The vintage Ortho thread

Discussion in 'Headphones' started by gurubhai, Jun 24, 2016.

  1. Philimon

    Philimon Friend

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    What it looks like with Loki+:
    YH2 philmod8 : closed mod and Loki+.jpg
    Scatter shot of EQ. Not tested. Just interesting. Number 2 and 5 look nice. Previous tests of boosting bass with EQ were not good.

    Edit: no.2 is good. Max minus 2kHz is correct (probably source of fatigue yesterday, Grado-heat). YH2 modded and EQed rocks. Anyone welcome to borrow if you have a Loki+. But I'd recommend just buying a cheap YH-2 and try modding yourself. Shipping back and forth for loan is nearly the cost of the headphone itself.

    Edit2:
    YH2 vs Emu-w (both modded and eq).jpg
    Love both these headphones. The Emu Ive increased eq slightly since, 'twas a very little dry and bright. (2k to 8o'clock, and 8k to 8o'clock), maybe due to new tube being less warm(?).
     
    Last edited: Dec 31, 2021
  2. Philimon

    Philimon Friend

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    Listened to YH2 for hours yesterday. Awoke with slightest of tinnitus. Building up those callouses. Tinnitus went away after about half an hour.
    YH2 mod8 with Loki edit.jpg
    Reduced highs a bit. Tone control Q is pretty wide so turning 8khz pulls down 2kHz even more which is good. This is what I settled on by ear while listening to music. Was slightly u-shaped, this corrects.

    As seen in @purr1n measurements of @rhythmdevils modded Yamahas, driver ringing occurs in the upper mids right where my frequency response measurements get wiggly (1-4kHz). The @dBel84 modded YH-2 was tuned for a bit of a depression in this area which made his mod sound smooth and much less fatiguing. philmod(8) / closed mod / noob mod / wtf without EQ, has more emphasis on bass which in relation puts the nasty upper mids further away. Damping driver reduces driver ringing further as seen in measurements of rhythmdevils mods by purr1n (including his hifiman mods)
     
  3. Philimon

    Philimon Friend

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    Me responding to another user why I like the cheap Yamahas most.

    @khbaur experimenting with sealing the back of the driver and getting fantastic looking results.

    I did similar mods as @khbaur earlier in this thread which also got fantastic results but the idea was pooped on. If anyone can explain why sealing the driver back would be bad that would be appreciated. My guess why it would be bad because reflections would crush clarity and imaging. The headphone already rings so whats the compromise by getting much more bass from sealing the back of the driver? If just clarity and imaging then Ill choose bass. Driver ringing is the elephant, we need a vintage ortho modder with better measurements. Im going to look into a fpc mig rig this year for distortion and csd measurements. And impulse response or square wave whatever hopefully can correlate transients... Ive not really looked into yet.

    In ortho round up old posts, there was much recommendation for “reflection” mods to improve treble by sticking non-porous materials to the back of the driver. I dont think they realize they were also adding bass and damping the driver at the same time too. Which would explain their appreciation of that mod.

    I had fun and learned lots modding. Way nicer to mod and learn on cheap headphones like vintage ortho. Emu teak and Fostex TRX00 were much more costlier lessons… Now I am adventuring again by modding HD800$ drivers, so dumb. But I do prefer doing cheaper experiments (about to diy some Grado with Peerless drivers). Just done modding vintage ortho (atleast until I get a fpc rig to verify some things).

    The End
     
  4. Jadeeast

    Jadeeast Rando

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    @Philimon I think there was awareness that the "reflex dot" had an impact on bass and driver damping. Walt mentioned it as a caution to using too large a dot impacting a driver's bass in an early post. Just for history's sake. The era was one of exploration and tuning what was found guided by mostly subjective tinkering. New era is certainly measurements and joining the two sides (subjective and objective). Hope you get that rig set up. Thanks.
     
  5. Philimon

    Philimon Friend

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    @Jadeeast from HF? Good to see you.

