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Ear resonance gain chart confusion

Nouvruaght

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I'm here to dispel all the erroneous information surrounding and regarding this graph
1631040777885.png

Actually, I don't understand it. Why does the black line 'total ear gain' look similar to diffuse field when clearly there's an 'Ear canal & ear drum' gain that if compensated for, would actually make the top flat. Is the explanation for this the ear canal & drum gain is already included in the various HRTF measurement apparatus'? I pondered upon this question and then asked myself why wouldn't said HRTF measurement apparatus include the total ear gain in it's totality anyway if that's the case. Well, wouldn't that be to allow it to measure not only loudspeakers but also headphones and iem's as well without compensating for any particular 'body part gain' unique to each respective form of audio dispensing device?
 
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solderdude

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HATS are calibrated for free-field and also diffuse-field (so using speakers NOT headphones)
For headphones and IEMs different correction curves are needed.
For IEM ear canal needs to be (partially) compensated.
For earbuds only ear canal
For on-ears ear canal + concha gain (but diffuse field or close to it but not the exact same)
For over-ears ear canal + conchagain and a touch of pinna gain (perhaps)

headphones and speakers are totally different ways of exiting the auditory system so needs different compensation if one is to derive the perceived tonal balance at a specific SPL.
One cannot use the freefield and diffuse field for headphones as the circumstances differ too much.
 
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Nouvruaght

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HATS are calibrated for free-field and also diffuse-field (so using speakers NOT headphones)
For headphones and IEMs different correction curves are needed.
For IEM ear canal needs to be (partially) compensated.
For earbuds only ear canal
For on-ears ear canal + concha gain (but diffuse field or close to it but not the exact same)
For over-ears ear canal + conchagain and a touch of pinna gain (perhaps)

headphones and speakers are totally different ways of exiting the auditory system so needs different compensation if one is to derive the perceived tonal balance at a specific SPL.
One cannot use the freefield and diffuse field for headphones as the circumstances differ too much.
Wouldn't the dummy head being used for IEM and headphone measurement naturally compensate partial ear canal gain for iem's and 5-10% spherical head, concha, pinna, and ear canal gain for headphones?
 

solderdude

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Wouldn't the dummy head being used for IEM and headphone measurement naturally compensate partial ear canal gain for iem's and 5-10% spherical head, concha, pinna, and ear canal gain for headphones?

It doesn't, one would need to apply a different target curve for different types of headphones just like you need to use different compensation curves for free-field and diffuse field circumstances for the same HATS.
For that reason the Harman IEM target (or should I say correction curve) differs from the over-ear target.
It would even make sense to make a separate one for on-ear headphones and ear buds but the on-ear one would be close to over ear.
 
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Nouvruaght

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It doesn't, one would need to apply a different target curve for different types of headphones just like you need to use different compensation curves for free-field and diffuse field circumstances for the same HATS.
For that reason the Harman IEM target (or should I say correction curve) differs from the over-ear target.
It would even make sense to make a separate one for on-ear headphones and ear buds but the on-ear one would be close to over ear.
So the dummy head is only used to get a seal for the headphones?
 

solderdude

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The dummy head is used to mimic the acoustic load the headphone 'sees' and the microphone inside registers the air pressure that headphone would create at the ear drum. It has a similar shape head as opposed to flatbed rigs (like the one Amir uses) which could help with getting better seal with larger ear cups and 'shaped' ear pads.

The pinna, concha and earcanal 'distort' (change the frequency response) of the what the sound is a few centimeters away from the ear (where the driver is).

Caveats: your ear may not have the same shape, your ear canal may differ, your hearing may not be as perfect as the microphone, the measured headphone may not have the same seal as on your head, the headphone may not have the same listening position as your head, the pads may not be the same depth, there may be unit to unit variance.

Those sound changes shown in the pot you posted are at the microphone (equivalent to what 'the average' ear drum would vibrate BUT that plot is only valid for sounds further away from the HATS and at an 45 degree angle.
Headphone drivers are very close at no degree (some headphones maybe up to 8 degrees) angle in a small sealed space that is also occupied by the ear so will differ from the posted plot.
So while it is a nice plot it has just some relevance to measuring headphones. For that other targets (correction curve + acoustic corrections) are needed.
Free field is complete wrong (a speaker in front of a HATS at a specified distance in anechoic conditions) and so is diffuse field (several strategic placed speakers at a certain distance in an anechoic room that are supposed to kind of mimic an echoic chamber)
 
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Cbdb2

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That graph is an average and will be a different for everyone. Just look at peoples earlobes. I once read for best dummy head reproduction (thru phones of course) you need to measure the response of your pinnea and ear cannel (a tiny mic in there) and EQ the signal to compensate for it. The result was to take the sound out of your head and surround you. Never tried it but kinda makes sense.
 

