Stax SR-009 Channel Imbalance Trouble / Driver Problem?

[arnaud]

Wachara, very interesting. I understand this is all speculations but still nice to hear from specialists like you! In your experience, how does the membrane tensioning affects the frequency response? Again, I am a total noob but, my gut feeling was that with too much membrane tensioning goes away the extension to low end of the spectrum. Or is it just affecting sensitivity?
 
I am seriously considering looking into this one with structural finite element code... Not so easy to handle pre-stressed membrane vibration but it can be done. It's all about membrane properties (is it mylar?) / thickness / tensioning though so probably not much to simulate unless I had the actual numbers though... 
 
 

 

[chinsettawong]

The tension of the diaphragm affects directly with its resonant frequencies (RF).  The higher the tension, the higher the RF.  Mylar is a typical material for making diaphragms.  In order to get the same tension every time, you need to make a mechanical stretcher.  You stretch the Mylar to your desired tension, then you glue it to the spacer.  
 
The normal and safe diaphragm width to spacer thickness is around 100:1.  For anything beyond that, you can either increase your tension or reduce the bias voltage.  That will again affect the RF.  It will take a lot of trials and errors to get everything just right.
 
As for Stax, I'm sure that they know what they are doing.  However, Mylar isn't very easy to handle.  Given its surface smoothness, it might just slip a little when stretching or gluing.  And that might cause some problems, IMO.   
 
Wachara C.

 

[edstrelow]

I don't recall discussing the max SPL of the 009 but the Stax site lists 118 dB/400Hz for the 009 as well as the 507.  I don't see a corresponding figure for the 007a, 307 or 407.  I don't know what that means, if anything.

 

[AudioCats]

adding more tension might not be easy, "super plastic" might be super strong but if the diaphragm is using super thin sheets, at some point it will stretch, the tension might not keep on increasing.
 
If the tension was already border-line too much, maybe the mylar slowly stretched itself after leaving the factory?
 
How thick is the 009's diaphragm?

 

[jgazal]

 
 
Quote:

That was my thought too (effect of small spacer and / or larger diaphragm), but Birgir says the diaphragm is nowhere near that flexible.
 
It's very intuitive but I thought it all made sense when put together:
 
1. Sensitivity has increased so indeed spacer might have been reduced.
 
2. I believe one of the specs is max SPL in the 120dB range or so (need to look this up but if I remember, Edstrelow mentionned this in one of the threads). Which I interpreted as some limitation to membrane displacement until arcing and what not occurs.
 
3. The hole at the center of the stator. Again, maybe very stupid idea but this gives you additional clearance (max membrane displacement is at the center) and maybe have been implemented to increase dynamic headroom.
 
 
 

 
Now this issue is getting more and more interesting. I thought larger stator diameter with the same D/S gap would already increase the sensitivity (a sightly increase, which seems to be the case). 
 
Quote:

That was my thought too (effect of small spacer and / or larger diaphragm), but Birgir says the diaphragm is nowhere near that flexible.
 
It's very intuitive but I thought it all made sense when put together:
 
1. Sensitivity has increased so indeed spacer might have been reduced.
 
2. I believe one of the specs is max SPL in the 120dB range or so (need to look this up but if I remember, Edstrelow mentionned this in one of the threads). Which I interpreted as some limitation to membrane displacement until arcing and what not occurs.
 
3. The hole at the center of the stator. Again, maybe very stupid idea but this gives you additional clearance (max membrane displacement is at the center) and maybe have been implemented to increase dynamic headroom.
 
 
 

 
How such hole affects the damping in the mid frequencies? I wonder if such increase in sensitivity comes from the mid-range (at least in the 400Hz) and not from bass (which might be more affected by the D/S gap). Anyway, most of the damping in the mid frequencies may be related to the chamber. Nevertheless, it might be hard to keep the whole FR even...

 

[jgazal]

Just for fun, drum tight: 
 
http://www.youtube.com/watch?v=_nPLN_71aFc
 
http://www.youtube.com/watch?v=v4ELxKKT5Rw
 
http://www.youtube.com/watch?v=STSWLX23xqc

 

[spritzer]

Since the diaphragms are using a new type of plastic (which we don't know what is) then that could be the issue.  I do doubt it though since nobody as experienced as Stax would mess up diaphragm tension or choose a material which isn't fix and forget like mylar.  You have to remember that once mylar is tensioned and heat treated then it will remain in that position for at least 50 years.  Why 50 years?  That's how old my still 100% functional SR-1 is and being the first electrostatic headphone, our best point of reference. 
 
For an electrostatic transducer to be linear and have vanishingly low distortion then the diaphragm has to be ruler flat and very tight.  The Stax units certainly are, you can make them "sing" simply by lightly blowing air on them.  Given how weak the electrostatic force is then it simply isn't possible for it to stretch or dislodge the film in any way. 
 