    And thank you for clarifying. “Reflex” (reflection) is now not cool despite excellent frequency response measurements. @rhythmdevils @GREQ and @dBel84 are not fans. I trust them. What I imagine happens is a loss of clarity (from reflection, example would be a horn speaker vs something with wide dispersion and sounding less clear with less defined imaging due to room reflections) but the bass and tonal response is nice! A fpc rig would help assess the trade offs. I would buy asap but am over budget currently. Our friend @GREQ just put up his Denon SH-90 with original box for sale but I regretfully cant afford. Would be a major luxury since I already have a Fostex T30. The Denon uses the same driver but its a closed back (vented)… very rare. GREQ is putting up because he has an extra copy (Jamo version).
     
    Last edited: Jan 9, 2022
  6. Jadeeast

    Jadeeast Rando

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    @Philimon It is me. I do think that the dot did loose favour overtime from when it was suggested. There was a few versions of that I have the Concept CEH version. Might be more of those in North America. That one have I never got a good fit on my head. I put it away for a rainy day project and have pretty much forgotten it. I did have to replace the voice coil after I blew off a trace in a turntable tonearm using a power amp as a headphone amp type accident that we all end up having... I should find that thing again.
     
  7. Philimon

    Philimon Friend

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    Not quite. The Concept CE-H and Grundig 223 have drivers from the Fostex T20. The Denon and Jamo while looking very similar had drivers from the Fostex T30. The biggest tell is the driver baffle and pads, they align with their Fostex counterparts. T20 and variants have a wider baffle with wider pads.
     
  8. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

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    The reflex dot was never a good idea as far as my damping methodology and understanding goes. You don't ever want to be reflecting anything. If you need more treble you need denser driver damping or a different material. If this kills bass this is when you need to learn orthos and get creative ;)
     
  9. Philimon

    Philimon Friend

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    @rhythmdevils do you still have a source on anisotropic drivers? Ive only seen one other person claim (demonstrated with pics on HF) a supply source.
     
  10. Drakkard

    Drakkard Facebook Friend

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    Reflective dot is not a good idea, but an acoustic impedance panel (half-closed housing) can work well :)
     
  11. Philimon

    Philimon Friend

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    Totally. Aperiodic venting / enclosure is stock design. We mod by damping to taste essentially. The stock foam is generally stale or disentegrated by now. We are basically refurbishing.

    @Ishcabible found drilling holes into the cups worth the hassle because he found it reduces 2kHz bump etc. Would correlate with my experiments on how sealing cup increases 2kHz*. @rhythmdevils can confirm.

    *Not just Yamaha YH series but YHD as well. Is it cup reverb or too much driver damping? Needs more data or someone with better driver / physics understanding to assess. But @Ishcabible says its cups and I cant disagree.
     
    Last edited: Jan 14, 2022
  12. takato14

    takato14 God of Ruin

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    ////////////////
    //--Abstract--//
    ////////////////

    A while ago, @Philimon started a loaner tour of sorts for a set of modified vintage planars, his NAD RP18 and Fostex T30, which have each been transplanted into a repurposed HiFiMAN enclosure.

    Those familiar with these headphones will know right off the top of their heads that we're dealing with what are widely regarded as the best of the best trandsucer designs in vintage ortho land -- arguably able to stand up to modern designs with proper adjustments.

    My ears and rig are always open for a fellow vintage masochist conniseur, so I gladly accepted his invitation to the tour.

    At first, I was only on the tour for measurements and impressions -- like everyone else -- but after a person before me in the queue measured an issue with the RP18's right channel, philimon also asked me to do some repair and retuning work on them.

    Since both designs are quite similar, and I have had experience working on both... challenge accepted.

    I would have preferred to make this all one post. For a while, it seemed like the forum software was going to let me too, somehow having exceeded the 10 file limit on attachments... which I did not know was in place. After being told to refresh the page, I had to start over and re-upload everything... if y'all're wondering why I stopped posting, it's issues like this. But I digress.

    We'll start with the NADs.
     
