In baseball, a "utility player" must have a specific set of skills, but his principal skill must be that he is pretty good at everything, but not necessarily superstar-level at any specific skill. The PM-1 is the headphone equivalent of the best utility player I've ever had the pleasure of putting through its paces. While there is no particular sonic parameter where the PM-1 excels, when you add up all the areas where it performs at nearly reference level, you wind up with a headphone that delivers a high level of enjoyment that rarely gets in the way of the music, regardless of the device it's tethered to.
The PM-1 is a very natural- but not neutral-sounding headphone. Music has a relaxed and organic quality, but it varies from ruler-straight neutrality. This variation occurs in the treble region, where the PM-1 sounds slightly rolled off. Compared with airy-sounding headphones, such as the Stax Pro Lambdas, the PM-1 seems slightly less detailed, and the overall soundstage size is somewhat smaller than the Stax's.
Headphone neophytes often complain that headphones don't produce a three-dimensional image like speakers do. Actually, headphones do produce a three-dimensional image, but instead of being "out there" in the room, the image is "in here" inside your head. Some audiophiles never get comfortable with that. It took me a while to get accustomed to the "in-head experience"; but, once you make the adjustment, you'll find that the imaging specificity and precision that you hear with the best loudspeakers is also available through headphones. In this performance area, the Oppos are very good, but not quite as spacious, specific, and precise as the image produced by the Audeze LCD-2 or Stax headphones.
Dynamic contrast and the overall dynamic range of music through the Oppo PM-1 headphones is almost on a par with the best I've heard. This is one performance area where the PM-1s will deliver somewhat better performance when tethered to a dedicated power amplifier instead of a smartphone. When hooked up to the SicAmp headphone amplifier, the PM-1s had slightly more slam and dynamic contrast (as well as a more silent background) than when connected to my iPhone's headphone outputs.
Bass extension through the PM-1 is good; but, for those devotees of dubstep who want enough of the "sub-bass" energy to get a full dose of deep throbbing, these are not the most bass-centric headphones around. I found for my musical tastes, though, that the PM-1's bass capabilities were more than adequate. Bass definition was good enough so that the essential organic character of the acoustic bass on my own live recordings came through clearly with minimal editorialization from the Oppo in the way of bass bloat.
The upper bass and lower midrange through the Oppo are a bit more prominent than ruler-flat, giving the PM-1 a slightly warmer-than-neutral harmonic balance. Although not as warm as some, such as the V-Moda M-80, the PM-1 will augment dry, cool mixes with a bit more richness and weight. Many of the 128-Kbps Internet radio feeds I listen to sounded especially good through the PM-1s - the radio feeds' tendency toward splitchiness was reduced slightly by the PM-1's harmonic balance.
The PM-1's most seductive sonic characteristic is undoubtedly its smooth midrange. Aided in large part by extremely low amounts of intermodulation distortion, the PM-1's midrange presentation has an exemplary clarity and lack of additive coloration. While not the ultimate in extreme low-level detail resolution, the PM-1's lack of midrange distortion makes it easy to listen to individual elements within a mix. Unlike some detail-oriented headphones like the Stax Pro Lambdas, whose greater treble energy output can make some less-than-pristine sources sound worse than they really are, the PM-1 tends to "improve" inferior source material by allowing the midrange to emerge with a level of finesse that counters some of the source's sonic inadequacies. If most of your music library is made up of 320 and lower MP3 files, the PM-1 may be a better overall sonic option than a more revealing pair of headphones.
� The PM-1s are efficient and easy for even a smartphone amplifier to drive successfully.
� These are among the most comfortable headphones on the planet.
� They are built to last with pre-tested pivots and yoke.
� Treble extension is slightly truncated.
� The PM-1s, like all open-backed headphones, do little to isolate the listener from their environment.
� The packaging is more deluxe than many prospective owners might like.
Competition & Comparison
If your headphone budget is slightly more than $1,000, you have many purchasing options besides the PM-1 headphones. If you desire more treble extension and a bigger bottom end, you should consider the Audeze LCD-2 ($995) headphones. For some audiophiles, the LCD-2's additional weight and less comfortable fit are out-pointed by their excellent sonics.
Another somewhat less-expensive headphone option is the Mr. Speakers Alpha Dog headphones. This $650 closed-ear design provides excellent isolation from external noise, as well as a very natural, articulate sound. Although not quite as comfortable or easy to drive as the PM-1, the Alpha Dogs are an excellent all-purpose headphone that delivers the best imaging I've heard from a closed-ear design.
If you have some upward stretch to your budget, the newly released Audeze LCD-X ($1,699) is another fine reference-quality headphone option. With a higher sensitivity and lower impedance than the other Audeze headphones, the LCD-X can be driven by a smartphone as easily as the PM-1.
If you are looking for the most revealing, highest resolution headphone regardless of fit or amplifier compatibility, the Oppo PM-1 will probably not make it on your short list. However, if you want easy-to-drive, ruggedly constructed headphones that are so comfortable, it's easy to forget you are even wearing them, the Oppo PM-1 may be just what the audiologist ordered. Although I had at my disposal several more revealing headphones during the review period, I often chose the Oppo PM-1s over those headphones because they are supremely comfortable and their midrange presentation is so clean and uncolored. For some audiophiles, labeling the Oppo PM-1 as "a music lover's headphone" might be the kiss of death, but I think that a large portion of audiophiles will find that the Oppo PM-1 ranks as the best all-around, general-purpose headphone currently available and can deliver more long-term musical enjoyment on a wider variety of sources and devices than the vast majority of "reference" headphones. After an hour with the Oppos, you may find, just as I did, that taking them off is the last thing on your mind.