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Headphone Measurements Using Brüel & Kjær 5128 HATS

Mad_Economist

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Please be aware that the 45CC is a QC fixture, and unsuitable for measurements of headphones which correlate to subjective response. It doesn't even have an option for pinnae!

Edit: the 45CA Amir has in at the moment is, of course, entirely suitable for task, and is what Sean Olive has used for a lot of the Harman work.
 
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amirm

amirm

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Excellent! Is this one compatible with the existing Harman Target Frequency Response or does it need to be calculated like it was for the B&K 5128?
Harman research was based on GRAS so we absolutely have the target response.
 

gwarlek

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What is this EQ software amirm uses?
Sennheiser HD-650 headphone BK 5128 Equalization Measurements.png
 

Robbo99999

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Jimbob54

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I think that is part of his ROON software.
https://roonlabs.com/

It absolutely is Roon- but I wouldnt buy Roon purely for its EQ as there are free options that allow the same control. I would and do buy Roon for its library management, combining streaming and local files seamlessly, control of multiple devices and rooms AND the built in DSP inc EQ.
 
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amirm

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DualTriode

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I think that was an OEM product from Gras. Now that they are one company, there is no reason to get the AP version.

The things that I learn, same same, Okay.

I am considering one stop shopping and tech support from the same people. Analyzer, APx1701 and test fixture all from Beaverton.

Thanks DT
 
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amirm

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I am considering one stop shopping and tech support from the same people. Analyzer, APx1701 and test fixture all from Beaverton.
I wonder if they still sell theirs though. When I contacted them to get the GRAS 45CA, that is what they sent me and didn't suggest their own version even though my contact is AP.
 

DualTriode

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I wonder if they still sell theirs though. When I contacted them to get the GRAS 45CA, that is what they sent me and didn't suggest their own version even though my contact is AP.

If GRAS 45CA is what they sell that meets my desire for one stop shopping and tech support from the same people. I will ask about the AECM206 HEADPHONE TEST FIXTURE.

In my years as a consultant I stayed with my favorite sales / tech support people who ever they worked for.

Thanks DT
 

Mad_Economist

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I think that was an OEM product from Gras. Now that they are one company, there is no reason to get the AP version.
To my knowledge, the AECM206 - and its Larson Davis equivalent, the AEC206 - were released after the 45CA. I am unaware of their provenance - it could well be a GRAS OEM unit, but memory serving from @SIY's review, it seems to have some small mechanical disadvantages compared to the 45CA, and I do not believe its pinnae are quite the same.

Edit: Wait, AP and GRAS are the same firm now?! How did I not hear about this?!
 
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DualTriode

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To my knowledge, the AECM206 - and its Larson Davis equivalent, the AEC206 - were released after the 45CA. I am unaware of their provenance - it could well be a GRAS OEM unit, but memory serving from @SIY's review, it seems to have some small mechanical disadvantages compared to the 45CA, and I do not believe its pinnae are quite the same.

Edit: Wait, AP and GRAS are the same firm now?! How did I not hear about this?!

Last things first:

Mid-bass waterfall or spectral decay as you call it is the first thing that I thought of in the conversation of high output impedance amplifiers and headphones with a high Q resonance peak in the mid-bass frequencies. I think of stored energy, resonance, smearing, color not just increased amplitude. I have the impression that a calibrated microphone placed in the canal a fake neoprene ear may show us some of what is going on inside the ear cup of HD650 headphones. Neoprene may not make a perfect ear, I am okay with that. In addition to the waterfall perhaps a sine burst as used by linkwitz when he tested drivers for his projects.

https://www.linkwitzlab.com/mid_dist.htm

Next thing:

Yes I am shopping for a headphone test fixture my bench. No I do not need it. I am leaning towards Audio Precision or sister company Gras for plug and play TEDS calibration. There are multiple ears to select from and also several microphones and preamplifiers to confuse things.

Thanks for the insights

Thanks DT
 
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amirm

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To my knowledge, the AECM206 - and its Larson Davis equivalent, the AEC206 - were released after the 45CA. I am unaware of their provenance - it could well be a GRAS OEM unit, but memory serving from @SIY's review, it seems to have some small mechanical disadvantages compared to the 45CA, and I do not believe its pinnae are quite the same.
Yeh the pinnae is likely different but the rest is identical to the 45CA down to where each screw is.
 

Mad_Economist

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Mid-bass waterfall or spectral decay as you call it is the first thing that I thought of in the conversation of high output impedance amplifiers and headphones with a high Q resonance peak in the mid-bass frequencies. I think of stored energy, resonance, smearing, color not just increased amplitude.
This may well be what you think of, but I hasten to reiterate my often-made point regarding the inherent tether between the time and frequency behavior of headphones - the stored energy yields an amplitude bump, the amplitude bump will be visible as longer decay time, but you fix one, you fix the other. If you like, I'll post some CSDs with minimum phase equalization tomorrow...


