HBK Electroacoustics Virtual Conference -- Important Presentations
Sep 25, 2021 at 11:50 AM Thread Starter Post #1 of 28

Next week -- September 28-29, 2021 -- HBK (Hottinger Brüel & Kjær) will be holding their HBK Electroacoustics Virtual Conference. Last year they held their Product Physics Conference virtually, and that covered many different disciplines, but this conference is focused on electroacoustics, so there are several sessions you will definitely want to watch.


While I will be presenting at this conference*, there are several sessions that are far more important than mine, and that I'd therefore recommend you prioritize. For Head-Fi'ers, some of the highlights (and so ones I suggest you check out) are the following (in ascending date/time order, Pacific Time):

Tuesday, September 28, 2021

Tuesday, September 28, 9:00 am. to 10:00 a.m. (Pacific)
TITLE: ElectroAcoustic Principles – The Complete Idiot’s Guide to Basic Electroacoustic Measurement
PRESENTER: Martin Alexander (Alexander Acoustics, LLC)

For those new to the field of electroacoustic measurements, this short tutorial provides an overview of the quantities that are basic to describing the performance of an electroacoustic system, whether headphones, speakers, microphones, mobile phones or whatever the future brings. The language of electroacoustics, including the many flavors of the decibel, the many ways to measure frequency response and which distortion measurements provide an undistorted picture of a products performance are just some of the concepts discussed.
JUDE's NOTE: Marty is one of my mentors, and I've attended classes he's taught. In every single interaction I've had with Marty, I have come away having learned something. This one will be worth watching, even if you feel confident about your knowledge of electroacoustic principles.​

Tuesday, September 28, 1:00 p.m. to 2:00 p.m. (Pacific)
TITLE: Why do so many of us like the sound of analogue recordings on vinyl when the measurements look so bad?
PRESENTER: Mark Serridge, Hottinger Brüel & Kjær

Simple frequency response measurements were made on a range of sound reproduction systems including:
1. Compact Disc​
2. Streaming Audio (MP3)​
3. A vinyl record player​
The measurements were then compared to a simple “blind listening test” involving a small group of listeners. Based on frequency response alone, it is clear that the measurements do not correlate to listener preference.
JUDE's NOTE: I do not know the outcome of this study by Mark, but when he says in the abstract "Based on frequency response alone, it is clear that the measurements do not correlate to listener preference" there is no way I'm missing this one.​
Wednesday, September 28, 2021

Wednesday, September 29, 9:00 a.m. to 10:00 a.m. (Pacific)
TITLE: Wideband impedance measurement technique in the human ear canal
PRESENTER: Søren Jønsson, Hottinger Brüel & Kjær

The multimedia evolution has led to full audio bandwidth performance in new generations of smartphones, headsets, headphones, as well as hearing aids. This calls for wider band performance of the ear simulators, and head and torso simulators used by the industry to evaluate these multimedia devices, which in return calls for a better understanding of the high frequency behavior of the human ear, that these simulators are supposed to replicate. Specifically the human ear canal that couples the external sound field to the eardrum and the solid parts of the middle ear. Acoustic input impedance measurements are an important parameter when characterizing ear simulators and the human ear. Today, this is quite well covered up to around 8-10 kHz. This session take a look at a unique measurement technique developed to enable wideband acoustical impedance measurement in the full audio band up to 20kHz. First the technique is used to obtain measurements on the widely used IEC711 ear simulator and compared to detailed simulations. Then the technique is applied on human subjects by including the first of its kind in vivo based magnetic resonance imaging study of the human ear canal. Masurements results of 32 subjects is presented and the mean human impedance is also found by propagated the measurements is each ear canal to a common reference plane across all subjects.
JUDE's NOTE: Søren** was one of the leaders in the key research behind the new Brüel & Kjær HATS Type 5128, which we are using now at Head-Fi as our primary measurement fixture. Because the 5128 represents the most important advance in hearing simulators in 40 years, understanding how it came about is critical. While I have spoken and exchanged many emails with Søren, I have never seen a presentation from him outside of our video chats. This presentation is one of my personal top-two must-see presentations at this conference.​
Wednesday, September 29, 10:00 a.m. to 11:00 a.m. (Pacific)
TITLE: 5128 High Freq HATS and conformance to the new ITU-T P57/P58 standard
PRESENTER: Lars Birger Nielsen, Hottinger Brüel & Kjær

