[Afghan Vet]

  I think that my modded TH900 does not have the soundstage limitation, at least not to this extent.
It's true that my modded Stax 007 has better stage, and so does the HD800, and perhaps even the HE-6, albeit that is a close call, and I agree that even the modded TH900 may not be as good/neutral/revealing as the HD800 and HE-6 when they are properly driven, but:
- I don't feel like having a distorting wall; when sounds seem coming from a far distance with the 007, they do so with the TH900 as well, albeit closer. The carbon foam pad filling helps a lot with soundstage. If you care more about sound stage than mids, you can try using the original dampers (the grey foam ring around the drivers) rather than the felt dampers. The felt dampers can overdamp easily, and every cutout will likely sound different anyway, it's so sensitive to minor and micro-variations, and then every felt sounds different, even from the same felt sheet when cut from different parts of the sheet.
- the main strength of the TH900 is still that it is a closed design, and that's exactly what I need most in it in the office, or when watching late night movies at high volume
- it works wonderfully with portable DAC's, and while it does scale with good amps, I get most of the goods right at the start of the range, from a Resonessence Herus, or even a Sony Z3 phone
- the modded TH900 is fun, and for me much more fun, with better stage, mids, bass and treble than the non-modded TH900 .
 
However, when in the evening I put on the 007 (not so much the 009 nowadays), I melt away.
So that's the context, and I have made peace that after a year of tweaking, I have seemingly reached the "good-enough" limits of the TH900, and it is what it is and no more .
I will notify this forum when I find a better closed headphone for the above purpose (the LCD-XC is not, at least for me, although I did not try to tweak that one).

 
Thank you very much Zolkis for this remarks about the nuances of the headphones themselves and the mods.
 
Thank you as well for that 'perspective'......one of the things that is daunting at times when reading descriptions of performance.....'compared to what?'.......If it is the TH900 on a decent amp versus a full Stax set up, then that context provides added insight. Recently I've been reading a number of reviews on CIEMs.....niggle here, niggle there.......from reviewers that may have units that are 2 or 3 times the cost of the one I may be looking at.....compared to my iPhone buds, those niggles are nothing
 
So, I may eventually look into a cable change with my Fostex (cable termination to balanced to connect to the Taurus, and potentially cable composition), but I'm just planning on enjoying them

 

[stjj89]

Thanks for the detailed feedback, @zolkis and @playitloud! While I'm pretty sure that I cut out the same inner diameter for both pairs of carbon foam rings, it might be that my hand wasn't as steady as I imagined while using the circle cutter on the carbon foam, and that one of the inner diameter openings is indeed larger than the other. Either way, the result wasn't exactly bad in either case--the bassier pads were more fun (very satisfying bass thump!), but sacrificed a little bit of air, midrange detail, and naturalness. The airy-er pads sounded more open and natural for certain genres of music (e.g. rock), but lost that fun factor for music that is bass-thump-heavy (e.g. EDM, hip-hop). Definitely a matter of preference there.

I think that my modded TH900 does not have the soundstage limitation, at least not to this extent.
It's true that my modded Stax 007 has better stage, and so does the HD800, and perhaps even the HE-6, albeit that is a close call, and I agree that even the modded TH900 may not be as good/neutral/revealing as the HD800 and HE-6 when they are properly driven, but:
- I don't feel like having a distorting wall; when sounds seem coming from a far distance with the 007, they do so with the TH900 as well, albeit closer. The carbon foam pad filling helps a lot with soundstage. If you care more about sound stage than mids, you can try using the original dampers (the grey foam ring around the drivers) rather than the felt dampers. The felt dampers can overdamp easily, and every cutout will likely sound different anyway, it's so sensitive to minor and micro-variations, and then every felt sounds different, even from the same felt sheet when cut from different parts of the sheet.
- the main strength of the TH900 is still that it is a closed design, and that's exactly what I need most in it in the office, or when watching late night movies at high volume
- it works wonderfully with portable DAC's, and while it does scale with good amps, I get most of the goods right at the start of the range, from a Resonessence Herus, or even a Sony Z3 phone
- the modded TH900 is fun, and for me much more fun, with better stage, mids, bass and treble than the non-modded TH900 .
 