  13. takato14

    takato14 God of Ruin

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    //////////////////////////
    //--NAD RP18: A Primer--//
    //////////////////////////


    rp18_stock.JPG

    This headphone has been shown off over here numerous times already so I will keep this part short. It is an OEM model of Fostex's original T50 from 1971, and has a couple of different versions. The unit Philimon has been sending around is the EP (early production) variant, also known as the "Bass Heavy" or "Kapton" version. The LP (late production) variant is referred to as the "Bass Light" or "Mylar" version.

    rp18_kapton_diaphragm.jpg

    Kapton, aka polyimide, refers to the diaphragm material. It's characterized by this admittedly piss-like translucent yellow, and is commonly used in the electronics industry to make flex cables and flex circuits, which are often used in place of traditional ribbon cabling or PCB.

    THD_COMPARE.GIF

    Kapton is slightly heavier and less flexible than Mylar -- polyethylene tetraphthalate -- and this manifests in the distortion characteristics of the driver. Kapton variants of this headphone only have a max input of around 250mW, despite being around 50 ohms nominal, and this is entirely due to how the kapton film behaves as it flexes. Mylar drivers with the same design (Sansui SS-100, Aiwa HP-500, and some RP18s) remain stable up to about 600mW continuous.

    Subjectively, this doesn't matter too much at normal listening levels, and manifests as a slight "edge" or "etch" to transients that frankly often sounds better as opposed to worse. On top of that, the bass distortion usually remains low despite the rise in distortion elsewhere, so they have adequate headroom for louder listening so long as you don't go much higher than 90dB -- the level the above THD measurements were taken at.

    RP18KA.png

    In stock form, the headphone has a midrange-centric tuning with good extension to both ends, and decent air -- but the earpad design holds them back. After aging, the pads are a mere 6mm thick in good shape, and the size of the pad opening leaves much of the driver covered. This is, of course, a deliberate choice -- more on that later.

    ... But that, is for the stock headphone, and Philimon's pair is a far cry from stock.
     
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  14. takato14

    takato14 God of Ruin

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    ////////////////////////////////////////////
    //--NAD RP18: Impressions & Measurements--//
    ////////////////////////////////////////////

    rp18_1.JPG

    So, how did he do?

    RP18_2.JPG

    Subjectively, these are pretty nice. I recognize these pads -- the same ones used on the BLON BL-30 70mm dynamics. These pads breathe a lot, which made me nervous at first, but once I put the cans on my head everything was pleasant, clear, and airy -- as it should be. T50 variants are characterized by their absolutely wonderful top end air, precise and tactile stereo image, and fantastic mid tone and clarity.

    The bass was definitely present, but it sounded a little weak to me, which struck me as odd. Usually the very first thing you notice with a T50 is the bass quality and impact, and it was the primary thing I missed while listening to it. Once I threw them on the rig... oh dear.

    RP18KMB.png

    The FR looks very nice, and is quite close to my rig's target response. The mid treble dip reminds of the Yamaha orthodynamics, which is a very popular tuning for orthoheads, and I was impressed with how linear and deliberate the trend was above 1kHz -- almost as if the FR had been sculpted by hand. However, my fears have been realized... these Kapton drivers are very unhappy with their new, much larger ear cavity, and are distorting quite violently. That rise in 2nd order hits almost 8% in the bass -- absolutely dreadful. Never seen a T50 do that before... no wonder the bass didn't sound right.

    RP18_3.JPG

    Spectrogram and impulse results suggest some kind of erroneous diaphragm behaviour, bouncing around as if it was resonant and underdamped -- but I can't even see into the cups, which suggests the opposite. Hmm.
     
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    Last edited: Jul 10, 2022
  15. takato14

    takato14 God of Ruin

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    //////////////////////////
    //--NAD RP18: Teardown--//
    //////////////////////////

    front.jpg

    Off come the pads... aww, come on. Why does everyone take the brown felt lens off the driver? It does nothing but correct the wavefront, which helps immensely with the acoustic phase response... oh whatever, I'll just make a new one later.

    At first I wasn't entirely sure what was going on here, thinking the black edge inside the galvanized bit was some vinyl tape to help with the driver-to-baffle seal, but once i pulled the screws I realized what I was looking at.

    rings.JPG

    Not sure why both of these rings were placed on the front... maybe to keep the screws from bottoming out or stripping out the plastic? Lots of tape residue...

    screws.JPG

    ... and there's this weird black stuff on a handful of the screws. Did he have to repair the screw standoffs or something?

    oh fuck.JPG

    ...oh.

    why.JPG

    Oh God. Why did it have to be Dynamat.

