Thank you so much for writing this out. This is what reddit is great for. Very interesting.

>First, headphones are tragically bad at it. Tuning a headphone is a nightmare as opposed to tuning a loudspeaker. They are often off by something like 10dB and it's not considered weird, that's how difficult it is to get that line flat. By comparison a reviewer's standard for a recommended loudspeaker is +/-1.5dB.

This is really interesting. As a non-engineer, can you explain why it is that tuning headphones is so practically difficult? Intuitively I know it to be true (hence all the substandard headphones, etc.), but have no sense of why it's so difficult.