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Electrostatic Headphone Measurements


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We should have some KGSSHV's up and running in a few months (I'm going to build a few) so a TOTL SS amp would be available for testing then. Still the KGSSHV is more of an effort to approach the Blue

cobra_kai, it's funny because I had the exact same thought process... When I failed to run Octave on either platforms, I looked into scypi since this actually might also become useful for my work. I s

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I wonder if HeadRoom still has their Orpheus cans? I'll check.

Thanks for the kudos guys, it was great fun.

I certainly will continue to measure estats as long as I can. Alex will need his amp back someday soon. I need to tell you that from Oct 11-21 the chamber will be in use doing the last burn-in test while I go to RMAF. I have mentioned to people to get their estats in for measure prior to that so I can send the amp back to Alex.

More than happy to continue on after RMAF, but that's Alex' call.

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Tyll, as long as cans keep coming, I don't mind it one bit. I really won't have time to do much listening until the 1st week of November, which is when I will be done with a personal project I am devoting most of my free time to (and I HAVE to do... it's kinda now or never for this). So, yea, 1st week of November is fine for me.

Of course, if the stat measurements experiment ends sooner, I'll take the gear back. But as I said, a month more won't affect me the least bit. Kinda have some other things to worry about...

...and I just like the fact all my gear is getting measured... hehe. So, if you can get some cans to measure between Oct 21st and the first days of November, it's ok with me. If not, well, send the babies back. I don't contribute much knowledge-wise (and can't), and this is the only way I know of how to give something back to not only the community, but the hobby itself. Music makes my life happy. I cannot tell you the times that something happens, and my memory, like a jukebox, brings a song to mind. As family members, friends, and a cute girlfriend here and there have stated, I have a crazy hobby/obsession here... but it's a damn healthy one.

If the stats measurement experiment is to continue, let's keep as many variables constant to make sure comparisons are as controlled as can be.

Edited by screaming oranges
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Awesome work Tyll, your efforts are much appreciated! Thank you to those that contributed gear as well. What an excellent community.

If I were stateside, I would love to contribute to the project and send over my SRM-717 or 323S to compare with the Blue Hawaii. Shipping to and from Japan would be brutal though.

I and likely quite a few others would be very interested to see how the 007s and 009s perform on a Stax amp and what differences show up in the measurements in comparison with the Blue Hawaii. There already is a bit of discussion on whether the 009s are $5000 phones or a $10,000 system. I feel perfectly content with the two amps I have but would like to see if the measurements reveal any deficiencies.

TMoney, if there is a Stax amp not too far from Tyll, that might be a reason for him to hang on to your 009s a little bit longer.

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Just a feeling atm but I doubt you'll see drastic changes on the SPL response, simply because differences between amps are of the order of nuances which would fall within repeatability accuracy of the tests... Not saying you can't hear it, it's just that our hearing is so much more accute than visible differences between 2 graphs. At least for SPL / impulse / step response graphs...

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Just a feeling atm but I doubt you'll see drastic changes on the SPL response, simply because differences between amps are of the order of nuances which would fall within repeatability accuracy of the tests... Not saying you can't hear it, it's just that our hearing is so much more accute than visible differences between 2 graphs. At least for SPL / impulse / step response graphs...

Given some relatively huge differences I've heard between STAX amps such as the SRM323 and KGSS/BHSE, I would be very curious about non-linear or even just harmonic distortion, especially at the low frequencies below 150Hz. The electrostatics do work very differently from dynamic drivers.

I just very quickly played a 50Hz tone at 90db on the SR009 (out of the SRM323), and I see large spikes -30db at the 2nd and 3rd harmonics on the RTA. I'm too lazy to calculate what this comes out to in terms of THD, but it seems rather high compared to Tyll's measurements of the 009 out of the BHSE.

Edited by purrin
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Marv, I agree that thd and such non-linearity monitoring graphs have more likely to show the differences. Actually, having compared te stock 323s and 727a amps driving the 009, I really thought I could hear significant differences in the lower register. It was with unfamiliar source and material, at a noisy store, so I guess the differences were not subtle...

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Hi arnaud, purrin

Well I have already stated my views on distortion and its measurement, although mostly regarding the phones rather than the amplifier. I believe IMD testing is necessary. I would be surprised if Stax got it that wrong but then I was so very surprised when Revox got it wrong. The multitone test that Linkwitz is so fond of might be interesting even when applied to an amplifier.

Of course, the dummy load for testing is just a capacitor. The difference between a simple capacitor and the phones is quite small. If people were really concerned and wanted to use the phones themselves as loads, turning off the bias voltage would prevent damage to the phones.

'T'll be interesting.

Regards,

Bob

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Tyll, this is EXCELLENT! Your measurements are really of amazing consistency (the 2 SR009). I was shocked to see the differences between the Omega2 Mk1 and 2.5. Seeing this and comparing to the 009, I think my pair (a late Mk2 e.g. SZ2 series) is closer to the mk2.5 than mk1. The mid bass hump / lack of infra-bass and warm signature with just a treble spike makes a lot of sense as these are basically the things I hear as large improvements out of the 009. Oppositely, Birgir is not noticing such drastic improvement going from his Omega 2 to the 009 and I guess it's because he worked out how to get Omega 2 to sound the best (using mk1 drivers, closing the vent, adjusting the ear pad depth and so forth...).

