Electrostatic Headphone Measurements

[spritzer]

That's how the Stax are wired too, + signal goes to the stator closest to the ear. The Sigma has this flipped but then again the signal is reflected 90° inside the earcup.

[justin]

did you measure the HE90 with that BHSE?

[justin]

birgir, is it possible that the pin-out of the stax jack we've been using for years has the polarity reversed?

[Tyll Hertsens]

did you measure the HE90 with that BHSE?

Yup.

[justin]

where are the measurements for that one?

[HeadphoneAddict]

Yup. It could be something as simple as the o-ring not seated properly. Wouldn't surprise me given the sub-par service Sennheiser has in the US.

I'm not sure I have the skills to rectify the situation - what you you recommend if neither I nor Sennheiser can do the job right?

Edited November 9, 2011 by HeadphoneAddict

[n3rdling]

Birgir can say for sure, but I think fixing the o rings should be pretty easy to do. Just take out a few screws, fix o rings, and rescrew. The main issue is making sure you don't get dust in the drivers and don't strip the screws.

[HeadphoneAddict]

Birgir can say for sure, but I think fixing the o rings should be pretty easy to do. Just take out a few screws, fix o rings, and rescrew. The main issue is making sure you don't get dust in the drivers and don't strip the screws.

What would have to happen to get get dust in the driver? Isn't there a dust barrier that's integral with the driver? You mean don't rip it, or does the barrier come off when you open the headphone?

[spritzer]

birgir, is it possible that the pin-out of the stax jack we've been using for years has the polarity reversed?

I just checked the SRM-717, 007t, T1, and T2 schematics (I'm nothing if not thorough... ) and the pinout we use is indeed correct. L+ on the top pin, R+ to the right of it seen from the front.

I'm not sure I have the skills to rectify the situation - what you you recommend if neither I nor Sennheiser can do the job right?

Sennheiser uses the service manual when rebuilding these things and it doesn't cover just how important it is to seat the o-rings properly. I'd guess that one doesn't sit correctly in the grove or the driver is just out of spec.

What would have to happen to get get dust in the driver? Isn't there a dust barrier that's integral with the driver? You mean don't rip it, or does the barrier come off when you open the headphone?

The dust barrier on the back of the drivers isn't a solid plastic sheet but rather woven nylon. It can let small dust particles through which are large enough to cause issues.

[Tyll Hertsens]

I just checked the SRM-717, 007t, T1, and T2 schematics (I'm nothing if not thorough... ) and the pinout we use is indeed correct. L+ on the top pin, R+ to the right of it seen from the front.

Well, I guess I'm going to have to do a little checking on my balanced outs or sumpin'. :/

[spritzer]

The BH is non-inverting so something is up...

[TMoney]

where are the measurements for that one?

I just went looking for the HE90 measurements as well. Were they ever publicly posted?

[edstrelow]

OMG - the Sigma response looks like a roller coaster ride and the 30 Hz square wave isn't. Not sure if this is the Sigma normal bias or the Sigma/404. Measurements bad, sound good.

Supposedly Tyll was sent a Sigma/404. But when dealing with a modfied phone, reporting the serial number does not actually identify the phone anymore since it is no longer a stock model. All the Sigma/404's started life as either Sigma Pros or low bias Sigmas so their SN is meangingless.

Actually John, the frequency response looks fairly good to me. It shows a marked but not extreme emphasis between 100 and 1kHz . +/- 5 dB is usually considered good with speakers and most of this curve is within these parameters. It's up 5 dB from 0dB, and very flat, between 100 and 1kHz, drops about 10 dB from 0 dB between1kHz and 2 kHz, and then gradually returns to -5. dB at 2kHhz, with a brief dip at 4kHz, to roll off again at 15kHz. Of course few of the men reading this forum can hear above this anyway. I think this treble is pretty good and these phones are the Sigma/404 since I suspect the low bias model would show a much more serious decline in treble. As regards bass, it is only 5dB down at 50 Hz and them falls off more.

The measurements shown for a regular 404 are almost flat down to 10 Hz. I have always thought the 404 had a great bass response, in fact it looks a better than the 007 (SZ3 model), slightly better than the 007 Mk1 and maybe a tad better than the 009. I am not surprised that the Sigma/404 can't match the original 404 because it is not a sealed phone like the regular 404. I wouldn't describe any of the Sigmas as having really deep bass, but - 5 dB at 50 Hz gives an impression of adequate bass.

The square wave responses in all of these measurements have been hard to decipher. In other people's reports I have seen showing square wave responses the electrical signal is shown superimposed over the measured response making it a lot easier to interpret what one is seeing, especially to see if there is any time lag. That one can't tell here. Still, the 300 Hz square wave looks very good.

I am assuming that part of the mess shown at 30Hz is because the Sigmas are wired out-of phase, so the square wave response ends up being reversed. It should also be remembered that the frequency response shows that the Sigma's are about 15 dB down at 30 Hz (from 0 dB) so I am not sure that you will measure much here other than an initial impulse. As well, a previous commentator noted that there appeared to be an electrical anomaly in some of the square wave measurements. I don't know if that issue was ever resolved.