However, when in the evening I put on the 007 (not so much the 009 nowadays), I melt away.
So that's the context, and I have made peace that after a year of tweaking, I have seemingly reached the "good-enough" limits of the TH900, and it is what it is and no more .
I will notify this forum when I find a better closed headphone for the above purpose (the LCD-XC is not, at least for me, although I did not try to tweak that one).

 
My feelings exactly! Even though I don't have either Stax, I still feel like my HE-560 is more transparent. However, the TH900 is closed, and has a slightly more aggressive, fun, and airy signature that I really like as well. Compared to all the other closed cans I've heard, the TH900 is really quite amazing.
 
I am kind of curious about the MrSpeakers Ether-C actually, but I'm going to wait till the next local meet to compare them side-by-side

 

[Afghan Vet]

I'd like to report that I am a very happy owner of a zolkis modified set of Fostex TH900 headphones. Thank you Sam (stjj89)!
 
My wife brought them home yesterday, and I got a 10 minute quick and dirty listen prior to dinner. I was immediately impressed - I purposely didn't 'review' Sam's and other's impressions....I wanted as fresh and unbiased of a listening experience as possible. The beauty of the mid range was the first and most obvious change. The vocals were front and center, and I perceived strings were much more 'present' in the mix.
 
I had never been 'annoyed' by the reported recessed mids......and possibly, if I hadn't read over and over that the 900's had these recessed mids....I may not have ever really perceived that. It wasn't something that immediately jumped out as a criticism for me - I only own one other pair of headphones (Senn HD530's) that I rarely listen to, and I don't frequently listen to many others....so I didn't have a lot to compare to. But, immediately when I put on the modded pair, it was apparent that a change had happened - and I enjoy the change.
 
Again, it might be my bias now (wanting to hear good things due to the work that Sam did, the investment, and the reports on this thread), but it seems that the midrange is just better - or at least more apparent - when it comes to strings of all types (violins, upper cello, acoustic guitar, electric guitar). 
 
And....the highs were never a deal breaker for me - there were times they seemed a bit hot on some tracks....or they would be a bit messy.....I have heard other phones that were smoother up top, and some that didn't have nearly as much energy up top - they were pleasing, but also a bit boring. I have the feeling that the highs are tamed just a bit - not dull, not muted, still very present - just not out of control. Again, psychoacoustics may be my friend here....and I've only listened for about 2 hours total time. 
 
Finally, the bass......Sam posted on here the difference between the pads with the newer carbon rings and the older carbon rings. He and I decided that I would likely want the airyer, less thumpy pads....and he was correct. For 95% of my music, and cleaner, more controlled sound is what would please me. Yes, the stock cans were very fun on some types of music when they would just move you with their slam......but I can certainly get that with my car system.....or with the Custom In-Ear Monitors that I'm hoping to get in the coming months.......my TH900's are intended to be a bit more 'accurate'. Now....there is certainly plenty of bass energy - it just sounds like the cool, fun, older brother to the wild child stock cans.
 
I'm looking forward eagerly to getting a side by side comparison with the stock cans soon to verify these early impressions. I'm also interested to get that fella who provided his impressions of the stock cans to give another listen. His impressions may not change....he may still not like them as much as the HD800's or the HE-6's.....that is just fine - his preference - that doesn't take away (to me) how good these cans are I'll circle back with some feedback once we have that G2G. 
 
I for one am very happy I stumbled on this thread, I'm thankful for zolkis and playitloud for doing the early work on this mod and for providing such exact information, and especially to Sam for taking so much time out of his busy life to complete this modification (that I wouldn't have attempted). What a great community we have on Head-Fi!
 
