeit snugly. My ears definitely touched the inner surfaces of the ear pads in several places; I know this is a deal-breaker for some, so those people will probably want to pass on the PM-1. The good news is that the pads didn't put any undue pressure on my ears where they made contact, and this, combined with the use of nice, touch-friendly materials in the pads, allowed me to wear the PM-1 for a solid four hours before the contact became mildly irritating. To give you a reference point for comparison, I can't tolerate wearing on-ear headphones for more than a few minutes, so the fact that I could comfortably wear the OPPOs for several hours speaks to their overall good comfort.
All of the ear pads are very comfortable -- the lambskin leather and microfiber velour both feel very nice against the head. They get warm after about 30 minutes of use, but at that point they sort of plateau and don't get hot, so I never had any problem with the thermal aspects. The latex cushion material used in the ear pads is a very nice choice, and I found it more comfortable than most other conventional or memory foam pads. Also, I've been using the same latex foam rubber pillow on my bed for years and years -- so if that's anything to judge by, I would say the padding in the PM-1's ear pads should hold up for a very long time.
Being a planar magnetic headphone, and in particular one that is built from such solid, high-quality materials, the PM-1 is a little heavier than most other headphones on the market (although still lighter than many other planar magnetic competitors). Fortunately, the weight never bothered me at all. The underside of the leather headband is very nicely padded and it distributes the weight evenly across the head. I never experienced any "hot spots" from excessive pressure on one particular area. Clamping force is also dialed in well -- it clamps just tight enough to sit securely on the head and not a newton more.
The HD800 still sets the standard in headphone comfort for me, but the PM-1 is no slouch either. If I were to give the HD800 a perfect 10 for comfort, the PM-1 would come in at a solid 8.
Sound
Just like comfort, sonic impressions are always highly personal, so take anything I write here with a grain of salt. For reference, I listened to the PM-1 on four different systems for a total of probably about 50 hours. Two were my home systems, consisting of a NAD M51 DAC feeding either a Schiit Asgard 2 or Sennheiser HDVA600 amplifier. The third was directly from my iPhone 4, and the fourth was directly from the headphone output of my HP laptop at work. The PM-1 is a fairly sensitive headphone, and none of these systems had any trouble driving the PM-1 to earsplitting volume.
Compared to many other headphones, I found the PM-1 to be relatively agnostic of amplification. They definitely sounded a little cleaner and more dynamic from my Asgard 2 or HDVA600, but the differences weren't that large. Some people will see this as a positive, while others will see it as a negative. Those in the positive camp will appreciate that it doesn't take much to get these headphones sounding near their best, and that the headphones deliver a consistent sound from almost any amplification. Those in the negative camp may be disappointed that the PM-1 doesn't scale up much with better, more expensive amplifiers. Personally I fall into the former camp -- why would I not be happy that the headphones can sound good out of almost anything?
I was particularly interested to see how the sound of the PM-1 would change between my Asgard 2 and HDVA600. The Asgard 2 has a relatively low output impedance (less than two ohms), compared to the HDVA600 which has a higher output impedance (43 ohms) that is tuned specifically with high-impedance headphones in mind. The PM-1 has a low nominal impedance of 32 ohms, so conventional wisdom would suggest that the Asgard 2 would be the better choice. However, I found the PM-1 to sound nearly identical from both amps. I suspect that this is due to the fact that the PM-1 is a planar magnetic headphone, so its impedance doesn't change very much as a function of frequency. This differs from dynamic headphones, which can have wild swings in the impedance curve due to electromechanical driver resonances and inductance in the voice coil.
So enough with the amplification discussion, how does the PM-1 actually sound? Very good! In a sentence, I would describe the PM-1 as a warm headphone with a forward midrange and a non-fatiguing treble response, yet still clean, clear, and open. Overall, it's a very appealing sound signature that provides a nice counterpoint to the traditional, analytical "hi-fi" sound that you get with Sennheisers, Beyerdynamics, and AKGs.
