Oppo PM-1 Planar Magnetic Headphones Review

Hobbies tend to have three stages - Novice, Enthusiast, Maniac. We can recognize these stages in nearly every hobby. Do you have an old train set you put up every Christmas? You're a Novice. Do you have a higher end set that you have in your office or maybe a few collector pieces on display? You're an Enthusiast. Do you have a basement for your train set that is complete with buildings, trees, and more all built to scale? Welcome to Maniac my friend. You've probably spent more money on trains than others spend on their cars. You consider your basement a selling point of your home even though it clearly isn't.

But that's okay. It's your hobby and you are allowed to enjoy it.

People that love headphones follow that same trajectory. They start off with an iPod or other MP3 player (or if you are old-school, a Walkman or Discman) and use the included earbuds. Eventually, they decide that the earbuds suck (or they fall out during activities) and look for something better. At this point they enter the Novice stage. They won't enter Enthusiast until they have two or more pairs of headphones, one of which is dedicated to a specific use (like having one for exercising, a second for listening around the house).

The first time a person thinks a headphone amp might be a good idea, they are straddling the line of Maniac. This is a person that has decided that a quality set of headphones is worth spending a good chunk of cash. Not only that, they are worried about the entire signal chain. No longer will MP3 be good enough for this person. No, now they require high quality tracks so that they can hear the music the way it was intended. Next, they start worrying about DACs, amps, cables, and more. All to experience the best possible sound. 

In all honesty, a high performing headphone setup will cost you much less than a pair of quality speakers. The barrier to entry is pretty low for those that want to have some top-notch sound.  There are many types of headphones but, almost universally, enthusiasts agree that Over-Ear headphones are the best for long listening sessions. Also an oft-repeated opinion is that planar or electrostatic drivers are the best.

That may be because they are the most costly, but we'll get to that.

If you've been to the Magnolia section of a Best Buy, you've seen a planar speaker. MartinLogan and others made these types of speakers famous with their large metal grille jutting out of a woofer box. These are not the same as electrostatic speakers as the driver is completely different. The main difference is that a planar driver has the magnets mounted to the front and back of the drivers while the electrostatic driver uses an electrical charge to draw the diaphragm toward or away from metal plates.

Planar headphones have had resurgence in recent years. They were popular in the 70's with offerings from the likes of Yamaha. The advantage of planar drivers is that they present a purely resistive load to your amplifier allowing them to play nice with most devices. While you'll want a headphone amplifier for the best quality sound, planar headphones don't require an amp like electrostatic headphones.

Oppo PM-1 and PM2 Headphone Comparison Review

First Impressions

The Oppo PM-1 arrived in a box large enough that I was convinced they had shipped their new HA-1 Headphone Amp with the headphones (not scheduled to ship until the end of the month). They hadn't. The PM-1 headphones are treated like royalty by Oppo. They come triple-boxed, the last one being a large, glossy, wood case that would be right at home full of expensive cigars. The box is gorgeous if on the large side. Oppo has included a carrying case that felt like it was made out of denim. The carrying case has molded sides but it is essentially a soft case. You wouldn't want to throw the PM-1 headphones around and expect that this case would protect them.

    

The grand unveiling

The Oppo PM-1 headphones came with a number of accessories. The normal perforated leather earcups were removable and Oppo included a second set that was covered in black velour. The earcups attached by small, plastic binding posts and had a small cutout for the 2.5mm input on each earphone. Both were equally comfortable though the opening for your ear was on the small side. I have smallish ears so it wasn't a problem for me, but I could see it being an issue for people with larger ears. An over-ear headphone shouldn't have a problem covering an ear and I can envision some people having trouble.

The backs of the PM-1 headphones have a grille that allows sound out. This is common for planar and electrostatic headphones and even some headphones with dynamic drivers. Most planar headphones employ a good amount of dampening and the PM-1s do as well. Sound leakage was evident, as you would expect, but not nearly as loud as I expected. You won't want to use these on a train or airplane but it isn't as if the sound from outside the headphones is the same volume as inside.