briskly

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I'm here to dispel all the erroneous information surrounding and regarding this graphView attachment 151961
Actually, I don't understand it. Why does the black line 'total ear gain' look similar to diffuse field when clearly there's an 'Ear canal & ear drum' gain that if compensated for, would actually make the top flat. Is the explanation for this the ear canal & drum gain is already included in the various HRTF measurement apparatus'? I pondered upon this question and then asked myself why wouldn't said HRTF measurement apparatus include the total ear gain in it's totality anyway if that's the case. Well, wouldn't that be to allow it to measure not only loudspeakers but also headphones and iem's as well without compensating for any particular 'body part gain' unique to each respective form of audio dispensing device?
-Similar to DF?
  • You can see the 1kHz midrange dip from shoulder diffraction. This dip will not be present in the DF response.
  • The 3/4 wave resonance should be driving up the response near 9kHz. The concha response drags down the sum such that there is a local minimum instead.
-I don't follow what you mean by "compensation". The acoustic response at the microphone would be subject to a linear distortion by the head. There is normally no electrical compensation for the usual gain of the model head.
-Also, the purpose of a dummy head is not to measure head-related transfer functions. Any object has a transfer function associated with it, but the dummy head is meant to recreate the transfer function of a "typical human" under some given circumstances. The black curve is an example of a function that a complete mannequin should be able to reproduce given a sound source some distance away from the head.

One cannot use the freefield and diffuse field for headphones as the circumstances differ too much.
The physics difference is obvious, but the choice of DF equalization in the first place was Theile's assumption that the brain interprets headphone sound output with no particular direction-dependence. To fit this subconscious association, Theile concluded that headphone equalization should reference no direction.
 
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Nouvruaght

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The dummy head is used to mimic the acoustic load the headphone 'sees' and the microphone inside registers the air pressure that headphone would create at the ear drum. It has a similar shape head as opposed to flatbed rigs (like the one Amir uses) which could help with getting better seal with larger ear cups and 'shaped' ear pads.

The pinna, concha and earcanal 'distort' (change the frequency response) of the what the sound is a few centimeters away from the ear (where the driver is).

Caveats: your ear may not have the same shape, your ear canal may differ, your hearing may not be as perfect as the microphone, the measured headphone may not have the same seal as on your head, the headphone may not have the same listening position as your head, the pads may not be the same depth, there may be unit to unit variance.

Those sound changes shown in the pot you posted are at the microphone (equivalent to what 'the average' ear drum would vibrate BUT that plot is only valid for sounds further away from the HATS and at an 45 degree angle.
Headphone drivers are very close at no degree (some headphones maybe up to 8 degrees) angle in a small sealed space that is also occupied by the ear so will differ from the posted plot.
So while it is a nice plot it has just some relevance to measuring headphones. For that other targets (correction curve + acoustic corrections) are needed.
Free field is complete wrong (a speaker in front of a HATS at a specified distance in anechoic conditions) and so is diffuse field (several strategic placed speakers at a certain distance in an anechoic room that are supposed to kind of mimic an echoic chamber)
If there were two speakers placed in front of the HATS in typical fashion of pro studios like this
monitor-placement.jpg

In an anechoic chamber bc it appears pro control rooms are often pretty flat, like less than -+2db in slopes.
Would it be a more accurate FR target?
I'm assuming this would rid the problem of FF & DF wrong angle and distance. I mean the HATS hearing this FR from the speakers shouldn't sound different than it hearing that same FR but from headphones?
 

solderdude

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For speakers the 45 degree angle and near field in a treated studio would come close to the plot you posted.
Should you use a HATS to measure the sound at the listening position then neither DF nor FF correction are correct nor is the plot correct as the HATS response will differ from the overly smoothed drawing.
So the compensation needed to calculate what the sound was approx 10cm before it entered your ear (which is what you hear) will differ IF you want to accurately know what that was.

However, in headphones the sound does not come from both sides, it does not come in from a 45 degree angle, it does not interact with the room but comes from a very short distance in a small (somewhat or completely) sealed 'chamber' so different compensation is needed to deduce what sound would come from the driver and what you would hear.

Trained listeners are needed here. A reference speaker setup would be needed here that is confirmed to reproduce faithfully in a treated room (studio) with speakers at a certain distance and music played at a reference level (say 80 to 85dB average).
You measure with a specific HATS and create a compensation curve so that what comes out of the HATS is similar in FR to what a linear mic would pick up.