Jason 

 

[stjj89]

  I'd like to report that I am a very happy owner of a zolkis modified set of Fostex TH900 headphones. Thank you Sam (stjj89)!

Spoiler: Warning: Spoiler!

My wife brought them home yesterday, and I got a 10 minute quick and dirty listen prior to dinner. I was immediately impressed - I purposely didn't 'review' Sam's and other's impressions....I wanted as fresh and unbiased of a listening experience as possible. The beauty of the mid range was the first and most obvious change. The vocals were front and center, and I perceived strings were much more 'present' in the mix.
 
I had never been 'annoyed' by the reported recessed mids......and possibly, if I hadn't read over and over that the 900's had these recessed mids....I may not have ever really perceived that. It wasn't something that immediately jumped out as a criticism for me - I only own one other pair of headphones (Senn HD530's) that I rarely listen to, and I don't frequently listen to many others....so I didn't have a lot to compare to. But, immediately when I put on the modded pair, it was apparent that a change had happened - and I enjoy the change.
 
Again, it might be my bias now (wanting to hear good things due to the work that Sam did, the investment, and the reports on this thread), but it seems that the midrange is just better - or at least more apparent - when it comes to strings of all types (violins, upper cello, acoustic guitar, electric guitar). 
 
And....the highs were never a deal breaker for me - there were times they seemed a bit hot on some tracks....or they would be a bit messy.....I have heard other phones that were smoother up top, and some that didn't have nearly as much energy up top - they were pleasing, but also a bit boring. I have the feeling that the highs are tamed just a bit - not dull, not muted, still very present - just not out of control. Again, psychoacoustics may be my friend here....and I've only listened for about 2 hours total time. 
 
Finally, the bass......Sam posted on here the difference between the pads with the newer carbon rings and the older carbon rings. He and I decided that I would likely want the airyer, less thumpy pads....and he was correct. For 95% of my music, and cleaner, more controlled sound is what would please me. Yes, the stock cans were very fun on some types of music when they would just move you with their slam......but I can certainly get that with my car system.....or with the Custom In-Ear Monitors that I'm hoping to get in the coming months.......my TH900's are intended to be a bit more 'accurate'. Now....there is certainly plenty of bass energy - it just sounds like the cool, fun, older brother to the wild child stock cans.
 
I'm looking forward eagerly to getting a side by side comparison with the stock cans soon to verify these early impressions. I'm also interested to get that fella who provided his impressions of the stock cans to give another listen. His impressions may not change....he may still not like them as much as the HD800's or the HE-6's.....that is just fine - his preference - that doesn't take away (to me) how good these cans are I'll circle back with some feedback once we have that G2G. 
 
I for one am very happy I stumbled on this thread, I'm thankful for zolkis and playitloud for doing the early work on this mod and for providing such exact information, and especially to Sam for taking so much time out of his busy life to complete this modification (that I wouldn't have attempted). What a great community we have on Head-Fi!
 
Jason 

 

 
Glad to hear you like them, Jason! We now have a grand total of 2 adopters of this mod in the US, woohoo!
 
Do let us know what you and other head-fiers think when you bring them to a meet. I'd be especially interested to hear what people think when compared side-by-side with the stock TH900. When I did the comparison myself, I was actually quite surprised that the stock TH900 still sounded quite good (I had a bad memory of it), but still recognized its shortcomings that I "fixed".
 
Happy listening!

 

[Shell of Light]

Hey all, read over this thread.  Some really great info and impressions, thanks everybody.
I recently purchased a pair of TH900s.  Was wondering how much this mod would cost me if I was to order all the materials needed?

 

[stjj89]

  Hey all, read over this thread.  Some really great info and impressions, thanks everybody.
I recently purchased a pair of TH900s.  Was wondering how much this mod would cost me if I was to order all the materials needed?