Oppo PM-1 Backs

The Oppo PM-1 headphones came with two cables. In the box was a three-meter cable that terminated in a 1/4" plug. This is perfect for AV Receivers and some headphone amps. These days, every portable device and many other devices are utilizing the smaller 3.5mm plug. Case in point - the Emotiva Stealth DC-1 external DAC and headphone amplifier. This devices has not one but two 3.5mm outputs for your headphones. Oppo has included a second cable that terminates in a 3.5mm plug, but it is only one meter long.

One meter long is comically short. Most headphone cables are at least two meters. One meter didn't quite reach to my knee and I'm not a tall guy. One meter would reach to the headphone jack of my laptop if it was on my lap, but not if it was on my desk. I would question if a one-meter cable would be usable for any portable device that was NOT strapped to your arm. The quality of the cables was also dramatically different. The 3.5mm cable was PVC coated, thin, and pretty unremarkable. The 1/4" cable had thick cables, a tech-flex jacket, and seemed like the highest quality. Oppo was sending a clear message about which connection type they thought you should be using.

Long, high-quality cable

The PM-1 headphones weigh 14 ounces (395 grams) without the cables. I'm sure there are people right now that are complaining on forums about how heavy that is but I didn't find them at all uncomfortable. The clamping pressure it 5 N (Newton), which works out to just over 1 pounds-force. The clamping pressure is tight enough to keep the headphones steady, even when you turn your head quickly, but not so tight as to create pain over longer listening sessions. The band on the top is well padded and is as comfortable as any I've used.

Oppo has used a lot of metal with the PM-1 headphones and they look really great. The slide mechanism clicks into place with each adjustment and holds firm without being hard to manipulate. My smallish head required a little extra room from the slide but there was plenty left for people with larger noggins. There is a unique serial number on the right slide, further conveying the sense of quality about the PM-1 headphones.

Comfy Headband

Oppo PM-1 Use and Listening Tests

One of the advantages of planar over electrostatic drivers is low power requirements. Because the planar driver presents a purely resistive load, there are no wild impedance swings across the frequency response (as we'd see with dynamic drivers). They also don't have the low impedance and high power requirements we see with electrostatic drivers. So, if your amp has the voltage to drive the planar driver at one frequency, it should do fine at all frequencies.

Nope, no cigars, nothing but high-quality headphones here

The PM-1s are rated at 32 ohms with a 102dB sensitivity (1 mW). This is not an extremely hard load to drive for most devices and I had no problems powering the Oppos with my phone, other portable devices, and the headphone output of my laptop. From the standpoint of the end user, this can be seen as a benefit or curse. If you haven't bought a headphone amp, you don't necessarily need one. But if you have, and you spent a bunch of money on it, you may feel like you've wasted your hard-earned dough.

Don't. The Oppos will love all that power.

I used the PM-1 headphones almost exclusively with the Emotiva Stealth DC-1 headphone amp and DAC. The Emotiva is a standalone DAC and headphone amp that I run in purely asynchronous mode. This completely eliminates any jitter issues. I paired the Emotiva with my highest quality music, which is encoded at 24-bit and up to 192 kHz. Since it has 3.5mm outputs, I had to use Oppos one-meter cable. To actually reach the Emotiva, I paired that short cable with an extender I had lying around. For those that have just purchased a $1100 pair of headphones, pairing them with an extender seems almost sacrilegious. You'll also want to be careful about the extender you use since I found, after some testing, that one of my extenders negatively affected imaging.

Leather Earpads

I tried out both the different earpads (leather and velour) and found the sound remarkably different. The leather had a more open sound and definitely had more high-end extension. The velour pads seemed more subdued and warmer with a more laid-back high-end. At first I thought my mind was playing tricks on me. Later, I examined the back of the earpads and found that the velour material was extended into the opening of the earpad. Compared to the leather, the velour covered about half the opening. This seemed to deaden the high-end frequency response and give an overall warmer sound to the presentation. Later I found out that both the headphones were supposed to have the additional velour extending into the opening of the earpad. I preferred the sound of the PM-1s without the additional material.