For the ear simulators that have been developed over the last 60 years the acoustic impedance and the geometry of the ear simulator have been the primary focus in addressing the increasing need for realistic, accurate and repeatable acoustic measurements. The session presents a new and standardized fullband ear simulator that provides unprecedented realism in audio testing, reduces the development time for new acoustic product and ensures product audio quality in the marketplace.
JUDE's NOTE: As the Brüel & Kjær 5128, again, represents the most important advance in hearing simulators in 40 years, this is the other of my personal top-two must-see presentations at this conference. This presentation runs at the same time mine does, but I strongly suggest you prioritize this presentation by Lars** above mine, especially if you want to better understand the new standard in hearing simulation that we are already seeing increasing adoption of. Lars is someone else whom I've learned a great deal from every time we've talked or exchanged emails.​

Wednesday, September 29, 1100 a.m. to 12:00 p.m. (Pacific)
TITLE: Modeling And Predicting Listeners’ Headphone Preference Ratings
PRESENTER: Sean Olive, Harman

A series of controlled listening tests have identified a preferred target response for around-ear (AE), on-ear (OE) and in-ear (IE) headphones that satisfy the majority (64%) of listeners. Two smaller segments of listeners prefer this target response with slightly more (15%) or less bass (21%). Two statistical models have been developed that predict listeners’ sound quality preference ratings of a headphone based on how much its measured magnitude response deviates from these target responses. My talk summarizes this research, and presents some new research related to how headphone measurements vary across different test fixtures including the B&K 5128. The goal is to be able to model and predict listeners’ preference ratings of a headphone using measurements from different test fixtures.
JUDE's NOTE: For many in our community, Sean needs no introduction. The preferred target response research from Sean and his team at Harman is, without a doubt, the most important such publicly available research of its kind, in my opinion (and the opinion of many).​

* While I will be presenting a talk titled "Audio Measurements As Consumer Content" -- which is an updated version of a presentation I first gave at the ALMA Annual Conference in 2018 -- I do feel strongly that it's much more important for our measurement enthusiast community to learn as much about the standards for hearing simulation from people who were actually involved in developing those standards. As such, I strongly suggest you watch Søren's presentation, as well as Lars' presentation (instead of mine) on Wednesday. You can then watch mine down the road when HBK posts these sometime after the conference.
I will suggest, however, that you watch my presentation given at last year's HBK Product Physics Conference, as it touches on the research Søren and Lars will be discussing in more detail. Here's a link: "Did we really need a new hearing simulation standard? Measuring headphones with the HF-HATS Type 5128"

** Since the work that Søren Jønsson and Lars Birger Nielsen do (and have done) flies under the radar for a consumer audience like ours, I wanted to point out that these gentlemen can be found cited in the bibliography of the IEC 60318-4 ("711") hearing simulator standard, which most headphone measurement enthusiasts here are quite familiar with (but that most have not actually read). (Click on the attachment below.)
 

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Sep 29, 2021 at 1:03 PM Post #3 of 28

ADUHF

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Thanks for the heads up on these, Jude. Unfortunately, I missed the registration deadline for both days (which was totally my fault). So if anyone (including HBK, Jude, etc.) has any followup info, details, impressions, etc. on some of these that they'd like to share with the rest of us, it would certainly be welcome.

I would particularly like to have heard Marty's talk on The Complete Idiot’s Guide to Basic Electroacoustic Measurement on Tuesday. :) And Soren and Lars presentations today, since I haven't heard anything by these folks before. But all of the above would've been interesting. Maybe HBK will post videos of some of these on their YT channel though after the conference is over?

Phew! CanJam, and a major HATS/measurement conference on the same days. There's just too much goin on in this hobby/field of study to keep track right now! :)
 
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Sep 29, 2021 at 4:38 PM Post #7 of 28

ADUHF

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Check your PMs.

