[spritzer]

At their core these drivers are all relatively similar.  What Chu was talking about are electrostatics in general but the Stax drivers are all mostly the same affair.  Move over to what Beyer, Sennheiser, Jecklin or Koss were doing and you'll see some very different designs.  Sony probably has the oddest one of them all if the literature is to be believed. 
 
Like I say below, it's not really a matter of dishing out more energy for a flat response but rather the amp being able to sustain full voltage swing into the given load.  The huge voltage swing of the BHSE and T2 are naturally a factor here since at normal levels the amps are just idling. 
 
Quote:

 
Indeed on the electrical side of things, I have no idea the different the load is to the amplifier. However, on the mechanical side, stax specifically refers to increase in "ease of displacement" of the membrane by using a thinner diaphragm (with less inertia). With the o2, isn't the issue of uncontrolled bass at least partly due to the lack of control of this membrane inertia unless the amplifier has sufficient drive capability? At least, this is how it works with traditional electro-dynamic speakers. The membrane mass in electrostatic transducer is much lower and the stiffness very high by it's still got some elasticity and inertia.
 
Then, in regards to the less is more, indeed I have no idea how different the 727 is from say a KGSS (not so different then?). But the point was also about the power: in an electro-dynamic amp, the first watt matters much more than the 300 Watts of reserve given this is 90% of the typical recording (unless you're listening to overly compressed crap recordings eh ).

Let's start off with one thing, the diaphragm doesn't move and it certainly doesn't flab around as it is tight as a drum.  The sound is produced by vibrating the very taught diaphragm.  If the diaphragm would move at all then the ultra low distortion figures would quickly disappear and be replaced by horn levels.  What we have is a reactive driver which is essentially a capacitor so any similarities to resistance based drivers have no bearing here.  While amps like the BHSE and T2 are massively over spec for the job at hand it is nothing like driving a headphone from a 300W amp. 
 
First thing to look into is Ohm's law and how that translates into impedance vs. current vs. voltage.  A planar magnetic driver has very little change to its impedance depending on frequency, dynamic drivers can vary quite a bit but electrostatics have a gigantic impedance swing.  To maintain the same output voltage into any given load then you need current, in fact a constant current supply.  The old way of using a resistor for this is inadequate and an inductor makes less than no sense.  The "tube sound" people often talk about is due to how the tubes are driven and plate resistors certainly are a part of that.  Take the SRM-007t, replace the tubes with 6S4A's, add a CCS for the output and a nice PSU and it is a damn good amp, none of that warm tube sound.  Let's say you are listening at any given volume (i.e. voltage level) and the amp is asked to reproduce some bass note but it lacks current to swing the full voltage into the given load.  What happens is that the amp doesn't have full grip on the diaphragm so the bass appears to be loose. 
 
There are naturally other factors to consider (slew rate, output impedance, psu design etc.) but this will do.  Now the improvement isn't just linked to the bass but the entire spectrum but most people seem to focus on the bass.  I for one value a lot more the benefits more power brings to the soundstage.  The goal of any good amp is to supply the transducer with enough power so it can do its own thing.  Sadly this is often very, very expensive and leads to insanely complex amps like the SRM-T2 (though at its core it is very simple). 
 
As for the 727, it is rather different from the KGSS.  It's more like a spruced up 323 but with the feedback loop cut tragically short.  Not a bad amp once that is fixed but as with most of the Stax amps, there are certainly ways to do it better.  It does improve on the KGSS by being fully CCS loaded (i.e. what the KGSSHV does for the KGSS plus extra voltage) but in practice the KGSS is a better amp to these ears. 
 

 

[jgazal]

 
[size=10.0pt]Thank you, Birgir![/size]

[size=10.0pt] [/size]

[size=10.0pt]According to Arnaud, the Stax representative says, in that interview to Fujiya, that a better amplifier means higher price and weight. I presume it is related to such current source (current sources at class A means more components and heavy heat sinks, haven't you said that once?). Well, this could increase all costs (including freight). [/size]

[size=10.0pt] [/size]

[size=10.0pt]What I find difficult is to define the concept "load". I thought load was strongly related to the transducer mechanics. If the transducer had better mechanics (i.e. 50% of the electrical energy is transformed in sound instead of 40%, while the rest is lost in heat etc.), then it would demand less energy from the amplifier. That's why I entered the mechanical model. [/size]

[size=10.0pt] [/size]

[size=10.0pt]So if you say an amplifier need to sustain a given current in order to cope with "load", then you are saying that it is delivering more energy to the transducer. If the amplifier is not capable of sustaining such currents, then it is not capable of delivering such energy to the transducer.[/size]

[size=10.0pt] [/size]