I have the impression that a calibrated microphone placed in the canal a fake neoprene ear may show us some of what is going on inside the ear cup of HD650 headphones. Neoprene may not make a perfect ear, I am okay with that.
In terms of analyzing the behavior of headphones, the ear is significant, though! What happens in the pad volume is dependent on the things in it, and the pinna is foremost among those things. If you want to look at what's happening at a point in space within the assembly, a probe microphone would probably be your best bet.
perhaps a sine burst as used by linkwitz when he tested drivers for his projects.

https://www.linkwitzlab.com/mid_dist.htm
If you want something equivalent and meaningfully more convenient, ARTA's Ivo Mateljan has a method to derive burst decay information from impulse response data referenced in section 5 here and accessible to all ARTA users, including those with free/unpaid licenses.

This said, broadly, a focus on the time view of headphone behavior will ultimately run into the frustrating conclusion that we could have been looking closely at frequency response plots for this same information all along...

Yes, the parent company of AP purchased GRAS in 2018.
Jeez, and I like to think I pay attention! I may need to read a little more news and a little less AES.

Yeh the pinnae is likely different but the rest is identical to the 45CA down to where each screw is.
Makes sense to me - the build looked identical, but the pinnae do look different - and I couldn't imagine GRAS offering a Shore A-25 pinna on a headphone test fixture!
 

DualTriode

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Mad_Economist,


Thanks for posting the link to this article.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.581.6863&rep=rep1&type=pdf

It is interesting the presentation of waterfall plots, sine burst plots and plots showing the smearing of a decay pattern with the response of the non delayed response.

From the article introduction section: “…loudspeaker resonances is of prime importance in loudspeaker design. Resonances represent the main cause of unpleasant loudspeaker sound. They affect three main loudspeaker characteristics: tonal balance, modulation dynamics and object perception.”

It may be as simple as the inherent tether between the time and frequency behavior of headphones. How are the three main characteristics: tonal balance, modulation dynamics and object perception shown in a frequency plot? The same concept as when I said, “I think of stored energy, resonance, smearing, color not just increased amplitude.”

The APx500 software can calculate many different acoustic graphic plots from the same set of time and frequency response data. Is that the type of tether you are speaking of? If there is a delay it will show up in both the water fall and Frequency Response plots. The waterfall shows more than just the FR.

Yes I would like to see your CSDs.

Much of this has been done before. I am a hands on kind engineer. I like to see it, touch it and feel it myself to know it.

Thanks DT
 

DualTriode

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Yeh the pinnae is likely different but the rest is identical to the 45CA down to where each screw is.

The GRAS 45CA comes in several different models; 45CA-1, 45CA-2 .... 45CA-12. (different microphone combinations) Which one do you have on your Bench?
 
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amirm

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The GRAS 45CA comes in several different models; 45CA-1, 45CA-2 .... 45CA-12. (different microphone combinations) Which one do you have on your Bench?
I don't have the details in front of me but it has the anthropomorphic pinnae and high-resolution coupler. I will be starting a thread on it soon and post measurements and contrast with BK 5128.
 

Mad_Economist

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I am glad you like it!

It may be as simple as the inherent tether between the time and frequency behavior of headphones. How are the three main characteristics: tonal balance, modulation dynamics and object perception shown in a frequency plot? The same concept as when I said, “I think of stored energy, resonance, smearing, color not just increased amplitude.”

The APx500 software can calculate many different acoustic graphic plots from the same set of time and frequency response data. Is that the type of tether you are speaking of? If there is a delay it will show up in both the water fall and Frequency Response plots. The waterfall shows more than just the FR.

Yes I would like to see your CSDs.

The minimum phase behavior of electroacoustic transducers - particularly in the headphone case - is the source of the aforementioned tethering of time and frequency domain behavior. Tonal balance, of course, is directly visible in (compensated) frequency response plots; "dynamics" as such would require from a strict perspective multiple level FR plots to determine if compression was occurring (which, certainly, it can quite abruptly in cases of high motion, such as resonances); object perception as such in the headphone case is a function of frequency response, but may include some dynamic elements (e.g. head tracking) for accurate perception of both sound and space. For a passive system, however, it too is frequency response derived.

Vis-a-vis the waterfall showing more than the FR, I'd be happy to supplement with some plots of my own tonight if you like, but this post may be worthy of your attention first. If there are any parameters you feel are insufficiently displayed or analyzed there, please let me know, I can test them myself tonight as said.
 
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