Thank you for your thoughtful and thorough response. I am invoking the ignorance card, however, regarding your above statement(s). Can you help me better understand your points, perhaps in newbie(r) terms?
The idea of "fighting" noise is curious - are you suggesting that I/we would have an active role in this? Or, are you merely suggesting that fighting noise is what we're all after, and it gets accomplished through a number of modalities, i.e. isolation, noise-canceling, etc.?
Perhaps, more intriguing is the idea that "
frequency response should fit (my)
own hearing" and that I "
should judge when (I)
get to feel a fairly well balanced response." I'm always up for a good challenge. What does this mean and practically look like? Perhaps, the root of my confusion on this matter is what you're meaning by "frequency response" and "balanced response", respectively.
Appreciate any additional insights you're willing to spend time divulging.
Warning /!\ I'm afraid that while trying to keep it accessible, I also made it overly long and not really easier to understand. Sorry about that.
About frequency response, there is a long lasting assumption that we will prefer and find more realistic a sound that we perceive as neutral. That assumption has been long demonstrated with speakers, and an idea of flat response has been pretty much set in stone along with the frequency response to achieve it. But it is more complicated with headphones as some of the ways your head and ears would affect everyday sounds reaching your eardrum are bypassed or altered by the position of the headphones. So some compensation is needed, and because we have different heads and ears you and I, the impact of a given headphone on our perception is going to be listener dependent in some more or less significant ways. As a result, there is no definitive standard of flat frequency response for headphones that can claim it will sound flat for everybody because that would be a lie. So if you want neutral, you're the one who can help you best(or some super rigorous measurements of your HRTF in a lab, sadly that's not very accessible).
Frequency response is a big part of what makes us feel like we're getting good sound or not(I'm not saying this, research is). So finding your signature(what feels "neutral" or "balanced" to you) is always going to be a big step toward getting good sound, both objectively and subjectively. I suggest to play around with EQ(although on a Sony DAP the EQ options are rather limited) if only to learn about your own preferences and also to learn to notice what isn't right in a given headphone. That way instead of just having the feeling that something isn't right, you can hopefully learn to identify the problem better, and maybe compensate for it or at least know not to get the same thing on your next headphone. That doesn't solve everything, and is easier said than done, but it's an obvious starting point when we look for good sound. The alternative to practicing with EQ, is to just try many headphones to find what comes close to your preferred signature.
But if you're going to stick with this hobby, you'll have to tackle frequency response at some point and find a way to know what you, specifically, need/like. Many people in the hobby think they're looking for something else, like some elements of soundstage, or the tightness of the bass, or whatever. But frequency response is almost always part of the answer, if not the answer.
About noise: trying to achieve the best sound means trying to have something as close as possible to some predefined reference. Here we're going to assume that it's the album. Between one DAP and another one, most of the music signal will be accurate on both down to maybe -60 or even -80dB. Those stuff are simply really good. Some obviously are better, but still, even many of the cheap ones do a good job nowadays. A headphone on the other hand will distort the signal(because it has moving parts and must fight inertia, the stiffness of the driver, and the air around). It's not rare at all for a headphone to have distortions reaching 1% or at least coming close to that. 1% distortion, to speak in the same units as before, means that for a given signal sent to the headphone(the music), it will create that signal and also some extra signal(the distortions) that will be 40dB quieter than the signal(1% means 40dB below signal). So -40dB. Between that and how headphones often have frequency responses that are very different from one another, it's obvious that the headphone is much more likely to be the one limiting fidelity. That's for audio in general.
Now, "I'm on a plane, I can't complain, I'm on a plain". Noises in the cabin reach maybe a stable 70 to 80dB SPL, which is rather close to the sound levels we use when listening to music. So if we had no isolation at all, we'd have noises from the plane as loud as the music
. The solution to "fight" that noise is either to isolate yourself from it, or to increase the music level so the noise becomes quieter relatively to music. The second option is very very bad for our ears on a long flight. So isolation it is.
But isolation, active or passive is limited. Even with my Etymotic in ear, I'm getting mostly between 20 to 25dB of ambient noise attenuation depending on the frequency of the noise. And that's when I get a very good seal with the tips. So if I listen to music near 80dB SPL, even with some of the best solutions I've found, noise is still likely to be only some -20dB below signal(at least if I don't turn the music up and keep a reasonable/healthy level).
And that is the long winded explanation for why I said that "Under reasonable circumstances the achieved fidelity is going to be settled by noise and how well you fight it". Because everything else(beside frequency response), is likely to only affect the sound at a much quieter level compared to how cabin noises are ruining the music you get to hear. Noise is the weak link in this context and will remain the weak link even with good active or passive isolation. So that's what you want to get right. Shure is making IEMs with good isolation. Not the very best, but better than most beside custom IEMs. My amateurish tests with a speaker and a mic gave my SE215 almost as isolating as my etymotic, but the etymotic was still doing better by up to 5dB at some frequencies. The obvious problem with etymotic is comfort. Depending on your ear canal, those IEMs might feel like torture(ear rape is often used to describe than brand). But some guys like myself happen to feel fine with them for hours, when I want to cry after 20mn wearing almost any on ear headphones. Again, no universal solution. What works for me might not be best for you.
The noise cancelling headphones I've tried didn't isolate as much as a pair of etymotic IEM. But I have not tried recent products, and again I happen to be lucky when it comes to Etymotic fit and comfort. So I perfectly understand that other people can be of the opinion that NC headphones do isolate better than IEMs. It might be true for them.
