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Studio Grade Headphones on the cheap - A DIY 3D Printable Project.

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JamesLynton:
This post is a copy of one I made elsewhere on the Alibre CAD forum following some trouble shooting, then I found out they have some competition on there right now, so decided to go all out in documenting the project, rather than just lazily post a few files. This post contains a complete break down of my research and (half cocked) analysis, hopefully this is useful to other people here too.
https://www.alibreforum.com/forum/index.php?threads/studio-grade-headphones-on-the-cheap-a-diy-3d-printable-project.22335/

This post mentions prices in £ and $ - these refer to UK Pounds and US Dollars.
(I will refrain from linking to particular parts listings, as if folks happen to all rush to the same place it might cause them to jack the price up, or run out of stock.)


In Short:
Spend as small an amount of money (and time) as possible and get awesome, robust, repairable studio performance headphones that should have cost you in the region of £300-600/$400-800 off the shelf, for a mere £75/$100 or so.
(and as small as £20-25/$28-35, if you compromise on drivers, and therefore accept certain limitations)




Ooooh, shiney. (also available in discrete plain black, white, pink (?) & so on)









Being +/- 5 dB of baseline is pretty typical of good headphone drivers.



Distortion measured at respective levels in dB SPL as shown on the right.
(Note: limitations of the test microphone also seem to also inflate measured distortion at lower levels)

** Files attached to this post for opening and editing in Alibre, and also the STL files for both default model versions for sending directly to printer without any further editing. **

Assembly Notes:
Just go with modifying your preferred cosmetic choice of PowerA Fusion headphones with aliexpress (etc) imported 'fostex' 50mm (32 ohm version) microfibre drivers installed in the provided 3D printed insert and cotton + pillow stuffing in the rear chamber, if you *just* want some best bang for the buck headphones that will blow your metaphorical socks off, and aren't too bothered about, or interested in digesting several pages of design intent and analysis.

Also I strongly advise removing the internal headphone volume control in the left hand ear cup, bypassing it electrically (its kind of silly, and gets in the way); followed by trimming the plastic supports which held it in place with wire cutters, or your weapon of choice. Then, fill the hole the shaft engaged with with glue to stop the earcup shim from rotating.

For Best Results:
Use a sound source, or dedicated headphone amp which is known to deliver decent power/current to them. The in-built headphone amps in some professional sound cards are pretty decent, and some mixers too.
I tend to use a portable xDuoo - XD05 headphone amp/dac - this is an affordable state of the art XMOS/AKM powered soundcard capable of playing back DSD material (if you have it), and can support 384 kHz at 32 bits (in theory, and quite needlessly excessive (you are a bat, right?)), and most importantly has massive output power (more than you'll need, but the transient dynamics will thank you). Also it can connect to PC/Phone via USB, Optical, or a lossless Bluetooth adaptor. Also, it is a mere £200/$289 for this top shelf product; lesser models, even from xDuoo, are available for around £50-120/$35-155 with various levels of compromise.
You will however, with headphones like these, realise just how irredeemably awful some sound sources/amps are. However, you can expect them to produce (more or less) the best sound any given device is capable of producing.
For sub bass (in particular) that will absolutely rattle your head off, natural dynamics, and clarity up top; be sure to invest in a proper headphone amp, or a decent source.

I like having the option of ramping / experiencing already prominent extremely low bass sometimes, and having the kick drums and bass drones rattle my head; it has a curious way of engaging you with the material, without annoying the neighbours (we're still talking headphones, right ?), distorting the overall tonal balance, or presenting any real risk to your hearing - unlike just turning up everything really, really loud.

Why would you want/need a pair?:
Well designed headphones are the cheapest and most effective route to truly high quality, private listening experiences which negate the need for spending thousands on a studio monitoring grade speaker setup, acoustic room treatment, and sitting in that one optimal sweet spot the entire time to get a similar result. (somewhat) recent advances in driver technology mean that this is both affordable too, exists in the realm of reality (not marketing-land); oh, and fits in your bag, and can go everywhere with you.

Also, the market is absolutely flooded with garbage headphones (even in the professional realm) which fail to reproduce material faithfully, or satisfyingly. The solution from there on out is to either know the good from the bad (whilst not getting sold snake oil by deluded salesmen) and purchase one of the few commercially available, faithful models at considerable expense... Or, build your own using known good parts for close to the materials cost the manufacturer of such pays.