 
$34 for the carbon foam (shipped) + $28.50 for Lawton Tune-up kit parts (shipped) = $62.50
 
I am not sure how much the wool felt costs--it might be tricky ordering from the recommended site. If you don't already have the tools, you'll probably spend ~$30 on them.
 

  do any mods make any big differences?

 
Yes. Read my previous impressions for more details.

 

[Shell of Light]

Hey Afghan Vet, after getting some more time with your modded TH900s how much do you feel they have improved?  Is it worth modding them and losing out on the warranty?

 

[Afghan Vet]

  Hey Afghan Vet, after getting some more time with your modded TH900s how much do you feel they have improved?  Is it worth modding them and losing out on the warranty?

I travel a lot, so I got some good time with them that first weekend. I haven't had any time with them over the last week. I can't give you a percentage.....(they are 20% better......or 70% better). 
 
So.....I can't give you any more opinions of the 'improvement' until I'm able to hear them compared to the stock TH900's that my buddy has. I'm hoping that will happen next Sunday. 
 
For me.....doing the mod was more about curiosity.......It wasn't that I didn't like the stock sound (I saw someone post on another thread....you should only consider modding headphones that you really like and want to keep)......and it was made easier for me that I saw that I could ask a respected member to complete the mod after he successfully completed his. I bought my headphones used from another member, so I wasn't really expecting to have a warranty. So....whether you are willing to 'risk' doing the mod is completely up to you of course, but I believe from my first impressions....it was totally worth it for me. 

 

[Afghan Vet]

This past Sunday I was able to go over to a fellow member's house to meet up and listen to the modded TH900's versus his stock cans. We listened to both on my AURALiC set up and on his Unison Research rig. 
 
For me, the forwardness of the midrange was the most easily recognized characteristic of the modded headphones. The voice is much more present - more in balance with the highs/lows. As stated previously - I never was 'bothered' by the 'V-shaped' sound. Once I started reading those descriptions, I would listen to the stock cans and kind of 'see what they were saying' - but I never thought, "these things are terrible because they have a V-shaped sound". And...it still wasn't extremely evident when I would take the Fostex off, and put another set of headphones on.
 
So, it was the first time I really understood what they were describing.......with most things being equal between the two Fostex examples, I could hear that the midrange was certainly brought forward in the mix. And with well recorded music, this midrange sound is amazing! With poorly recorded music - electric guitars, screechy female vocals - that forwardness could make you reach over to drop the volume just a tick.
 
I felt the bass / sub-bass was a little more controlled on the modded pair - a little bit of the 'boominess' was 'tamed'. Now - I'm not sure if that was the preconceived bias of what the mods were 'expected' to do or not. I guess the best thing about that is that the mods didn't eviscerate the bassy nature of these headphones.
 
Again, different ears, different impressions.....I didn't perceive a night/day difference on the highs.....in one particular track, the stock cans didn't seem to have the sparkle that I got on the modded phones.....but overall, I didn't feel the mods 'killed' the highs, made them too intense or anything in that nature.
 
Now, the member who owns the stock TH900's of course perceived the midrange being drawn forward in the mix, didn't really perceive much difference in the bass qualities, but his main point of feedback was that there was much more treble energy. I joked that he was politely saying he felt they were 'hot'.......he said, no.....just more treble energy And he reiterated that in his PM response.
 
Tom, the other listener described the difference as such: 
 

Per the modded TH900, I noted overall significant changes from the original. First, a layer of warmth seem to be removed. The sound become more neutral like my HE-6, relatively speaking. To my ears, there are both an increase in sound clarity and increased darkness of background. Second, there may be a trend for increases in certain treble frequencies. Third, lateral soundstage may be extended to some degree with the mods. Still, both TH900s have less width but greater height and intimacy in soundstage as compared to my HE-6. I no longer detected the warped border of the soundstage as apparently as I felt in the previous meeting---maybe my brain is adapting or due to the sharp contrast with the unusually wide soundstage of the HD800.