The PM-1's bass is very good and characteristically similar to other planar magnetics I've heard from Audeze and HiFiMAN. It is tight and well-controlled, and it extends very deep. However, the tuning is somewhat different when compared to many dynamic headphones. I've found that most dynamic headphones tend to have a bit more emphasis on the mid-bass compared to the sub-bass, and this adds the impression of slightly more punch and impact. On the other hand, the PM-1, like most planar magnetic designs, has a relatively flat bass response with the mid-bass and sub-bass coming in equal quantities. To those who are accustomed to dynamic headphone bass, the PM-1 can sound like it's lacking a little bit of impact at times, but it makes up for this by giving you more of those deepest frequencies. I wouldn't say either presentation is right or wrong, but rather just a matter of preference. In terms of bass quantity, I felt that the PM-1 was just about right, providing a solid foundation for the other frequencies to build upon.
The midrange is definitely where the PM-1 excels. The PM-1 puts the mids forward in the overall presentation, and they are velvety smooth and alluring. The mid-bass transitions seamlessly into the mids, and the lower and upper mids are present in roughly equal quantity without any abnormal peaks or troughs in between. As a result, all vocals sound exceptional on the PM-1 -- the lower mids lend body and texture to male vocals, while the upper mids deliver the clarity and realism needed for female vocals. There is a good amount of detail present in the mids, though they may lack the last ounce of detail retrieval that some other flagship headphones can produce. The midrange presentation of the PM-1 reminded me a bit of the venerable Sony R10, though I think the Sonys still retain their crown as the king of mids.
From other reviews, I was initially worried that I might find the PM-1's treble too subdued and dark. I had this problem with the Audeze LCD-2 (1st revision), which sounded very dead and claustrophobic to me with their weak treble response. I'm happy to report that this was not at all a problem for me with the PM-1. I found that the PM-1 lacks only in treble extension, not in treble quantity. The treble response is very clean and well-behaved, without any of the peaks that make many headphones fatiguing. It provides a nice sense clarity and openness to the overall sound, though it doesn't quite have enough extension to give that last measure of air in the highest registers.
I quite liked the spatial characteristics of the PM-1's sound. Imaging was very nice, though not quite as good as the best dynamic headphones like the HD800. For me the imaging was better than any other planar magnetic headphone I've heard -- maybe due to the tangerine-like waveguide in front of the driver? The soundstage is modest in size but nicely spherical in shape, with roughly equal height, width, and depth. I liked the soundstage size; it provided a more intimate presentation that can be very appealing for certain types of music. One of my favorite things about the PM-1 is how it pulled off a sense of decay -- you can clearly follow sounds as they reverberate and trail off into the blackness of the soundstage. I think this sense of decay comes from the PM-1's ability to reproduce the full dynamic range of music from the loudest to the softest sounds.
I found the PM-1 to be versatile, sounding good with a wide variety of genres. The forward mids worked very well for rock, though they could occasionally sound just a bit congested with metal. The clean bass and treble provided for a very good listening experience with electronic music. As for acoustic music, the PM-1 generally acquits itself very well. Plucked strings sound excellent, from bass to guitar, banjo to mandolin; as a result, folk and bluegrass was quite appealing on the PM-1. Bowed strings were also good, but perhaps not up to the level of realism provided by the HD800. Interestingly, the PM-1 was also outstanding for movies, TV shows, or other spoken material -- the forward mids make speech very intelligible.
As I had mentioned previously, the PM-1 comes with three sets of ear pads, each of which alters the sound signature. The alternate lambskin leather pads were my clear favorites, followed by the original leather pads, with the velour pads bringing up the rear. The sonic impressions provided above were for the alternate leather pads. Comparatively, the original leather pads sound more closed-in, with somewhat less treble and a bit more bass. The velour pads move the headphones even further in that direction, boosting the bass and shrinking the soundstage even more. I wouldn't call the PM-1 a neutral headphone, but the alternate leather pads were definitely the closest to neutral of the three.
Conclusion
Overall, I very much liked the PM-1. The design and build quality are top-notch. It offers a very appealing and unique sound signature compared to most other high-end headphones, though it may fall just a hair short in terms of ultimate resolution and technical ability. I didn't really find the PM-1 to be neutral, so I'm not sure I would choose it as my only headphone, but I think it would make an excellent complement to a more neutral flagship like the HD800(S) or T1.2.
In terms of sound quality, I personally think the PM-1 may be just a little bit pricey at the full retail price of $1099; however, the build quality and accessories certainly go a long way in justifying the price tag. I think the PM-2 is probably a more compelling bargain, offering the same sound quality with fewer accessories and slightly less-premium materials at the lower price of $699.
Again, I'd like to thank OPPO for the chance to demo the PM-1, and I may be adding a PM-2 to my collection in the not-too-distant future!
