Fostex RP discussion and mods thread: all variations of TxxRP, T-X0, and RPKIT50

[isostasy]

I've had a good look around and can't find any threads on ASR regarding this series of headphones from Fostex, using their RP planar-magnetic drivers, which are a very popular basis for modifications. I've been hacking away at a set of these for months now and have only recently struck upon a vaguely neutral, or at least listenable, frequency response. There are already various threads on other forums, articles published on audio websites, as well as plenty of commercially available mods, but I have problems with all of these, most of which boils down to a dearth of evidence for the modifications suggested, even the most popular ones. Let's make way for some more scientific based discussion.

The headphones I'm talking about, so you are clear and so we show up in search results:

• T20RP, T40RP, and T50RP, spanning three revisions (marks I to III)
• T60RP
• Massdrop T-X0
• RPKIT50

If you want a more detailed breakdown please let me know, though specs of all these are available online.

My intention in making this was that we could share measurements we have made showing before/after a variable is changed, as well as measurements of our overall final products. I understand changing a single variable isn't necessarily always helpful, however e.g. it makes little sense to compare very breathable velour pads with non-breathable leather pads without also modifying the bass response via front or rear venting, as these two changes need to be made in tandem really.

Some guidelines I think would be helpful:

• Please share details of your measurement rig!
• Unless you're using a coupler which complies with standards, it would be extremely useful to provide measurements against a well known reference, with limited unit variation, such as a Sennheiser HD6x0 series headphone. I know this doesn't at all confound the drawbacks of FPC measurements, but otherwise your measurement of what may look like a perfectly neutral T50RP mod is almost meaningless.
• Well-annotated graphs, comprehensible legends, and a reasonable y-axis resolution are welcome
• Restrained subjective description is valuable

I know I don't have the power to enforce rules, but if I could make one it would be: no claims made about any mods without evidence. Graphs or it didn't happen.

Stick around and hopefully I'll some findings of my own to share. It's tricky because once you have tweaked something to a point you're happy with you are cautious about reversing things in case you can't get back to that point again! Additionally, I'm a hypocrite because I'm lousy at making notes on what changes I've made, or even keeping past measurements at all, which is not scientific in the slightest. I might get hold of another pair just so I can make changes from scratch to share with you all.

I'll quickly share where I've got so far with my RPKIT50, as I'm happy to have finally produced something not awful. I've flouted pretty much all my above guidelines but I don't want to bog down this first post with before/after measurements etc. so just want to put this here to show one example of what is possible and to have a timestamp for where I got up to on this day!

My coupler is a cardboard box chosen to match the width of my head, with the contact area made of craft foam and acoustic damping foam, and measurements taken with a Superlux ECM-999 into a Scarlett Solo. The ~5kHz dip is not audible and needs investigating.

Thanks and look forward to seeing what others have come up with

 

[IAtaman]

My coupler is a cardboard box chosen to match the width of my head, with the contact area made of craft foam and acoustic damping foam, and measurements taken with a Superlux ECM-999 into a Scarlett Solo. The ~5kHz dip is not audible and needs investigating.

Thanks and look forward to seeing what others have come up with

Sounds like fun. I think the main issue for me, and I suspect many others as well, will be to put together a reliable measurement rig. Can you maybe tell us more about your measurement coupler and how you build it and how you control for measurement variation?

 

[solderdude]

Blue Monkey Flyer (head-fi) has done a LOT of experiments with Fostex RP drivers and mods and there is a huge thread on this.

I too have done some tinkering with mods and EQ and the Fostex'es can be made to sound good but ultimately the driver is limited in certain ways.
It was fun to experiment with for a while but in the end one can only achieve so much. More of a fun hobby thing.

Just like Dan Clark I realized that one can only take it so far and there are better sounding drivers than just trying to get the most out of the RP driver.
I found these drivers (modded quite a few) have substantial variations between them (mostly in distortion but also FR).

Nice headphone to tinker and play with. The drivers can take a beating and are not very fragile which makes them suited to 'play' with.

 

[isostasy]

Sounds like fun. I think the main issue for me, and I suspect many others as well, will be to put together a reliable measurement rig. Can you maybe tell us more about your measurement coupler and how you build it and how you control for measurement variation?

I've been doing some more tinkering about with my rig just today actually.

before I had a circle of acoustic damping foam immediately around the mic, and craft foam surrounding that. I had to push the mic out slightly further than the flat mount because the treble would roll off otherwise. Turns out this was partly the mic capsule itself, because I soldered on a different capsule and the high frequency response is much better now.

A picture would make more sense so I'll upload one tomorrow when there's more light.

In terms of controlling measurement variation, if I'm interpreting you correctly, just making sure the mic is in the same position each time is the most important thing. This isn't a problem if you build a proper rig like @solderdude, but because I've just got a measurement mic stuck through a box (and which I do sometimes want to remove to do speaker measurements), I do need to make sure it's changed position because this can impact measurements alot (again I'll share some evidence of this tomorrow).