    Welp, these won't be going back together the way they came in, that's for sure. Couldn't even if I wanted to. Time to have absolutely no fun taking this driver out...

    pain.JPG

    ...yeah, called it. This stuff is horrible to work with. Once its applied, the only way you're getting it off is via destructive force.

    dynamat.JPG

    For those who don't know, Dynamat/Damplifier Pro/etc are a speaker cabinet damping material intended for baffle plate mass-loading on subwoofers. It consists of a very tacky plastic putty (right), layered on a thick aluminum foil substrate (left). The way it works is simple: the putty absorbs vibrations from the baffle plate of the speaker in a wide frequency band, and transfers it to the aluminum foil. The foil resonates at a higher frequency than the baffle, which effectively allows low frequency resonance to be turned into higher frequency resonance, offering an efficient and cheap solution for cleaning up the bass response.

    ... However, this is a full-range driver, not a subwoofer. Using this stuff on anything but a woofer or subwoofer... yeah, don't. Best case scenario, this stuff will do nothing, which is what it was doing for this RP18. Worst case? Say hello to the biggest, sharpest, filthiest 3kHz peak you've ever heard. If you absolutely need mass-loading, just use poster tack, it is more than adequate.

    gunk.JPG

    He wrapped the edge and I guess segments of the rear face of the driver with this stuff to help mount it in the chassis... hard to really tell after pulling it. Crude, but quite secure, as this stuff bonds on the molecular level. With other materials, I would just say "whatever" and leave it be, but one: I have to open the driver for repairs, and two: this stuff is dangerous. That polymer-putty gunk has this nasty habit of creeping into crevices over time and getting into places it shouldn't be. I've had it destroy headphone drivers on more than one occasion, and I'll be damned if I'm gonna let it claim an 80mm Foster as its next victim.

    rear.JPG

    The rest of the rear chamber is much simpler (and cleaner), with a chunk of open cell urethane (?) foam over the driver vents, and a layer of craft felt followed by a layer of micropore tape over the rear mesh.

    diagram.PNG

    Assuming there was a decent seal between the rear chamber and the driver -- which there likely was -- what he ended up creating here was essentially a reverberation chamber like the one on the Sony MDR-Z1R; not quite closed, but impermeable enough to trap a vast majority of the backwave. What this does is send a reflected, time-delayed and phase-inverted copy of the driver's backwave at the diaphragm, causing what's called destructive interference.

    In the case of the Sony, the shape of the earcup was carefully designed and optimized to take advantage of the benefits a design like this can have, acting as the "room" for the headphone driver if we're comparing the scenario to speakers. In this case though... it probably wasn't intentional, aside from him noticing that it imaged better when listening to it. The reflected wave doesn't do much damage to higher frequencies, likely because it doesn't survive the journey through the foam, but low frequencies travel through surfaces much more readily due to their wider wavelength. Both the reflected wave and the driver's frontwave are fighting each other inside of the ear cavity. Which order of distortion this causes is usually up for grabs, but in this case, it's 2nd order. Most of the times I've witnessed this problem, it was 3rd -- like on MDR-Z1R, CAL, or the Cleer NEXT, but I have also seen 2nd order happen before, with a pair of modified Monoprice Retros.

    While I'm not a big fan of some of the materials he used, he definitely demonstrates the potential of these headphones with his mods, and the tuning he chose is rather nice -- even if the bass is a bit too weak for my basshead tendencies.
     
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    Last edited: Jul 11, 2022
  16. takato14

    takato14 God of Ruin

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    ////////////////////////
    //--NAD RP18: Retune--//
    ////////////////////////


    I had already formed a decent gameplan for how to approach the retune while disassembling them, so I got right to work on assembling what I assumed would be the final version of the damping right away. The right channel is the one that needs repair work, so I started with the left. Obviously, this was an intentional decision because I was worried of how the damaged driver might come apart when disassembled, and not because I forgot which channel was broken. (Shut up.)

