Hey wje... any status updates on your "OEM" drivers and their performance post-burn in?
Out of the box, it doesn't really sound like any of the drivers you acquired are capable of producing the full audio spectrum... well at least not without some roll off at the ends.
I am still eye-ing those 600 ohm drivers.
I was able to take some of the drivers that I had purchased from the 4 pair that were received a bit over a week ago.
One pair had some problems during the installation - the solder tab literally melted right in front of my eyes. That one hit the trash.
The 2nd pair were mounted in the wooden cups and tried again after some time with applying pink noise and music to hopefully kick the drivers into gear. Sadly, the headphone signature really didn't change.
The last 2 pair have had some issues with the mylar on the drivers suffering from a bit of hardship since the driver cone is not protected, you really have to handle these things like fresh eggs. The drivers are not toasted, but I feel that they might be compromised. The drivers, though, from my first impression were certainly nothing that impressed me. One of these two pair happened to be the Sony MDR drivers with the red cone and clear mylar appearance. I still have a suspicion that the drivers I had purchased might do a bit better when installed in some closed cups with a bit of damping material. The sound could really come alive. Again, this is just a suspicion. But, then there's another force at play here which would be the size of the closed cup used. This could determine if the driver would perform just "good" or maybe "great". When I purchased up three pair of Auvio headphones for the headbands, I did keep one pair of cups and the ear cushions. As time permits, I think I want to try the Sony MDR drivers in the closed cups and see how different the direction might change. That could still be a few weeks away -- still a lot on the plate in front of me.
Meanwhile, 3 additional pair of the PX100 drivers are incoming over the next 4 days or so - this is all based on the mail service returning to somewhat normal, but I'm a bit pessimistic since the east coast of the U.S. was pelted with bit of winter storm applying about a foot of snow, rain, sleet and freezing rain.
However, there is some positive news where I'll close out this response. Here in the U.S., Sears (and possibly some KMart stores - if they are still open in your area) have the Koss KTXPro1 headphones. Normally, their in-store price for these are at $19.99 - even though the MSRP is $29.99. I found a few pair a bit over a week ago for under $11.00 a pair. They only had 2 pair, or I'd have moved on about 2 additional pair for various hack jobs and trying in the wooden cups with various testing scenarios. What is so unique about these drivers on these particular pair of headphones is the rear of the drivers. They are designed to work in an open environment as that is how they come configured. But, the backs of them are quite a bit different than the KSC75 drivers as those drivers have a silver pained rear dome with holes applied - but not nearly as open in the rear as those from the KTXPro1 headphones. I suspect that the drivers are basically the same driver, but the manner in which Koss has deployed them for their applications has changed a bit since the KSC75 uses the outer silver "dome" as protection for the rear of the driver as that area is exposed and in the open. The driver in the KTXPro1 has the protection of the vented plastic to protect the rear of the driver.
My impressions of this variant of the Koss drivers? Impressive. Very impressive. Are they on the same level of the Sennheiser PX100 II drivers? Not quite ... but close. I'll have to build out a 2nd pair of the PX100 drivers in wooden cups in order to perform some adequate side by side testing. But, this particular variant of the Koss drivers is performing nicely. I'd be willing to be that the Koss drivers are better than the Grado SR-60/80/125 drivers and the Koss drivers don't need any of the holes to be vented on the rear of the drivers like one might have to do with the Grado drivers. The details and the highs are there - just not quite as apparent as the Grado flavor -- but far from ever being a muffled tone either. The drivers are quite good at instrument separation and the sound stage is there - wide, yet not quite as wide as the PX100. Again, still very, very capable drivers and I'd certainly recommend them over the KSC75 at this point in time due to the additional open-ness on the rear makes for a bit of a less congested sound than one might face with the KSC75. If you can find these on sale, you could get them for nearly 1/5th the cost of the PX100 by Sennheiser. Those in the U.S. can pull up the local Sears or KMart store and check if they are in stock at the local store and available for pick up before heading over. The flange of this driver fits nicely into the wooden cups just like the KSC75 with a bit of room on the outer rim. But, still a much tighter fit than any of the 4 pair of OEM drivers that I had tried which needed quite a bit of work to get the fit just right. As many might recall, BlueMonkeyFlyer had posted some information a while back where the Grado / Magnum drivers were more in the range of 45mm as opposed to 40mm. But finding a driver in that range is tough. So, that is why I had settled on the 40mm size.
If one really wanted to "go over the line" they could head to madisound.com where they have a pretty good selection of drivers in the 1.5" to 2" range from makers such as Peerless and others. Their prices range from about $20.00 per driver up to $58.00 per driver. They are drivers that can handle 10 to 15 watts of power and are built like a tank. Again, the only hold back would be the size. If someone were to cut a pair of cups with a bigger diameter - more in the range of 2" to hold the driver, one could really have a pair of ear speakers. Then again, the weight of the driver - due to the serious magnet might be a drawback. Also, some of the flanges on the front are square so one could mount them in a wooden speaker enclosure, so using something like a Dremel would be required to round off the corners for the proper fit would be in order. But, the 2" drivers do have the proper round shape, so they could be dropped into the 2" opening on a wooden cup. A 2nd drawback to using a larger cup would be the ear pads. We'd have to rethink the process of using the G-Cush or L-Cush pads. The Sennheiser 414 pads might work since we can basically cut the rear opening to a desired size to fit over the cup.