Okay you caught me out. I don't find the HD650 treble rolled - off at any volume outright - but relative to other cans? One must acknowledge the differences in opinion and consolidate somehow in order to, y'know - keep the peace. Cheers.
The HD650 is laid back. I never found it dull or dark, just not edgy in its treble. Whether that's a good thing or a bad thing is subjective. One good thing about it is that you could crank it fairly high without ear fatigue, though I sometimes had sessions where I wondered if I hadn't gone too far. "Veiled" is a controversial tag since one person's veil is another's common sense.
I had an issue with a GS1000. I had just gotten it and it bugged me how sibilant is sounded, especially on certain 80s tracks which seemed a little sweet to begin with. In retrospect, I realize now that the problem was in thinking it would drive just fine without an amp. The jumbo cushions had increased the ear/driver distance while their wider aperture had widened HF dispersion and extended it. In short, there was this tonal shift that felt excessive. I didn't realize that without more power and more air flow, there was no way the bass could catch up with that extra treble. I ended up blaming the problem on the pads, which I eventually sliced back a few millimeters until the sibilance went away. (When I got my amp, I realized I never needed to snip the pads to fix the tonal balance.)
It was while banging my head against the wall on this issue that I came to realize the obvious: sibilance is just too much treble. It's an issue of tonal balance. One reason the plastic Grados use smaller cushions is to retain a certain tonal balance. Plastic isn't the world's greatest material from which to construct an air chamber, so the lower Prestige cans use the smaller cushions to keep the ear close and even filter the HF (comfies are "veiled" while un-modded flats can feel muted). If the point is to maintain a certain tonal balance, there's a logic to maintaining that balance on both sides. If the bass is not getting much help from the air chambers, it's not a good idea to open up the HF any further than necessary. Not surprisingly, the iGrados are the most veiled of the Grados, followed by the SR60. As you go up the Grado tree, more is done to increase the efficiency of the air chambers (through better screens, larger chambers and better wiring). As the effectiveness of the air chambers improves, the comfies are replaced by bowls. The SR325 is probably the most controversial, with its love/hate divide between those who love its edgy sparkle and those who find it too bright. An easy fix for that is to switch to flats, but the whole controversy comes from that balancing issue. The RS1 isn't any less sparkly but it brings into play mahogany air chambers. The wood balances out the sparkle. When Grado reached for the jumbo pads, he had to balance the out with huge hammer-head mushroom cups. Even so, this appears to be the moment when, for my money, Grados finally needed the benefit of a strong amp.
I bring this up because the HD650's "veil" may be common sense at work. The HD650 has as big a mouth as the GS1000. If memory serves, it digs lower than the GS1000 using the Sennheiser strategy of filtering the treble. In fact, all of the wide-mouthed circumaurals - including the K701, the HD800, the HD600/650 and the T1 - use some form of filtering to restrain the treble. I'm not sure what the big difference is between the HD600 and the HD650 but they use different drivers. Maybe there's a difference in the thickness of the diaphragm or the cushions used to attenuate the treble. Whatever the case, the HD600 and HD650 seem like pretty close cans, except that the 650 has better bass extension while the 600 has the greater HF extension. The HD800 seems to have split the difference, but at quite a hike in price. I can easily see putting some money into the cabling and/or the amp to avoid having to shell out the extra freight.
I own an HD800, which is a marvelous set of cans, but it's hard not to look wistfully back at what the HD650 did - for one-sixth the price (I bought my HD650 used). Still, I missed the edgy treble of the Grado. Having owned the PS1000, the HD800 and the T1, I'm convinced that they're all trying to claim the same real estate. They're just reaching for it from different directions.
