Oppo PM-2 - Any Good?

I removed all stock damping, and damped the entire back of the driver covering all vents with a material that is extremely good at bringing up clean treble. It is the only thing that creates clean treble with vintage orthos. Along with some resonance absorption. With the PM-2, the treble will not come up, even when over damped with this unique material. If it won't do it, nothing wil. I suspect different preferences are at play here.

I don't trust any measurements taken by manufacturers, or many measurements at all other than Marv's honestly. Look at how off his HD800 measurement is. And Tyll's measurement are so hard to interpret because flat is not a flat line. You have to try to interpret it through his ideal curve. Not that easy. I don't get much from them.

I disagree. That diagram is a marketing material. They conveniently leave out the fact that the diaphragm is also moving across the whole surface of the oval. They show nothing there, but in reality there is probably all kinds of fucked up random crap coming off that part of the diaphragm even if what they show is correct, which I doubt.

I still thinik an ortho driver need to be better controlled by magnets than this. And I think the measurements reflect this lack of control. Distortion is exactly what you'd get from that huge oval moving without sufficient magnetic control.

 

I've done all listening with the crappy thin 3.5mm stock cable because the thicker 1/4" cable had a bad connection. I just got an audiophile ninja cable in, as well as new pads. I don't think the cable could cause the problems I'm hearing, ut I'll give them another listen with the new cable and pads...

 

@rhythmdevils Did new cable help or is PM-2 a good candidate for the worst sounding headphone you’ve ever heard?

 

What do you mean the diaphragm is moving across the oval? the magnetic flux lines and current traces are all correct. The diaphragm only moves up and down, which does not affect anything on the diagram. The cross sectional view of the diagram is correct no matter where you slice it (assuming that slice is made through the central axis).

 

the diagram was produced as marketing materials and is not trustworthy. It conveniently leaves out all the funky sound waves I’m guessing are coming off this part of the diaphragm that is not controlled well by magnets.






Here is some marketing jargon from a different planar magnetic headphone that reinforces what I’m saying.

The TS-1024 features full-sized 103mm custom transducers balanced within Timsok’s proprietary chambered magnetic array. The array was calculated and designed to maximize the surface distribution of the powerful N42 neodymium magnets across the transducer, resulting in an incredible magnetic flux​

I could definitely be wrong. This is just what I think is happening.

 

Think of it this way... A dynamic driver only has a coil controlling a proportionately tiny fraction of the driver surface. Sure there's some rigidity to the rest of the diaphragm, but it's not gonna be perfect and there will undoubtedly be some standing waves and vibrations/ripples/whatever that travel across the surface. So by your argument, is a dynamic voice coil driver uncontrolled?

The oppo driver in this case is behaving a little bit like a big fat voice coil and the outer area of the diaphragm is behaving like a cone/surround/whatever you want to call it. It will produce the same as the signal put in because it rides along with the primary area. Yes there's going to be some standing waves and other oddities coming out (based on dimensions and tension), but that's true of literally every driver out there.

One could argue that the old Fostex drivers have uneven magnetic flux density because they will be denser in the middle due to using only single magnets on each side. Note that all modern designs avoid this and the "dense" area of flux is where you do not have effective traces. DCA created his pleated diaphragms because he claimed that driver tension resulted in bowed diaphragms during excursion, though somehow conveniently ignores that those same pleats make it easier for flexure to happen as you no longer have the same tension restoring force.

Anyhow, I'm not refuting that you're hearing distortions or other things, and we clearly hear things differently based on our other conflicting reviews, but you're drawing bigger conclusions here than is warranted.

 

This is starting to look like the BHA-1 thread, where I posted honest negative impressions of a piece of gear and people who liked it came up with all kinds of excuses to invalidate my impressions.

The thing here @Armaegis is that the PM-2 has MEASURED high distortion. Well designed ortho drivers have extremely low distortion. Not to mention the fact that this is the first ortho I’ve ever worked with where I could not get treble extension out of the driver. These are unrefutable problems.

Instead of trying to pick holes in my theory as to why it has these problems, what do YOU think is causing it?

What you are saying is nonsense. You can’t compare an electrodynamic driver to a planar magnetic driver and claim all of that diaphragm space that has no magnetic force on it is acting like an electromagnetic driver. Electromagneetic drivers are driven by one spot in the center, like this driver. But they therefore have to be extremely rigid and well engineered (all the spiral patterns you see on electrodynamic diaphragms, the HD800 ring radiator, etc) to avoid the cone breaking up from only being driven by the center. This rigidity adds mass to the driver, slowing it down, and cone breakup is inevitable to some degree, among other problems.

Planar magnetic drivers advantage is that they do not need to be rigid because they are flat and driven across the entire surface of the driver so there is no diaphragm breakup and they can be much much thinner and lighter.

All that space around the center circle is not driven by magnets, and is not rigid like an electromagnetic driver. It is also much much larger than the “surrounds” of an electrodynamic driver, which are very thin rings around the rigid part of the driver (and probably introduce problems into the signal). The undriven part of the PM-2 driver is at least twice the size of the driven part. And it is not rigid. It’s not just “following along with the rest of the driver”, it’s probably rippling and moving in ways counter to the signal. Causing distortion.

