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Fostex TH900 Impressions & Discussion Thread - Page 522
Gear mentioned in this thread:
grand canyon, right? how was it?
No hipster beard, Kurochin, no tightrope, no injuries either. Lots of hiking always down which means always an up.
Edited by Whazzzup - 8/31/14 at 4:11am
Th900 for that heavy bass and lcdx for luscious midrange
may be we need a TH-LCD 900XC ?
A few months ago, Zolkis published his experiments with the Fostex TH-900 ear pads (see this post: http://www.head-fi.org/t/595683/fostex-th900-impressions-discussion-thread/6930#post_10537146).
It got my immediate attention because I was experimenting with different ear pads as well. (see post: http://www.head-fi.org/t/595683/fostex-th900-impressions-discussion-thread/6270#post_10241637).
What attracted me most to his post was that he also found out that deeper/angled ear pads on the Fostex will increase the recessed midrange. I had similar results. I got into contact with him, and he send me some material to experiment with. And experimenting I did.
I focus on the experiments which to me have the most profound effect on the sound of the Fostex Th-900: the earpad and dampers. The damper is the gray foam that surrounds the driver if you take off the ear pads. If you read the post of Zolkis, you will know that in order to experiment with different fillings of the ear pad, you have to remove the earpad grill. (see instructions on how to do this in the Zolkis post). Hence, my experiments, and comparisons are all related to the Fostex ear pad without the grill. From memory, I think that removing the grill already opens up the sound and makes it more clear. But I was not able to test this (still waiting for my replacement Fostex pads; they can be ordered from your distributor. In my case they cost 25 Euro a pair, which equals about 30 dollar ).
Based on Zolkis experiments with ear pads I tested the active carbon filling against the original foam filling of the ear pads. A picture of the active carbon filling is shown below (google active carbon sheets to get an impression). It is commonly used to filter air.
I have kept the original foam filling intact, but experimented a lot with the height and angle of the active carbon pads. To be honest, I have no idea as to why active carbon is a suitable material for ear pads. It just followed up on Zolkis findings. The active carbon sheets are quite stiff and have a very open structure (you can see through it). It is sometimes used inside loudspeaker cabinets, but that is all I know. Maybe Zolkis can explain the merits of using active carbon as ear pad filling. Because the active carbon sheets are quite stiff, e.g. much stiffer than foam, I was afraid it would be very uncomfortable. It is not. The original Fostex pads are also quite stiff, because they really stuff the foam inside the pads. That being said, it is still a bit less comfortable than the original Fostex pads (the structure of an active carbon sheet is coarser than foam). I can handle it….
The sheets of active carbon I used were about 15mm thick. I have made quite a few different pads out of them, and in the end settled on a relatively thin pad (8mm in the front slowly increasing to about 15mm at ¾ of the pad and then kept constant at 15mm). Thicker pads of active carbon sheets (e.g. increasing the front height) result in a more spacious sound, but also in less bass and more treble (at least subjectively). I preferred the active carbon pads that are relatively close to the ear. Your mileage may vary.
Next, I experimented with the dampers (the gray foam that surrounds the driver). Based on the advice of Zolkis I have used 100% wool felt for that. In the end I settled for dampers made out of 5mm wool felt. Thinner felt (e.g 3mm) made the sound underdamped (thin and hollow). Thicker (7-8mm)wool felt resulted in a overdamped sound (thick, and dry). But you will have to experiment with the ideal setting. There are differences in felt, and differences in personal preference. What works for me, may not work for you. Although I believe Zolkis also settled for 5mm wool felt.
I tested the following pad/damper combinations
Original pad (without grill) original foam damper
Original pad, 5mm felt damper
Carbon pad (the thin pad), original foam damper
Carbon pad (the thin pad), 5mm felt damper
My findings are that the original foam damper (compared to the 5mm felt damper) increases spaciousness and increases (mid)bass, but midrange is thinner. The felt dampers improve the midrange, making it fuller. Timbre is more correct. And basically that is also what the carbon pads do. Midbass is reduced, instead (lower) midrange is increased (fuller). It is a cleaner sound. This effect is enhanced by putting the drivers closer to your ear. With the thin carbon pads, I get the most correct timbre of all settings. When I compared the difference between the carbon pad and 5mm felt damper with the original setting (foam pads, foam damper), the effect on sound was quite profound.
When I, after many experiments, returned to the original Fostex Th-900 setting, I enjoyed it a lot. It got me thinking: well isn’t this just the best setting of all. What I like is just the right amount of a ‘v-shape’ type of sound. The midrange is indeed a bit thinner and less upfront, but the total sound picture is not laid back. It is relaxed without becoming boring. “Relaxed with Pep” (Erik B. and Rakim). I can completely understand why Fostex went for this type of sound. It is a very appealing sound. It is clear and spacious, but also full, because of the well defined but present bass….It is difficult to explain, but I believe the Fostex engineers had a clear philosophy about how the headphone should sound, and followed that idea completely. It just works…..
