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.
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.
To replace stock grills with new ones that are more acoustically transparent but still protect the drivers from dust and debris, as well as accidental pokeage.
~~Hifiman Re-grilling mod ~~
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.
1x medium size steel mesh (strainer / pen tray / garbage bin, anything with a good air:mesh ratio)
1x piece of fabric with tulle net weave (or something similar, with dense but acoustically transparent weave)
------------------------total cost: ~$5 (assuming dollar store)
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, 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.
Difference in transparency (and in turn, of acoustic transparency *** note that the fabric in both grills are almost 100% acoustically transparent, so the important thing is the degree of obstruction of the grills themselves):
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.
Evaluating efficacy of new grills vs old grills:
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!
Edited by jerg - 11/5/12 at 3:55pm