Electrostatic Headphone Measurements

[nnotis]

Yes, I saw those when he posted them. But I wonder how consistent the old measurements are with the new ones Tyll just did?

[manaox2]

Spritzer, were there any perceived audible differences with the early version mk1s and the later version with the slightly different frame? I'm wondering, didn't realize there was any differences other the the carbon fiber box. I own the earlier version.

[deepak]

Really nice work Tyll. Looking forward to your subjective review of the SR-009

[monsieurguzel]

That's it, everybody is gonna ditch their Stax setups in favor of the HD800s!!

[anetode]

Very impressed by both the 007 & the 009s in the measurements. As purrin mentioned, very low distortion in the bass. This correlates well with what I always thought was that magic trick the 007 played with digging so much detail out of the bottom end.

The decay graphs show some inconsistencies between the L&R driver pairings, it's a little troubling to think that some Omega drivers might have a random ringing in the treble.

On the impulse response graph, it seems that the 009 overshoots quite a bit further than the 007 when coming back, visible also on the square wave responses.

Awesome work, Tyll. Are you up for receiving the 404LEs to join the fray?

[arnaud]

Edit 9/24: CSD and FRF graphs are now equalized to compensate for the dummy head response (not sure for which heading, does not appear to be diffuse field, Tyll?)

That's it, everybody is gonna ditch their Stax setups in favor of the HD800s!!

Hehe, I agree that interpreting these results appropriately is no easy feast... The data varies also widely across test setups, maybe because I am processing non-equalized data. As Purrin said earlier, it really only makes sense to compare curves from the same test setup like the most recent 007/009 comparisons and the following...

@nnotis: I have Audeze LC2r2 data from Tyll as well so I could generate the comparisons. It gets a bit crowded when comparing all 4 together though...

All 4 headphones:

HD800 with SR009:

HD800 with LCD2r2:

Edited September 24, 2011 by arnaud

[arnaud]

I'm confused, the shape of the frame tells me your left pic is the 007A, yet the gold color of the electrode tells me the right pic is the 007A.

Here's a pic of my 007A (late SZ2):

No closeup that I could find and the drivers are packed away in storage. The stators resemble a chain link fence so the copper is woven together.

There is the unofficial Stax site in Japan but they rarely pull anything apart for diagnoses. It takes somebody as insane as me to rip this stuff apart...

Nothing wrong with linking to the nearest alternative but Stax has changed the internal design quite a bit. So the lineage is like this:

SR-007 Mk1 early version (different driver frame plus some minor material changes, older style carbon fiber box),

SR-007 Mk1 late version (the version tested here and the most common of the Mk1's, S/N either 7xxxx or SZ1-xxxx),

SR-007A/SR-007Mk2 (S/N SZ2-xxxx, Stax change the earpads, how they sit and introduce a port to the earcups. Sound is a mixed bag depending on fit but can be fixed to sound pretty much like the Mk1)

SR-007A/SR-007Mk2 (S/N SZ3-xxxx, often called the Mk2.5, Stax supposedly change the diaphragm which results in a much more forward sound signature)

Now you should point out that these are indeed SR-007 Mk1's just for the sake of clarity.

While we are on the subject, does anybody want to play "spot the difference" between the earliest and the latest SR-007 drivers?

[Dreadhead]

Tyll, Thanks for the 800 data. Fun times. I'll have to see if I can do anything fun with it soon. Looks like I'll be able to take the 800s and turn them into a easy facsimile of the 007s or 009s with very little pain. The joys of IRF.

Now all I need is a way to do that without having to go through a PC. I think there is an IRF plugin for SlimDevices but that's a lot of work... and well I love the 800s.

[arnaud]

The decay graphs show some inconsistencies between the L&R driver pairings, it's a little troubling to think that some Omega drivers might have a random ringing in the treble.

Not sure it explains everything but there is quite a bit of variability with the fit and - as far as I understand Tyll's methodology - the decay graphs come from a single position measurement (MLS test) of the impulse response. See below a reprocess of Tyll's 009 FRF data:

[screaming oranges]

Since I have no stat amp at home right now I cannot do anything with the 009 that I bought (which will ship to Tyll once Andy gets it). Wouldn't this be a good opportunity to do the below?