A great test of system dynamics is Eivør Pálsdóttir's album Slør - It is a curious mix of varied bjork'esue (but much better) Keltic/tribal sounding music which mixes acoustic instruments, female vocals, massive drums and pins the lot together on a bed of minimal electronic synthery, and general weirdness.
(She is good, and varied - give her your money)
Find a copy in *uncompressed* format Flac/CD, whatever ...and then compare it to what the version on youtube sounds like, the difference in detail and dynamics is absolutely shocking.
(I prefer the version *not* in English)
Whatever your music tastes, you might find something to like about it, its an interesting album.

Use Responsibly:
With all of the headphone drivers mentioned later, you will find optimal listening levels between 10 o'clock and 12 o'clock on the xDuoo XD-05's volume dial on the first gain switch setting (yes, this headphone amp has a silly name). This translates to a rough median output range (source material dependent) of 60-80 dB SPL at the ear. Which in the background 'silence' of headphones, is perceived as louder than you might think. Generally, its quite safe, particularly if you stick to around that average of 60-80 dB SPL

Official guidance on safe SPLs whilst limiting the possibility of long term hearing damage is as follows.

Permissible exposure times:
82 dB - 16 hours
85 dB - 8 hours
88 dB - 4 hours
91 dB - 1 hours
94 dB - 30 mins
97 dB - 15 mins
100 dB - 7 1/2 mins
106 dB - 3 3/4 mins
(yay, fractions - remember those ?)

For content that isn't heavily compressed, this is my general observation for listening level comfort:
50-55 dB SPL - somewhat quiet.
60-65 dB SPL - normal quiet.
70-75 dB SPL - normal clear.
80-85 dB SPL - getting loud.

By that measure, i assume my personal headphone, and other sound exposure tendencies to be generally quite responsible. Which explains (in part) why despite not having been a teenager for some time now, I can hear roughly 16 khz or so with no apparent attenuation just fine.

All of these headphones have been measured as generally capable of 100-106 dB SPL (although some might burn out quickly), and remarkably some of them handle that with no appreciable increase to distortion (the fostex like 50mm driver for one). In as much, consider using (overall) volume controls responsibly.

Also, consider measuring typical listening levels once in a while with a reputable spl meter (not your iPhone - sorry), if you want be 'sure' accuracy, play a 1 kHz tone with the headphones on something other than your head, and observe the measurement for the meter jammed in the cup. regardless of exposure weighting settings of the meter, this is at a frequency all good meters give zero calibrated attenuation to.
All in, if it sounds uncomfortably loud, or you observe a reduction in hearing threshold after use, consider your life choices.


Curiosity Note 1: The entire dynamic range of a CD / typical (universal baseline) 16 bit audio file is a 'mere' 96 dB - go figure on how that factors into all such relating considerations ;)
As for film soundtracks, its higher at 24 bits, at a theoretical 144 dB - for heavily impactful transient reproductions of key scenes at high levels when played at 'full' volume. Given that most 24 bit or more DACs can actually often struggle to keep the noise floor in control below 20 bits - a clean 120 dB; theres plenty of interesting audio engineering discussion rabbit holes to disappear down.

Curiosity Note 1B: The total useful dynamic range of human hearing is around 120dB, the threshold of pain is around the same. As for perception of quieter sounds against louder ones at different frequencies, it is much narrower (and at last count currently actively debated). In as much, the critical perceptibility of distortion is lower than you might expect, depending on the source material, and where in the frequency range it occurs.

Curiosity Note 2: Due to reduced direct sensitivity of the ear to (low) bass (you feel the majority of it at high spls), you can safely tolerate it at much higher levels without need to reduce exposure. Quite why clubs and bars 'insist' on loud consisting of the distorted mid-high mess comparable to the mating calls of serenading angle grinders is quite beyond me (its not fun, or healthy frankly - and as for the poor (bar) staff, well).

Note 3: For more information of this sort (if you love details, and whatnot) and my working method, see the final sections of this post.