Otherwise positioning the headphone for consistent measurements is easy. I cut the foam to the shape of the HD6XX pad so it is easy to match up most headphones in exactly the same position, and even slight variations don't introduce changes due to the nature of the coupler.

Here's my new measurement after messing about with my mic as I described above. So alot of changes, yet you can see the relative differences between the HD6XX and RPKIT50 measurement are almost the same as the earlier graph; at least in the same places. There's some definite differences in the sub-bass and treble.

Blue Monkey Flyer (head-fi) has done a LOT of experiments with Fostex RP drivers and mods and there is a huge thread on this.

I too have done some tinkering with mods and EQ and the Fostex'es can be made to sound good but ultimately the driver is limited in certain ways.
It was fun to experiment with for a while but in the end one can only achieve so much. More of a fun hobby thing.

Just like Dan Clark I realized that one can only take it so far and there are better sounding drivers than just trying to get the most out of the RP driver.
I found these drivers (modded quite a few) have substantial variations between them (mostly in distortion'closed back HD600' but also FR).

Nice headphone to tinker and play with. The drivers can take a beating and are not very fragile which makes them suited to 'play' with.

True, and I've had a good look through it. GREQ's posts are useful too. However, many of the posts are simply mayflower mods being shared over and over, along with the same old blu tac on the back of the baffles, dynamat in the cup, hyperbolic claims of how much better it sounds and no measurements to back it up. And even when there are measurements, no reference measurement such as a HD6x0 to compare. The fact no measurements show the extremely high treble peaking with pads deeper than the stock pads I measure in my RPKIT50, and the T20RP mkIII I had before (which can't be tamed with damping alone) makes me untrusting also.

The drivers in my copy do vary on measures such as distortion but nowhere near the extent yours did. Maybe due to being assembled from scratch?

You're right, I invested in these thinking I could make a good set of closed-back headphones. Reality: it's really hard, and probably not possible to make anything better than even affordable closed-backs available now. It is fun though, like you say.

 

[Soandso]

Here's my old pair of Fostex RP T20 I rewired to balanced cables with insides personally modded. I've resurfaced both ear cups with very soft leather, additionally plumping up the cushions so my ears can nest inside and have an old salvaged Pioneer headband connected. Sure these look uncouth but they have comfortable padding and by chance ideal clamping force since I wear eyeglasses. Certainly their original sound signature altered, none the less these put out quite nice sound with substantial bass and are my go to cool weather pair to put on when heading out to local city streets.

 

[lordearl]

Interesting thread - I'm keen to get involved!

I have the T60RP and am considering getting the RPKIT50. Who has built the RPKIT50 and does the sound signature differ much form the T60RP?

Also, are the instructions in English?

 

[solderdude]

and does the sound signature differ much form the T60RP?

It will because it uses different pads which make the biggest difference in sound.
All these models use the same driver, just different damping and pads.

These headphones are fun to tinker with. It is a robust driver so the chance of damaging it is small making it ideal for novices to play around with damping materials and pads.
The driver does have its limitations and is quite insensitive so one can only take performance up to a certain level and not beyond that.

 

[lordearl]

Okay great, thanks - looking over the range of headphones that use these drivers I must say the pricing of the kit is interesting. It's about $100 more to buy the kit than the 50th Anniversary edition of the T50RP which was just released.

Is the flexibility of the kit worth the additional cost?

 

[isostasy]

Interesting thread - I'm keen to get involved!

I have the T60RP and am considering getting the RPKIT50. Who has built the RPKIT50 and does the sound signature differ much form the T60RP?

Also, are the instructions in English?

It will because it uses different pads which make the biggest difference in sound.
All these models use the same driver, just different damping and pads.

These headphones are fun to tinker with. It is a robust driver so the chance of damaging it is small making it ideal for novices to play around with damping materials and pads.
The driver does have its limitations and is quite insensitive so one can only take performance up to a certain level and not beyond that.

The RPKIT50 comes with 2 sets of pads, one of which are the same angled pleather pads as on the T60RP. With these pads I disagree with solderdude, I think the sound would probably be similar. I don't have the T60RP but it looks like the thick wooden sides leaves less room inside the cup than the plastic models which might have some effect.

The instructions are in English.

Okay great, thanks - looking over the range of headphones that use these drivers I must say the pricing of the kit is interesting. It's about $100 more to buy the kit than the 50th Anniversary edition of the T50RP which was just released.

Is the flexibility of the kit worth the additional cost?

I personally wouldn't get another pair of headphones in this range at all if you already have the T60RP because of what solderdude says: they are all the same driver with different damping and pads which you can change anyway. Unless you want to keep your T60RP completely stock or worried about making irreversible changes.

Additionally, the T60RP already has the suspension headstrap and has a better jack than any other model. The twist-lock thing on the side of other models doesn't look as good, isn't compatible with other cables you might already have, and isn't very reliable.

The RPKIT50 has a balanced 2.5mm plug which is even more annoying. For $100 you're basically paying for 2 sets of pads, 2 different densities of baffle foam, and a big pack of stickers.