So the measured frequency response pretty much matches my perception of these phones. The tonal balance emphasises the lower mid/upper bass region (i.e. elevated between 100 and 1kHz). Deep bass i.e. below 50 Hz and trble above 1kHz could be better.

Should the Sigmas Unique Driver Location Require a Different HTRF?

However and this a big HOWEVER, if you look at the difference between the corrected and uncorrected measurements, the tonal balance I describe in the above paragraph is all the result of the "corrections." I.e. the uncorrected response for these phones is much flatter. Essentially the corrections apply a HRTF frequency adjustement to correct for the resonances and head and body effects of using a dummy head measuring system. But I am not sure you would use the same HRTF for a phone like the Sigma, which because the driver is away and ahead of the ear, interacts with the ear in a very different way than does a conventional phone where the driver sits right on top of the ear.

Still, as I say Idon't find these measurements bad at all and they match my own take on the Sigma sound which i quite like.

[arnaud]

Tyll is using an average of multiple headings (not quite diffuse but not quite free field either), my guess is that it's an average of a few representative heading for loudspeakers (around 30-45 degrees).

[Tyll Hertsens]

What I'd really like is the HRTF for two off axis speakers, but alas, they don't have that curve to use.

The answer to your question is: no. I need to use the same HRTF for everything to make it comparable.

We really don't know where "flat" is for headphones.

[eggil]

The Stax Sigma 07381 is indeed a Sigma/404 that Mark from HighEnd WorkShop converted for me in September of this year.

(I can see the red rim of the 404 drivers).

[Dreadhead]

What I'd really like is the HRTF for two off axis speakers, but alas, they don't have that curve to use.

The answer to your question is: no. I need to use the same HRTF for everything to make it comparable.

We really don't know where "flat" is for headphones.

We don't know what flat is for anything. There are standards but they aren't necessarily flat.

That said last I looked your head did not have artificial ears in it so all your measurements are off for that reason too. The kemar and head acoustics ones look like they are more accurate as far as loading the headset etc but I get the impression that they are far more expensive than the neumann. The head site has a cool doc about equalization too.

None of this is a swipe at your methods just an observation. I think someone at stereophile had one of the artificial ear setups. It would be very cool to see the two compared.

Not that I have aes access but this looks interesting:

http://www.aes.org/e-lib/browse.cfm?elib=6107

Keep up the good work

Edited November 21, 2011 by Dreadhead

[John Buchanan]

The Stax Sigma 07381 is indeed a Sigma/404 that Mark from HighEnd WorkShop converted for me in September of this year.

(I can see the red rim of the 404 drivers).

....and what do you think of their sound, Eggil?

[John Buchanan]

Here is a copy of the original Stax Sigma frequency response chart.

[eggil]

I love the Sigma. It can at times be a little boomy but the mids are just wonderful.

I know measurements are difficult to compare, but between 100-1K both the normal bias and Sigma404 have a hump, somewhat more pronounced on the normal bias.

Comparing graphs, the normal bias Sigma has a drop between 2K-4K Hz, but the Sigma404 stays flat.

The normal bias Sigma climbs between 6K and 10K but the Sigma404 is relatively flat.

I will defer to the experts on the meaning of these differences.

StaxSRSigma07381.pdf

Edited November 21, 2011 by eggil

[edstrelow]

What I'd really like is the HRTF for two off axis speakers, but alas, they don't have that curve to use.

The answer to your question is: no. I need to use the same HRTF for everything to make it comparable.

We really don't know where "flat" is for headphones.

The point of the HTRF correction is to compensate for the effect of the head, body and ears on the frequency response. However when the phones attach differently to the head than the standard phone where the drivers sits atop the ear, the correction should be different.

For example if you measured an IEM which sticks into the ear, that portion of the HTRF which corrects for the resonance of ear canal would be wrong, because the canal would now be shorter.

With the Sigma the drivers are mounted ahead of the ears and the effect of the head would presumably be different.than for a driver sitting on top of the ears.

I am uncertain as to how big the difference would be and certainly at this point in the measurement game what you are doing is all we have to go on.

[edstrelow]

Here is a copy of the original Stax Sigma frequency response chart.

Looks similar to the Sigma/404 mesurements, certainly shows a family resemblance with the broad lower mid/upper bass range. Of course we don't know how Stax carried these measurements out.

[Tyll Hertsens]

The point of the HTRF correction is to compensate for the effect of the head, body and ears on the frequency response. However when the phones attach differently to the head than the standard phone where the drivers sits atop the ear, the correction should be different.

No, don't think so.

The curve is what flat is to the ear drum, how to get the sound there is the manufacturers problem.

They have to make the compensation, not the measurement.

[morphsci]

No, don't think so.

The curve is what flat is to the ear drum, how to get the sound there is the manufacturers problem.

They have to make the compensation, not the measurement.

[Tyll Hertsens]

I'll have to write an article about it.