    Before worrying about the actual transducer damping, the micropore tape and craft felt had to go. While I do appreciate what phase delay can do for soundstage perception, trading the headphone's bass response for it was out of the question. Craft felt is different from acoustics-grade felt as well, and I've never seen it used to good effect in modding headphones. Far too reflective. Anything you're going to use felt for, use Thermolam instead.**

    **Can also sometimes make do with generic fleece from Amazon if you're feeling cheap. Acoustics-grade felt is best, but I've only ever found that inside of vintage Sonys, Fostexen and Beyerdynamics, never a new-production source.

    After pulling that off, I thought for a few minutes on how to darken the rear mesh of the headphone. What'll be going in there won't look as good as the white does... and I'm not too keen on the white as it is. The stock silk would probably be fine, but it was not included... then I remembered something.

    fabric.JPG

    I have some nice, thin and breathable spandex fabric leftover from an old project.

    swatch.JPG

    I strung a swatch of it over the rear mesh with just a tiiiiny bit of tension, and pressed it into the earcup.

    insert.JPG

    After installing the retainer ring, all I had to do was trim the excess off for a perfect, wrinkle-free insert for the rear mesh. You can still kiiiinda see the edge of the fabric between the ring and the cups, but don't tell anyone. I'dve used an X-Acto, but the fabric is so stretchy that it just pulls... tough shit I guess.

    seethru.JPG

    This will be acoustically transparent enough to let the backwave out unrestricted. Well, mostly.

    As for the sound-based adjustments... I am glad you asked.

    My modding expertise is vast, detailed and refined down to an absolute science. Gone are the days where I spend hours testing and retesting things over and over. I am now a machine. A true engineer. A genius. I already know exactly what this headphone needs, and here it is.

    prelim.JPG

    In order from back to front, we have:
    • 0.2g Twaron Angel Hair acoustic batting
    • FK CF-1 scrap cotton sound deadening insulation -- halved thickness
    • 3M Micropore medical tape -- tan
    • GV Polyester wetmop pad -- absorptive layer
    • a new frontwave lens, made from Thermolam fleece insulation
    • self-adhesive closed-cell foam, to seal the pad mount ring/baffle to the driver
    This, will be perfect.

    RP18COMP.png

    ...is what I think to myself, every time, and every time, I am wrong. Some things never change... While my THD results are quite an improvement, and the treble is technically smoother... yeah, this ain't it cheif.

    final.JPG

    The final configuration ended up being quite a lot more aggressive, due to these drivers simply being that potent. High-Q planars are rare, but they do exist, and this is one of them. You would expect them to be low excursion due to the thin stock pads and small opening, but the D/M gap is almost 4mm -- over twice that of an LCD-2. The real reason the pad opening is so small is almost exclusively for the purpose of mitigating their power handling issues and squeezing better mid-band sensitivity out of them.

    From back to front:
    • GV Polyester mop pad -- absorptive layer
    • FK CF-1 scrap cotton sound deadening insulation -- one half
    • 0.2g Twaron Angel Hair acoustic batting
    • FK CF-1 scrap cotton sound deadening insulation -- other half
    • Mystery Foam™ courtesy of Philimon
    • Closed-cell foam front seal
    Since I'm not 100% sure what type of foam this is, I strung some fully acoustically transparent liner cloth around it, just in case it rots sometime in the future. This will prevent it from falling into the driver vents and causing any serious issues even if it dries up into nothing but black powder.

    After that it was just a matter of selecting the right earpad and taping it down.

    former.JPG

    Brainwavz Oval Velour behaved the best with these, despite their tendency to dip 1~6kHz out a little too harshly. I used the galvanized steel bits to act as a former and make the pads circular for a clean fit on the 100mm HiFiMAN baffles.

    stencil.JPG

    I also cut up a new front lens for both drivers, using Thermolam as aforementioned. I spent a considerable amount of time trying to find something that wasn't stupid to use as a stencil, but unfortunately, the only thing I had even remotely close to the correct size was a cap from one of my old medicine bottles.

    done.JPG

    It worked, so whatever. I'll be using 3M 468MP transfer tape to adhere the pads -- which I just barely had enough of on hand for this headphone. Time to order some more...