The max SPL limit of any electrostatic driver is set by the inherent voltage limits of the drivers and not excursion.  The voltage limit is normally around double the bias voltage which means the driver will start to burn up once it is surpassed.  Now with most of the Stax amps this isn't a problem since 1200V P-P is a lot of voltage and more than they could ever output.  Only a handful of the DIY amps can output at these levels so damaging the drivers isn't very likely.  Now with the normal bias sets it was a very different story and Stax did try a lot of different things to stop people from burning up the diaphragms.  Sadly none of them really worked... 

 

[hentai]

Guys, hmm Stax has informed me that they will replace mine with a new unit. Hmmm how sure it will be for the new unit to be flawless.

 

[Tadj]

Hey Guy,
 
Just for my own opinion that I do not believe the "Microscopic Dust" has caused the "Channel Imbalanced" issue here, I have been working with and fixing STAX Headphone in Thailand for awhile now and most of the dust do exist in the older model( but has never caused andy noise at all!) but not the newer model's, due to how the newer model assembling in the dust free room environment, e.g. SR-507's the Diaphragm is a totally dust free assembly and the Diaphragm is now has a systematic even spacing dimpled surface to increase surface strength and total surface space! 
 
These are the series of event that happened on the first SR-009 that we have,...

1. The first SR-009 in Thailand was experienced the Righthand side Channel Imbalanced and start the Rumbling sound if pressing during the Live Audition with my Woo GES amp after it had been audition continuously for hours.
2. We decided to stop the audition and start checking for the cause by turn off the Woo GES Amplifier and check the SR-009 by pressing lightly on each side of the phone, then the Farting start coming from the Right side and try pressing with the Amp was on, the Rumbling keep going on like a resonance in low frequency, then we decide to stop the testing for checking again, all the padding were very humid
3. After stoping and kept the SR-009 on the Rack for a night, and start testing again all the Rumbling was gone but then after start auditioning for awhile everything coming back, the Farting, the Rumbling! 
4. We noticed that the lambskin leather part was very humid or wet! and the internal chamber was also very humid, Were they the causes of the Channel Imbalance? 
5. After heavily tapping( by the owner himself !) on the outside of SR-009 a few time to check if there was any loosen item(s) inside or not, the Cans return back to normal with out any sign of the Channel Imbalance or Farting/Rumbling again!!!
6. After carefully study these events, without disassembly the Cans! (he wouldn't allow me to!) In my own opinion, there must be some obstruction to the air-relesasing/pressure releasing hole, which in the O2MK2.5 it is at the cable connector, 
7. Up to today, this demo SR-009 seems to behave nicely and has never experience any further Noise or Channel Imbalanced any more....

 
With these observation, there may be possible that the SR-009 designer may over looked the design to protect the pressure locked inside the space between the diaphragm and the stator, the dust guard plastic on both side, or using the wrong filler that not react fast enough to the pressure changed inside the dust protectors !!!!
 
These are only my observation and could be totally wrong, so, please accept my apology if this is not what it happen for you guys!
 
PS: I would love to take this SR-009 apart if someone allow me to!...hee...heehe ;-0

 

[spritzer]

There really shouldn't be a "pressure valve" there to begin with so I doubt that is the issue.  No Stax headphone prior to the Mk2 had anything like that, certainly not the Mk1 or the SR-Omega.  The 4070 had bass reflex ports but that's different. 

 

[chinsettawong]

The more I've read, the more I'm sure that it's the problem with diaphragm sticking to one side of the stators. Why do I know? Because, my DIY headphones used to have that problem all the time. Stretching the diaphragm a little more solves this problem.

There isn't anything that you can do to fix the problem by yourself. Sending it back to Stax, and let them fix it for you is the best option.

Wachara C.

 

[Sundance]

My question for the Stax experts is will the future models sound different from the release batches due to factory corrections?

 

[livewire]

Buy a crystal ball.
Seriously, nobody has the answer to that question. (yet)

 

[Currawong]

The more I've read, the more I'm sure that it's the problem with diaphragm sticking to one side of the stators. Why do I know? Because, my DIY headphones used to have that problem all the time. Stretching the diaphragm a little more solves this problem.

There isn't anything that you can do to fix the problem by yourself. Sending it back to Stax, and let them fix it for you is the best option.

Wachara C.

My SR-5NBs had that problem too, as the membrane was warn and they have perforated plastic on the ear side, so it does give the impression of a membrane failure.

 

[edstrelow]

Quote:

The more I've read, the more I'm sure that it's the problem with diaphragm sticking to one side of the stators. Why do I know? Because, my DIY headphones used to have that problem all the time. Stretching the diaphragm a little more solves this problem.

There isn't anything that you can do to fix the problem by yourself. Sending it back to Stax, and let them fix it for you is the best option.

Wachara C.

Doesn't that imply either a very loose tension in the membrane and/or very limited spacing between the stator and membrane?
 
Any fix of this type of issue seems likely to result in a marked change in the sound.