Originally Posted by autumnholy
Have anyone here any idea what do those mean? I'm quite fond of both HD650 and also K701. But the idea of "needing extra goody amp" held me back. I wonder if I'm not investing a better amp, thence I'm not listening to music?
That depends. As mentioned already, sometimes the amp inherently alters the sound of the source too much, the easiest examples being tubes with the stereotypical "tube harmonic distortion", and "bass boost" amps for AKG K70x cans.
However, consider that most sources' headphone amplifiers have inherent design limitations, like space and power supply design (a single PSU powering everything in a full-size CDPlayer, or the need for extended battery life in a portable device). A separate amp can sound better by having its own power supply (assuming its well designed) and not as restricted in packaging components into a single, multi-purpose chassis. When you can't notice significant if any difference between using an amp with a source or not, reasons can vary greatly:
1) The amp could be transparent enough that it doesn't alter the sound, but...
2) ...assuming it could have improved dynamic range, if the source doesn't have much of that either even before it gets to amplifying the headphone, then the amp can't improve on that
3) Maybe the amp itself isn't up to the task, but this isn't simply a case of bad amp or better amp vs the rest
Note : many portable devices can drive "harder to drive" headphones well enough, surprisingly, so separate amps being inadequate is a bit less likely to not drive such headphones well. Also, if you look at some transducers (headphones or speakers), impedance to freq response graphs for some harder to drive designs tend to be less constant, which means your amp for example has to have a lot of current if not voltage as well. Plus cans more than speakers can vary widely in impedance, so while most objective parameters can weed out badly designed amps, among the ones with acceptable performance here, some may just be better on a more limited range of headphones. This is why you should pick headphones (and speakers) first - the amp will just squeeze more performance out of them, and then you go out and choose the one that can do that.
4) The music doesn't have dynamic range to begin with, and if any improvements are there it's mostly just "louder" (like "loudness wars" CDs, or older compression formats)
5) Human factor - the listener him/herself can't hear the difference
Note : some are too enthusiastic, ie your typical splurging audiophile, while some are too skeptical, so biases come in. At the same time, the best 'test subjects' I've had were my friends who were in a band. They aren't audiophiles, and before my headphones used only bundled earphones and monitors in the studio; they're registered since I egged them to for attendance in local meets but don't really hang out online in audio forums, but to see them wide-eyed - even with just adding an amp or a better source, not just a better (or colored) headphone - validates my findings. However, even they have biases too - they prefer Grados (SR225 and up) over pretty much everything else besides the K1000, although they validate descriptions getting thrown around when they first listened and then took off the Grados and go, "just like standing front row!" then with the HD600, "great with a jazz, sounds like a bistro," or "(otherwise) a 'safe' all-rounder for anyone who wants just one open headphone at home." (sic)
In the end, you have to balance objective instrument measurements with your own listening. Personally, if the first says they are too flawed, don't bother unless of course there's a feature you need and are wiling to compromise (ex, a 'good' music phone, so you only carry one device), just don't forget there's a compromise to be made. However, between a better objective score and one that's slightly behind that but you prefer the system as a whole better, then don't feel bad if you go for the latter - just be aware that objectively it's farther from perfect. I mean, in the end, you'll be the one listening, not the USB mic with analyzing software, right? And to that end, it's up to you too if you'd prefer to save money or spend it.
And just because you're not using "proper" gear, doesn't mean it's "not music." I can still enjoy music like the ambiance audio in a lounge, for example. Design compromises doesn't always mean "horrid" or "unlistenable."