I'm not looking for an idea of whether the foam mod would be worth every HD558 owner's time and effort, but only of whether it'd be worth mine. Nor am I, at least in terms of my music collection, "most people"; I rip my discs via EAC to FLAC, and the only MP3s I have are the 320K CBR transcodes I use in contexts, such as my phone, where storage space or codec compatibility constraints preclude FLAC. (Before someone raises the point, it's not that I imagine I can hear a difference between FLAC and 320K CBR; I just don't see a point in throwing away any information I don't have to, and disk is so dirt-cheap any more -- my primary storage right now is a four-disk 1TB RAID-1 which cost me less to build than I paid for the first 500MB hard disk I ever bought -- that I really don't have to.)
I'd like to see a double-blind trial as well, but that's not what I'm after here; all I'm looking for, in the comment to which you replied, is a sense of whether it's worth my time to modify my headphones. Will I hear a difference? If I do, will it be genuinely there or simply a result of the placebo effect? Who knows? Who cares? If we were talking about $1000 cables, then, sure, it's worth asking those questions. But this is a non-destructive, easily reversible fifteen-minute modification to a pair of $150 headphones I already own, and can afford to replace if I slip and impale a driver or something. Given the minimal stakes, I'm strongly inclined to just go ahead and see what happens. If it makes, or seems to make, a difference, then great! I'll stick with it. If not, I'll put the foam back. Either way, I figure it's worth a shot.
None whatsoever, actually, with either music (1938 Karajan/Berliner Philharmonic recording of the overture to "The Magic Flute"), or the "Ultimate Headphone Test" files; any difference made by removing the foam is evidently so subtle as to be completely lost on me. I don't feel like dismantling my headphones again to put the foam back right now, so I'll leave it out (stuck to the inside of a Zip-loc bag, since I don't have any proper backing paper handy to preserve the adhesive) until the next time I take the pads off for cleaning, and put the foam back in then. I doubt I'll notice any more difference in sound at that point than I do now.
> I wouldn't do it because I'm a ham-fisted klutz and I'd probably damage something.
On the other hand, the modification really is as simple as its adherents purport it to be, especially since the cord is detachable; the only even vaguely dicey moment I had was when I took out the left driver and found that its connection to the cord socket PCB is made by a wire that's both quite short and very fine, and that the foam would have to come out past the wires to both drivers. If I'd dropped the driver, I'd probably have needed to trim the wire and heat up my iron, so I'm glad I didn't do that. Other than that, it was a snap; anyone can do it in ten minutes who has screwdriver, tweezers, and reasonably steady hands.
Edit: Now I think about it, what I really should have done was take the foam out of one side, but leave it in the other, and see if I could pick out any difference that way; having both sides in the same state makes it essentially impossible to compare. Perhaps, when it next comes time to clean my pads, I'll give that a try.
I'd like to see a double-blind trial as well, but that's not what I'm after here; all I'm looking for, in the comment to which you replied, is a sense of whether it's worth my time to modify my headphones. Will I hear a difference? If I do, will it be genuinely there or simply a result of the placebo effect? Who knows? Who cares? If we were talking about $1000 cables, then, sure, it's worth asking those questions. But this is a non-destructive, easily reversible fifteen-minute modification to a pair of $150 headphones I already own, and can afford to replace if I slip and impale a driver or something. Given the minimal stakes, I'm strongly inclined to just go ahead and see what happens. If it makes, or seems to make, a difference, then great! I'll stick with it. If not, I'll put the foam back. Either way, I figure it's worth a shot.