Analysis of Two Modded Fostex Vintage Orthos (T30 and RP18)

Background

I would like to skip the general introduction of vintage orthodynamics headphones and earlier models Fostex released decades ago because I’m not the best qualified person for such an explanation. Instead, this specific thread will focus on how the two specific pairs of Fostex open-back vintage headphones (T30 and T50/RP18 respectively; modded by @Philimon) sounded and measured in the dummy ear measurement context.

A brief background is I’ve seen many hypes arguing vintage orthos (conditioned by proper modding) wins over today totls. I’m curious if such bold statements hold for MZ/Meta-verse childish audio tastes like mine. RD’s RP18 and HP500 early this year were an interesting experience. But I still want to collect more data points as I’m not fully convinced yet. @Phillimon kindly offered a loaner tour opportunity a couple of weeks ago and I immediately jumped in.

Let me make clear that these two headphones are NOT in the stock housing. Their drivers were transplanted to HFM enclosure+headband. Because I am not super familiar with all the mods and housing transplantation processes, I’d like to let him chime in and explain about his babies.

My analysis will be posted in the following order. Will put relevant links below as I update posts.

• Subjective summaries about RP18 and T30
  • https://www.superbestaudiofriends.o...intage-orthos-t30-and-rp18.11635/#post-365682
  • https://www.superbestaudiofriends.o...intage-orthos-t30-and-rp18.11635/#post-365683
• Measurements
  • https://www.superbestaudiofriends.o...intage-orthos-t30-and-rp18.11635/#post-365684
  • https://www.superbestaudiofriends.o...intage-orthos-t30-and-rp18.11635/#post-365685
• Comments on Measurement Results: https://www.superbestaudiofriends.o...intage-orthos-t30-and-rp18.11635/#post-365731
• Additional thoughts: TBD

In my evaluation and measurement, Soekris dac 2541 was used as a main converter and a main headphones amp.

 

NAD RP18 Phil Mod Subjective Summary

What I like

• I have zero idea about what was the original tone balance of stock RP18, but probably not as good as this pair. Phil’s mod had a nice down-tilting response and great balance between bass, mids, and highs. It’s a little more up my alley compared to another RP18 I tested months ago which RD modded but was too aggressive to my liking (note: RD said he changed the voicing after I returned).
• They could go down to very deep sub-bass. Furthermore, Phil’s RP18 does not depend on airtight pads and seals -- this isn’t very often seen even among greatest bass performers. The pads slapped on this RP18 didn’t make a good seal on my ears, which introduced no problem in bass performance during my evaluation.
• Original RP18 headband was almost a torturing machine for my big head. HE-X4 headband increased the comfort level a lot, which allowed me more head time than RD’s RP18 aforementioned.

What I don’t like

• When tracks were complicated with signals of various dynamic and detail levels, RP18P felt like they lost authority a bit. This introduced congestion/lacking clarity from time to time. Congestion was heard in the entire spectrum, but more problematic in mids and up compared to bass.
• I heard minor resonances in two different places. One was in the lower to middle midrange. This midrange resonance seemed to make female vocals a little boxy and muddy. The other was associated with mid treble, which created some fatigue after a long listen. Neither to a very serious extent by any means. Maybe that’s simply relative perception caused by my estat-love status these days.
• The HE-X4 headband used in this pair was less comfortable to me than the other HFM headband Phil used for the modded T30 loaner pair. I’m not a big fan of velour pads creating leaks on my skull, either. These are just ergonomic complaints and don’t look associated with sonic demerits at all though.

Comparisons or other thoughts

• This RP18 pair was quite reminiscent of the ESX900 I tested a while ago. I was a little surprised that orthodynamic headphones can do this kind of bass. I won’t say their bass presentation is identical, but they both convey similar styles of thick and organic bass.
• I found the loaner T30 better in many aspects, which is a little weird as T50 is higher tiered than T30.

 

Fostex T30 Phil Mod Subjective Summary

What I like

• Voicing was similar to the RP18 I evaluated above. Similar downtilting tonality but this pair showed smoother and more cohesive connection over all the frequency spectrum.
• Bass hit a little less aggressively than I thought but nuance and articulation was very good. I really liked how T30 articulated the bass texture.
• The HE400S headband does look cheap (more so than HE-X4 headband), but it is a lot more comfortable to my head.