** PART 2 of 7 Follows.. **

JamesLynton:
** PART 2 **

The Details - (the meaty stuff):

Project Background and Design Considerations:
This project started late last year when I became aware of high quality headphone drivers finding their way onto aliexpress (kind of a Chinese amazon for industrial parts) for sensible, and sometimes amazing prices. In relation to this, I was also looking for an affordable, tasteful looking, comfortable and high performance way to house these drivers.
Having owned and used various high end studio headphones over the years and found most lacking in certain areas - comfort, durability, sometimes aspects of sound reproduction and all too often charging far too much; the motivation was taken to make something that could enable housing of such drivers cheap, easy, and facilitate future repair - such that in cases of damage or loss its never a huge amount of money or time down the drain. These headphones would be designed with firm knowledge of acoustics and measurements of results applied, alongside listening to the results, of course.
The results I got in the end I greatly prefer to my previously owned Denon AH-D2000's (made under an oem contract by Fostex), so much so; that I sold them.

Initially it was assessed whether to do a fully 3d printed version. This was ruled out due to a need to process and form some metal parts (for headbands, etc), and some fairly tricky leather/textile work. Given that (otherwise) good quality headphone shells with rubbish drivers in are fairly easy to come by for less than the cost of the diy materials needed (and all the time involved); a commonly available, exceptionally nice model was selected to base this on.

The model selected as the base is the fairly sensible, minimalist looking PowerA Fusion headphone set. These can be found everywhere for around £8-25/$10-35 new and used; and are available in numerous colours to suit your tastes. The basic look of this model is comparable to dj & studio headphones, however they are aimed at the gamer market and have a detachable mic (which you might also find useful). The frame and finish is robust and comfortable to wear, and they feature a fully modular 3.5mm headphone cable; meaning you will never have to worry about accidentally catching or breaking the cable.
It is also possible to buy very nice bare wooden shell headphone shells on aliexpress for around £50/$60, though I don't like the aesthetic and functional design intent of any of them so far; and of course, you'll 'need' to protect them from cosmetic damage - that adds extra cost to the project at no strict, true benefit to sound quality (the core aim).

From there a 3D printable insert designed for it which allows the universal use of almost all headphone drivers (40-50mm - or anything with modification + with, and without preinstalled metal grilles).
This piece also includes acoustic design improvements which share similarities to those seen in the likes of the excellent Fostex and high end Denon headphones. The main improvement over most headphones here (aside of decent drivers) is the inclusion of baffled vents that couple the rear headphone chamber to the ear pads, the benefits of doing so are many:
When properly (low pass) filtered with baffling materials and pads, this results in sub bass the drivers would not otherwise produce being coupled to your head via the ear pads over a larger area than the drivers themselves. It also serves to help reduce noise pollution coming from the headphones with any sound from the driver at normal levels trying to escape the ear pads being cancelled out by the (upper) frequencies coming from the rear chamber there being out of phase (in reverse polarity) with those from the front. Also, with this you get all the benefits of both open backed headphones and closed ones - and none of the disadvantages (its a super munchkin card, okay?). Unlike open backed ones, you get incredible, realistic bass response and great noise isolation from the environment; and unlike typical closed backed ones, you get an open, natural sound due to effective elimination of unwanted chamber resonances and reduced back wave pressure stress on the driver.
Another notable improvement (not seen in Fostex, or any professional headphones i've seen so far) is to tilt the drivers axis slightly off the baffle plane, this takes the driver out of parallel plane relationship to rear chamber surfaces, greatly reducing the chances/effects of strong standing wave resonances those geometries would normally define. Also this serves to better aim sound into the ear and likewise reduces parallel surface issues on the head side as well.
Finally, the other mandatory modification is in adding a modest amount of damping to the rear chamber, this includes one cotton pad on the rear chamber surface, polyfibre stuffing as used in pillows (its basically the same as acoustic fibre which is sold at inflated prices) placed lightly stuffed in the chamber, and another cotton pad cut to shape to fit the rear rim of the rear chamber vents (serves as a slight flow restrictor and low pass filter).
In fact, if any headphones (especially big ones) are lacking a fibre filling, you should add it by default; it reduces/eliminates chamber resonances and slightly increases apparent chamber volume to the driver, therefore slightly deepening bass response for 'free'. See below for how it improves even the stock, unmodified Fusion headphones. It flattens and deepens the bass hump, eliminates the 300-500hz chamber resonance dip, reduces overall HF losses and virtually eliminates some dips in response in the 10-20k presence region. Also, harmonic distortion (THD) is *greatly* reduced throughout the frequency and output range.