Thank you again, Maya. No great surprises there (for anyone who's been paying fairly close attention to these subjects). So I'll reserve comment until after the other interested parties are ready to post/share something on this.
 
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Sep 30, 2021 at 5:01 PM Post #8 of 28

ADUHF

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Dr. Sean Olive has now posted a few images and comments from his Wednesday presentation on his Twitter feed. So I assume it's ok to comment on some of this now.

His and Harman's basic findings were that some headphones measured lower in the bass on the HBK 5128 rig than on the GRAS gear with custom pinna that they were using previously for their research. And there were also some differences in the response in the higher frequencies, which could perhaps be related to differences in the way the ear canal (and drum?) are simulated on the two rigs (my thought). (The 5128 uses a more anthropomorphic ear canal which is based on scanned human ear canals, whereas the GRAS uses a cylindrical coupler to simulate the ear canal response.) Therefore a somewhat different target is needed for the 5128 rig than the current GRAS-based Harman headphone target, to get comparable ratings on the same headphones.

Both of the above findings were not especially surprising from looking at the available measurements on the two rigs. Here are links to the related images he posted today on his Twitter account...

Comparison of DCA Stealth raw responses on GRAS45CA-10 & HBK 5128:
https://twitter.com/seanolive/status/1443643368525889538/photo/1

Preference ratings, and compensated response of AKG K701 on both rigs, based on GRAS Harman headphone target:
https://twitter.com/seanolive/status/1443644714176024577/photo/1

Preference rating, and compensated response of AKG K701 on both rigs, using GRAS target for GRAS measurement, and new (undisclosed) 5128 Harman target for 5128 measurement:
https://twitter.com/seanolive/status/1443647369925435393/photo/1

-----------------------------------​

Some more recent HBK 5128 measurements made by the SoundGuys, in case anyone's interested...

AKG K371
Audeze Mobius
AudioTechnica M40X
Beyerdynamic DT-770 (80-ohm)
Beyerdynamic DT-880 (250-ohm)
Bose NC 700
Bose QC 35-II
Sennheiser HD 280 Pro
Sennheiser HD 6XX
 
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Sep 30, 2021 at 11:02 PM Post #9 of 28

ADUHF

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Since this has now also come up on Dr. Olive's Twitter feed... Yes, it would probably not be that difficult to reverse engineer the target Harman is using for the 5128 measurements from some of the above data.

Would I recommend doing that?... No, I wouldn't. :) For a wide variety of reasons. But mostly because it isn't really necessary or beneficial imo.

If you want a target response curve for the 5128 measurements, there are other more constructive, and potentially much more accurate ways of doing it imo. Some of which I've already touched on or discussed in some other topics on this, and another popular audio science forum. And I'm happy to talk about them here too, if anyone cares, or is interested (as my time and energy permits)... Maybe in a different topic in Sound Science. (I was thinking about starting a new topic there anyway just to have a place to keep track of all of the 5128 measurements, since they are currently sort of scattered all over the place.)

The best and most accurate approach imo though (short of actually measuring the in-ear responses of some neutral loudspeakers in a typical room) is to use the average sound power responses of neutral loudspeakers as a target for the 5128 measurements, compensated with the 5128 diffuse field curve. This is something I've been working on for awhile now. And I'm fairly close to having a decent beta version. But not quite there yet (because I'm just, like, really slow at this stuff:) ). There is nothing to stop anyone else from trying a similar approach though. The sound power data for something like this is not that hard to find, if you know how to read a spinorama plot.

And the (correct) DF compensation curve for the 5128 (with head and torso) is on at least a few of Amir's ASR 5128 plots. And also in some of the HBK 5128 literature. So it's not hard to find either. (The DF curve on the SoundGuys site is not correct though.)

I've posted a few of my "pre-beta" versions of a 5128 target which are based on a similar approach in the K371 topic here though...

https://www.head-fi.org/threads/akg-k361-k371.916764/page-64#post-16587461

And those are probably not a bad starting point (with perhaps some of the add'l notes I've also included).

