KSC75 Over the Ear Project

  1. Ohaple
    The project was initially inspired when I ran across the StratoKOSSter thread by accident while troubleshooting a problem with my Sony MDR V6. I read the thread and was pretty encouraged by the results claimed. Since I am somewhat handy I thought I would come up with my own design. Here is a sample of where we are as of 7/31/17:

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    The idea was to use the Sony MDR V6 style headband and ear pads (for comfort and availability of parts) and the KSC75 drivers. I researched other drivers in other threads but had a hard time finding anything else that was widely available and sounded great for a relatively low price. We have access to a CNC machine so I planned to make a design that would fit the Sony-style parts and the Koss KSC75 drivers. I came up with an open-back four part design that worked as a proof of concept, but turned out far uglier than we had imagined. We used the opportunity to make tests between open back and closed back designs. We tried tuning the closed back design, but were never able to get similar results to the StratoKOSSters, and coming from only closed back headphones in the past I really appreciated the soundstage of the open design, so we decided to stick with open back since it was less touchy and maintained the open soundstage. We made this set from maple, afrimosia, and purpleheart.

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    Since they sounded good and were far more comfortable than the clip on design for extended use, we decided to move forward with a second design. We found many errors in the original design making it hard to assemble and with poor tolerances. Also the "cup on a plate" design was not very pleasing, though it worked. So I spent some time redesigning from the ground up. This is what I came up with:

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    We made a set using maple and red acrylic. We found a few problems with how the CNC toolpathing was working, and how the stereo jack section was designed. Despite those issues, we were able to finish that set up for more tests. You will see we made a design with one vent hole and with many. We ended up preferring the sound with more vents. The idea is to stack the acrylic plate on the maple cups, creating a lip where the driver is secured. Then it is capped off.

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    Once assembled we tried them out some more. Here they are with velour pads. I used them for a couple of weeks (and am actually still using this pair at work) to find out what needed changed.

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    We did some (unscientific) tests to find out about the frequency response and general quality. We started by comparing the sound to the sony MDR v6, Bose QC15, Shure e4 IEM, Monoprice Over the ear headphones, earpods, and some B&W speakers. It is a very wide range of products, but we wanted to make sure we preferred them to the low end stuff, and that they could at least somewhat compete with some of the better sounding options. I understand IEMs, in-room speakers, and over the ear open headphones are apples and oranges but we found the test encouraging. I then used Neutralizer to test the headphones, thinking the EQ graph would be about the closest (though inverted) I could get to a frequency response graph without testing equipment. The idea is that Neutralizer is supposed to allow you to get a flat response from any headphones through EQ using the level you can no longer hear the sound as a benchmark. Assuming the EQ works as advertised, the inverse of the EQ graph should approximate the frequency response curve. Here it is for ours, and for the Shure E4 to compare.

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    The graphs pretty much matched what we heard. Our customs were a little low on the bass (but considerably better than the stock KSC75). The bass I believe is improved due to the over the ear design, but some of the sparkle the KSC75 is known for was reduced. We were getting some sort of resonance in the ~500hz range that was not noticeable on quiet tracks but didn't sound great on fuller songs, especially those with a lot of mids.

    We revised the design next. The changes were primarily in the efficiency of the CNC toolpathing and creating a better fit with the parts, including expanding the slot for the cable. We also increased the internal diameter of the cup hoping to eliminate the resonance. We made these from Walnut and Cherry, and made a jig to help us drill the holes accurately each time (even though we got chip out on one). The cherry is not finished in these photos.

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    The toolpathing changes increased the quality of the parts and the diameter did fix the resonance as far as we could tell. Could have also been the choice of wood. We need to do more tests to be sure. Besides the resonance they sounded the same as the maple set above. We went back and amended our design again. This time we added a little texture to the cups and changed the curves slightly to allow the headphone slot to be ever deeper and larger again, to support more cable types. We have not assembled or tested these yet, but they are cut out. This time green acrylic, with alternating holes and dashes in the caps to add a little more visual interest. In the photos nothing is glued or soldered.

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    Thanks for looking! I am happy to answer questions about the project, take criticism, or take suggestions. We have been having fun refining these and I am looking forward to having a custom set of headphones that sound better than most everything else I own. I plan to keep revising. The hope is to make this a sort of budget headphone that sounds good and looks unique. One of our next changes is to use a laser for the acrylic parts since it makes a cleaner cut.
     
    Last edited: Sep 1, 2017
    nick n likes this.
  2. HiGHFLYiN9
    Very nice work! If my recollection serves correctly, I think Koss themselves had an over-ear headphone that either used the KSC35 or KSC75 drivers for a short period of time. I'm sure having the wood frame would be a huge improvement though. I love the KSC35/75 and Portapro house sound, they are a true cult classic.
     