1) Test another 009 and see how much (if any) deviation there is from the 1st 009 he tested.

2) Test "burn-in" as it applies to the 009 (if any)

In regards to burn-in (or break-in), though, I suppose that this would mean that -in order to maintain as much control of the experiment as possible- the headphones shouldn't be moved from their place once the "sweet spot" on the dummy head has been found. But this isn't feasible, I'd say, because other headphones are constantly being measured to keep the website flowing... I don't know... but I'm just throwing suggestions out there since we might not get another opportunity like this any time soon.

Edited September 22, 2011 by screaming oranges

[Nevod]

While we are on the subject, does anybody want to play "spot the difference" between the earliest and the latest SR-007 drivers?

Well, driver on the left has a large port around contacts. IIRC, this port is covered by cable attachment, I've seen some pics.. Driver on the right has the area covered with two intentional ports left.

Stator material is different, but it's hard to guess how just from the picture.

Hi Purrin,

I had a look at your distortion plots of the ESP950s. They are most interesting.

First, a look at the harmonic distortion measurements. Fortunately you show the spectral distribution of the distortion rather than just the THD. I find it interesting that the second harmonic distortion is higher than the third. The theory of push-pull ES consistently shows that the even harmonics should be very low, much lower than the third (actually, theoretically zero). There is a caveat, this cancellation of the even harmonics requires a high diaphragm resistance (the usual quoted value is 10exp9 per square or above, preferably 10exp11 per square). So either there is a problem with the testing <sorry>, Koss has got the diaphragm resistance wrong, or there is some other factor in play that I don't understand.

I believe (as in, I don't have anything to back up) that this could also be due to damping. To cancel even harmonics, you need symmetry, and usually, there is no symmetry in headphones - outer side radiates freely into air, inner is loaded by a sealed cavity. Granted, backside is usually damped, but it is still nowhere near symmetric. To obtain symmetry, one would need ports on the inside, and the ports should provide resistance equal to backside resistance. To make this controlled you'd also need well sealing earcups..

And, I don't want to steal any discussion, but..What really bugs me is LCD-2s square wave and impulse responces - they look near perfect. Minimum overshoot and flat zones are really flat on square wave (though I guess that en even more mighty amplifier for Staxes would correct that). But impulse responce seems to be much better than any other headphone, regardless of technology - most of them dip instead of peaking on the impulse, while LCD-2s plot looks like "it's just as it should be". Makes wonder about the construction of the driver and damping.. Or, reciprocally, why all other phones, Stax included, dip on the impulse.

[arnaud]

Unfortunately the diaphragms do not display the pure planar behaviour that we intuitively believe should occur. Streng proved it mathematically using Green's function (Memory?) and then validated the proof with measurements on a test speaker - I must really find a copy of his 4 papers. From memory the modal breakup was somewhat different to the rigid piston model and was entirely of the annular ring form, I vagely remember that the annular nodes actually swept across the diaphragm as the excitation frequency changed. The breakup resulted in localised 'movement of air’ parallel to the diaphragm from the 'in phase' part of the diaphragm to the 'out of phase' part of the diaphragm. One of the outcomes of the work was that a relatively small amount of damping material, close to the diaphragm, 'disrupted the air flow' and damped out the modal breakup - this may have consequences for people who like to remove damping in their ES headphones or who build ES speakers without damping.

Now, if the diaphragm does breakup, the deflection will increase, the inherant non-linearity will increase, the distortion will increase, thus my reference to using IMD (and the not mentioned - THD) to indicate possible membrane resonance. Here is a possible avenue to explore, if a CSD shows a problem resonance and a distortion plot shows a peak in distorion at the same frequency, does this indicate that there is a high probability that the resonance is from the diaphragm rather than elsewhere in the headphone - just a thought, could be wrong.

Hi Rob,

Thank you for your response. I need to think more about this IMD stuff, I guess my work skews my vision as I am systematically modeling linear systems .