Performance scope of the original fusion headphones before replacing drivers:











Whoops forgot to change that dB SPL scale:
(-90)20 dB/30/40/50/60/70/80/90/100/110(0)

If you are feeling super, super cheap - you could just stuff the stock headphones and call it a day, whilst accepting that they have a frequency peak at 8k, a slightly softened presence region (10-20k) and are limited to 70-80db for clean sound reproduction - this limitation also tends to noticeably 'flatten' the sound of music/material with good dynamics (not compressed to death like almost all mainstream pop music from the late 90s onwards). For once, the stock drivers in some cheap headphones weren't actually entirely terrible, but still have the limitations that costing a probable mere $1 to 50 cents brings.
(still, you can gut those drivers with wire cutters, and make amazingly effective fridge magnets with them)

** PART 3 - Coming Next... **

JamesLynton:
** PART 3 **

Choosing and Testing Driver Candidates:
After considerable searching, 3 models of drivers were selected and tested as worthy of consideration.

The first two of these are often listed on aliexpress (and elsewhere) as being Fostex/Foster drivers, or alluding to as such. Whether these are the genuine article or not, is unknown, and I will not assume as such, but the performance is no less impressive (no obvious branding is present on these import drivers - oem?).

Notes: it would be nice to have an official source for the certified original article at a fair price, though I have yet to see one.

The reason for selecting these is the use of a microfibre driver cone, like real speaker cones; is that it imparts time tested, excellent damping properties. It reduces/eliminates driver resonances and harsh bell modes often present in bad/average drivers - this lends itself to an extremely natural sound and incidentally massive power handling capabilities with negligible distortion increase relative to output levels; great for dynamic music/material and for fatigue free listening at 'all' volume levels. Incidentally, they also do bass/sub bass far better than any pure plastic/metal driver i've ever heard, or expect to.

Fostex like 40mm Drivers - 16 ohm Version - MODIFIED Vents:




The first of these, the 'fostex' like 40mm, is the cheapest available at a remarkable £14/$20 or so per a pair delivered. output level is impressive for such a small driver. The sound is natural, clean and handles dynamic material in a revealing manner, which will impress if you are not used to it from other sound sources. The drawbacks are (still excellent) more limited power handling capability compared to the 50mm version.
As this models default configuration is bass light, I open up two of the rear vent holes on the rear flow restrictor (carefully!) with a screwdriver by default. This functions to loosen the manufacturer imposed damping on the driver which normally constrains the bass output of this driver at the cost of overall power handling. I do this such that the overall tone balance of the driver is more natural, and reaches far deeper. The cost of modifying the drivers out of design spec in this case, is an increase in measured harmonic distortion from the bass region; which is remarkably only particularly evident, and measured, when pushing these headphones hard.
If the use case isn't for listening to mega thumpy wumpy bass at rather high levels, and is more talky/general use content focused, then these will probably be just fine for you.









Whoops forgot to change that dB SPL scale:
(-90)20 dB/30/40/50/60/70/80/90/100/110(0)

Fostex like 50mm Drivers - 32 ohm Version:



The second of these is the driver I currently, and somewhat confidently consider the absolute daddy.. The 'fostex' like 50mm comes in at roughly £50/$70 a pair; and includes a preinstalled metal grill. Similar story to the 40mm versions, except absolutely massive power handling, and it is capable of the deepest sub bass i've heard out of headphones yet. Ripe for eqing slightly for preferred sound profile in certain instances.
Distortion barely perceptibly (and measured) increases no matter how much you spank these within levels/durations which will leave you with ears good for listening with.

Note 1: This appears to be the same (unbranded) driver as I had in my Denon Fostex made OEM headphones, and which also features in their line-up - or is at any rate, something that behaves very similarly from personal experience.

Note 2: There is also a 'gold' plated metal version of this driver; I have not tested it, and the seller provided frequency plots aren't too encouraging (soft up top) ..Avoid it (or send me some to test), and go for the black glass reinforced, injection moulded plastic versions instead.