    [​IMG]

    After all that, this is what my finalized frequency response looks like. Largely the same, with a bit of a fix in the mids, and a bit less mid treble dip... but the real improvement is in the THD and spectrogram results, where we can see a marked decrease in persistence and non-minimum phase behaviour.

    [​IMG]

    [​IMG]

    [​IMG]
     
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    Last edited: Jul 10, 2022
  17. takato14

    takato14 God of Ruin

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    [reserved #6/6 -- repair]
     
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  18. takato14

    takato14 God of Ruin

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    [reserved #7/6 -- closing statements]
     
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  19. dBel84

    dBel84 Friend

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    Awesome work Tak, I was just thinking of revisiting mine the other day as the bass was sounding a little thin in the legs and I had cut out an acoustic lens but not yet fitted it. Time to peel off the pads and make this happen :D
     
  20. Biodegraded

    Biodegraded Friend

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    Yamaha YH-2 modding: a noob’s progress (part 1 of 3)

    Background
    A while back @Philimon went through a phase of acquiring every vintage iso/ortho he could get his hands on, measuring & modding them, and distributing the ones he didn’t fancy around the community for cheap or free (see his posts throughout this thread and @takato14 ‘s posts immediately above). Knowing nothing about these but being both curious and cheap, I was lucky enough to benefit from this generosity to the tune of 2 pairs of YH-2s, the first modded by renowned orthoknowledgegist @dBel84 and the second by Phil himself.

    Between life interruptions since they came in, I’ve been listening, modding, reading a bit of history (but not too much – I mean that HF thread is almost 1800 pages) and pestering Don & Phil for guidance, and it’s now time to summarize the results and what I think I’ve learned from the process. Because I haven’t done exhaustive research, ortho old-timers might find a lot of this mystifying, either because none of it’s new to them or because some of my conclusions are crazy. Despite the help from the gents there probably remain many errors in fact or interpretation, all of which are mine. Please school me when you find them.

    While this looks like a lot of measurements and might lead to charges of ears-closed measurebation, a lot of listening was done at all stages. Not to every variant, sure, but particularly toward the end of the process, the more successful versions were given quite a bit of ear time – to the extent that I almost stopped at a point that, to me, would with other ‘phones seem to be very bass-light.

    Also, although this might read like there was a staged strategy in how it was done – a proper plan for formulating and testing hypotheses (science, in other words) – the reality was closer to random trial & error (the ability to quickly test the frequency responses of different configurations is both a blessing and a curse of having a measurement rig). The attempt to organize the results in some sort of logical progression that’ll hopefully be useful to others came only after a lot of sober (mostly) reflection.

    Yamaha HP/YH-2
    I won’t say too much about HP/YH history and design because it’s already well summarized in a few places. Good starts are wualta’s posts on the first couple of pages of the Head-Fi Orthodynamic Roundup thread and Yamaha’s own marketing material, like this YH-series brochure. Because they influence modding strategies though, there are some things about the driver sandwich construction and the stock rear damping that bear repeating here.

    Regarding driver sandwich construction, here’s @dBel84 from a PM:
    This is from a discussion of bass distortion, but I include it here mainly because it supports Don’s philosophy of ‘differential damping’: figuring out which parts of the driver to work on to change the frequency response in the desired ways.

    Regarding rear damping, the wisdom has always been that the stock materials are inadequate to control driver diaphragm resonances and more/denser damping is needed directly over the holes in the rear magnet plate and inside the cup. Here are a couple of photos of the stock materials, the first by ericj from early in the HF thread, the second by Philimon from later in the same:

    [​IMG]

    [​IMG]

    The strips of black felt cover the vents around the cup edge, making for a semi-open design, and the back of the driver sandwich (which has holes mirroring the ones in the front) is covered by a single layer of foam. In both photos the foam is showing its age: in the first, a section of it has disintegrated and fallen out into one of the slots in the central metal cup insert, and in the second, part of it has stuck to the back of the driver and is about to rip apart. Whether this foam ever provided adequate rear damping seems unlikely, but it obviously hasn’t aged well since the late 70s or early 80s when these ‘phones were manufactured so it’ll be less effective today.