In regards to diaphragm "break-up" modes, it's actually Bessel functions of first kind in the case of circular membranes ( http://en.wikipedia.org/wiki/Vibrations_of_a_circular_drum ). Green's function is a completely different wolf and I won't get to it (partly because I barely understand it lol). Probably break-up naming is not appropriate here because there's no rigid body motion of the diaphragm in the case of tensioned membrane vibration (as opposed to the piston motion of an electrodynamic cone before so-called breakup modes catch on).

As for wave cancellation for higher order modes, again it's not that simple when you are looking at headphones because these modes actually radiate energy in the near acoustic field (it just happens to not propagate efficiently to the far field due to the +/- cancellation effect). Anyhow, I am about to create a simplified numerical model of the SR-009 to investigate this as well as the effect of spatially distributed forcing on the diaphragm and possibly to estimate acoustic resonances in the ear-cup. If only someone had some measurement of only the electrode to estimate the natural frequencies of the tensioned diaphragm ......

[Robbo1802]

Hi arnaud,

Some references,

The Streng papers and a copy of the Baxandall ES chapters out of Borwick (1st Edition by the looks)

http://quadesl.nl/en/tech-corner.html

The site is very interesting, but then I did have some ESL57s so I am probably more interested than most.

A Download of a late JAES paper on electrostatics

http://lahorde.is.fr...USTICS_HIFI.PDF

A search for documents on the one thing site,shows some the original Wireless World papers

http://www.google.co...=utf-8&oe=utf-8

Linkwitz site on distortion in woofers

http://www.linkwitzl...m/frontiers.htm

I found this page on Linkwitz looking for a reference on multitone testing of loudspeakers. But Linkwitz's work has always appealed to me

A site with a lot of papers on distortion in loudspeakers

http://www.klippel.d...ure/papers.html

Although concerned with conventional speakers, the general discussion is still quite useful.

Linkwitz's use of a 5 tone multitone test, is not a standard method but I find it quite illustrative of how even relatively simple signals get very complex very quickly as the non-linearities create harmonics and sidebands. Perhaps Tyll could took at this as it is well within the capabilities of his test rig. (Ooops, Tyll, I am sorry for referring to you in the third person.) Most of the dynamic phones show the classic rising distortion in bass caused by the increase in deflection and thus non-linearity. How would they compare to say the ES and magnetic planar headphones under this test. The assessment would be necessarilly subjective, along the lines of messy/verymessy/clean etc.

As to the high order modes, I will stop using the term 'breakup' although I cannot think of another descriptive term that applies. I did remember the Bessel functions but Green's always stuck in my head because I had so much trouble with it, I would not even attempt it now. In any case, he uses Green's function in the "Sound Radiation from a Vibrating Membrane" paper - my memory is not so bad after all. In the papers, he demonstrates mathematically that almost all the cancellation occurs within a Z axis of .25 of the radius of the diaphragm, so say within 15mm of a ES headphone.

Ahhh, linear systems, I remember the Quote of Stanislaw Ulam : "Using a term like nonlinear science is like referring to the bulk of zoology as the study of non-elephant animals.” >>>)))

See ya,

Bob

Edited September 22, 2011 by Robbo1802

[edstrelow]

Frankly, I'm a n00b re:Stax. I just linked to the closest thing I could find on the Stax site. I'll be happy to change the lnk if there's a better place to go.

Given that there appear to be changes in both the 007 and 009 during manufacture, It could be useful to have serial numbers of both phones.

[arnaud]

Hi arnaud,

Some references,

The Streng papers and a copy of the Baxandall ES chapters out of Borwick (1st Edition by the looks)

http://quadesl.nl/en/tech-corner.html

The site is very interesting, but then I did have some ESL57s so I am probably more interested than most.

A Download of a late JAES paper on electrostatics

http://lahorde.is.fr...USTICS_HIFI.PDF

A search for documents on the one thing site,shows some the original Wireless World papers

http://www.google.co...=utf-8&oe=utf-8

Linkwitz site on distortion in woofers

http://www.linkwitzl...m/frontiers.htm

I found this page on Linkwitz looking for a reference on multitone testing of loudspeakers. But Linkwitz's work has always appealed to me

A site with a lot of papers on distortion in loudspeakers

http://www.klippel.d...ure/papers.html

Although concerned with conventional speakers, the general discussion is still quite useful.

