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The Nature of headphone Measurements

Because it does not matter. The relationship between measuring with a microphone or measuring with a microphone put in a dummy average ear is essentially fixed (in extreme detail there will be changes depending on e.g. directivity etc but those are essentially negligible).

If you measure frequency response X with a microphone, you measure frequency response Y with a manikin, there's a mathematical function which can convert between those measurements and simply said it depends only manikin ear shape, nothing external. One can be calculated based on the other and vice versa. Using a different speaker there does not change that function. Unlike for an IEM measurement for instance where tip shape and insertion depth immediately produce a different response, and those are external to the transfer function so need to be measured. Hope this makes things clear :)
That is incorrect. A HATS system is specifically designed to analyze binaural effects and the HRTF of human hearing.Whereas a free field response with a mic measures the SPL across a band frequencies. It is an objective metric of the pressure at a given set of frequencies. The HATS system has a mic in it but the sound must pass through a passage way and a wave guide which places a set of acoustic filters over the top of what a free field mic would pick up. It matters quit a bit. And it has nothing to do with the headphones acoustic response. That transfer function should not be involved in the process (the mathematical function) of evaluating a headphone. The target function for IEM's should be different than what a headphone is in the current way we measure headphones. If it did not matter , Klippel NFS would be using a HATS system to measure loudspeaker. We listen to loudspeakers with the same ears we listen to headphones too.
 
The answer is simple... why introduce more measurement errors ?
You mean the way we do now by adding a variable and unnecessary transfer function to headphone measurements?
 
You mean the way we do now by adding a variable and unnecessary transfer function to headphone measurements?
Yep, there is no way around that for head/ear phone measurements when done on a HATS.
For speakers that would be an unnecessary introduced error.
Klippel is more than sufficient to characterize speaker response and is a lot cheaper than complicated measurements in anechoic rooms.

How those measurements will translate to perceived sound in one's room is indeed another story. :)
 
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which places a set of acoustic filters over the top of what a free field mic would pick up
But that's exactly what I meant with the mathematical function converting between a HATS and free field measurement. If you know one, you can calculate the other. Again, minus tiny variations which as far as I'm aware do not matter; why do you think this set of acoustic filters changes with a different speaker, enough such that it would invalidate what we get from a free microphone? Note I'm genuinely interested, because what I'm writing here is what I was taught by people running experiments with HATS. They could be wrong or overly simplifying, but they seemed qualified enough.

Yes HATS is designed to test binaural effects, but that's usually for things like stero, sources at different angles, and so on. For reproducible speaker measurements the source would always remain at the same position, right in front of the manikin, right? Also meaning both its microphones will measure the exact same signal (unless room or manikin itself aren't symmetrical but that's not useful), so there's nothing of binaural interest going on.

edit don't have a lot of time now but: this figure from https://headphones.com/blogs/features/diffuse-field sort of seems to explain what I mean; the top-right is the frequency reponse of the HATS which comes as a calibration file with the device, for various elevation/degrees. Unless I'm missing something it tells you the fixed relationship between measuring with a freestanding microphone, and what you'd measure at the HATS' eardrum. And the 'perceptual' is also what you get when measuring the genelec with a freestanding microphone roughly at the head position, no?

DF_Image_7_copy.jpg



And, quote from the same page:
Speaker sound is of course very different from headphone sound. Speaker sound conforms and adapts to your full HRTF, because it is actually interacting with all of it. Thus our brain does as it normally does, subtracting the effects of our specific anatomy & resulting location-based FR cues, leaving us only with “the sound of the speakers.”

This can be safely assumed, and this is why we generally don’t measure and judge speakers with HATS microphones: being able to assume the interaction between speaker and listener greatly reduces the variables we need to account for and makes well done speaker measurements among the easiest to interpret.
 
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That's the part that is completely irrelevant …
O/k, let‘s do the same trick as with the nozzle. Remove from the equation individual properties of the customer‘s hearing facilities ;-)

Target for over/on ears: a diffuse homogeneous frequency neutral sound field onto the pinna ( see above German academic Günther Theile). Again easy as a theoretical challenge. No reflections, please. And that was it, except for a bit of phase-wise decorrelation of (un)certain sections of the sound field emanating from the driver. A planar driver may do, because its sound field is everything but „planar“ in the treble—to the contrary, a guarantee for sheer chaos. Of course the ear pads shall not reflect, neither the driver‘s fixture.
See also Sennheiser HD414, the canary, or Jecklin Float, the fat man.

