Zero isolation with an IEM needing a bulky energizer kinda doesn't help with the fit issues.
I've never understood why isolation is automatically assumed to be a positive thing. It has an important place in headphonedom, sure, but unless there's a specific reason I need to block out noise, I loathe wearing isolating headphones and IEMs. I think it's antisocial to starkly cut yourself off so much, and sounds worse besides
Electrostatics shine at high frequencies and low levels - NOT a good choice if you listen mainly to MP3, as these compressed impersonations of recordings will get mercilessly exposed for what they are. The better the signal into electrostatics - the better the sound quality.
Your last sentence is correct, obviously, but your beef with the entire mp3 format is misinformed. Studies have repeatedly shown that 256kbps and above are sonically transparent, you cannot tell them apart from lossless. Neither can I, nor anyone else. I don't know specifically that these tests were run on Staxen Boxen, but it's not like Stax is the only revealing game in town.
Obviously this is assuming discipline to never compress a file that was previously uncompressd, and that it was encoded using appropriate settings etc. These concerns or similar ones apply to any digital format, so it's hardly unique to mp3.
Stax or any electrostatic can not rally deliver in that department
I don't know what a "basshead" is or what they would like, but I listen to EDM where the bass is the most important part of the spectrum. In my opinion and experience, the low end is where the Stax Lambda models I've heard stand out the most. Lots of headphones have excellent mids and/or highs, but bass seems the hardest part to do at a high level. I've never heard anything that can match electrostatic bass. It's clear, articulate, and effortlessly detailed and textured and precise (and I only own the entry level Lambda Pro, which is said to sound flabby in comparison to more expensive Stax). Granted, I'm fine with trading impact for articulation, but I don't think I even have to. Sure, dynamic drivers can slam a little or so they say, but I'm so spoiled by the Lambdas that almost any dynamic headphones sound ill-defined and one note to me, and usually not even the
right one note.
This has had a huge effect on the kind of music I go for. A lot of the stuff I liked before getting my stax rig has embarrassingly simple basslines, but ones that sound good and loud in low-end cans. The music I'm most excited about now sounds fantastic on electrostats, but boring on dynamics because they can't reproduce any of the nuance, so it just gets left out.
I'm learning that some high-end planars (the Mr. Speakers Alpha Prime, for instance) can get respectably close to electrostatic bass quality, provided they're paired with a great amp. But I've never owned a true TOTL amp so I don't know how high they're capable of getting. This is what's motivating me to learn to make my own DIY amps, so I can afford to try more of them