Linkwitz's use of a 5 tone multitone test, is not a standard method but I find it quite illustrative of how even relatively simple signals get very complex very quickly as the non-linearities create harmonics and sidebands. Perhaps Tyll could took at this as it is well within the capabilities of his test rig. (Ooops, Tyll, I am sorry for referring to you in the third person.) Most of the dynamic phones show the classic rising distortion in bass caused by the increase in deflection and thus non-linearity. How would they compare to say the ES and magnetic planar headphones under this test. The assessment would be necessarilly subjective, along the lines of messy/verymessy/clean etc.

As to the high order modes, I will stop using the term 'breakup' although I cannot think of another descriptive term that applies. I did remember the Bessel functions but Green's always stuck in my head because I had so much trouble with it, I would not even attempt it now. In any case, he uses Green's function in the "Sound Radiation from a Vibrating Membrane" paper - my memory is not so bad after all. In the papers, he demonstrates mathematically that almost all the cancellation occurs within a Z axis of .25 of the radius of the diaphragm, so say within 15mm of a ES headphone.

Ahhh, linear systems, I remember the Quote of Stanislaw Ulam : "Using a term like nonlinear science is like referring to the bulk of zoology as the study of non-elephant animals.” >>>)))

See ya,

Bob

Thanks for looking these up Bob, I now remember I also have a reference on loudspeaker design (Van Dickason or some similar name) which may have some info. Will look these up.

Green's function is used to solve boundary integral problems so indeed this may have been used to simulate the radiation of baffled plate. The "acoustic near field" is defined as ka<<1 with a the source dimension and k the acoustic wavenumber (2 pi / acoustic wavelength). So, actually, near and far field is a function of frequency. Another thing is that the paper you reference most like looked at a baffled source radiating in free field which again is very different from an small ear cup.

But, anyhow, I have been proved to be very wrong several times when guessing about headphone behavior so best is to simply simulate it, and I have the luxury to do that. The software I use has a so called "Boundary Element Method" formulation which is essentially making use of acoustic's green function for solving a boundary integral problem (radiation of surface / diffraction in an acoustics domain), albeit numerically not analytically (so any shape can be solved not just simplified ones). It turns out it's much more efficient to use traditional Finite Element Method though but I am investigating both ways at the moment ...

Humm, not totally relevant discussion for this thread, sooner or later hell is gonna fall on us

arnaud

[Tyll Hertsens]

This thread humbles me.

Great plots, Arnaud. The HD-800 looks very good, but damn, the LCD-2 looks every bit as good, from what I can tell.

I did get a chance to listen to the estats yesterday. Thought the 009 was spectacularly fast and articulate without being edgy or dry. The bass was very good, not LCD-2 good, but the best I've heard on a Stax. Basically a GREAT headphone listening experience. The 007 seemed dry, thin, and grainy in comparison with the 009.

Thanks so much for your help with the gear guys. Assuming y'all think the measurements are what's needed, I'm willing to receive more headphones. It needs to happen quickly, or we're going to run into RMAF. I will be doing the (hopefully) last breaking test with a Q701 and it's going to tie the chamber up for two weeks starting Oct 11. Alex has said I can hang on to his amp for that long, but I'd rather try to get through the tests quickly so that his gear is back to him sooner rather than later. After all, he's got a brand new pair of 009s to melt his mind with.

Thanks guys. Please PM me before you send gear so I know it's coming.

[Nevod]

arnaud,

The normalised FR plots make me think how far headphones still are from real flat responce..

[spritzer]

Spritzer, were there any perceived audible differences with the early version mk1s and the later version with the slightly different frame? I'm wondering, didn't realize there was any differences other the the carbon fiber box. I own the earlier version.

To my ears they always sounded pretty much the same.

That's it, everybody is gonna ditch their Stax setups in favor of the HD800s!!