What I don’t like

• T30’s drawbacks were more preferential and taste-dependent. Thus, please take my complaints below with a grain of salt.
• T30 wasn’t the best headphones to enjoy analytic listening. The headphones were tuned for rather prolonged listening. This includes a little flat presentation, slowness (relatively), and lack of incisiveness.
• Ear pads were not my cup of tea. Ear holes were too small for my large ears. I was persistently bothered by the feel of my outer ears touching soft fabric. I always prefer to allow enough physical space around my outer ears to touch nothing.

Comparisons or other thoughts

• Like the loaner RP18 reminded me of ESX900, this pair sounded like an ortho-version Gen G to my ears.
• Things I didn’t like in RP18 were better controlled to an acceptable (i.e., good enough for me to consider as a daily driver) extent. T30’s vocal presentation was much clearer and more articulate than RP18. I also liked T30’s timbre over RP18.

 

NAD RP18 Phil Mod Measurements

1. Frequency Response for both channels



2. Individual Harmonics Plot (95db@300hz) for both channels




3. THD Distortion Plot By Amplitude (90, 95, and 100db@300hz) for both channels




4. CSD Waterfall Plot for both channels

 

Fostex T30 Measurements

1. Frequency Response for both channels




2. Individual Harmonics Plot (95db@300hz) for both channels




3. THD Distortion Plot By Amplitude (90, 95, and 100db@300hz) for both channels




4. CSD Waterfall Plot for both channels



My comments and thoughts to come later.

 

Several thoughts on the measurements.

RP18

• Small peaks around 400hz and 4khz shown in FR sustained long in CSD. Also audible as I reported in the subjective evaluation. Because of their locations in frequency, I'm betting they were created by respectively different root causes. Upper one looks like a classical ortho wall. More inspection or investigation seem required to argue more strongly.
• THD plots show the specific loaner pair suffers from amplitude-dependent non linearity issue. There can be many hypotheses with many different sites. But I'm curious if this nonlinearity was associated with my perception of congestion to any extent (I'm not listening to music at this loud level.. so I don't think they're directly related tho).
• Even adjusting against different signal scales, the results were largely different from RD's RP18 I measured with the same system. Probably due to different modding approaches I guess.

T30

• Resonances also observed in both FR and CSD (in quite similar pattern to RP18). I wonder if softer and more absorbing nature of hybrid pads T30 equipped played any beneficial roles to smooth out resonating stuffs.
• Distortion results look better with T30, but still don't seem confident with large excursion.
• Except two obvious resonances, CSD generally look quite linear in time axis. I'm sure that's because of pads used in this mod.

Since neither is stock, it's very difficult to say if it's good vs bad outcomes from ebay/hf gambling. But this kind of unit to unit variation is something to keep in mind for any noobs diving into the vintage ortho world.

 

Awesome analysis @Vtory . I cannot disagree with any of your impressions.

Wondering if my RP18 is a bad example due to the measured imbalances in distortion and CSD. Hoping @takato14 can illuminate by comparing to his sets, unit variation vs condition. The driver membranes are not mint, slight wrinkles and/or dents (including T30). However to my ears, this RP18 did not sound different to the RP18 that @dBel84 has… Vintage ortho is a gamble. These headphones are nearing 50 years old!

Also possible a driver came loose in shipping. If youre not comfortable inspecting @Vtory then leave that to @takato14 (next user on tour). Its even possible the driver casing is coming apart. Both RP18 drivers had screws loose. I had to replace screws with slightly larger ones and wrapped in damplifier to help keep secure.

The drivers are held to Hifiman enclosure by screws/washers/bolts. Then applied a layer of damplifier pro to make sure there is a good seal and for some resonance control. Its totally Macgyver(ed), or MacGruber(ed) in this case.

Vintage ortho were the rage 10+ years ago because they were freshly rediscovered and were very cheap used. But hype grew, so supply/demand makes attaining no longer easy or cheap. Now they are more interesting as history and as a different flavor if you buy at decent prices. Yamahas are still cheap and common and make for a decent closed back, but that's for another thread (@Vtory now owns an HP-1 ).

Afaik vintage ortho are not special in terms of sound quality (at current prices) but impressive in terms of design and build vs modern planar. Particularly the driver membrane tracing, and the choice to use thicker and lighter tensioned membranes.

T30 is technically lower tier and smaller, but the lower tensioned mylar membrane of T30 sounds better overall. The vintage ortho king Sansui SS100 is a hybrid of T30 (membrane material) and RP18 (tracing + size + magnets ?) with a much prettier enclosure.


