[Asurada]

It has very impressive sound but I do not like because of distortion at mid-bass.

 

[bigshot]

  It has very impressive sound but I do not like because of distortion at mid-bass.

 
Then distortion is actually in the low mids, but it is very narrow and not particularly high at normal listening levels. If you turn your music up to very very loud volumes, it *may* be an issue, but odds are you will hear distortion from the high volume itself pummeling your ears before you hear the distortion in the cans.
 
Distortion audibility depends on the frequency band it inhabits (1kHz to 4kHz is the worst range), the width of the response curve that it affects (a wide swath across lots of frequencies is more audible than narrow bands) and the amount of the distortion. (1% is a conservative general rule of thumb as the threshold of audibility). The PM-1s have an extremely narrow range (about a third of an octave), the frequency range is down low where human ears are more forgiving, and it only gets to 2% even at a fairly loud volume level. In practice, listening to typical music, it isn't going to be a problem. It probably is several times lower than anything you could hear with normal music listening. I would worry about it if you wanted to listen to bass heavy hip hop at ear splitting volumes, but these really aren't the headphones for that anyway.

 

[Asurada]

   
Then distortion is actually in the low mids, but it is very narrow and not particularly high at normal listening levels. If you turn your music up to very very loud volumes, it *may* be an issue, but odds are you will hear distortion from the high volume itself pummeling your ears before you hear the distortion in the cans.
 
Distortion audibility depends on the frequency band it inhabits (1kHz to 4kHz is the worst range), the width of the response curve that it affects (a wide swath across lots of frequencies is more audible than narrow bands) and the amount of the distortion. (1% is a conservative general rule of thumb as the threshold of audibility). The PM-1s have an extremely narrow range (about a third of an octave), the frequency range is down low where human ears are more forgiving, and it only gets to 2% even at a fairly loud volume level. In practice, listening to typical music, it isn't going to be a problem. It probably is several times lower than anything you could hear with normal music listening. I would worry about it if you wanted to listen to bass heavy hip hop at ear splitting volumes, but these really aren't the headphones for that anyway.

Yeah, actually 200~500Hz range. I feel something 'dirty' sound because of that even normal volume range(80~90dB).

 

[bigshot]

At the loudest volume you normally listen, the distortion would only occupy a range of only 2 1/2 musical notes and it would be over 30dB down under the music. The ear is much less sensitive to distortion in this range than at higher frequencies.  It really isn't likely to be particularly audible under music. You might be able to hear it with the right test tone, but not music.

 

[tinyman392]

I don't think I'm being defensive regarding Oppo's decision related to the PM-2 tuning and the PM-1's new alternative pads. Rather, I'm being realistic. I was a beta tester for the PM-1 and I know that I put in easily over 100 hours of listening time between various beta PM-1's and various beta pads. Lot of other people did too. And I'm no Oppo fanboy--like Hastur said, the beta testers were Oppo's worst critics. I know the work that went into voicing the PM-1 just on our (the beta testers') end. I can't even imagine how much work went into it by Oppo's designers and engineers. Therefore, when you state that Oppo has realized it made some sort of colossal blunder because it did not test the PM-1 thoroughly, I just have to shake my head. On second thought, maybe I am a little defensive, because by indicting Oppo's work on tuning the sound of the PM-1, you are in part impugning me.

 
I don't think anyone is saying that Oppo made a colossal blunder, or any blunder for that matter.  Rather, they tried retuning the headphones, though pads, to be more linear, a criticism that came across from Head-Fiers.  I do, however, feel that trying to do this was a mistake as it increased edginess and sacrificed bass extension in the process (if the PM-2 is to say anything about the PM-1 in contrast ignoring pad differences).  After hearing what a more neutral, treble-focused headphone the PM-1 could have been, I feel that they made the right decision with the original PM-1 by taming the treble a bit to rid of edginess.  

 

[bigshot]

  I don't think anyone is saying that Oppo made a colossal blunder, or any blunder for that matter.  Rather, they tried retuning the headphones, though pads, to be more linear, a criticism that came across from Head-Fiers.  I do, however, feel that trying to do this was a mistake as it increased edginess and sacrificed bass extension in the process

 
What we are saying as people who are pretty familiar with these cans is, the PM-1s already are linear in their response. The differences you are pointing out aren't addressing any problem in the PM-1s. It sounds like it's just a completely different sound signature- not flat but leaning toward the upper mid/treble side.

 

[zilch0md]

Personally, I think all the talk about pads is just a way to convince people who had a bad impression of the PM-1 that they should check out the PM-2. Odds are all the pads sound basically the same.