P7 like 40mm Drivers - 24 ohms:




The third is a curious beast, it is allegedly the driver used in the B&W P7 headphones, it comes in at around £34/$45 a pair delivered, it also looks kinda cute; and it is yet another microfiber driver which remarkably manages almost the same sub bass output as the 50mm 'fostex', but seems to run out of steam when pushed really, really hard.
It has a similar tonal profile and lack of distortion throughout most of its range, but is let down by what looks like one final step of driver design polish production didn't go thru. It has a roughly -12db dip at around 3 kHz, and a harmonic distortion level of around 0.6% there; Which then spikes up from the average level, by another +12db or so at around 8 kHz - the prominent 2nd and 3rd harmonic distortion components of 3 kHz are 6 and 9 kHz respectively. when material gives cause to excite these harmonics and peaks the result can sound rather shouty in this particularly sensitive part of the hearing range; I first suspected this when I found listening to a female news broadcaster on them at normal levels somewhat uncomfortable. This is likely the product of unusually strong cone breakup/bell modes resulting from the choice of construction which could of been changed just slightly in the design phase to eliminate/tame it. Unfortunate, as otherwise they are quite excellent drivers. Possible mitigations for these are narrowly notching out the 3 kHz'ish excitation frequency, and moderate eqing; but when the budget fostex like 40mm is dirt cheap, and the 50mm is a mere £15 a pair more - why bother ?




** PART 4 - Coming Next... **

JamesLynton:
** PART 4 **

Mystery Coated Cone 40mm Drivers - (not very good):



Tried these weird looking things for a laugh, on closer inspection on receiving them it looked like someone had taken a 40mm fostex like driver (cost about the same) and sprayed the cone with stone finish plasticote paint. The result sounds absolutely awful. the extra mass on the driver dulls the hf response greatly, and disproportionate increased rigidity of the cone results in some pretty harsh bell harmonics and time smear ringing. If I could be bothered to reinstall these, i'd measure them properly. Short of it is don't buy these, you could of had a decent, cheap meal for the price - or bought the actually decent budget fostex like 40mm drivers for the same expenditure.










Tesla like 45-50mm Drivers - (I would try them):



Seriously considered sampling these - Allegedly Tesla (not the car company) drivers, the magnets are absolutely bfg massive, and powerful - implying possible high sensitivity, fast transient response and ferocious damping. The mottled cone design seems to indicate an effort to break up potential for cone bell modes and therefore permit using heavier plastic without excessive cone breakup distortion. Though the seller provided graphs (they can be totally wrong) appeared mediocre (although key versions of the real deal drivers are actually good); and well, given that these are just a shade more than the 50mm fostex like drivers, I wasn't in a rush to buy them just for testing - however, I will gladly test a pair at someone else's expense, if it interests them.

Outside of this, so far I have not found much of huge interest from budget sources that would seem like it'll be available over the longer term. Most of the basic plastic and metal drivers are kind of mediocre by nature, or more commonly shockingly bad. Though you might find some surprise gems if you go digging.

Bonus Content:

Denon AH-D2000 Teardown:












Heres whats inside the genuine article Denon headphones made by Fostex under an OEM contract back in the day. You can see from here various aspects of the construction.
Kicking myself for not getting current, proper measurements of these before selling them on, so I could post some more concrete measured analysis of how they compared; but oh well.. that opportunity passed.

Update:



Borrowed this from an old headroom post, illustrates the frequency plot measurements they took of the Denon's and some others.
On a personal level, I prefer the results I've been getting and theres still further scope for tweaking/adding to the hardware of the diy ones here later, of course ;)

** PART 5 - Coming Next... **

JamesLynton:
** PART 5 **

Sony MDR-V150 - (for comparison):



Not very good headphones frankly, posting them as a yardstick of what £15 gets you elsewhere. They sound muddy, have poor power handling and are rather uncomfortable. And frankly the 30mm driver they contain is barely fit for the dollar store (imho). The measured results are however quite revealing, and surprising, its a lesson in taking even reliable frequency plots of drivers with a pinch of salt, as whilst they do go 'flat' up to 17 kHz or so, it doesn't sound like it. The reason for this muddiness masking the sound lies elsewhere, in this case the THD vs Frequency plot gives away the likely cause, a massive amount of harmonic distortion below 200-250 Hz *at all listening levels* and particularly bad at normal ones. And when the fundamental bass response below 150 Hz is dropping off like a stone, all of that 'bass' content is getting turned directly into harmonics filling up the mid range (and more) with garbage.

In final conclusion on that one, its also interesting to note how whilst modifying the 40mm fostex like drivers for more bass did result in a rise in distortion which looks superficially similar to this, its not on the same order of magnitude & remains controlled/virtually non existent at normal listening levels.



Note: Graph above also shows the original Fusion driver plot (they are way better than these things :)





** PART 6 - Coming Next... **

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