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Oh, and one other thing I just realized is that we can actually see the influence of acoustic resonances in the earcups and the effective damping by looking at the isolation graph. In particular, I believe the negative sound isolation (so an amplification of the signal when wearing the headphone) is a sign of a resonance with peak amplitude at the microphone location. Interestingly, the mk2.5 has very peculiar isolation performance which probably gives away the frequency at which the vent is tuned. I am quite interested in trying a few things out through simulation now wink.png

Edit: humm, why does the sr003 show the exact same negative noise isolation as the other headphones? Isn't this result just an SPL difference without/with the headphone in place averaged over a few speaker locations in the test cell? Or maybe the FRF is also going through this "independent of direction" equalization hence I am just seeing the shape of that filter? It should cancel out in the SPL difference though, humm...

PPS: The isolation curve is SPL_withheadphone - SPL_without ? I am confused because normally, the term noise reduction implies "reduction of SPL due to the device" hence a positive value means there is attenuation. But your graphs are plotted the other way around no? (-10dB means that SPL went down by 10dB) huh.png

Edited by arnaud
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There is something "off" about the SZ3 units and the measurements just confirm it. I ripped mine apart last week, installed Mk1 drivers and the sound is completely different so Stax did this on purpose by messing with the drivers.

Tyll, this is EXCELLENT! Your measurements are really of amazing consistency (the 2 SR009). I was shocked to see the differences between the Omega2 Mk1 and 2.5. Seeing this and comparing to the 009, I think my pair (a late Mk2 e.g. SZ2 series) is closer to the mk2.5 than mk1. The mid bass hump / lack of infra-bass and warm signature with just a treble spike makes a lot of sense as these are basically the things I hear as large improvements out of the 009. Oppositely, Birgir is not noticing such drastic improvement going from his Omega 2 to the 009 and I guess it's because he worked out how to get Omega 2 to sound the best (using mk1 drivers, closing the vent, adjusting the ear pad depth and so forth...).

Well there isn't a port on the Mk1 so that is a non issue but the devil is indeed in the details with the 007. Getting the arcs bent just right and also getting the earpads angled properly is all crucial to getting most out of them. Also, if the earpads have ever been removed it is vital to install them correctly. Same deal on replacing them once the foam has perished.

As it stands now the 007Mk1 does things that the 009 just can't do, and vice versa for that matter, but the 007Mk1 wins out in my book by simply being more natural sounding.

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10kHz @ 50% humidity attenuates 4dB over 30 meters, while 100Hz has essentially none; over 3 meters which is a more realistic listening room distance the difference is inconsiquential. So there is high frequency roll-off, but it's quite a small number. My understanding is that most of the percieved HF roll-off in listening rooms is from higher absorption of the highs in furnature or carpet in the first reflection and reverberant sound.

This article shows significantly more high frequency roll-off http://www.regonaudio.com/Records%20and%20Reality.html

Here is a quote:

"Now you see why concert hall response is at least potentially flat across the midrange, but tends to roll off as soon as air absorption becomes a significant factor, for around 4 kHz up. There just is not much higher frequency energy around in the reverberant soundfield because, as the sound bounces around the hall, the air soaks up the highs even if the walls don't. "

Overall it gives a good discussion of such matters and some interesting measurements of concert hall acoustics.

Getting back to what should be the right high frequency response of headphones, the other part of my observation was that many recordings seem bright. For me this is shown by a comparison of recordings with the old Telarcs which often made a ppoint of using simple 2 channel mic setups with no equalization and no highlighting of individual instruments with near mics such that hf attenuiation hasn't kicked in. To my ear these sound pretty good with most phones, but often somewhat mushy through speakers.

As well, as the above article notes, in concert hall listening the sound gets even less bright because ambience and reverberation become a bigger factor. One of the halls gives what looks like a 25+ dB drop at 8kHz. for sound measured at the loge level, which would be the first balcony. The other hall shows about 10 dB down but doesn't state where the sound was measured.

Which leads to my last point. One of the big differences in headphone sound vs live and evens peaker sound is the balance of direct vs reverberant sound. In halls, reverberant sound is quite prominent. Even with speakers at normal distances (not near-field set-ups) there is still going to be a lot of reverberant sound. However, most phones shoot their sound right down the ear canal at the ear drum with virtualy no added reverberation. When you also factor in the prevelance of bright recordings, I believe we are getting a an excessively dry (i.e. unreverberant) and bright sound (i.e. too much highs) out of most phones.

Probably this concern comes from spending so much of my listening time with Stax Sigmas, which try to give something of the reverberant field. I am not suggesting they do this perfectly but they are listenable with a wide range of even badly recorded material . I think this is because they mount the drivers away and ahead of the ears and create a sort of faux reverberation in the earcups.

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