^ Stock Fostex T30 (mine)


^ Stock NAD RP18 (mine)


^ Fostex T30 driver tracing


NAD RP18 (kapton) tracing


^ Abyss driver tracing for comparison. Of course tracing is not the whole equation. Not sure what denser tracing does actually. Is pretty.


^ Sansui SS-100

 

Additional Thoughts

So, I gave a few more days of head time to both orthos and collected more thoughts on them.

1. I want to make it clear that RP18 doesn't sound as bad as its measurements seem. I hope everyone does not over-interpret any graphs I posted above. Perceptually it lacks some performance abilities (not easily shown in measurements) I want to hear in certain situations. But they’re quite engaging and enjoyable to say the least. I initially thought T30 destroyed RP18 in every aspect, but after spending more time with both, my thought changed a bit. To me, RP18 out-engages and out-articulates T30 in highs.

2. I may want to suggest reducing the damping material a bit. Of course I am very estat-head these days and honestly think 99.9% of audiophile headphones out there restrict drivers too much.. But even considering my personal bias, neither RP18 nor T30 was successful to prove better transients than my HD6XX (Kiss+Ev mod). This kind of tonality-technicality tradeoff isn’t rare but I believe there could be a more agreeable optimal balance. To be clear I had this issue with ETA headphones I tried out (to less extent than Phil’s mods tho), which indicates I have a very biased preference for open and unrestricted sounding compared to SBAF median.

3. RP18 and T30 weighed 495g and 455g respectively with my scale. Very good numbers for good magnet orthos. Particularly, T30’s weight did not cause much annoyance even after long listening.

 

Try without the damping? Its a dramatic difference in technicalities especially on the untensioned Yamahas.

Remove grill and felt inside. Replace when done. Will the tradeoffs be worthwhile? Perhaps @dBel84 is right about micropore tape being too reflective. Remove the grills / damping! Do iit.

My Yamahas YH-2 stock you may borrow. Also it would be most interesting if @rhythmdevils sent you his modded HP-1a to compare to your stock set.

 

Transients in bass I cant imagine is better on the 6XX. Mids and highs transients definitely better on 6XX. Maybe I need to try Senn with better amp than Vali2.

 

Of course all my comments are speculation as I have zero knowledge about driver-level facts.

But in general, what I think truly nailed in technicality had pretty minimal front/back damping. Such as Focal or Stax. I also prefer HFM and Nectar without grills. I prefer reducing foam disc area and removing front damping on 6XX. My prior experience is saying anything related to air in/out- flux restriction might be double-edged sword or maybe necessary evil.

I meant the latter. I regard 6xx as a restricted-LF transducer and have no expectation in bass beyond a certain threshold.

For your reference, I certainly prefer modern top ortho (both Audeze/HFM) transients to 6xx in any frequency. And those weren't with much back damping. That's why I made such speculation.

 

100% If youve heard a stock vs modded T50RP you would understand the dramatic difference. And you can go too far either way. Fully open T50RP is like a tweeter. Or imagine open baffle speakers if youre familiar, need a huge baffle or lots of speaker driver to compensate for the lack of enclosure. Compromises, and more compromises if you need to meet budget and form/space requirements.

Good. Thanks

 

Clearly!

I am not claiming I found an optimal balance. And I do believe you can improve on both the tonality and technicalities vs what Ive done here.. The goal of the vintage ortho tour was not to test mods but to share and increase knowledge on the old tech. Though I do believe the mods are appreciable improvements over stock and obviously ergonomics.

I compromised on not getting an Audeze LCD2C to be frugal. Modded vintage orthos and T50RP instead. Also read many times how HFM and Audeze are unreliable… But that doesnt seem to be as common an opinion anymore. In fact some of the biggest vintage ortho proponents like @rhythmdevils and @purr1n have totally changed tune on Audeze which I am glad because Ive always wanted one. HFM consistency has always been pretty good but their tech seems to have gotten worse subjectively from original lineup whereas Audeze seems to have been improving (atleast recently).

If you do try removing damping mods from T30 + RP18 do know that the effects arent as dramatic as would be with Yamaha or T50RP. Im guessing because the latter pair use untensioned membranes.

More open headphones are more better but compromises particularly related to budget (I would love some L700). Just going to have to diy some Grado style headphones like @Roderick and @spoony using cheap but good Peerless drivers. I wont pay that much for a new RS2x.