That said, if you're in the UK I am thinking of selling my RPKIT50 as I don't use it or tinker with it anymore. I've changed the paper on the back of the driver which is the main drawback but I've accumulated various pads over time (Shure mainly) to play around with.

 

[solderdude]

That cable connector is indeed a poor concept (in the older ones) and had intermittent contact. Cleaning the contact helped a bit. I removed the connectors and hardwired my T40 and T50RP's

The pads on the T50RP(2) and T40RP were not deep enough and uncomfortable with thick pleather.
The 50RPmk3 had somewhat better pads but also not good enough for my taste.
I prefer the Shure 940 pads and 1540 pads (fenestrated Alcantra).

The ones I modified I used with EQ and that sounded good and dynamic but still not as good as I wanted it to be.
Lying somewhere in some cabinet gathering dust.

Probably the same reason Dan started making his own drivers. The membrane of the Fostex driver is simply a flexible PCB which is limited in excursion and there is quite some variance in response. Sometimes I modified a few at a time and swapped drivers between them to get good matching pairs.

 

[lordearl]

Well you guys are not filling me with confidence - what's the next logical step after theT60RP then?

 

[solderdude]

For tinkering or enjoying music ?

 

[lordearl]

Ideally both - I've found the most enjoyable gear is the stuff that I've either modded or built from scratch.

 

[solderdude]

There are many headphones that can be improved with tinkering but it would require some measurement fixture to check changes or at least a non-modded version or a reference you can compare modifications too. To reset your hearing as it were. It is very easy to prefer a modification even when it technically set you back. The brain adapts quickly and can fool you. This is less likely to happen when you have a reference you can use.
The downside of the latter is that when you already own a reference there is no need to tinker anymore.

The most obvious and cheapest tweak method of course is EQ though when it is for sound.

 

[lordearl]

Tend to agree - without measurements there's too much subjectivity, which can be fine unless one is aiming for a 'reference' piece of gear. Of course, this is what brings most of us to this forum!

In terms of building a set of headphones from scratch - is RPKIT50 the only kit available?

 

[solderdude]

From scratch ?
Nah... you can buy lots of drivers on line and make your own headband or even your own drivers (think Verum).
Pads also are widely available from known manufacturers, Dekoni, Poyatu, and many Chinese sellers.

The difficult part is finding the drivers, construction and pads that already work together nicely.

You can also use donor headphones for headbands, cups, drivers and whatnot.

 

[isostasy]

RPKIT50 isn't really building from scratch, soldering is the only bit that requires more than the ability to screw things together. By the end you've just got a Massdrop T-X0 which you had to put together yourself.

A few people have used Peerless 40mm and 50mm drivers for fully DIY headphones.

e.g.

https://www.thingiverse.com/thing:5151002
https://www.thingiverse.com/thing:5090443
https://www.thingiverse.com/thing:5103331

and I remember seeing some others on reddit.

You don't even have to 3D print stuff. I've bought a few headphones with broken drivers to use as base for other drivers. I'd recommend most open-back Sennheisers as a base for 40mm drivers and audio technica open backs for 50mm. Some superlux models look good for 50mm drivers too.

It's a lot of work though and I think you need to invest in quite a large array of different pads before you can start putting things together that work. I would sort of sit on ebay and buy pads here and there when they came up for sale but that's too slow, you wait a few days to arrive and within minutes find out it's not a good match. What you really want is a baffle you can quickly and easily fit different drivers to, every conceivable pad type on hand, and some precut materials for damping and acoustic screens etc.

Maybe ideally you'd even have some different materials to stitch pads together such that you can insert different densities of foam.

I don't really have the motivation for this myself.

 

[Alchemist_]

For tinkering or enjoying music ?

What advice would you give for enjoying music? Instead of T60RP.

I always thought the T60RP had a different driver than the T20/40/50RP MK3. Am I wrong?
Once in the store, I listened to T50RPMK3. I was given Chinese ear pads, I don’t remember velor or leather... but the speaker was further from the ear and sounded most in the region of 150-350 kHz.
The T60RP has almost no damping, a foam ring under the ear cushion, which differs from the MK3 in that it is smaller.
And the hole on the wooden cup is sealed with foam rubber and all the damping is done. But headphones sound differently, so it always seemed to me that the speakers in the 60 were new. I didn’t disassemble the MK3, but there’s less top, probably some foam inside.

ps The manufacturer's approach to matching its speakers to each other is disappointing.

 

[solderdude]

Driver in T20/40/50/60/500RP is the same one.
They only differ in enclosure and pads and damping.

The drivers are decent and EQ can lift the sound quality substantially but has limits.

 

[Alchemist_]

Driver in T20/40/50/60/500RP is the same one.
They only differ in enclosure and pads and damping.

The drivers are decent and EQ can lift the sound quality substantially but has limits.

What do you mean by restrictions?

I thought that you said above that instead of Fostex it is better to buy something else; If. Did I understand you correctly, what do you think is preferable to Fostex and why?