 
He is the fella I quoted earlier after the mini-meet regarding his impressions of the stock TH900's compared to the HE-6 and HD800. 
 
A small 'improvement' brought on with the mods were comfort. It really is unexplainable - when you put the modded phones on, they almost feel 'sloppy' because the ear pads are not stuffed as full. They are almost on the ear instead of around the ear. Most headphones give me that weird sensation of nausea brought on by putting pressure on the mastoid process (that point under the ear lobe where the jaw connects) - if you push on it, you get this sick feeling. I don't get that as much now with the modded ear pads, and the top band doesn't hurt the top of my head anymore - again, unexplained. 
 
I listened all day on Wednesday with the Fostex connected to my AURALiC Taurus using an iPod Classic as source with 320 MP3's......completely enjoyed the experience. 
 

 
So, I don't think this bunch of typing revealed anything new about the headphones themselves or about the mods, but it was a good excuse to get two excellent Head-Fi'rs together to listen and swap amps/DACs around  

 

[Howlin Fester]

  This past Sunday I was able to go over to a fellow member's house to meet up and listen to the modded TH900's versus his stock cans. We listened to both on my AURALiC set up and on his Unison Research rig....
 
...Now, the member who owns the stock TH900's of course perceived the midrange being drawn forward in the mix, didn't really perceive much difference in the bass qualities, but his main point of feedback was that there was much more treble energy. I joked that he was politely saying he felt they were 'hot'.......he said, no.....just more treble energy And he reiterated that in his PM response. 

I had a great time getting together with Afghan Vet and TomNC on Sunday.
Everything that Afghan Vet stated is how I saw it.  
 
I, too, have always enjoyed the Fostex sound signature and have never found it lacking.  (recessed mids).  I just like the way it is presented.  And I love my guitars, so that should be hitting right in the mids, but I've never found rock music to be lacking in any way on the stock TH900s.
 
On the modded 900s (great job, by the way) I immediately noticed what I called "Increased Treble Energy".  It seemed to me like there was more high end, and possibly a little bit more clarity.  On almost everything I heard, I enjoyed it immensely.  I have always enjoyed a little extra treble, and I have never been bothered much by sibilance.  It was the same for the modded TH900s except for one particular condition.  I was listening to Jo Harman - Sweet Man Moses from computer>Schitt Gungnir > Unison Research.  With that setup, Jo's vocals were extremely sibilant.  But with lyrics like "Sweet man moSeSS. Sweet aS the daylight on the roSeSS....)  She is hitting the alliteration Sibilance Sweet Spot...
 
As for the bass, I didn't listen to anything specifically to determine if the bass tightened up or not.  What I noticed was that there was no significant change to me in bass impact and quality.  Unfortunately, I didn't listen to a lot of extremely familiar tunes.  I was just listening to different things on different equipment and having a good time.
 
Great time Jason and Tom.

 

[zolkis]

Thanks guys for the nice impressions.
 
The perceived increase on treble energy on the modded TH900 has been addressed earlier in this forum. I wonder if this mod had the relevant part of the Lawton basic kit installed? In my experience, applying the damping on (and eventually around, although I did not use that) the magnets has calmed down the treble just well. My modded TH900 does not sound much different in the treble than my modded Stax 007 Mk1 (although the latter is more fluid).

 

[stjj89]

Thanks for the wonderfully detailed impressions, @Howlin Fester and @Afghan Vet (and @TomNC)! It really helps confirm the changes I think that the mods brought about.
 
Quote:

 
So, it was the first time I really understood what they were describing.......with most things being equal between the two Fostex examples, I could hear that the midrange was certainly brought forward in the mix. And with well recorded music, this midrange sound is amazing! With poorly recorded music - electric guitars, screechy female vocals - that forwardness could make you reach over to drop the volume just a tick.

