So in headphones, yes frequency response at your eardrum (not what is seen on a FR graph), is in theory everything that matters. Given that distortion is below the audible threshold, and the headphones are operating in minimum phase.

The frequency response of a headphone affects the sound waves that are generated, and how they are shaped when combined. When it comes to "Technicalities", yes it can be linked back to FR, but not simply as something that you can point to one area and pick out. More how different frequencies are emphasized and what is affected by auditory masking.

That aside, there are a lot of outside factors that can affect what we hear or perceive, such as how the headphones feel, how spacious the cups are or how isolating they are.

Our senses are a mix of "simple" systems, that are filtered through our brain and can be changed by other senses, or interpretation

here

The biggest things that impact the sound other than frequency response would be soundtsage, timbre, distortion, and comfort.

Soundstage and timbre are both things that are described as being felt more than being heard. That's why just a frequency response graph can't describe the experience of a headphone.

Distortion is an obvious example of a difference of an expensive and cheap headphone. Very cheap headphones will have distortion on some notes even when the frequency response looks not bad.

Comfort might not seem like an aspect that will change a headphone's sound, but it can drastically change the listening experience. An open headphone which barely puts weight on your head can make you feel like you aren't even wearing headphones and getting incredible sound.

I have also wondered what makes headphones hood for a while. I have been in this hobby to know a lot about it, but I am still curious about why some headphone share better. I once made an interesting post where I posted a few frequency response graphs and gave a list of the headphones and wanted to see how well people can match the headphone to the graph. It was to prove that frequency response and tests alone can't give the full story on what a headphone is like. More recently I asked physically what makes a expensive headphone better than a cheap headphone? What are these companies spending r&d on that makes them better? I got a few responses that answered the question, saying it's mainly the driver housing and earcup design which impacts the sound greatly, and they basically use trial and error to find what shape produces the best sound.

The reason it's repeatedly stated it's all about frequency at the ear drum is because blind listening tests showed that to be the major if not only factor in what determines what people perceive as different about a given sound setup.

Everything else audiophiles talk about is currently completely subjective and "some" hear these differences and some don't.

The reason people don't think it's just frequency is because they can't eq one headphone to sound like another and assume that is proof it's not just that. Ignoring the fact that they most certainly did not achieve the same frequency at the ear drum.

There are some actual differences, such as the feeling of bass with your body from a subwoofer.

it's not necessarily something you hear, but feeling air being pushed at you is a real feeling and some headphones with bigger drivers and thicker pads can give you the feeling of more bass presence and that physical feeling cannot be eq'd.

Yes

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