Now you have a target curve... for THAT specific HATS in that particular room with particular speakers at a specific angle with specific room conditions (treatment, speaker placement, console, chairs, windows etc.)
That will differ from the plot you posted and won't be 'smooth'.
Difficult part... it won't represent every other studio, not even when the same speakers are used.
So more research ... more measurements, more listening, more plots with the same HATS.
More averaging of the compensation etc.
Now there you will see something looking like the plot you posted. It won't fit every studio/circumstance but is better than nothing.
That last bit is where a single compensation curve comes in... it is somewhat accurate in general usage.

Now... headphones. Angle and circumstances differ.
Trained listeners, could even use a really good studio and do the comparison there.
Same (measured) average SPL, listen, compare, EQ the headphone (most far more wonky than speakers) and get the sound to be the same.
The measured response is how the trained listener hears the 2 situations. The HATS response is known. We can calculate the needed correction.
That curve will differ from the one made with the speakers.
problem... put another headphone on the head and repeat... somewhat different compensation is needed. Repeat with 10 headphones.. all result in different compensation curves. move the headphone a cm and different yet again.
Now this is impossible to use so we need to look at the average and use that to get an idea of how it 'sounds' to a trained listener compared to a reference with speakers in a well treated (one may hope) room. That compensation curve will be smooth and 'on average' correct up to a few kHz.

You can do a similar 'thing' with the same excellent speakers in a 'good' emulation of a somewhat treated domestic room.
Use a HATS and trained and untrained listeners (the public you want to sell to) and obtain a somewhat different average correction.
Bass and treble is often an issue so let listeners play with tone controls that are fixed in frequency response but can control dB's.
Again, heavily smooth the average measured response on a specific HATS and you obtain a somewhat correct response up to a few kHz.
One can say 8kHz tops or 10kHz tops but in reality it will be lower than that.
One can differentiate the responses for certain groups of listeners. This is nice as research.

Guess what... Harman research...

Now we need to sell headphones to the general public so average the set amount of bass and treble from the research and come up with something that is preferred on average (is not the same as professional in studio circumstances) and you end up with the Harman curve for 1 specific HATS.

Using that specific HATS you can get a good grasp of what the tonal balance will be from bass to say 6kHz or so (one can always claim 8kHz or even 10kHz) provided a good seal is obtained. The latter is not always the same and the positioning is not always the same either.

So headphone measurements... it is a somewhat averaged measured response that can give a clue but is definitely not an exact response.
This is why, even with accurate EQ based on such measurements, will not result in the exact same sound but on average, in perfect conditions, will make headphones sound very similar in tonal balance but can still differ above say 6kHz where the most gremlins will be.

conclusion: headphone measurements is not an exact science. FR measured by a HATS is an indication at most for tonal balance and EQ should not be based on an 'exact' opposite of the measured response on one specific HATS in one specific circumstance using one specific 'correction including tonal preference IF you want something 'exact'.
That said you can make headphones sound more similar to a specific target.

And guess what... on average people seem to prefer a scientifically obtained target. Others may prefer a different 'target'.
Harman response is just that... for the average public (that likes some bass boost for whatever reason) when those headphones are measured on that specif HATS, or in the Harman case a specific GRAS flatbed fixture with a specific pinnna and coupler. When every one would use it.

But there are many different test fixtures with different responses..... the horror.

Take measurements of headphones for what they are... not as an absolute truth. Regardless who does the measurements with what fixture.
You want to be close to Harman ? use the same fixture.
 

Sharur

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Take measurements of headphones for what they are... not as an absolute truth. Regardless who does the measurements with what fixture.
You want to be close to Harman ? use the same fixture.
I feel like driver quality at least is easily extractable from measurements with a good seal. If you're always going to be using EQ, raw frequency response doesn't matter much if THD is on the floor. There are some examples like Hifiman Susvara which can't be 'fixed' with EQ, but in general it's not the case.

On a personal level, I would never buy a headphone like the Audeze LCD-24 that requires EQ to sound good regardless of how much potential the drivers possess. As a consumer, I want a product that measures well on the rig because it's easy to say its better than competitive products.
 

solderdude

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Measurements (the basic ones) can say something about some of the qualities in specific conditions. They won't tell the whole story unless you found a way to extract something like stereo imaging from the basic plots for instance.
But FR plots can say something about tonal balance and distortion plots at different levels compression at higher listening levels but not how it impacts sound exactly. Conditions are the test fixture and its compensation are accurate enough.
Also seal is not a constant for everyone which may be head size dependent and affects bass response mostly.

So measurements are useful to figure out some of the important aspects but I would not buy a headphone based on some measurements only.
Not all headphones that measure well are keepers.
 
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