Koss A250 modding help

Discussion in 'Headphones' started by redrich2000, Jan 3, 2018.

  1. redrich2000

    redrich2000 Facebook Friend

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    No one is replying in the ESP-950 thread and they're different headphones so I thought I'd create a thread. I suspect none of you have these, but I'm hoping you might be able to guide me with general modding experience... The A250 is the dynamic little sister to the ESP-950. They have the same shell. I'm looking to tame the treble and boost/improve the bass.

    Below is the back of the driver. That's 10mm thick foam filling the housing. I was thinking maybe a dynamat circle on the back of the magnet and maybe a drawer liner donut over the plastic ring around the magnet. How does that sound?

    [​IMG]
     
    Last edited: Jan 4, 2018
  2. Sqveak

    Sqveak Friend

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  3. redrich2000

    redrich2000 Facebook Friend

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  4. spoony

    spoony Spooky

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    Dynamat will only lower bass distortion. Whatever you do, don't block the two small vents on the back cover of the magnet assembly, or you will likely kill all bass.

    To actually boost the bass response you have to either:
    a) Improve the seal with the head / ear-side pressurization
    b) Allow the driver to make a greater excursion by altering the dampening scheme

    I'd play with a lot of pads before irreversibly modding the driver, you can also try sealing the baffle vents to the cups (holes usually lined with felt / paper) with tape if there are any. However, if the former doesn't work, you can try poking a hole into one of the back vents of the driver (the holes with the white paper, try a small hole frist!), this generally boosts the bass response and attenuates the lower treble. Distortion will probably increase with the bass level.

    Happy modding.
     
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  5. redrich2000

    redrich2000 Facebook Friend

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    Okay, so on the other side, the foam filling the cavity around the driver housing is completely corroded. I will need to replace it. Will any foam of the right thickness work or do I need an acoustic foam?
     
  6. spoony

    spoony Spooky

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    Can you take a picture of the front-side of the baffle? The back of the cups is open, right? It's probably there to add impedance between the cup and the ears. If there are indeed baffle ports, sealing them will effectively nullify most of the effects of said foam. Depending on the density, you can probably replace it with felt, coffee filter paper, micropore, etc.
     
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  7. Mach3

    Mach3 Rando

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    Curious as to how this would sound compared to my ESP-950. To bad A250 are so hard to find these days.
     
  8. redrich2000

    redrich2000 Facebook Friend

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    Below is the front of the baffle. The back is open (wire mesh). They originally had a thin layer of felt over the wire mesh but I had one driver replaced a few years back and it came back without the felt on that side, so I've taken it off the other side.

    There don't seem to be any ports on the front. The two halves of the cup are held together by four screws, which are under a layer of sticky paper, I peeled that back to get at the screws.

    [​IMG]
     
  9. spoony

    spoony Spooky

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    It isn't clear from the picture whether any of the fabric-like materials are permeable, nonetheless, I would try cutting and placing a stencil made from felt / filter paper / microfiber cloth over the area marked here:

    egxXMFPl.jpg

    This could potentially allow an increase of bass pressure in the ear-side chamber. Pick a material that restricts the air passage, you can do a 'blow test' (try to blow through it with your mouth) to gain a rough idea of the extent in which airflow will be affected. Be aware that if the black fabric-like material is very permeable, the 'openness' of the sound could be affected by the use of less permeable stuff.
     
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  10. redrich2000

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    Behind those cutaway sections are three pieces of thin felt. They are somewhat permeable, I can blow through the three of them together.

    They originally had a piece of thin foam that covered that whole area. The Vesper pads though have just a very thin stocking-type material. I was going to put a piece of shelf-liner under the pads to cover that whole area.

    I've discovered that the magnet housing on the other side has four small holes and those two green stickers with 00 on them are covering two of the holes in the picture above. I think it was probably the replacement driver that had all four holes uncovered. I had put dynamat over the green stickers, and in pulling off to check whether there were holes there, the green stickers have come off. So I'll leave leave all four holes uncovered on both sides. Would a thin layer of foam over those holes (as with the folder foam disc in the HD650 KISS mod) be useful?