Then I tried the ‘new setting’: thin active carbon earpad/5mm felt damper. The midrange is more upfront, and more dynamic. I remember the eloquent review of ASR (Please read that review: http://new.head-fi.org/products/fostex-th-900/reviews/10204), where he argued that the TH900's dynamic range went from pianissimo to fortissimo (pp to ff), but not from pianissimo to fortissimo possible (ppp to fff). I can understand that now. With the thin carbon pads, the TH-900 moves (much) closer to ppp-fff in terms of dynamics. That is what I call impact. Because of that I have to be more careful with the volume knob. This setting is less relaxing compared to the original setting. It is more open, clear and detailed (or at least, you hear more of the subtle nuances in the music), it is more captivating, maybe even more analytic. Timbre of instruments is good. In fact (much) better than the original setting. You notice this especially when compared to the original Fostex foam pads and foam damper. Because of the correct timbre I can handle the driver very close to my ear, even when horns are blasting in my ear. Imaging is fine, Soundstage is wide and has enough depth, but the leading vocals and/or instruments are (very) close to you (conductor position). Not all of us appreciate such a perspective, but I do (most of the time). To me, this setting is all about excitement, about feeling part of the concert…
One last word about the bass. Do not get the impression that there is less bass with the active carbon pads and felt dampers. There is more (deep)bass, and it hits harder too, but it is more recording dependent than with the original setting. To be honest, from a bass perspective I think the original setting cannot be beat. Difficult the explain why but the bass is just so well tuned by Fostex…
That is it really. Hence, there are two settings that I like for different reasons. I also found out that it is not possible (at least till now) to have both. You either maximize on spaciousness, but at the expense of timbre (midrange fullness) and impact (original setting); or you maximize on midrange fullness and dynamics, but loose on spaciousness (thin active carbon earpad/ 5mm wool felt dampers). The in-between settings (original foam pad-felt damper; or carbon pads/original foam damper) just don’t do it for me. They are nice, but ‘fail’ when compared to the more extreme settings. Although the effects mentioned here are clear and immediately noticeable, the Fostex TH-900 is still the fun headphone we love so much. But with some experimentation it can show you another part of its character.
A final note. At first I hesitated to do these mods. You have to be able, or learn how to cut felt and active carbon sheets, and willing to ‘destroy’ the original pads (you lose the grill). But new pads can be bought ‘cheap’, and the material involved is plain cheap. It may take some time to find the right material, but I enjoyed the ride, and now love my Fostex TH-900 more than I ever did….
Last but not least, a big cheers for Zolkis for his help with collecting materials, his advice, and his initiation of this whole endeavor….
Edited by playitloud - 9/7/14 at 8:19am
These experiments show a few things:
- it is possible to make the TH900 sound with better midrange and less V-shape sound, with better deep bass and less midbass
- anyone can achieve most of that in a reversible way, by changing the foam dampers to 4-5-6 mm thick 100% wool felt
- in addition, it is advised to get a second pair of pads, non-reversibly remove the grill, and also change the pad fillings
- these mods are favorable with most music genres I listen to, but some may prefer the original voicing of the TH900
- it is possible to further increase the spaciousness beyond the original setting, but it goes beyond the tipping point for me; therefore, users of high pads should consider also replacing the cups.
- the cup filling has a little effect; I advise halving the thickness of the polyfill. Alternatively, a 7 mm thick carbon foam pad may work even better. I (actually both of us) have ordered the Lawton tune-up for the cup, being curious about the effect.
The materials used in these mods change the sound in the same direction when used in modding my Stax earpads, and it's also good that Playitloud's experiments had the same results as mine. We perceived all changes in the same way, given similar test setup and materials. After all, experimental physics works, no news there :). But all these are subjective things, and it's good to have some checks and repeatability.
Active carbon is a good acoustic damper, it's used in a range of high end speakers as well (in a different form than here). How is it possible that it makes a difference in an earpad filling, sealed beneath leather, it's a kind of mystery; - but it's not completely sealed. The form used here, with its a very loose and strong foam structure with active carbon particles attached, is likely suboptimal from acoustic point of view, but it provides the mechanical stability needed in earpads.
The (foam or felt) damper makes the most difference, since is at a critical point where the reflected waves from the cup enter the earcups cavity and traverse the dampers. It's an interesting loading, reminiscent to a short transmission line, and it's likely responsible for the TH900's prodigious bass. When you remove the damper, the bass disappears. Overdo the damping, and the only thing you get is bass thumping. Small changes have huge effect. This gets as complex as tuning a transmission line speaker...
A bigger cup will likely make bigger effect in the same direction (better bass and space), but it will likely have a problem with the midrange, especially with higher pads (Lawton mod). However, by combining these two mods, one could get the best of both worlds: even more spacious sound with better midrange and even deeper bass.
That's why I said I feel these bio-cellulose Fostex drivers would deserve some more research in cup design and acoustic loading, since they seem to have yet unexplored potential.
After all these mods, the TH900 is still not as refined and detailed, nor as spacious as my (modded) Stax 007 Mk1, but it has bigger and more dynamic bass, and I often prefer the TH900 with certain music genres. It's perfect for work, and then at home I enjoy the differently surprising Stax system.
I believe I should add to this, too, as I have also consulted with zolkis about modding the earpads. Although I my case I worked on a heavily modded Denon D2000 (see http://www.head-fi.org/t/350721/denon-d2000-d5000-md2000-md5000-appreciation-thread/3495#post_10348740). The activated carbon pad I ended up buying from amazon.com was this one: http://www.amazon.com/dp/B00LUD3ZU8/ref=pe_385040_30332190_TE_3p_dp_1. It was rather messy to cut it and laborious to sew back the earpads, but the end result is indeed a much improved midrange. By the way, just as zolkis had noted, cutting the original foam in a slanted manner also works in the same direction, but the improvement is not as remarkable as in the case of using activated carbon. I am just not sure about the durability of the new earpads, because this material is less resilient than the original foam. One other possible drawback; I'm not sure about it, but isolation from environmental sounds may have further diminished with the new pads. Comparing to the Focal Spirit Professional that I also own, the modded Denon is now more balanced across the whole spectrum, which is something that I first imagined impossible!
First image shows the original foam with the material that was removed from it:
Second image displays the opened earpad (top left), the polyester fiber and activated carbon pads (bottom left and right), and the new earpad already sewn up:
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