For example, on something like Senheiser HD5xx or HD6xx, I can hear the distorsion if I listen to loud levels.
If I am to boost the bass on the above mentioned (as both lack sub-bass), the distorsion would become audible even
earlier. And on those even at medium levels, the bass in not as clean as on the Oppo PM-3.
Initially my expectations were very high in regard to this headphone.
Most reviews said they're very easy to drive and sound fantastic. While they do sound fantastic (with EQ), they're certainly not very easy to drive as you will see below.
HOW EASY THEY ARE TO DRIVE:
For me, easy to drive means they can be driven at fairly loud levels from pretty much anything, including a phone/dongle.
That is clearly not the case: these pair will require a fair amount of power to be driven loud. And while they can be driven at low to moderate volumes by pretty much everything, you will definetely need a DAC/amp for these if you want to go above moderate SPL levels.
While there are headphones that are much harder to drive out there (like the 120Ω HD560S, the 300Ω HD6xx and the 470Ω AudioTechnica R-70x among others), something like the SONY MDR-1AM2 is significantly easier to drive. That's why I want to put this in context.
That said, most DAC/amps and DAPs with decent power output (like 200mW RMS or more) will be able to drive these without an issue.
Despite the PM3 have a pretty high clamp force, they're very comfortable and can be worn for many hours without fatigue.
The original leather is very breatheable, you won't get hot or sweat unless the environment is very hot.
One of the best leather ones that I've tried, however there's also a big downside to this: genuine pads are very expensive to buy (if you can find them at all), while the headband itself cannot be found.
The headband can be repaired with the right materials as it's only clipped on (I have the limited edition version). When I will repair it, I intend to replace the material with something velour-like which will last a lot longer.
Problem is velour will be of a different color, typically black so you will have to accept the looks as they are.
When buying these, do keep in mind that leather will wear sooner or later and you will have to find a replacement.
I have ordered a pair of black velour pads for future use, but they have not arrived yet. I will update the review if I find those pads to be a suitable replacement for my taste. Velour pads will likely attenuate the bass, requiring less EQ.
Also do keep in mind that most aftermarket pads are not as high quality as the original.
This is by far the biggest disadvantage of the Oppo PM3.
The sound quality on these is exceptional: they sound good and clean even without EQ, but depending on how certain tracks are mastered you will hear too much boomines (due to very elevated upper bass) and a bit muffled lower treble.
To my ears they sound the best when you apply EQ to them, as this way you will benefit from both a very low THD and a frequency response that's very very close to the Harman curve.
Overall I would rate the sound quality a 5/5 with EQ and a 4/5 without EQ. This means that while it can be used without EQ and it can even be beneficial on tracks that have less bass than normal due to poor mastering, using EQ will make this headphone sound neutral and without any coloration.
Contrary to what another review has said, this headphones are not neutral without EQ: the upper bass is quite too boomy,
while the lower treble does sound a bit muffled (both show up on measurements).
It is also to be mentioned that neutral ≠ flat frequency response. Neutral means that the frequency response that we perceive audibly is flat and that is obtained by the Harman curve (which is not flat) because the head transfer function
is not a linear one.
Overall, this is one of my favourite pair of closed-backs due to very good comfort combined with top sound quality and a relatively standard cable. The big downside is these are no longer made and aftermarket pads are not of the same quality. Given these have quite a following, maybe we'll see better pads and even headbands in the future.
I recommend getting the Oppo PM-3 if you have no problem with using EQ and if you find a pair that has the original leather still in good condition. Then be prepared to replace pads and repair the headband.