This is the only planar magnetic driver ever designed like this AFAIK.

Maybe instead of coming up with yet another reason why this theory is incorrect, you propose your own idea to explain the high distortion and inability to produce treble.

 

I have never heard these headphones and am just swooping in with an idea for something to try as a proof of concept.

If your theory is correct about the edge of the driver (which you colored in red) being the design aspect that's introducing distortion, why not totally block the front frame piece that allows that portion of the driver to reach the ear so you're only listening to the 'sweet spot' in the middle of the driver? You could tape over (or filter) this whole part (grey X's).



Maybe this plus a pad swap will give a bit more treble and lower distortion. Or maybe I'm wrong and this will just roll both ends and kill your dynamics.

 

Man, I'm not even defending the PM2. It's been too long since I've heard it to make any valid audio comparisons anymore. I'm simply challenging what I feel is a weak conclusion based on large leaps.

To what extent are you saying it is rippling and moving? The driver diaphragm is under a light amount of tension so it doesn't just move purely on it's own out of nowhere without an outside force. Yes there are standing waves and other reflections that undoubtedly come from the driven portion after signal is applied, but those would happen regardless if you had more magnets or not.

Waves that travel longitudinally (or radially if you prefer the term) through a diaphragm do not necessarily get squashed out by more magnets. That's just basic physics as waves superimpose. Now if you had more active traces, that means more tension and that's a different matter, but longitudinal waves still travel through regardless.

My assertions were to challenge, not drum up my own hypotheses based on insufficient data, but since you insist... I made the comparison to the dynamic driver because the Oppo holds a fairly unique position as a planar driver with a really weird impedance rise and phrase variance which coincides with the distortion peak, which is generally a dynamic-like behaviour. Some have even been measured with double impedance peaks, with a corresponding double distortion hump. These peaks are also around 300Hz, which is where your ear is far more sensitive, compared to something like the Senns where the hump is broad and around 100Hz). The impedance and phase also starts to slope up as you get into the treble region; some other orthos exhibit this, but the Oppo slopes up stronger and earlier. All this to me smells like a resonance issue rather than a magnet one.

As for the treble or lack thereof, rather than trying to trying to find an explanation from magnet/diaphragm coverage ratios, after thinking about it I think the simplest explanation is as seen in the FR and it just naturally rolls off. No funky explanation other than the driver is simply sluggish and doesn't do highs. There's maybe a whiff of that in the rising impedance plot, but of course correlation is not causation.

 

@rhythmdevils Your assertions for why the PM-2 is a poor design are reasonable and comes with a decade of experience modding orthos.

@Armaegis Appears to be someone from the scientific field that is used to requiring information be peer reviewed before accepting as data. He is testing the validity of your methods and conclusions before accepting. He wants to know if you’ve considered all the possible reasons for these patterns. If you would write a long ass post with tons of your data then he’d probably ask more relevant questions that would feel less condescending to you.

rhythmdevils start a thread about planar mods (without revealing the specific materials and exact methods that make your mods succesful). Explain how planar manufacturers are defecient at tuning and why its worth modding. I’ve piecemealed knowledge through the many ortho/planar threads but to have a foundation and dedicated thread to theory would be great sorta like ortho round up at HF but much more condensed and helpful with welcomed debate (armaegis) / the SBAF way.

 

any chance you could share the name of this material? I would like to try some out.

The front of the driver plate has all those holes covered…they only exist in the back.

Edit: quotes didn’t work, but i think you’ll know what i mean

 

You might change your mind, because this is the stock tuning. PM-1 on top, PM-2 on bottom:



The back felt is significantly thicker on PM-1 than PM-2.

I am starting to think that damping on these circular orthos is about more difficult because there is less surface area that the driver is moving. I think the original idea was make it circular like dynamic drivers, but then Oppo thought let's have the best of both worlds. I am having the same issue with my old Fostex T-20's. Different pads affect the bass, but none can address getting more top end out of them - and they are super super hard to drive, unlike the Oppo's, which are as easy to drive as HD600/650's.

I don't doubt you @rhythmdevils in what you are hearing. These have little air, and the PMx2's certainly have more air. Even the PM-3 can sound rolled off, but sometimes that is welcome, because some of us are sensitive to trebles on long periods.

Maybe modding the Monoprice M1060's or M1060C's might be easier.

 

I did find this interesing...I compared Tyll's PM-2 w/Velour pads to the PM-2, and there is not much difference. I know @Ksorota has PM-1 and PMx2 and says they are very different headphones.



(plus I wanted to mess around with the fancy screen capture stuff I got for work, so pardon the fancy gif, but it is handy)

 

Here is PM-1 vs PMx2 just to show:

 

As mentioned, the driver casing only vents to the back, not the front. But ortho drivers put out the same sound signal out the front and the back, so the back wave has a huge affect on the signal that comes out the front, as the back wave mixes with the front wave and adds to/ changes the signal. You would be amazed how much the front wave is affected by even the smallest bit of back wave. And how the back wave finds ways to sneak into the front wave. It is also the opposite signal, so can cancel out the front wave if not delayed or eliminated.

