CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => Headphone Measurements => Topic started by: Hands on October 19, 2014, 10:15:54 PM
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Update: Latest mods/tweaks and measurements as of 4/2/15: http://www.changstar.com/index.php/topic,1841.msg61995.html#msg61995
I thought the PM-2 had several disappointing aspects, so I decided to see if I could improve it with mods. Stock, it has good bass and mids, but treble has issues. Either too depressed in some spots or too peaky and rough in others. Bass was clean and fairly neutral but lacked balls. Not sure what it is, but some headphones that measure fairly flat in the bass sound powerful, and some do not, assuming both are well driven from big boy amps. The PM-2 falls into the latter category, IMO. So, it kind of had this soft, almost too laid-back, yet also slightly too rough sound. Yeah, no thanks. I thought the HD600/650, especially damped, made it sound silly. The PM-1 had a better response curve but was overall too dark and constricting sounding. I liked it overall despite this, but it was kinda boring.
You know what comes next. I replaced all the internal damping with my trusty open-cell foam I got from Foam Factory! And I mean I removed all internal damping, including the stuff glued to the back of the driver. I replaced it with a 3-layer damping stack sandwich party of the following stuff:
On bottom, closest to exterior cup grill, a layer of this (1/4"): http://www.foambymail.com/CR/solid-charcoal-regular-foam.html (http://www.foambymail.com/CR/solid-charcoal-regular-foam.html)
On top of that, 1/4" layer of this: http://www.foambymail.com/P/poly-foam.html (http://www.foambymail.com/P/poly-foam.html)
Lastly, a layer of this on top of all that (i.e. closest to back of driver): http://www.foambymail.com/CF0-125LF/1-8-inch-charcoal-regular-foam.html (http://www.foambymail.com/CF0-125LF/1-8-inch-charcoal-regular-foam.html)
It does take some force to get it closed with all this shit in it. If you do not have hands or arms, I do not recommend you attempt this mod.
I also closed up portions of the cup grill with Creatology adhesive foam squares. Basically, I'm just trying to reduce the amount of cup venting. I left the side of the cups pointing to my face more "open" inside and the back side more "closed" with the foam squares. This will make more sense with pictures. I also put a lot of drawer liner inside the cups.
To make this all work right, I purchased the OPPO velour ear pads. Nothing else done on the front side. Just pooped the velour pads all up on there. I'm not sure how the PM-2, with its slightly different internal damping vs. the PM-1, would sound with just swapping to velour pads. I don't think I like the stock PM-2 pads all that much.
How does it sound? Well, the first thing I noticed was extra bass. It's a touch more boomy and perhaps not quite as clean as before (can't do a direct comparison), but still pretty damn good. Gives a better sense of power and kick. Not so much limp-dickage as before. PM-2 is no longer pre-pubescent sounding. I think I like a bit of a tasteful, clean bass-bump on most headphones. Treble also sounds considerably cleaner and smoother. Moar and better detail, but smoother. Upper-mids and lower-treble seem to be better integrated and less recessed. Tone and smoothness reminds me more of the PM-1, but without the constricting soundstage and noticeably dark treble. I'm enjoying it.
Is it perfect now? Well, no, but IMO a big step up in balance and refinement over either the PM-1 or 2. The best part is I no longer listen to these and just feel like something isn't right or that something is missing. I think these drivers have a lot of potential but are held back by the enclosure design and stock damping. Someone that has more patience and audio knowledge than me could certainly get something great out of these.
Attached measurement 1: This is the stock PM-2 with stock pads after I stretched it out for a wider, less clampy fit. Do note that stretching them out for less clamp did affect measurements, and I do believe I've posted these results before.
Attached measurement 2: Modded PM-2 with velour ear pads. The distortion characteristics in the low-bass might be a bit weirder and worse, but I'm not too concerned about that. Didn't save it, but the impulse response on this looked great. CSDs still good as always, but didn't save that either. You can find my later PM-1 measurements here for some level of comparison (also velour pads): http://www.changstar.com/index.php/topic,1590.msg44503.html#msg44503 (http://www.changstar.com/index.php/topic,1590.msg44503.html#msg44503)
Anyway, I must say I am happy with the measured results, especially since I did this all by ear.
The first mod screenshot shows the cups mods with some of the exterior grill portion blocked with foam squares (this is the left cup, so the foam is concentrated towards the rear of the head). You'll also notice a bunch of drawer liner. The second screenshot shows my foam damping sandwich. Then a picture of it inside the cup (thin foam on top). Lastly is a shot of the driver's naked backside. Please don't attempt dangus insertion.
