You who do EQ with headphones . EQ setting,it's based on subjective, liking and taste in terms of sound, right? Subjectively because frequency curves and headphones are pretty pointless (how measure?) to start with because our ears look different, right?
Or what do I know there may be special microphones that you push into your ears and measure?
Indeed there are many questions and viewpoints.
Some EQ based on taste, others based on measurements, and yet others based on measurements and listening (both can be incorrect)
Some insist measurements should be averaged (positional or samples).
Some insist the EQ should be the exact opposite of a measurement (set) of the averaged result which is published.
Some insist using tones, some insist using noise (bands), some prefer sweeps.
Some insist using a specific type of fixture.
Some insist only 1 specific 'target' (boosted bass for whatever reason) and treble roll-off based on things they believe is correct.
Applied EQ can certainly improve tonal accuracy but when the measurement is incorrect it can still be somewhat wrong.
EQ based on the wrong measurement(s) or someones (flawed) sense of how things should sound can produce results some may like but others do not.
Measurements and listening to actual headphones will reveal placement of the headphone (on head and fixture) as well as seal and pads can substantially change the sound (in bass and treble region)
Measurements differ between test fixtures... which one is correct or are all of them somewhat wrong ?
Can fixture 1 be more correct than fixture 2 on headphone A but headphone B be more correct on fixture 2 ? Which one is the most correct one ?
Yes, there are mics that can be put in the ear canal entrance.
They block the ear canal which also imparts some emphasis in specific frequencies.
You would have to compensate the mic as well.
It would measure that pinna only so would only be valid on that ear with the headphone in a specific position. When you change its position the curve will change. Which one to use ? average or not ? and when you do what positions ?
You can measure ear drum levels with special mics but you can't do that simply at home.
Besides.. you only will know the SPL at that point and don't know tell what tonal balance to EQ to.
I see it this way:
Measurements are leading because they are more trustworthy than your average ear.
Trained ears with access to references. Your brain can get quickly accustomed to a sound signature and erroneously except it as a reference so a true reference will be needed to compare the DUT to.
Both are valuable tools and can help with improving tonal accuracy as a whole (NOT exact)
So what you should do when you want to apply EQ.
Look at various measurements done with various types of fixtures (so not all using the same fixture !)
Understand the measurement conditions.
Look for commonalities in various measurements.
When the needed correction is substantial (say over 6dB) look for another headphone.
Then use some basic EQ that adresses the aspects. The fewer needed and the smaller the better.
Listen to the headphone with and without EQ and validate the EQ'ed version to a known reference.
Chances are that EQ will be objectively the most correct.
Then use basic tone controls to correct recordings (these can be totally off).
Yes... difficult and the reason why one can find many different EQ's for the same headphone.
Tonal improvements, in general, are still to be expected so can be worth it.