But even if the driver casing didn't vent to the back, sound waves created by this part of the driver would travel along the driver and mix with the sound being let out through the hole in the middle (which lets the sound out that you hear). Here's a pictures showing this.



The only way to truly test if this part of the driver is causing problems would be to pinch the driver all around the inner circle, so that the outer portion is not moving at all. But I suspect, given the size the inner circle, that that outer portion is required for full bass response.

I've actualy written something like this. A guide to modding the T50rp, because it is the most complicated ortho to mod, as it involves so many aspects of ortho acoustics. A small driver with interaction with the baffle, and a closd cup with interactions with the cup. It winds up explaining a lot about how orthos work. But I have no job right now, and I've put so much time into figuring out how orthos work I'd like to make at least a part time job out of modding orthos. If I can.

As stated above, I'd love to share this with fellow DIY'ers, but other commercial companies would copy it very quickly. I'd rather keep it to myself for now unfortunately. It took me 10 years of learning to figure out to use this material. Along with the other materials I use.

 

Of course a large section of diaphragm not controlled by magnets will start to move in ways not created by the signal. This is just physics. I have no idea where you are drawing these conclusions from. Picture a 3 foot long diaphragm driven on one side by a magnet. The end opposite the magnet would not be creating a faithful signal. This is quite simple and obvious.

You and me think very differently. I have butted heads like this with people who think the way you do in real life too. I think sort of by way of concepts and intuition and logic. You are all numbers. You seem to be unable to look at this as a system and think about how it functions. Your post is just a bunch of numbers that you are drawing conclusions from. Which mean very little to me.

The thing is that all of your "challenges" to my proposed idea here are very easy to refute using simple logic.

I'd also like to emphasize that what I posted here is just an idea. A hypothesis. I'm not saying this IS the problem, Im saying that based on my experience and understanding, this seems likely to be the problem. It might not be. I understand that the way I think is not legitimate to you and you want numbers. But I don't have them. I have never measured an ortho in my life and probably never will.

So my posts here are not going to satisfy you. We might as well stop going back and forth. I proposed an idea, and so did you. We can leave it at that.

The real point is the PM-2 is not a good sounding ortho to me. including cheap Russsian kickoffs of the Yamaha orthos. But at least it is damped (though poorly) stock and has a balanced sound without severe peaks. That’s definitely significant and probably why some like them.

 

This isn't worth it. I cede to your definition of physics.

 

rhythmdevils - a few things to consider: as you find your PM2 to be so different to how others find it, could yours be faulty: I have two different Beyers and cannot abide the awful shrill treble of either. You say the treble is very rolled off - when was the last time you had a hearing test in a proper anechoic chamber. Even though I'm old I am still able to hear when a treble response is harsh. I don't doubt your physics.

I do not want unnatural bass or treble, perhaps you have become used to hearing both as 'natural or normal'. I remember going to a Black Uhuru (Reggae) gig back at the end of the 70s' the bass was literally offensive, it actually hurt in the stomach - I left - others loved it.

If we know that indeed you like more than natural bass and treble, it would go a long way to explain your opinion of the PM 2. Yes I think most would agree than bass could go lower but what there is is layered and sounds natural and above all else - it's a pleasure to listen to music using these cans.

 

It's not "my definition of physics". A lot of this is just common sense. My intention wasn't to insult you though, I like you and always enjoy your posts and have a lot of respect for you, and have for a long time in this hobby. I'm glad you're here. My intention was to point out very different ways of thinking and that you would never be satisfied by my hypothesis or explanation of it.

I would love to see you take a tensioned 3 foot long diaphragm with a magnet on one end, and measure perfect response on the other side.

I would also love to be proven wrong, because then I would learn.

Haha, anyone who knows me would laugh pretty hard at this idea. I'm more sensitive to exaggerated treble than anyone I know on this forum. At least historically I have been. I hate the DT880, stock HD800, John Grados, Ultrasones, etc.

Also, telling someone to get their hearing checked because their impressions dont match yours is kind of a douch-y move. Yes, my unit could be defective in both drivers, with both drivers being matched defectively. That seems very unlikely to impossible to me though.

I can understand why the PM-2 is a pleasing listen to people, it's pretty balance and has no peaks like many headphones. I might prefer this headphone modded to the stock Hifiman Edition XX with it's plastic-y timbre. But I have test tracks for treble response that are very revealing and I know the sound of distortion like this. I also compare all headphones to the response of my Mackie HR624 MKI active monitors which measure dead flat. So I don't see how my hearing can be to blame here.

I'm pretty impressed by Audio Zennith for his chutzpah getting this headphone to sound better, but also baffled as to why he would pick this headphone to work on.

 

With all this new discussion on the Oppo phones that even Oppo gave up on, ;-) I thought I share that when you buy new screens from Oppo, you get the whole cup assembly.

As I removed and replaced the rear screen a few times I ended up causing some damage (bends and dents). So ordered a new set of PM1 screens and this is what arrived.



Just too bad they dont have headband assemblies anymore. I could use a new one!