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Wow, that must sound almost like a regular closed-back headphone (with all the material stuffed inside), doesn't it? p:8
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Not really, no. The foam is not as dense as you'd think. OTOH, the OPPO headphones aren't super open sounding to begin with. Doesn't sound closed, though.
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Looks very interesting though, I really like it! Thank you for posting it...
Have you noticed anything about the enclosure (or maybe even driver itself) so far that would be worth talking about? It doesn't look very similar to Audeze or Hifiman... And I am not sure whether this is a good or rather bad thing. Would be interested to learn something about it.
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Hmmm...enclosure is convenient for mods? Haha. It is more similar to something like the HD598, I guess...Not quite as open. Build quality is good, plastics aren't too thin, but not super thick either. This driver needs damping and not too open of an enclosure.
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I might be getting the PM-1 on the Canadian tour. Would similar mods apply?
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As I understand it, the PM-1 and PM-2 should be identical except for slight internal damping variations, assuming the same pads are used. Mods should apply to either but do require you to take off any glued damping material behind the driver. Stretching out the headband for a lighter fit and using velour pads on either PM-1 or 2 probably goes a long way, if your tastes are like mine.
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Now that's a nice improvement!, do they remain easy to drive?
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Seems like it. Gets loud, not ear-splitting, from my Galaxy S5 on material that isn't as compressed and loud as most modern music. Music with normal, crappy DR and loudness gets very loud before full volume. Sounds good from the phone. I think the extra bass helps it overcome sounding too weak from lesser sources, which was one thing I had a problem with stock.
Edit: If you occasionally find the treble a bit too sharp in this config, that 1/8" foam works well if inserted in the ear pad opening, sandwiched between the felt donut and protective mesh (on velour or original PM-1 leather pads). One or two circular layers. Just makes them sound more laid-back overall, not a huge measurable change except slightly more rounded treble response around 10Khz and a slightly larger dip in that area, but nothing that sounds off.
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Quick update. Changed the internal damping config to look like the attached pic (sweet paint skillz), still have drawer liner covering everything. This helped focus the sound a bit and clean up the bass (in a good way - less boom and more punch) at the expense of making them sound a bit less open. Still not claustrophobic like the PM-1.
As for attached measurements, I also put a couple discs of that 1/8" foam in front of each driver to darken the sound a bit for my overly sensitive ears. So, while this measured response looks more like the PM-1 with velour pads that I measured, it's still not quite as laid-back and packs more of a punch. Sounds noticeably more lively than the PM-1, based on my memory. I'll need to grab measurements without those discs in place to see what just the damping changes brought to the table.
Interesting that the distortion in the mids seems to be better now. I'll need to take more measurements to verify if it's actually smoothed out now. The weird bass THD spikes are probably an artifact, as I'm working on a new measurement rig (very early in the experimental stages), and it was rather clean in the bass in terms of distortion.
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Where did the spikes go?, enclosure resonance?
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Maybe. If you see graphs of mine in this style, they're just quick measurements, not averaged, of one channel (usually left). I'll have to take more measurements to see where that distortion spike went, if anywhere at all.
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Wanted to follow up real quick that I took multiple measurements of that channel, and though I didn't necessarily remove all front damping to verify that was affecting measurement, it would appear distortion is reduced in the midrange with this config.
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Hans
Thanks for all the info you've shared. New user, but registered to say thanks.
Where would you ultimately end with the mods for the PM-2? In this thread I see you discuss some damping mods, and in the other PM-2 thread I saw you experimented with some foam filtering that pushed the peak more toward 10k. Did you end up leaving both? I am thinking about experimenting just a bit for fun as it is interesting to me.
I like the PM-2 simply because it's pretty good sound to me (I know many probably disagree) that I can power from my iPhone/Mac at a price point that I can take with me when I travel and not look totally weird sitting in an airport, hotel, etc with massive headphones on my head. I can also throw my IEMs (for in-flight) in the Oppo case and not take a ton of space in my personal item bag.
Thanks!
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Stock PM-2 sounds OK, just wasn't stellar in my mind. Overall sounded wimpier and less balanced or generally less capable than the HD600 or HD650. Its main selling point was its ability to run from about anything pretty well along with looks, build, and fit or comfort. I think different pads alone can make a positive difference, as the stock PM-2 pads leave something to be desired with the sound. My goal with this mod was to see if I could tune them more to my liking with the most basic and cheap modding/damping materials already in my hands. Nothing fancy, nothing advanced, and nothing that took a whole lot of time to implement beyond going through quite a few experiments.
After a few different experiments, I decided I wanted to target a sound that was a bit more bass emphasized but otherwise fairly balanced beyond that. Partly because I already have the HD650 if I want a relatively neutral sound and wanted something that was more fun sounding, and partly because I think the OPPO driver can be a bit weak sounding down low even if it measures about the same as the Senns, for example. I wanted to give it a bit of an extra kick and sense of thickness without killing the mids or treble.