Spoiler: Warning: Spoiler!

I can't imagine Oppo wanting pads to be anything other than basically transparent, presenting the sound of the transducer as straightforwardly as possible. If they did significantly alter the sound in a mechanical way, it would probably be different sorts of a shift at different volume levels or with different people's head shapes. Tuning the transducer is a lot more consistent and predictable than trying to tune the sound with soft, squishy lumps of leatherette and foam rubber. When you have to stuff a sock in it to get it to sound good, something is seriously wrong.

As others here have said, I am very happy with the response of the PM-1s too. I don't see any need to "improve" the response of the PM-1s in any significant way, Igor Levitzky obviously signed off on the sound of the PM-1s with the stock pads, so it was good enough for him. If Oppo can do the same thing for a lower price with the PM-2s, it will be a very popular product with people who couldn't afford the PM-1s. I do see that they might want to indulge in a little bit of advertising spin by planting a subjective seed that the PM-2s are "new and improved" or "different but the same" to take the curse off the price drop from the PM-1s. A smart businessman once said, "You can raise your price, but lowering it is even harder. Raise the price and some people might get mad. But those are the people who haven't chosen to buy your product yet anyway. However, if you lower your price, you anger the people who have already proven they are your customers by buying at the higher price in the first place." That may be what all this is about.

I really agree with the sentiment of the remainder your post, but I have to respectfully disagree regarding the pads "all sounding basically the same." The absence of a felt ring makes a big difference to my ears (PM-2 pads vs. PM-1 lambskin) - far less subtle than the difference between PM-1 lambskin and velour pads.

Mike

 

[Justin_Time]

While it is relatively easy to SHOW the difference between things we can SEE, it is much harder to show the difference between what we can HEAR. We can only attempt to describe it which leads to a lot of unnecessary arguments. But that would not stop us from trying

From what I can hear, the voicing of the Oppo PM-1 is pretty neutral with just a little trouble in the trebles--Just a tad lacking. This minor shortcoming may be fixed with different pads.

To my ears, however, the problems with the Oppo PM-1 sound is more fundamental: a lack of transparency and resolving power (plus a constricted sound-stage but that is secondary). More trebles may artificially fix this problem but it would be just a band-aid.

To hear what I was alluding to, you can listen to the PM-1 and focus only on the voice in the center, ignoring the bass and trebles. Now you can switch to the LCD2/3, HE-6/500/560, HD800, TH-900 and even Ultrasone 8. Again focus on the voice and ignore everything else: if you hear what I hear, it would seem that you have just removed your hands that were cupped around your mouth--I am exaggerating here--or lifted a veil from the sound.

My speculation is that there is a problem with the dampening of out-of-phase sound. Like all dipoles, the PM-1 produces direct sound to you ears and 180 degree out-of-phase sound moving away from your ears. If this latter is not allowed to dissipate away like in other dipolar headphones like the HE6/HE-500/HE-560 or the LCD2/3/X, then in must be properly absorbed (dampened) within the inside of the ear-cups. Or it will create havoc with cancellations of the direct sound leading to its degradation. I guess this may be what is happening with the sound of the PM-1.

I think that Oppo may have bitten off more than they can chew in their very first dipolar headphones. Audeze did not attempt the closed ear cups for their dipolar drivers until recently. HiFiMAN has not attempted it yet. But I have faith in Oppo. They have always served me well in the past 10 years or so with fixing problems and providing upgrades to customers with very reasonable prices.

I am anxiously awaiting the alternate ear-pads ad hope that they will prove me wrong.

 

[arnaud]

While it is relatively easy to SHOW the difference between things we can SEE, it is much harder to show the difference between what we can HEAR. We can only attempt to describe it which leads to a lot of unnecessary arguments. But that would not stop us from trying

From what I can hear, the voicing of the Oppo PM-1 is pretty neutral with just a little trouble in the trebles--Just a tad lacking. This minor shortcoming may be fixed with different pads.

To my ears, however, the problems with the Oppo PM-1 sound is more fundamental: a lack of transparency and resolving power (plus a constricted sound-stage but that is secondary). More trebles may artificially fix this problem but it would be just a band-aid.

To hear what I was alluding to, you can listen to the PM-1 and focus only on the voice in the center, ignoring the bass and trebles. Now you can switch to the LCD2/3, HE-6/500/560, HD800, TH-900 and even Ultrasone 8. Again focus on the voice and ignore everything else: if you hear what I hear, it would seem that you have just removed your hands that were cupped around your mouth--I am exaggerating here--or lifted a veil from the sound.

