By chance I came up on this modding idea by Plin, in this thread of his:
Basically the stock grills on Hifiman headphones is a fairly obstructing (acoustically) grill with a dust-blocking fabric annealed to it, and HE-500s seem to improve sonically with the grills off.
A more technical explanation is that the stock grills impose fairly crude and unnecessary damping on the treble, that ends up giving it a slight unnecessary veil. Without the grills, or at least with less obstructive grills, that crude damping effect is minimized, and improvements occur to the openness and decay nuance of treble.
Some of my earliest tests:Warning: Spoiler! (Click to show)
I tried taking the grills off my HE-400s, and while holding them in hand, quickly moving them on and off where they seat on the headphones, while playing music, and the effect is indeed quite noticeable - the grills cause the cans to sound more closed-in, with a headphone-ish sound, because it created a chamber that caused small amounts of resonance; without the grills, the sound opens up width-wise and especially apparent with live music (concert music etc), it just sounds more speaker-like and three-dimensional.
NOTE that there is a better, more objective and definitive, method of evaluating the effects of different grills on the HE400 sound, it uses pink noise. It is described at the end of this mod guide. Through this method, RINGING caused by grills can also be evaluated.
Also, a quick read to a post-script description of one of the earliest form of regrilling Hifiman headphones, turns out to be done by Dr Fang and Hifiman themselves!!! Check it out, it's a great read that describes the sonic goal of the mod eloquently:
Warning: Spoiler! (Click to show)
|Postscript. Shortly after my review published, Fang Bian wrote in: "About the veiling which you reported, my engineer and I came up with a solution after a telephone meet last night. Please read the following link." The fix—for those only who concur with my criticisms of course—is the removal of the thin cloth grill attached to the inside of the honeycomb cover. With a very thin-bladed jewelry screw driver, gently unseat the inner ring which affixes the perf cover to the frame. The ring is held in place by four tiny protrusions. Be sure to not deform the ring too much so it won't break while you snap it out.
Once the cover is free, peel off the cloth cover, then put everything back. The four ring catches must meet their corresponding recesses to snap back. Naturally, this mini surgery also removes a dust barrier which protected the Mylar diaphragm. What the long-term effects might be isn't known. I can only tell you that sonically, it's far from subtle.
Naturally, the only frequencies affected are those actually damped by the cloth - the treble. Astonishingly, it's not even the forward but backward radiation of the film's HF energy that's altered (originally absorbed/damped, now left to pass). Why should air moving away from your ears improve airiness? I can only speculate that the damping of that part of the rear wave to which the cloth isn't transparent also impinges on the free development of its front wave. Experiments with Franck Tchang resonators and his peculiar but effective approach to harmonic liberation have taught me that the biggest enemy to complete overtone restoration is overdamping. Damping the rear wave of the tiniest diaphragm flutters also damps the full development of the frontal output.
Fang Bian responded: "The first prototype was made without grill cloth. It has been used for more than four years without any problems."
To replace stock grills with new ones that are more acoustically transparent but still protect the drivers from mechanical damage / large debris, and optionally against dust.
Warning: Spoiler! (Click to show)
Just stock grills, but without the stock fabric backing (just rip that off).
Prototype 2.5 (bare mesh, no fabric)
***This version sounds the best (cleanest, with the most open sound), but of course it has the least protection.
Materials & Tools:
1x medium size steel mesh (strainer / pen tray / garbage bin, anything with a good air:mesh ratio) ***
1x wire snip / cutter / shear tool, or some other heavy-duty tool that cuts steel mesh cleanly
some cardboard to trace templates with
OPTIONAL 1x piece of fabric with tulle net weave (or something similar, with dense but acoustically transparent weave)
OPTIONAL 1x superglue
------------------------total cost: ~$1-5 (assuming dollar store)
*** RECOMMENDED MESH TYPE
How to pop the original grills out (the following image is Hifiman's official guide, no those are not my hands :P):
Key thing to note is that the 4 tabs of the thin retaining ring are at the 1:30, 4:30, 7:30, and 10:30 positions, so try your best to not burst any of those tabs off when you wiggle the retaining ring out.
I traced the circle of the original grill onto a carboard template, cut that out carefully, roughly cut out two pieces from the steel mesh, trimmed them to the correct dimensions against the carboard template with scissors / wire cutters, and thus the most barebone regrilling mod is done. The new mesh-only grill can now be popped back into the cups, and secured down by the plastic retaining rings.
That is the most acoustically transparent while still retaining mechanical protection, but no dust protection. I like to use this.
If you live in an environment with lots of wind / abrasive dust, then do extra steps to adhere dust-proof fabric, as follows (note the following photos were done with prototype 1 steel mesh material, which is inferior to protype 2 or 2.5 mesh type shown and described in materials section of guide).
Cut out the fabric (a bit larger than the cut-out new grills), and popped em onto the headphones.
Later I took them off, applied superglue to the outer rim of each steel mesh cut-out and laid the fabric on, and let cure for about 10 mins.
Left = new grill, Right = stock old grill
Then I trimmed them closely to the dimensions of the original grills...
...and installed them, voila!
soundstage is much more open and less closed in, width-wise, especially noticeable in live recorded tracks. Imaging is more 3D and natural, feels more speaker-like.
Also depending on the mesh used, ringing is reduced, thus cleaning up the sound noticeably.
Update aug 9, '12: after a couple of weeks of listening with this mod, I begin to also pick up that the entire treble region is indeed raised up by a couple of dBs due to this mod, which really seems to balance out the tonality of the cans, any hint of darkness is gone, it sounds so balanced complemented with the fun intrinsic colouration.
TO LONG DIDN'T READ version: The mod improves the openness of the sound, and unveils the upper reaches of the treble to allow a lot of air and upper register nuance to come through.
Evaluating efficacy of new grills vs old grills:
Warning: Spoiler! (Click to show)
This is a test that can be used to easily and definitively evaluate how the new grills improve upon the sound, and how close they are to being acoustically transparent.
Start by downloading a high bitrate pink noise file, then listen to the pink noise on loop through the headphones at a clear volume.
Meanwhile have the grills off the headphones, and hold the grills to be tested (whether it be the stock or new grills) and hover them on and off where they seat on the headphones. Pink noise is used here because it is by far the easiest way to discern resonance / ringing / soundstage objectively without delving into expensive measuring instruments.
Also try to minimize hand and finger movements when hovering the grills on and off during this test, as those movements also induce a noticeable change in the pink noise sound.
Focus on judging two variables through this test:
1) how the soundstage changes with and without the grills
2) how much additional resonance / ringing is induced by the grills
Note that regardless of how good you choose your materials, with a composite grill composed of a steel mesh + fabric, it WILL decrease soundstage and induce resonance/ringing, the aim is to produce a pair of grills that minimize those two negative effects.
So far my rev.2 grills (picture at top of post) are the best compromise, it reduces soundstage moderately (between stock and rev. 1), it also induces the least ringing.
Rev. 1 grills affect the soundstage the least out of the three, but induces the most ringing probably due to it having the densest steel mesh.
Stock grills close the soundstage in the most, by far; it induces moderate ringing (between rev. 1 and 2 grills I made).
Nothing from the stock headphones is destroyed with this mod, the only thing replaced is the grill which pops off of course. Completely reversible.
Comment, like, favorite, try it out if you like. Cheers!
Edit: partially revised on Aug 17, 2013
Edited by jerg - 8/17/13 at 6:45pm