In case the above derived prerequisites are given (Guenther Theile‘s included, though) the headphone is warranted to work with everyone, regardless of a specific head related transfer function.

I‘ll stop here, because I don‘t see to much of either confirmation or well appreciated controversy. Must be I‘m not qualified as the newbie I am. ❤️

After reading my own sermon a second time, thing is: how would a perfect headphone, on/over ear, look like on a dummy head, measurement wise, and starting again from that, how to achieve this perfect performance? @solderdude , what if the headphone would not reflect a second time, re-reflect, the sound waves reflected by the flat plate you use? We would expect a flat amplitude frequency response without ondulations as an ideal—that is what we expect for an outer diffuse field hitting the flat plate to look like. If that is achieved with a headphone on a flat plate, then the headphone generates a diffuse field, frequency neutral … . Mission accomplished, for all ears, no need for individual HRTF and other complications.
 
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But that's exactly what I meant with the mathematical function converting between a HATS and free field measurement. If you know one, you can calculate the other. Again, minus tiny variations which as far as I'm aware do not matter; why do you think this set of acoustic filters changes with a different speaker, enough such that it would invalidate what we get from a free microphone? Note I'm genuinely interested, because what I'm writing here is what I was taught by people running experiments with HATS. They could be wrong or overly simplifying, but they seemed qualified enough.

Yes HATS is designed to test binaural effects, but that's usually for things like stero, sources at different angles, and so on. For reproducible speaker measurements the source would always remain at the same position, right in front of the manikin, right? Also meaning both its microphones will measure the exact same signal (unless room or manikin itself aren't symmetrical but that's not useful), so there's nothing of binaural interest going on.

edit don't have a lot of time now but: this figure from https://headphones.com/blogs/features/diffuse-field sort of seems to explain what I mean; the top-right is the frequency reponse of the HATS which comes as a calibration file with the device, for various elevation/degrees. Unless I'm missing something it tells you the fixed relationship between measuring with a freestanding microphone, and what you'd measure at the HATS' eardrum. And the 'perceptual' is also what you get when measuring the genelec with a freestanding microphone roughly at the head position, no?

DF_Image_7_copy.jpg



And, quote from the same page:
Well, you are partly correct. The bottom metric is an in-room response. Whereas the two on the top are anechoic. So the bottom curve should be flat (theoretically)or more accurately the free field response of the Genelec. The bottom curve is what you are aiming for , so that part is correct. The only thing I am arguing is we could eliminate the HRTF curve completely and make this much easier to interpret.
 
Well, you are partly correct. The bottom metric is an in-room response. Whereas the two on the top are anechoic. So the bottom curve should be flat (theoretically)or more accurately the free field response of the Genelec. The bottom curve is what you are aiming for , so that part is correct. The only thing I am arguing is we could eliminate the HRTF curve completely and make this much easier to interpret.

What kind of measurement system do you think we could use for headphones which would "eliminate the HRTF curve" (i.e. not a HATS)?
 
What kind of measurement system do you think we could use for headphones which would "eliminate the HRTF curve" (i.e. not a HATS)?
I am not certain at this point. But I believe one that measures the headphone and not how humans hear is imperative to good objective metrics. I think that a some sort of a flat plane for a headphone (not that simplified though) and a standard coupler for a IEM's(modified from the current standards). I do not know the answer without the resources to conduct all the experiments needed to complete the research.
 
But I believe one that measures the headphone and not how humans hear is imperative to good objective metrics.
Believing is fine but objective good metrics and headphones don't go hand in hand ... by nature.

I think that a some sort of a flat plane for a headphone
Its actually how I measure but arguably, around the ear-gain band, it isn't really accurate and it has issues with 'head-shaped' larger pads (I have to pull out the bag of tricks).
Also on-ears are difficult to test this way.

Another thing when using pinna-less fixtures is angled drivers, no tragus, and different amount of air inside the ear area as well as damping of resonances of that particular ear chamber.
Personally I am with you on measuring pinna and ear-canal less but has limitations. Science nerds will always directly discard any FP measurements for those reasons, regardless of the possible advantages.
 
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