  3. Ohaple
    Thanks. They do sound great on their own but I found them to be too light in the bass and too uncomfortable for long listening sessions. I usually will wear headphones for 4-5 hours a day to listen to music at work and play video games, so the comfort and bass increase has really been nice for my own uses. I used to use the Sony mdr v6 daily, but now I find that I prefer the way these sound.
     
  4. Ohaple
    Got a chance to finish up the green and walnut set yesterday and documented the assembly. I think we finally have the design refined. For fun we tried the sony MDR v6 drivers in the old walnut set since they fit. They sounded good but I prefer the openness of the KSC75 drivers. Looks like this design would work with about any drivers that are greater than 1.7" in diameter. Wondering if there are some other drivers that would be worthwhile. The fun thing about the project is that it is so modular. Many drivers will fit, many ear pads will fit, any cable will fit. Considering selling a kit at cost to get someone else's feedback on the project. Onto the photos:

    All of the parts laid out.
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    Before and after the finishing process. Walnut in particular has a striking difference. It goes from a dusty brown-grey to a rich brown.
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    We have messed with smooth sides and textured. I like the textured, but it can easily be sanded flat for those who prefer it that way.
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    With the earpad plates glued on. These serve to create a lip for the drivers to secure to, and also a gap around the perimeter for the earpads to slip into.
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    Feeding in the first driver
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    This is the hole to accept the wire from the headband, so the right driver doesn't need a separate cord.
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    Soldering in the right driver
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    Got it all hooked up to the stereo jack
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    Once its hooked up, we screw the jack in place
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    Time to glue the drivers in place
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    Now that they are pretty much done, its time to test them and then glue on the caps.
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    Once the caps are glued on, we just need to install the earpads and plug in the cable. Done!
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    Excited to get a laser cutter in the next couple of weeks. It makes much cleaner cuts on acrylic, and will allow us to do more complex and interesting things with both the plates and the caps. I have been using this pair with velour pads, but I think they benefit from the bass from leather-style pads. Happy to have the design refined some since we have been working on it for the last six weeks or so. Besides the laser cutter, thinking of tinkering with other driver choices if anyone has any suggestions. Cheers!
     
  5. MrMan
    Have you tried HM5 pads with this design ? They make some of the most comfortable pads for oval cups. You can go velour, pleather, hybrid and even angled if you want too.

    Also audio technica generally sells drivers for quite cheap. ranging from $7 per up to i think 53 per driver. They are nice 53mm drivers that give a very full and detailed sound.

    Here is a link to them being used in a mod project.
    https://www.head-fi.org/threads/ms2000s.733413/
     
    Last edited: Sep 3, 2017
  6. Ohaple
    I havent, we have only tried the Sony OEM pads, the Beyerdynamic velours, and some off-brand ones that are very similar to OEM. I will look into them more, reviews online look promising.

    I found a source for Audio technica drivers and may give them a try. Thanks for the link.

    I am sending a kit out to someone today and am hoping they will be able to give good feedback on the project from an outsider's perspective. Will update as they work on it and update me.
     
  7. MrMan
    For audio technica:

    PARTS:
    To check parts availability, price or to order parts, you may email PARTS@ATUS.COM or call Parts at 330-686-2600 ext. 5002. If the line is busy please leave a message. We do get back to you as promptly as possible.

    The phone call works much better then e-mail. They don't like to sell drivers to people who plan to transplant them. People just say their headphone broke and they want to replace the drivers. They will try and say you can send them in and they will do it. I always say I want drivers from the same batch and I want to replace them myself. Their Ad700 drivers I think were $23 a pair shipped. Their ad2000 for a pair I think was $115 shipped. Not sure how much the ones in the middle were.
    /
     
  8. crazychile
    That's really outstanding. I have experimented with these drivers a bit also, but having access to the CNC tools would really let the creativity fly. The wood looks great but is a big part of the weight and wearability issue. If I were doing it and had your tools, I would start with plastic enclosures until you were happy with the bass tuning. Then revisit the wood idea.
     
  9. Ohaple
    I think maybe I wasn't clear. To clarify, the ones we built are very comfortable. The ear cups fit exactly like the mdr v6, and I just weighed them at 7.4 ounces which happens to be exactly how much the Sony mdr v6 is advertised to weigh, though the coiled cord makes the Sony feel heavier. Any discomfort referenced above is likely about the stock Koss.

    Plastic (acrylic in our case) would be heavier than the wood we are using since we are not doing a molded shell design. Wood is actually (usually) pretty light. Acrylic is nearly twice as dense as walnut (640 kg/m3 VS 1163kg/m3). That would mean I would need to remove about half of the material currently on the cups to make them as light or lighter with acrylic. It is much more difficult to design a heavy hollow part than a solid light one on cnc, so the wood has been a great material to work with. Besides, I think wood looks weigh nicer even if it wasn't also lighter.
     
    Last edited: Sep 6, 2017

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