My speculation is that there is a problem with the dampening of out-of-phase sound. Like all dipoles, the PM-1 produces direct sound to you ears and 180 degree out-of-phase sound moving away from your ears. If this latter is not allowed to dissipate away like in other dipolar headphones like the HE6/HE-500/HE-560 or the LCD2/3/X, then in must be properly absorbed (dampened) within the inside of the ear-cups. Or it will create havoc with cancellations of the direct sound leading to its degradation. I guess this may be what is happening with the sound of the PM-1.

I think that Oppo may have bitten off more than they can chew in their very first dipolar headphones. Audeze did not attempt the closed ear cups for their dipolar drivers until recently. HiFiMAN has not attempted it yet. But I have faith in Oppo. They have always served me well in the past 10 years or so with fixing problems and providing upgrades to customers with very reasonable prices.

I am anxiously awaiting the alternate ear-pads ad hope that they will prove me wrong.

 
All headphones are dipole transducers with some form a baffling. There's no particular reason I see why planars would be more difficult than other types of transducers to sound right in an open back arrangement (please someone educate me if I am missing something). The problem with planars is how critical it is to damp the driver as you seem to always get these nasty resonances in the 7-10kHz region. I would guess the PM-1 was voiced so as to prevent the humongous 10kHz resonance to sound disjointed from the rest of the spectrum but instead leverage its low Q by applying plenty of damping and still getting reasonable extension in the highs.
 
BTW, the PM1 sound the same when placing ones hands against the open back, which is another proof that your theory may not hold the water. It turns out the driver back wave is so so heavily damped the open back or closed back does not seem to make much of a difference.

 

[TMRaven]

Which is why the PM-1 should be truly open back.  I feel all that damping behind its driver is suffocating its sound.  From all the talk and impressions, the pads also seemed to be hampering it a bit.  
 
Planar Magnetics are truly dipoles compared to regular dynamic drivers.  They don't just leak sound if they're in an open-back form, they project it out.  Ask anybody who's heard an open dynamic headphone vs an open planar headphone and they'll tell you the Planar Magnetics can basically become like speakers if you give them enough gain on the amp.

 

[Justin_Time]

 
All headphones are dipole transducers with some form a baffling. There's no particular reason I see why planars would be more difficult than other types of transducers to sound right in an open back arrangement (please someone educate me if I am missing something). The problem with planars is how critical it is to damp the driver as you seem to always get these nasty resonances in the 7-10kHz region. I would guess the PM-1 was voiced so as to prevent the humongous 10kHz resonance to sound disjointed from the rest of the spectrum but instead leverage its low Q by applying plenty of damping and still getting reasonable extension in the highs.
 
BTW, the PM1 sound the same when placing ones hands against the open back, which is another proof that your theory may not hold the water. It turns out the driver back wave is so so heavily damped the open back or closed back does not seem to make much of a difference.

 


[All headphones are dipole transducers with some form a baffling. There's no particular reason I see why planars would be more difficult than other types of transducers to sound right in an open back arrangement (please someone educate me if I am missing something)].

That is not quite true. "Dynamic drivers" like in the majority of headphones and loudspeakers are NOT dipolar, i.e their sound emanates mostly from the FRONT of the drivers toward your ears with only minimal reflrected sound dissipating away from your ears toward the back of the earcups. This type of sound is relatively easy to absorb and prevent from coming back to interfere with the direct sound.

Dipolar drivers (also now called orthodynamics) vibrate sound EQUALLY from the front-face of the membrane or diaphram directly toward your ears AND from the back-face of the membrane/diaphram away from your ears toward the back of the cup. These signals are of equal strength and exactly 180 degree out of phase from one another, thus the much greater risk of signal cancelation if the back-firing signals are allowed to reflect back and interfere with the front-firing signal. HiFiMan and Audeze, in nearly all of their early models, chose to allow the back-firing signals to dissipate away out of the back of the ear-cup. That's why you can hear the difference when you put your hand on them.

[... the PM1 sound the same when placing ones hands against the open back, which is another proof that your theory may not hold the water.]

That actually confirms my "theory"! Oppo elected to use the other, much harder solution: (almost) completely absorb the signals back-firing away from your ears by using some dampening process or material within the earcup. That is why you could not hear any diffrence when you placed your hands over the cups: the back-firing sound is NOT allowed to escape which exactly proves my "theory.". You can check with Oppo if you like. This problem with "dipolar" or planar transducers is well known. We have planars (as opposed to traditional dynamic) speakers for decades and we are always plagued with the problem of having to place these planar speakers (Magneplanar, Accoustat, Martin Logins...) at least 5 to 6 feet away from the back wall to allow the back radiating sound to freely dissipate and not reflect back from the rear wall. Dampening the backwall (roughly equivalent to closed ear-cups) is a lot harder and much frequently less successful. You do not have the same problem, at least not to the same with dynamic (non-planar) speakers.

