Whether the overblown bass in some of today's music blows over or not, a serious reproducer should ideally be flat from 20 to 20k. In practice, price points have to be hit, SPL limits have to be observed, size and weight issues have to be faced, and so on. For 1975, the SR-X Mk 3 was better than any consumer source and better than most of the electronics. This says more about sources and electronics of the '70s than it does about the SR-X, but you'll get a whiff of how strange the SR-X was to those of us who were trying to get by with the affordable speakers of the time. Suddenly we were hearing what our stuff really sounded like, but though we suspected this to be true, we didn't know for certain at the time-- how could we? Needless to say, the thin bass was the least of our worries, and yes, we could tell even 30 years ago that the bass was thin.
And yes again, before it was declared immoral, illegal and fattening we did turn up our bass controls a little to compensate (for that was our odd little way at the time) and all was well-- so well that we could tell that our turntable arms resonated, our records weren't white-room clean (even after Preening and Parastatting!) our styli mistracked asymmetrically on inner grooves, recording engineers weren't always fast enough to pot down before the orchestral crescendo saturated the tape, our Dust Bugs made this awful wooooodge sound that echoed back and forth across the undamped LP surface, our solid state amps were full of grunge, our phono preamps had the transient response of Jell-O, and so on. Only by violently concentrating could we listen past this stuff and enjoy Iona Brown's soaring violin or the rough harmonies of CSN&Y.
It was hell, I tell ya! [waves cane menacingly]
John Lennon sang "just gimme some truth" and here the truth was, and we could hear the tiny dropouts in Lennon's vocal track. Talk about irony!
So to me it's amazing that a bunch of kids has taken up with this amazing old headphone and actually enjoys listening to it. Yeah, the bass was traded off for the cleanest high-SPL reproduction you're likely to hear outside of a recording studio. Yeah, there's a bit of a rise, very broad, in the upper midrange that masks some of the highest treble. And yeah, the headstage is truncated by the damping material in the back of each earcup. But take a look at how big the SR-X is, how big the diaphragm is (too small to be fully damped by its air load); consider that it cost only about as much as an average pair of speakers back then (even the vaunted Dahlquist DQ-10 sounded like a paper cup by comparison), and that they're still here more than 30 years later being discussed in glowing terms while being used on systems that the audiophiles of the time would've killed just to hear, let alone own, and wonder.