The only slight hitch with the sound power approach is that there are relatively few speakers (with built-in subs) that extend as deeply into the sub-bass as the Harman target. And those few speakers aren't necessarily typical of the sound of an "average" neutral loudspeaker in every respect, because they have somewhat better cross-over designs. So there are some nuances that come into play with this approach as well. (And none of this is particularly easy.)
 
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Oct 1, 2021 at 12:04 AM Post #10 of 28

ADUHF

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Still interested in hearing other impressions and any other info that anyone wishes to (and can safely) share from some of the other presentations in this event, from those who were able to participate. I'd love to hear some thoughts on the Idiots Guide to Measurements, just as an example. Cuz that sounds like more fun than some of the above. :)
 
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Oct 1, 2021 at 3:46 PM Post #11 of 28

Tonmeister2008

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Dr. Sean Olive has now posted a few images and comments from his Wednesday presentation on his Twitter feed. So I assume it's ok to comment on some of this now.

His and Harman's basic findings were that some headphones measured lower in the bass on the HBK 5128 rig than on the GRAS gear with custom pinna that they were using previously for their research. And there were also some differences in the response in the higher frequencies, which could perhaps be related to differences in the way the ear canal (and drum?) are simulated on the two rigs (my thought). (The 5128 uses a more anthropomorphic ear canal which is based on scanned human ear canals, whereas the GRAS uses a cylindrical coupler to simulate the ear canal response.) Therefore a somewhat different target is needed for the 5128 rig than the current GRAS-based Harman headphone target, to get comparable ratings on the same headphones.

Both of the above findings were not especially surprising from looking at the available measurements on the two rigs. Here are links to the related images he posted today on his Twitter account...

Comparison of DCA Stealth raw responses on GRAS45CA-10 & HBK 5128:
https://twitter.com/seanolive/status/1443643368525889538/photo/1

Preference ratings, and compensated response of AKG K701 on both rigs, based on GRAS Harman headphone target:
https://twitter.com/seanolive/status/1443644714176024577/photo/1

Preference rating, and compensated response of AKG K701 on both rigs, using GRAS target for GRAS measurement, and new (undisclosed) 5128 Harman target for 5128 measurement:
https://twitter.com/seanolive/status/1443647369925435393/photo/1

-----------------------------------​

Some more recent HBK 5128 measurements made by the SoundGuys, in case anyone's interested...

AKG K371
Audeze Mobius
AudioTechnica M40X
Beyerdynamic DT-770 (80-ohm)
Beyerdynamic DT-880 (250-ohm)
Bose NC 700
Bose QC 35-II
Sennheiser HD 280 Pro
Sennheiser HD 6XX
Your proposed method doesn't take into account that there are significant differences in bass between headphones measured on the 5128 vs the original GRAS45 CA -MOD pinnae.

So if you measure an calibrated loudspeaker in a room with a 5128 and then equalize an on-ear headphone to that curve you will have to add a considerable amount of bass to match the two curves because the shape of the head leads to headphone leakage effects as illustrated in this example below.

Moreover, you will have a produce a considerable about of controlled listening test data on headphones to convince me that the subjective ratings correlated with your target curve measured on a 5128.. Maybe the marketing department won't care -- but people who are fact-driven will want some scientific evidence.



1633117326806.png
 
Oct 1, 2021 at 3:48 PM Post #12 of 28

Tonmeister2008

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Your proposed method doesn't take into account that there are significant differences in bass between headphones measured on the 5128 vs the original GRAS45 CA -MOD pinnae.

So if you measure an calibrated loudspeaker in a room with a 5128 and then equalize an on-ear/around-ear headphone to that curve you will have to add a considerable amount of bass to match the two curves because the shape of the 5128 HATS leads to headphone leakage effects as illustrated in this example below.

Moreover, you will have a produce a considerable about of controlled listening test data on headphones to convince me that the subjective ratings correlate with the headphones measured on a 5128.. Maybe the headphone marketing department won't care about this data -- but people who are fact-driven will want some scientific evidence that it predicts what people hear and prefer.



1633117326806.png
 
Oct 2, 2021 at 5:26 PM Post #13 of 28

ADUHF

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Your proposed method doesn't take into account that there are significant differences in bass between headphones measured on the 5128 vs the original GRAS45 CA -MOD pinnae.