 
Precisely! There is so much detail you get from hearing more mids that is just lost when they are recessed. I would describe the modded TH900 midrange as clean and neutral--just the way I like them
 

 
I felt the bass / sub-bass was a little more controlled on the modded pair - a little bit of the 'boominess' was 'tamed'. Now - I'm not sure if that was the preconceived bias of what the mods were 'expected' to do or not. I guess the best thing about that is that the mods didn't eviscerate the bassy nature of these headphones.

 
The cleaning up of the bass boom/bloom is the next most prominent feature of the mods for me (after bringing forward the mids). I felt taht all-enveloping bass bloom on the stock TH900 was kind of distracting, and made the overall sound signature somewhat dark and veiled. Removing this bloom is a big part contributing factor to the increased level of clarity, I think.
 

   
Again, different ears, different impressions.....I didn't perceive a night/day difference on the highs.....in one particular track, the stock cans didn't seem to have the sparkle that I got on the modded phones.....but overall, I didn't feel the mods 'killed' the highs, made them too intense or anything in that nature.

 
Same here. I think that the mods changed the treble the least. More on this below.
 

Per the modded TH900, I noted overall significant changes from the original. First, a layer of warmth seem to be removed. The sound become more neutral like my HE-6, relatively speaking. To my ears, there are both an increase in sound clarity and increased darkness of background. Second, there may be a trend for increases in certain treble frequencies. Third, lateral soundstage may be extended to some degree with the mods. Still, both TH900s have less width but greater height and intimacy in soundstage as compared to my HE-6. I no longer detected the warped border of the soundstage as apparently as I felt in the previous meeting---maybe my brain is adapting or due to the sharp contrast with the unusually wide soundstage of the HD800. 

 
Layer of warmth removed? Check! More neutral? Check! Like I mentioned above, we have the midrange improvement and bass bloom fix to thank for this. I personally feel like the modded TH900 is a lot closer to "reference" neutral cans I've heard, including the HE-560 that I use at home. I definitely get what he means by the "warped border of the soundstage" on the stock TH900 as well--the modded TH900 definitely fixes this and makes the soundstage feel more natural.
 

   
A small 'improvement' brought on with the mods were comfort. It really is unexplainable - when you put the modded phones on, they almost feel 'sloppy' because the ear pads are not stuffed as full. They are almost on the ear instead of around the ear. Most headphones give me that weird sensation of nausea brought on by putting pressure on the mastoid process (that point under the ear lobe where the jaw connects) - if you push on it, you get this sick feeling. I don't get that as much now with the modded ear pads, and the top band doesn't hurt the top of my head anymore - again, unexplained. 

 
I think you just explained the "unexplained" improvement in comfort I, too, find the modded TH900 more comfortable now (I've finally found my sweet spot!). The dense foam in the stock pads don't conform to the shape of your head as much as the angled carbon foam does. It might also be the case that the explicit angling of the carbon pads is also helping comfort here. The stock foam is actually not angled, but is made to appear angled when stuffed in the pads by compressing the front part of the ring (since that part of the pad is stitched to be lower.  
 

  I had a great time getting together with Afghan Vet and TomNC on Sunday.
Everything that Afghan Vet stated is how I saw it.  
 
I, too, have always enjoyed the Fostex sound signature and have never found it lacking.  (recessed mids).  I just like the way it is presented.  And I love my guitars, so that should be hitting right in the mids, but I've never found rock music to be lacking in any way on the stock TH900s.
 
On the modded 900s (great job, by the way) I immediately noticed what I called "Increased Treble Energy".  It seemed to me like there was more high end, and possibly a little bit more clarity.  On almost everything I heard, I enjoyed it immensely.  I have always enjoyed a little extra treble, and I have never been bothered much by sibilance.  It was the same for the modded TH900s except for one particular condition.  I was listening to Jo Harman - Sweet Man Moses from computer>Schitt Gungnir > Unison Research.  With that setup, Jo's vocals were extremely sibilant.  But with lyrics like "Sweet man moSeSS. Sweet aS the daylight on the roSeSS....)  She is hitting the alliteration Sibilance Sweet Spot...
 