    I actually suspect the foam that fills the housing cavity might be an issue. I hadn't used them for a few years until recently and sound much brighter than I remember. I had put that down to my hearing changing with age but it could be because of the breakdown of that foam.
     
  11. redrich2000

    redrich2000 Facebook Friend

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    I think what I'll do with the dynamat is emulate the KISS mod (roughly ) like so. It had such a positive effect on the HD650 bass..

    [​IMG]
     
  12. spoony

    spoony Spooky

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    Try not covering the holes with the white paper, you may decrease the driver excursion = less bass. You will likely gain better bass presence if you install the stencil I drew earlier over the baffle on the ear side. Easy reversible mod.
     
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  13. redrich2000

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    Okay will give that a try with smaller dynamat on the back and maybe experiment with foam of draw liner just over the driver in front.
     
  14. redrich2000

    redrich2000 Facebook Friend

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    Update 1: Okay today I replaced the foam in the driver housing. The original foam was about 8mm, the closest I could get was 12mm. It was difficult to work with but I got it in there. I didn't mind the 12mm because the stock foam looked more dense, so I hoped packing it tighter might be good. I also got some thinner filter-type foam. I decided not to use that because it's texture is harder to make it oil and water resistant and it was much less dense.

    I also put a dynamat cross over the back of the magnet housing. I used two thin pieces so it wouldn't cover any holes but would damp the magnet and the edge of it's frame. I also made holes in the white filter paper under four of the vent holes.

    I haven't been able to get any felt yet to do the suggested mod to the front. But I thought I'd try it as is to check progress. I had cut out some shelf liner already, so I put that under the pads for now.

    I think it may be mission accomplished. These are back closer to the tonal balance I remember, the treble is completely tamed (maybe too much) and they have MUCH better bass. It seems a similar result to what the HD650 mods do, the bass feels more prominent because it's better defined and detailed. They may have lost some of the air/soundstage they had, it's hard to tell because it's a few years since I heard them without the foam disintegration.

    I'll look out for some felt and maybe experiment with replacing the shelf-liner. But the damn pads on these are a NIGHTMARE to get on.
     
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    Last edited: Jan 9, 2018
  15. redrich2000

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    I've taken the shelf-liner out, it was too much filtering with that. Might still try the less dense filter foam too.
     
  16. spoony

    spoony Spooky

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    If you find you overdid the hole-punching thing, you can put tape over the section with micropore.
     
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  17. redrich2000

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    I've never heard the ESP-950. The A250 is very fast, open and airy. A little lean but fantastic treble sparkle. I thought of them as closest I'd heard to a full size ER-4 if that makes sense. There are some old threads on head-fi from back in the day.

    My pair are still a work in progress I think. The currently quite a bit warmer than stock. But I don't think I've got them quite right yet. Koss are sending me replacement cup foams I want to see how they sound with those and play with re-covering some of the driver venting I pierced.

    I have always loved and would rate them in the same league as the HD650 and HE-4XX. And they look so amazingly awesome.
     
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  18. crazychile

    crazychile Eastern Iowa's Spiciest Pepper

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    The ESP-950 is also a bit lean but improves some with the Vesper pads. I don't know if I would say it has treble sparkle though. But my hearing above 12k rolls off pretty quick. I'm guessing that the A250 is probably a little more colored which I think I might actually prefer. I use my HD650s a lot more than my ESP-950s. The '950s are almost too "monitor" like for my tastes but sometimes I'm in the mood for that type of presentation.
     
  19. Mach3

    Mach3 Rando

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    My ESP-950 with angled Vesper ear pads is absolutely sublime at the moment, running off my heavily modded SRM-252S. The sound I would describe it like the HD600 only with ridiculous speed, soundstage and uber micro details. My girlfriend who isn't an audiophile prefers the ESP-950 off the SRM-252S over my HD800 off a balance Beta22 setup which has no 6khz spikes. Get the Vesper angled ear pads with all leather as they seal much better.
     

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