K1000 Weaknesses:Keep in mind that some of these can be reduced with better/more synergous equipment/cable upgrades, but I feel they can never be truly resolved:
1. Cannot reproduce lowest bass notes; this is coupled by an unnatural decline of bass starting at 50Hz or so.
2. Soundstage: I actually prefer the soundstage that normal headphones provide (especially the R10 and HE90); the K1000 is very wide, but it lacks vertical placement and sounds actually sounded too distinct (which sounded unnatural to me) – this means the headphone lacks cohesion compared to others, IMO.
3. Treble: this can be too harsh and/or strident with the wrong equipment (some may prefer to sacrifice smoothness for detail - the T-amp achieves this); I prefer the K1000 with the RVK (with that amp there were no treble issues).
1. Though expanding the temple pads and moving the headband help alleviate most of the issues, I always felt slight discomforts when using the K1000 for a prolonged amount of time.
2. Looking up or down, or lying down are near-impossibilities with the K1000.
The K1000 requires a power amplifier or headphone amplifier that can produce 2-7 watts of power (the Corda Prehead and RKV are headphone amplifier solutions), and until the advent of the T-amp, the cheapest amplifier for the K1000 was the ~$400 nOrh; I found that even a maxed-out $250 T-amp was no match for the RKV (which is ~$1000).
The very nature of the K1000 mean that it leaks more than any other headphone (or earspeaker) ever made - it doesn't attenuate noise at all, and loud environments severely reduce the K1000's bass performance.
The K1000 is still one of my favorite headphones and one of the best I've heard - the design was brave and groundbreaking and it deserves its status as a reference headphone. That said, the K1000 simply wasn't for me and it's as simple as that, but I feel every serious head-fier should live with it for several months to find out for themselves.