So if you measure an calibrated loudspeaker in a room with a 5128 and then equalize an on-ear headphone to that curve you will have to add a considerable amount of bass to match the two curves because the shape of the head leads to headphone leakage effects as illustrated in this example below.

Moreover, you will have a produce a considerable about of controlled listening test data on headphones to convince me that the subjective ratings correlated with your target curve measured on a 5128.. Maybe the marketing department won't care -- but people who are fact-driven will want some scientific evidence.

Thank you for the above reply, Dr. Olive.

I'm still looking over some of the info that you've posted here and on your Twitter account. But should have a few thoughts on the above before the weekend is out.

Re the differences in bass measurements between the 5128 and GRAS rigs, it would help if you could post some comparative FR data for some of the other headphones that were used for computing the correction curve for your new 5128 target. So that I and others could see a little better whether the responses on the DCA Stealth and AKG K701 shown above are fairly typical of the differences. Or in the more extreme column... if that's something that you can share. If you're not ready or prepared to put any more info out on this though, then I'd certainly understand and respect that.

Just to be clear, I have no interest personally in trying to extrapolate a 5128 target response curve from any of the above data. I'm actually very pleased with the results I've been getting using sound power and the 5128 diffuse field compensation curve for that. (And may also post a little more on that later.)

I'd also be curious to hear some of Jude's thoughts or impressions on the differences in response between the rigs, since he apparently encountered some similar discrepancies on some of his IEM measurements. I believe those turned out to be related more to differences in the design of the simulated ear canals though, rather than being related to poor coupling between the headphone and rig (ie leakage or seal problems). I think this video (which I suspect you've already seen, though maybe some others here haven't) explains a bit more about that...

 
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Oct 2, 2021 at 5:39 PM Post #14 of 28

ADUHF

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Here is also a higher resolution image of Jude's 5128 DCA Stealth measurement used in one of the above 5128/GRAS comparisons, in case anyone wishes to give the plot a somewhat closer look. This was posted in another topic here on Head-Fi, so I hope Jude doesn't mind the image simply being reposted to this topic.

11564371.jpg


This is the unsmoothed version of the graph, btw. So it shows a little more detail in the treble.
 
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Oct 2, 2021 at 10:47 PM Post #15 of 28
Thank you for the above reply, Dr. Olive.

I'm still looking over some of the info that you've posted here and on your Twitter account. But should have a few thoughts on the above before the weekend is out.

Re the differences in bass measurements between the 5128 and GRAS rigs, it would help if you could post some comparative FR data for some of the other headphones that were used for computing the correction curve for your new 5128 target. So that I and others could see a little better whether the responses on the DCA Stealth and AKG K701 shown above are fairly typical of the differences. Or in the more extreme column... if that's something that you can share. If you're not ready or prepared to put any more info out on this though, then I'd certainly understand.

Just to be clear, I have no interest personally in trying to extrapolate a 5128 target response curve from any of the above data. I'm actually very pleased with the results I've been getting using sound power and the 5128 diffuse field compensation curve for that. (And may also post a little more on that later.)

I'd also be curious to hear some of Jude's thoughts or impressions on the differences in response between the rigs, since he apparently encountered some similar discrepancies on some of his IEM measurements. I believe those turned out to be related more to differences in the design of the simulated ear canals though, rather than being related to poor coupling between the headphone and rig (ie leakage or seal problems). I think this video (which I suspect you've already seen, though maybe some others here haven't) explains a bit more about that...


Sure, @ADUHF, I'll offer some detailed thoughts when I'm back in the office. (I'm on a much-needed vacation.)


Here is also a higher resolution image of Jude's 5128 DCA Stealth measurement used in one of the above 5128/GRAS comparisons, in case anyone wishes to give the plot a somewhat closer look. This was posted in another topic here on Head-Fi, so I hope Jude doesn't mind the image simply being reposted to this topic.

11564371.jpg


This is the unsmoothed version of the graph, btw. So it shows a little more detail in the treble.

No, of course I don't mind you sharing this here.
 

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