I've spent a lot of time with the HD800 and I think I'll keep my Stax... I do think it is time I tried my new M3 amp with the HD800 so a trip to the Sennheiser dealer is in order.

I'm confused, the shape of the frame tells me your left pic is the 007A, yet the gold color of the electrode tells me the right pic is the 007A.

Here's a pic of my 007A (late SZ2):

The SR-007Mk1 also uses that frame but those drivers are from a early Mk1 and the SZ3 Mk2.

[TMoney]

I did get a chance to listen to the estats yesterday. Thought the 009 was spectacularly fast and articulate without being edgy or dry. The bass was very good, not LCD-2 good, but the best I've heard on a Stax. Basically a GREAT headphone listening experience. The 007 seemed dry, thin, and grainy in comparison with the 009.

Wonderful work so far, Tyll. Can't wait to see your full written review.

I'm hoping to see a bit of a comparison between the current contenders for King of the "Headphone" Hill if you have the time to work one in to your review. Given that the 007s, 009s, LCD2s and HD800s all seem to measure exceptionally well, I'd be particularly interested to hear any thoughts you might have on how they compare to each other in both measurements and subjective impressions. In particular, I love to read your explanations of how your subjective impressions match up (or contrast with) with the objective measurement data.

As others here have mentioned, to the untrained eye it looks like the 007 is outperforming the 009 on the two square wave tests and in impulse response tests you posted earlier this week. I would think the greater overshoots by the 009 would give it an edgier sound than the 007, yet in your subjective impressions the opposite is true. I'm wondering something similar about the LCD-2s as they seem (again to the untrained eye) to have the best square and impulse measurements of any headphones you've tested. Wouldn't that suggest that they should seem faster than the Stax? I've personally found the opposite to be true, but I'd love to hear your 2 cents. Any explanation you could give would be really helpful in the context of the current review as well as in interpreting your future data.

I've been listening exclusively to the HD800s since I sent the 009s in to you. Could you include them in a compare and contrast section if you end up writing one? While I almost always found myself reaching for the 009s over the HD800s when both were here, I'm impressed by how well the HD800s have carried the load while the 009s have been away.

Again, many thanks! Can't wait to see more 'stat measurements in the future.

Edited September 22, 2011 by TMoney

[Tyll Hertsens]

^^It is interesting, eh?

Maybe the math geeks and engineers can chime in on this one, but if you look at the impulse response of the 009, just prior to the impulse there's some pre-ring. I'm wondering if there is something going on that, with very fast headphones, causes artiacts that aren't exactly representative of what's actually going on. The first spike on the HD 800 also is very fast and has significant spike and undershoot. Also, we have to remember that while the FR plots are compensated, the square waves are not, so what appears to be an error (big initial spike) may actually be desirable. Dunno. Love to hear some thoughts.

One thing to note on the 007 vs 009 is that there's a significant rise in the treble at 10kHz on the 007 that's not there on the 009. Also there's more noise in the long tail of the 007 impulse response.

Another thought that's come to mind is that when we're talking about splitting hairs with great cans, hte ear may be better at identifying the character of the headphone than the measurement system. Measurements slice the apple in numerous ways for a good looksee, but it's nothing like biting into it for a taste.

[morphsci]

...The 007 seemed dry, thin, and grainy in comparison with the 009.

Well somebody has to say it so I will. Even as a comparative statement I find this statement strange. Though I do have some problems with the 007 MK I, those particular attributes would never enter the description.

[Tyll Hertsens]

It was a limited listen ... maybe it was my expectations? I'll do more serious listening today.

What problems do you hear?

[spritzer]

Yeah, doesn't sound like a SR-007 to me. Same is true about statements that the SR-007 is less smooth than the SR-009, not true to these ears unless you are listening at whisper quiet levels. The SR-007's crowning achievement is to remain smooth even at silly levels. Push the SR-009 just a little bit and they bite, hard.

[grawk]

tyll's definitely a quiet listener, tho.

[Dreadhead]

Arnaud how did you generate those comparison plots for frequency response? I am using Tyll's data and getting something that looks different. I checked it 3 times.