As for the bass, I didn't listen to anything specifically to determine if the bass tightened up or not.  What I noticed was that there was no significant change to me in bass impact and quality.  Unfortunately, I didn't listen to a lot of extremely familiar tunes.  I was just listening to different things on different equipment and having a good time.
 
Great time Jason and Tom.

 
I actually just listened to the same track (streamed from Google Play Music) and I did not notice this sibilance. I am running my TH900 directly from my PC right now (new DAC/Amp incoming), so perhaps this is truly a setup-synergy thing.
 

  Thanks guys for the nice impressions.
 
The perceived increase on treble energy on the modded TH900 has been addressed earlier in this forum. I wonder if this mod had the relevant part of the Lawton basic kit installed? In my experience, applying the damping on (and eventually around, although I did not use that) the magnets has calmed down the treble just well. My modded TH900 does not sound much different in the treble than my modded Stax 007 Mk1 (although the latter is more fluid).

 
Yes, I did install them on Afghan Vet's pair and my own


 
Personally, I found that the treble of the modded TH900 isn't very different from stock. However, when I first put the damping strips on, I thought that they improved and smoothed the treble noticeably. Perhaps it is the case that the mods (without the damping strips) increase the treble energy of the stock TH900, and the damping strips bring them back in line?

 

[Thenewguy007]

Does the shelf liner mod for the TH600 work with the TH900?
 
http://www.head-fi.org/t/631594/fostex-th600-dynamic-headphones/2400#post_11109568

 

[zolkis]

Does the shelf liner mod for the TH600 work with the TH900?
http://www.head-fi.org/t/631594/fostex-th600-dynamic-headphones/2400#post_11109568

 
You can certainly try. I didn't have good experience by adding more damping to the TH900. In fact, I had to remove damping, and add other kind of damping. For me the treble was "fixed" by applying the stripes from the Lawton basic mod to the back of the drivers on the magnet (how curious, right?). It's more about handling reflections and interference than a problem with the direct sound source. You can treat the symptoms by taming the direct source (and that may be part of the problem indeed), but I like minimal solutions, and also prefer a hair underdamped rather than a hair overdamped.
 
Other folks also added the Lawton stripes to the sides of the assembly as well, but I felt the partial application sounded better with my other mods. Since you can't make two mods exactly the same (because felt thickness and density variation, and small variations in cut dimensions for the earpads and damper), it is possible that different degree of damping is needed to get the treble right. So when is it right? When you can make instruments (cymbals, percussion, violin, wind instruments) sound with no additional trails of shimmering and haze, or alteration of the natural frequency spectrum. If you add more damping, you scatter the sound more and becomes more smeared and diffuse. Treble has to be very well defined, timing is everything. That's why I would use the absolute minimal damping that is needed, and avoid secondary sound sources. It takes a lot of experimentation with relevant musical material until an optimum across various instruments rendering can be found. Also, having one or two reference headphones helps in that: I have used the Stax 009 and 007 Mk1.
 
That said, there are limits of the driver and the construction. Even the modded TH900 cannot reach the treble definition, fluidity, smoothness and naturalness of the Stax 009 and the modded Stax 007 Mk1 (same goes for midrange and bass). But it gets close enough, and man it's a closed headphone, with a sensational sound in the modded form, easy to drive, so far more portable and usable than my Stax with their huge amps. It can give a run for the money to bigger names, too (dynamic and orthodynamic alike). When I don't hear it next to my Stax, it sounds as good as it gets for enjoying the music. The next level of extreme mod would be a wooden driver plate, like the Sony R10.

 

[Thenewguy007]

Any videos on any of this?
Opening up & disassembling the headphone for mods can potentially lead to headaches if I do something wrong or don't put the right piece back in correctly.
 
Or even step by step picture guide?