Warmer is also how I'd describe the experience of wearing the velour earpads. The material didn't breath as well and was physically hotter than the leather. Personally, I preferred both the comfort and the sound characteristics of the leather. Having an earpad that physically EQs the sound was an interesting choice by Oppo and one that I haven't seen before.

Velour Earpads

 

With an open-back headphone, you are always worried about sound leakage. As I mentioned, the sound from outside the headphones wasn't nearly as pronounced as I expected. You could, however, hear the headphones from across a quiet room. Letting exterior sounds in was also an issue though not an unexpected one. I've had my parents living with me for the last few weeks as they look for a home in the area. I couldn't follow their conversations while l listened at a comfortable volume, though I could certainly hear that they were talking and found it to be very distracting. If you are looking into open-back headphones, you'll want to make sure you have a quiet location to use them.

Listening Tests

While the Oppo PM-1 Planar headphones could be driven easily by all of my devices, I definitely felt they sounded the best with the Emotiva Stealth DC-1. Pairing it with some high quality 24-bit tracks certainly allowed the PM-1 headphones to sing. I found, from a power standpoint, that the PM-1s could take up to 5dB more power from the DC-1. Part of that was that they just required more power. When I tried to A/B the PM-1 with other headphones (the DC-1 has two outputs), the volume differences were pretty dramatic.

    

Also dramatic - this box

But I found, over time, that it wasn't just that the PM-1s were power hungry. Instead, the sound was so clear and undistorted that I could turn them up louder without running into issues for driver breakup or fatigue. This clarity of sound was most evident in the midrange. The Oppo PM-1s midrange was so dramatically better than my other headphones that it was like comparing a Honda to a Ferrari. Sure, they are both cars, but you didn't need to be a car expert to tell that one had a performance advantage over the other. 

Vocalists in general and female vocalists specifically sounded much more forward and much more "in the room" than with other headphones. The result was a presentation that made it feel as if the vocalist was directly in front of you. The PM-1 headphones had more of an "inside your head" feel than other headphones I've experienced but not one that was distracting. The soundstage was wide but not as holographic as I expected. I thought with a planar driver, I'd have more of front and back movement in the soundstage but the PM'1s performed similarly to other headphones. This wasn't as much a knock against them as it was an adjustment of my expectations.

    

Less dramatic - this case

The bass response on the PM-1s was phenomenal. For the first time in all my headphone experience, I heard music down to 20Hz. Not noise, which is what most headphones produce in the bass region, but actual music. Not only was the bass response well extended, but also it was absolutely even as I flipped through the test tones. Sweeps from the bottom of the range up to the top maintained a subjective uniform volume level that I have never experienced. With tracks like Crazy from Seal, Junior B from Yello, and more, I heard bass as extended and clear as any headphone I've tested.

The top end of the frequency response is, traditionally, a sticking point for planar drivers. Subjectively, I liked the top end of the PM-1s. I put on Electric Counterpoint Version for Percussion - III by KUNIKO (96kHz/24-bit). This track features nothing but xylophone and a few other percussive instruments. Usually, the extreme top end of this track quickly becomes fatiguing after a few minutes on lesser headphones as the drivers distort or clip. Not so with the PM-1s. I could listen all the way through without feeling like the high notes were grating or piercing. Subjectively, I thought the top end of the PM-1s was a little rolled off. The notes that were there, however, sounded fantastic.

    

Oppo PM-1 Slide and Swivel

If I had to use a word to describe the PM-1 headphones from Oppo, it would be "clear". The biggest difference between the planar drivers and traditional dynamic drivers is the amount of silence you hear. When the music isn’t playing and it’s supposed to be quiet, it is. Notes start and stop without any “smearing” or  holdover. The dynamic range of the music seemed to increase exponentially compared to other headphones. This allows you to hear deeper into the music than you ever have before. You can hear nuances that were previously obscured by the less sophisticated driver technology of other high-end headphones.