For internal damping, I've attached a picture of the configuration I've stopped at a while ago. See below. Sorry about the crappy paint job. It's just not worth opening them up just for a shot of the internals when I can do it in paint in seconds. Basically, you have the eight middle squares (or, rather, two middle rows) blocked and sealed off, the four "edges" in each "corner" (above and below) are half covered. Then the two upper and lower squares in the middle area are half sealed. These are all still covered with drawer liner.
The damping foam I use is still the same 3-layered configuration. The squares closed with foam more or less control the bass quantity, so it's fairly tunable in that regard. I did try closing the four middle columns before, and while that actually measured fairly flat in the bass, it wasn't what I was going for and may have made things sound too thin. There are other tradeoffs too when closing these squares. More open squares will generally give a more open sound at the expense of it sounding more diffuse, less focused, and, of course, bassier. Closing too many, or closing squares in a certain config, can start to make things sound too thin and sharp, IME. The config I settled on gives me that extra bass I wanted and balances the sense of openness with focus.
Alternatively, you can use more or less dense damping material for the same purposes. The stuff I use is considerably less dense overall than the stock OPPO damping material, so I have to rely more on controlling airflow/venting from an enclosure perspective for bass tuning. Personally, I think the stock OPPO stuff is too thick or dense and stifles the driver's performance to a degree.
As for front damping, when compared to my earlier experiments with stock internal damping (shortly after I got the PM-2), I'm now just using discs of that 1/8" open-cell foam to help further smooth things out. This really comes down to personal preference. It will sound brighter and sharper with nothing in front of the driver. Smoother and more laid-back the more stuff you put in front of it. I will likely settle on having one donut of this foam and one full disc in front of the driver for my tastes, but others may like less material (or, I suppose, even thicker material).
I will say that I most prefer the velour pads with this config...and just in general with the OPPO PM-1/2. Stock PM-2 pads measure pretty funky with my mods.
There does seem to be a spot around 400Hz, maybe a resonance spot or something where it shows a small dip in measurements, that can become a bit more pronounced with these mods. Depends on how much bass you want. This is audible but not necessarily detrimental overall. A bit of PEQ can show you what I'm talking about. I believe you'd need more advanced mods, perhaps even enclosure, baffle, or driver modifications, to alleviate that. I also noticed my mods seemed to clean up THD results on the left channel. After further testing, this did not appear to be the case on the right channel, for whatever reason.
Again, these are super basic, super cheap, super easy mods. I think they work well for my needs and my goals - namely the PM-2 now sounds more fun and powerful down low and more balanced up top. Just more life to them overall. Bass levels are tunable. I think it's a step up from stock, but don't expect everything to be miraculously solved or amazing about them. If you want something more advanced, there's the upcoming Audio Zenith mod (pricey) at least. Not sure if anyone else has any mods they'll be putting out for these in the future or not. The AZ mod targets a different sound than I was (more linear, less bassy, generally more laid-back and a touch darker sounding), but the more advanced nature of the mods do bring more benefits to the table beyond that.
Hopefully that answers all your questions and more! Let me know if you need anything else or have other questions. Two points of advice if you try something like this mod. First, make sure you put any adhesive material against some fabric or something (peel and re-stick a few times) so that it will be easier to remove later if need be. Second, be careful tightening the baffle screws on the PM-1/2, because you can start to wear down the plastic if you get too forceful with them like I did.
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Is this the mod I heard at CanJam?
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If you're talking about Alex's Audio Zenith PMx2, then no. I've also made further changes to my mod in the past couple months. You know how it is...get too used to things and wrapped in your mods, so you take a break, come back, and find something you think you could improve. Lots of the same ideas still, just slightly different implementations and further tweaks.
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If you're talking about Alex's Audio Zenith PMx2, then no. I've also made further changes to my mod in the past couple months. You know how it is...get too used to things and wrapped in your mods, so you take a break, come back, and find something you think you could improve. Lots of the same ideas still, just slightly different implementations and further tweaks.
Ah darn. At CanJam a couple days ago, I spoke with a guy who had a really nice pair of modded Oppo's - we talked for a long time about his design and his philosophy on neutrality, wanted to find him because he was obviously a smart guy and we had a fun time talking about interpretations of sound.
Your measurements here are pretty impressive too!
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I'll post some new measurements and stuff on my mod soon. Maybe. Trying to be more patient, since I always seem to find something to tweak and have to go back on what I brought up earlier. :)
There's a thread on the PMx2 with measurements and impressions from Ultra and I: http://www.changstar.com/index.php/topic,2117.0.html
Feel free to chime in if you heard these and have thoughts you want to share.
