Hifiman “Fuzzor” Mod
This modification, which applies directly to HE500, HE5LE, HE4, and HE6 drivers (but derivative mods can be done on other HFMs as well as planar magnetic drivers in general), evolved from a number of things I tried.
Audeze’s recent LCD-X and XC had a new driver technology called “Fazor” which is a waveguide array that sits on top of the drivers and help direct the soundwaves more uniformly out of the diaphragms through the slits. I really wanted to do something similar with my HE-500s but couldn’t find any suitable material. Its design always sat at the back of my head though.
Meanwhile, I was fooling around with tuning the upper end balance of my HE-500s with felt discs; it never worked out right as it would introduce peaks and dips despite broadband attenuation of the frequency response. But one phenomenon I observed was that the felt discs always made the clarity better, the transients faster, which dumbfounded me as they were blocking everything and toning down the treble and thus should blur the clarity rather than enhance it.
I saw a modification done by purrin on his Abyss headphones, where he used damping material on the baffles of the driver cups to tame the treble peak, the mechanism described was that it helped diffuse away backwaves that bounced between the face and the baffle interface introducing unwanted reverberations.
And then it occurred to me that I could do a very precise damping scheme to completely cover the reflective surfaces of the HE-500 drivers without hindering any of the magnetic array slit openings. After some fooling around and a few revisions it came to fruition.
I did encounter a caveat initially with doing this modification, where the stiffened felt is somehow rigid enough, that it acts as a waveguide too well especially for the treble region, and the end sound was stringent around 10kHz. The simple solution to this, I found, was to taper off the right angles of the felt strips; that extra step has been included in the below guide to the mod.
Tools & Materials
1x sheet of Adhesive-backed Stiff Felt
(Creatology-brand 9’’x12’’ sheets are only $2/sheet from Michael’s Arts/crafts store; online you can find 9''x12'' adhesive-backed felt for around $3-5/sheet plus shipping)
1x metric ruler
1x fine-tipped pen
1x sharp scissors / xacto knife
1x relatively thick pen or rod (~2cm diametre)
As the main goal of this mod is to more adequately damp the soundwaves perpendicular to the drivers, between the drivers and the face, the felt is to be applied to the inner (face-facing) sides of the drivers, which can be exposed simply by taking off the earpads.
Below is a schematic of the cutouts you need to do out of the adhesive-backed felt sheets in order to apply proper damping to the HE500 (as well as HE4, HE5LE and HE6 drivers which have the same magnet grid patterns).
My method involves outlining all these cutouts on the waxy backing paper of the felt, with a fine-tipped pen; then going around cutting these out precisely using scissors or xacto knives.
Note that the cutouts are colourcoded in my diagram, this way I can show where they go and how they go onto the drivers in the below photo that has been colourcoded to correspond to the pieces from the cutout diagram, as seen below (click it to magnify and see the details and colour-coding clearly).
(note that the outer ring of felt as seen above, is actually part of the HE500 driver, it's a half-arsed but commendable attempt from Hifiman to damp the baffles of the drivers).
When applying the adhesive-backed felt stripes and pieces to the drivers, make sure to line things up well enough that you never block the driver opening slits; this requires patience and more patience, as they lay down those felt strips onto the metal surfaces of the drivers.
This is a more direct mod than any of my other mods (regrilling mod / jergpads mod) so it makes sense that you aspiring modders out there want to be more stringent through this process, get all the measurements and cutting and adhering neat and down to the tee.
One last step after successfully applying the felt is to round off / taper off the right-angled edges of the felt cuts, so that they don't interfere with the treble (as mentioned in the Prelude section of this guide). It's quite easy, just find a thick pen, and use its rear end to reshape and smooth out the edges of the felt. A stylized diagram is shown below:
It took me about 40 or so passes of the pen to smooth out each edge of the stiff felt, you can do more or less as you feel fit.
Optionally, you can also do the same procedure to the outside-facing faces of the drivers (that are under the Hifiman grills), that is far less important but you can do it for aesthetic reasons, and of course, you can never have too much non-intrusive damping!
And with that, you can completed the Fuzzor mod!
Edited by jerg - 11/29/13 at 2:45pm