    The usual first step in modding these ‘phones is to remove at least the foam and put something heavier, eg dense felt, right over the back of the driver (and then think about different densities in different places). Comparing stock vs no-damping vs modded measurements, it seems that the degree of blocking of the cup-edge slits and of the slots in the central metal insert, which vent into a rear chamber which is open to the outside around the pivot mount at the back of each cup, are also critical considerations.

    Stock vs dBel84 & philmod8 mods
    Below in green, red & blue, respectively, are @Philimon ‘s EARS measurements of the left channel of the @dBel84 -modded pair (henceforth pair1), the stock config of the pair Phil modded (pair2), and his philmod8 (final) config of the that pair, roughly aligned with each other through the lower mids. It’s evident that philmod8 has extended the bass and brought up the treble, but has also introduced a big 2k peak; whereas the dBel84 mod, assuming a stock FR similar to pair2, has linearized the bass and brought up the high treble, but has also generated a big peak at 7k. The few dB below red around 2k might be significant, too, if stock pair1 and pair2 were close there.

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    Pair1 was discussed in this post and the few below it; pair2 measurements, descriptions & philmodding start from this post. Note pair2 is not the same as in the photo I used above – in contrast to that pair and to pair1, pair2 has the conical magnet holes (pair2 driver unit photo in post #488).

    How do these sound? To me, the dBel84 pair is lean in the bass & lower mids but has great resolve, speed and clarity. After a while that lower treble peak gets tiring and with some material it’s immediately a killer. The overall balance, though, plays to the Yams’ strengths. philmod8 has IMO a better tonal balance but is less lively and yet more fatiguing with time, likely because of that 2k peak (which gives notable shoutiness to some vocal ranges). I didn’t get to hear a stock pair. @Philimon ‘s brief impressions of stock (actually of an HP-2) are here; his pr1 dBel84 impressions here and here; and his final impressions of his own philmod8 mod are here.

    Don’s pair1 mod materials are shown in the photo below. In this mod all original materials are removed, a ring of ‘Arctic fleece’ (a synthetic silk ~2 mm thick) with an inside diameter that fits around the black plastic central cup ring (34 mm diameter) and an outer diameter big enough to cover the cup-edge slits is laid inside each cup, a patch of dense black foam of diameter about equal to the central cup ring is placed in the middle, and a patch of densely-woven thin microfiber is taped over the back of each driver. Not shown in the photo are ~14mm diameter pieces of black foam that are taped to the bowls in the centre of each metal insert; I was worried about ripping them apart so I didn’t remove them for the picture. Also, Don sticks the drivers to the front baffles with speaker caulk.

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    Pair2 philmod8 is as philmod3, the top photo below, but with the micropore tape over the centre insert replaced by a taped-on circle of thin but dense red craft felt (bottom of the second photo) and overlain by 1/32” red and blue felts of different densities covering the entire driver as in the bottom photo. Phil refers to this as the ‘closed mod’, the butyl and damplifier completely sealing the cup edge vents (there’s some on the backs of the baffles, too) and the layers of felt both damping the driver and covering the vents in the central insert.

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    It’s evident that the damping philosophies are rather different: the dBel84 mod baffles but doesn’t seal the cup edge vents, and damps the inner and middle sectors of the driver more than the outermost sector; philmod8 completely seals the cup edge vents, damps the entire driver with 2 dense layers, and puts an extra layer over the slots in the central cup insert. The differences that various components make are revealed by disassembling each mod and measuring again.

    All following measurements will be with my flat-plate setup, with no compensation, and therefore not directly comparable with Philimon’s SBAF-compensated EARS measurements. A major shortcoming of my system is that the bass rolls off too early: depending on the headphone, bass starts to drop from around 120-100 Hz. With some ‘phones that’s ok – eg HD6xx, because those really do roll off from around 100 Hz – but with others it’s quite deceptive. Despite on-ear phones being tricky to seal on EARS because of the, er, ears, Phil’s measurements don’t start rolling off until 50-60 Hz below mine. Bear my rig’s bass weakness in mind when looking at my measurements – which start in the next post.
     
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