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As mentioned above, I went through several more tweaks on my modded PM-2. There was always something, and very likely will be small things I want to try to correct down the road. Usually, I would spend a lot of time focusing on modding the PM-2 and then take a break. I'd come back and find something annoying my ears had adjusted to previously during the modding process. I'd also occasionally incorporate comparisons with other headphones whenever I had them available to get a better feel for my PM-2 mods as well.
When modding the PM-2, I knew I wanted to give them some more life. Stronger, more erect, ballsy bass and a lifted, still smooth (smoother than PM-2 w/ stock pads), and more balanced treble response. To me, the PM-1 or 2 need a bit more of a bass boost when measured to match the subjective level of impact and bass quantity of some other headphones, generally dynamic or large-size planar headphones. I had headphones like the HD650, Slant, Alpha Dog, and AZ PMx2 in mind for my PM-2 mods, trying to combine some of their better traits while keeping some of the OPPO PM-1 or 2 sound in place. Hearing the most recent PMx2 was of some help identifying oddities in my prior mods, though I still have absolutely no idea what has been done to the PMx2 aside from a few of the pad tweaks. My new mic also assisted me in pointing out some treble issues that my old mic had troubles showing, due to how far I could insert it in my ear. This new mic was used later in the game, after I started picking up on subjective annoyances.
I will say that trying to get a good balance on these was a bit difficult. Lots of balancing between too much bass and slightly aggressive or rough treble. I think a more experience modder could get more out of these.
A lot of the core mod ideas are the same and revolve around using cheap, easy to source, easy to apply materials that almost anyone could do. Nothing out of the ordinary in terms of headphone mods. But here are some things I've changed or left the same:
- Removed all internal rug liner. The interior sides of the cups are now lined with Creatology adhesive foam. Some strategically placed strips around the edge before you come to that grill area, bordering the sides. This helped some of the treble weirdness and likely does a better job with enclosure resonance control.
- Went back to an earlier grill damping/closing pattern. The two middle horizontal rows of the grill are still covered. The 4 outside squares on the top and bottom "corners" of this are fully covered too. That's all. Think of it as an 'I' on its side. This was something I tried early on.
- Still using that 3-layered foam solution, with the bottom layer, closest to grill, being 1/4" charcoal open-cell foam, middle being 1/4" white open-cell foam, and then the 1/8" layer of open-cell foam. I've posted links of these before. All sourced from Foam Factory/Foam By Mail.
- However, this 1/8" foam layer has been trimmed down to more of an oval shape to fit neatly over the back of the entire driver enclosure and not necessarily fill the cup like the other two foam layers. A hole has been cut out in the middle of the foam where the back of the driver is exposed, which is the biggest change.
- Tiny circular dots, using a hole punch, of Creatology adhesive foam placed around the edge of the back of the driver and one right in the middle of the back of the driver. There are little circular dimples on the back of the driver enclosure lining the edge, and I put a "dot" right on each of those. I think there are 10 or 12 lining it. The idea behind this was to help give some spots around the back of the driver a bit more breathing room with the foam pressed against it. Might have extremely minor resonant control properties too.
- A bit of adhesive material from a "permanent" glue stick was applied to each of these surrounding "dots," and the newly shaped 1/8" foam disc was placed on those so that it would be easier to center and remain centered when putting the headphone back together.
- A few foam "dots" and strips on the back side of the clear-ish, plastic baffle, bordering the driver enclosure itself. Again, just utilizing what little free space there is for extremely minor resonance control.
And that's all. Use velour pads - very important. No front damping should be necessary.
Measurements attached. As always, keep in mind that I make no guarantees for THD results, especially those below 100Hz. This is a limitation of my current setup and methods. In-ear mic placement depth can noticeably impact treble results as well, but the new mic does a better job picking out treble performance than my old one despite this variability. I usually do some averages with varying insertion depths to get the best picture I can. CSD results are based on one take and not the average response, so they won't match up perfectly.
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Pretty good looking results man. I can clearly see your progress. Maybe one day I could hear it too. Looks like those OPPOs are a never ending adventure ;-). Way to go :)p1
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Thanks man! Not sure if you had/have further tweaks to make on your PMx2 still (like you said, can be a never ending adventure), but it would be cool to compare them back-to-back. My PM2 mods were a bit rough sounding in comparison at the time I had your most recent PMx2. I'd be curious to see how they stack up now. But, based on memory, I think you squeezed more subjective refinement across the board out of your mods. Then again, I'm purposely going for simple, cheap mods and trying to maximize that.
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Did quite a bit more since the last version you heard. Will send you one, hopefully soon.