[ It turns out the driver back wave is so so heavily damped the open back or closed back does not seem to make much of a difference.]

Exactly! But you are mixing design philosophy and end result. Close-back means you dampen the sound which is relatively easy with dynamic drivers but very hard to do with dipolar drivers and that's what Oppo elected to do. That's why you cannot tell the difference when you put your hands on the earcups. Oppo should be congratulated for tackling a very hard problem in their first attempt even if the results are not perfect.


In a nutshell, the problem with front-firing (dynamic) drivers are completely different from the problem with the front-and-back firing diolar (planar or orthodynamic) drivers. Audezee and HiFiMAN so far elected to allow the back-firing sound to escape or dissipate; Oppo elected to dampen it, which is a much more difficult solution that even Stax, for example, never attempted to my knowledge atfer over 30 years of using planar/dipolar drivers (electrostatic insead of electromagnetic but the dipolar challenge is the same), and Audeze just recenty tried in thet closed-cup model. All other problems about resonance etc. within the cups are roughly similar in both dynamic and dipolar drivers.

I hope that clears it up.

 

[Justin_Time]

Which is why the PM-1 should be truly open back.  I feel all that damping behind its driver is suffocating its sound.  From all the talk and impressions, the pads also seemed to be hampering it a bit.  


 


Planar Magnetics are truly dipoles compared to regular dynamic drivers.  They don't just leak sound if they're in an open-back form, they project it out.  Ask anybody who's heard an open dynamic headphone vs an open planar headphone and they'll tell you the Planar Magnetics can basically become like speakers if you give them enough gain on the amp.

 


Thak you for the clear and succint explanation, something that I failed to do.

I tried for years to no avail to dampen the back wall so that I could place my Maggies 3.7 (dipoles) near the back wall to keep the boss happy.

You've got to respect Oppo though for trying in their first attempt to do something that Stax never dared to do in over 30 years of making planar (diploar) electrostatics. Or perhaps Stax is older and wiser...

 

[kkcc]

To my ears, however, the problems with the Oppo PM-1 sound is more fundamental: a lack of transparency and resolving power (plus a constricted sound-stage but that is secondary). More trebles may artificially fix this problem but it would be just a band-aid.

....

I am anxiously awaiting the alternate ear-pads ad hope that they will prove me wrong.

 
 
This is exactly what I find with the PM1 too.  And transparency is one of the most, if not THE MOST, important criteria for me when evaluating headphones/IEMs.
 
 

  Which is why the PM-1 should be truly open back.  

 
I also wondered if a "grill mod" would help open up the sound and improve transparency.  But it would defeat the main reason that attracted me to the Oppos - their aesthetics!  
 
I keep having a feeling Oppo were kind of undecided between, or want to be a blend of, a portable/closed back/leisure listening and a open-back/hi-fi/reference sounding headphone.  This could also be a result of the beta / public testing approach they took.

 

[Justin_Time]

 
 
This is exactly what I find with the PM1 too.  And transparency is one of the most, if not THE MOST, important criteria for me when evaluating headphones/IEMs.
 
 
 
I also wondered if a "grill mod" would help open up the sound and improve transparency.  But it would defeat the main reason that attracted me to the Oppos - their aesthetics!  
 
I keep having a feeling Oppo were kind of undecided between, or want to be a blend of, a portable/closed back/leisure listening and a open-back/hi-fi/reference sounding headphone.  This could also be a result of the beta / public testing approach they took.

 


I believe that the back could be opened without any noticeable change to the aesthetics. They just need to replace the existing grills/or mesh with closed holes (what a concept!) with the same grills/mesh with tiny holes just like the Beyerdynamics T1 or the Stax 009-007.

The diaphrams/membranes and magnets work the same way with the cups either opened or closed. Opening the cups, however, will drastically change the sound (and voicing). Then they have to re-tune the frequency response.

 

[HiFiAudio]

I keep having a feeling Oppo were kind of undecided between, or want to be a blend of, a portable/closed back/leisure listening and a open-back/hi-fi/reference sounding headphone.  This could also be a result of the beta / public testing approach they took.

 Oppo did not have public testing, only private beta testing.  IMHO this is a open-back/hi-fi/reference sounding headphone that also offers some portable/leisure listening aspects.   Its very comfortable to wear, might not have the external noise isolation for some noisy situations but it works well for a lot of uses.