Oppo PM-1 Planar Driver

One thing you'll hear from reviewers is that a speaker or headphone is unforgiving of poorly recorded music. This usually manifests itself on the top end where the presentation becomes harsh and the compression artifacts seem to be exacerbated. I found that the Oppo PM-1 headphones didn't display this propensity. Instead, EVERYTHING sounded great. The slight roll-off on the top end likely contributed to this impression. Sure, I could hear that some music was recorded and mixed better than others, but it wasn't as if I couldn't tolerate MP3s or streaming services like Pandora and Spotify.

If anything, this made me like the PM-1 headphones even more. Who wants to spend $1,100 on headphones you can only use with HD music? If I spend that much, I want to be able to use them with all my music. The PM-1 headphones were the perfect headphone - they could let your high quality tracks sing while being kind enough to streaming services that you could use, and enjoy, them even for casual use.

Oppo PM-1 Measurements & Analysis

Oppo claims the PM-1 driver is made of a very thin and light diaphragm whose entire surface area is evenly driven exhibiting piston like behavior.  The double sided diaphragm provisions for twice as many conductors within the magnetic field allowing for greater efficiency, reduction in inductance related intermodulation distortion also making the headphones a purely resistive impedance. 

Oppo PM-1 Impedance & Phase Response

Oppo’s claim of purely resistive load seems very plausible.  As you can see the PM-1s essentially measure like a straight line at 32 ohms with no appreciable phase shift in the entire audio band.  This should allow the PM-1s to sound consistently good regardless of the headphone amplifier output impedance which is an excellent design goal.

Oppo PM-1 Frequency Response

I constructed a very primitive ear by placing a microphone inside a styrofoam cup and positioned the headphones at the open end.  As you can see from the graph, these headphones are extremely linear.  In fact this is the best measurement I’ve ever pulled on a headphone system and explains why these headphones sound so tonally neutral and accurate.

 

 

Oppo PM-1 Comparison and Conclusion

I compared the Oppo PM-1 headphones to all the other headphones I have in my stable. The headphones I own range from $300 to $500 a set. Were the Oppos better? Yes. Were they 2.5x to 4x better? I'd have a hard time saying yes. The clarity was certainly there as was the bass extension. The dynamic range was very good (bass even at low volumes was very good) but I didn't feel like the imaging was as good as it could have been. Side-to-side pans were well executed but for $1100, I expected more pinpoint imaging in a 3D space. The high frequency response was pleasant but could have been better extended. I'm interested to see how the soon-to-be-released PM-2 headphones perform. At two-thirds the price of the PM-1 headphones, I expect these to be much more competitive.

As a side note Gene DellaSala directly compared the PM-1s to his reference Sennheiser HD600 headphones and found the Oppos to be more dynamic and forward sounding.  They not only sounded louder but fuller, especially in the midrange.  However, he felt the high frequencies were a bit more laid back on the PM-1s while they were a bit more detailed and airy on the HD600s.

Oppo PM-1 and PM2 Headphone Comparison Review

Conclusion

The Oppo PM-1 Planar Magnetic headphones surprised me on so many levels. I expected them to sound great with high quality music, and they did. I expected them to be clearer and crisper than other headphones with traditional drivers, and they were. What I didn't expect was phenomenal bass response, a midrange that was absolutely pristine, and the ability to be driven by nearly any device. They were even forgiving of poorly recorded or compressed music. For $1,100, you want a great headphone but you might expect that they could only be used with high quality music. The PM-1s were perfect for not only critical listening, but were great for casual listening as well.

Oppo PM-1 Planar Magnetic Headphones

MSRP: $1099

www.oppodigital.com

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Build Quality
Appearance
Treble Extension
Treble Smoothness
Midrange Accuracy
Bass Extension
Bass Accuracy
Imaging
Soundstage
Dynamic Range
Fit and Finish
Performance
Value