[size=10.0pt]I was working with the hypothesis that SR-009 could indeed have better mechanics than other electrostatic transducers, so that to achieve a flat frequency response a given amplifier would need to deliver less energy (as current or as voltage) than the energy it would had to deliver with SR-007.[/size]

[size=10.0pt] [/size]

[size=10.0pt]Now I realize that the real benefits are not in the mechanical model (although it might have slightly easier mechanics), but in resonance and reflection from the stators, as KG said from the very beginning. [/size]

[size=10.0pt] [/size]

[size=10.0pt]What I find interesting with high power amps is that they are usually storing and even sinking a lot of energy and when the input signal is demanding (and here I think you are using the concept "load" as a synonym of a tough input signal, with demanding low and high frequencies), they have an auxiliary circuitry to route/wreak such energy to the transducer (energy as current or as voltage in the signal path).[/size]

 

[size=10.0pt]Am I right about the meaning you have been given to the word "load"? [/size]

[size=10.0pt] [/size]

[size=10.0pt]At the amplifier side, I do agree that more power might improve soundstage focus and coherence. But that I am still trying to understand. I have read about slew rate. I know that it relates with the higher frequency response. I suspect that if the amplifier is able to deliver energy to the transducer (enough voltage at a very small period of time, V/us), no distortions would occur and then the sound would be reproduced at the very correct time, improving imaging. But if there is still enough slew rate to deliver high frequency response, why it would affect time coherence between both channels? Still trying to find and understand a logic cause.[/size]

[size=10.0pt] [/size]

[size=10.0pt]You know that I am always asking the same questions to you. [/size]

[size=10.0pt] [/size]

[size=10.0pt]Each time I read your answers I realize a new detail.[/size]

[size=10.0pt] [/size]

[size=10.0pt]Forgive me for being so slow with the understanding.[/size]

[size=10.0pt] [/size]

[size=10.0pt]Anyway, your post should be stick.[/size]

 
 

 

[spritzer]

It's the bias, as in how much current is passed through the output stage that sets how much heat will be generated and how much in terms of reserve the amp has.  This does mean weight, both due to a larger PSU and heatsinking.  What Stax are up against is making amps on a shoestring budget which is why the larger amps all share a chassis and transformer.  They also use the simplest PSU they can get away with. 
 
I very much doubt that there is any real difference in the mechanical properties of the SR-009 drivers compared to the SR-007 units.  From what info I've gathered the construction is identical but with the SR-009 using very complex stators to emulate the stiff nature of the 007 units but with a more open structure like the SR-Omega. 
 
The load is the impedance of the driver which varies with frequency.  That's all there is to it, as the impedance drops you need more current to maintain the same output voltage.  We aren't in any way talking about large values here but at 300+V even a tiny bit of current adds up. 
 
As for slew rate, it is a measurement of voltage change and has nothing to do with the FR of the amp unless it is very compromised.  It is just a measurement of how quickly the amp will respond to a sudden rise or fall in the input signal (translated through the fixed gain of the amp) per us. 
 

 

[visualguy]

Quote:

I currently run O2 Mk. 1 using a BHSE amp.  I like the sound, but of course, if something comes along that sounds better that is great.  I would welcome any form of progress.  My problem is that I don't really know of anywhere that I could audition the new model. 
 
Also, I am NOT one of those in the camp of O2 owners that think it is too dark or warm sounding.  I would NOT want greater "clarity" if that means a leaner midbass.  I would only consider a model an improvement if it were actually a bit warmer sounding.  If I read comments saying that it is warmer, then I would find it worth my time hunting down a dealer that would allow me to hook up my BHSE amp for a trial.

The SR-007 is already crystal clear... In general, I can't really find any significant weaknesses in the sound of my SR-007/KGSS. If I really had to come up with some downside, the only thing that would cross my mind is that maybe the sound is a little too "airy" and lacking in "weight". However, based on a couple of listening impressions of the SR-009 that people posted, it didn't seem like the SR-009 changes that.
 
The main thing that stops me from pulling the trigger on the SR-009 is a suspicion that there will be only very minor differences in sound between the SR-009 and SR-007 when driven by the KGSS or BHSE.
 

 

[monsieurguzel]

out of curiosity, is the stator of the SR-009 bigger/smaller/same as the original Omega driver? (which is known to be pretty huge)

 

[spritzer]

Quote:

out of curiosity, is the stator of the SR-009 bigger/smaller/same as the original Omega driver? (which is known to be pretty huge)

Probably a bit smaller. 
 

 

[arnaud]

Quote:

Let's start off with one thing, the diaphragm doesn't move and it certainly doesn't flab around as it is tight as a drum.  The sound is produced by vibrating the very taught diaphragm.  If the diaphragm would move at all then the ultra low distortion figures would quickly disappear and be replaced by horn levels.  What we have is a reactive driver which is essentially a capacitor so any similarities to resistance based drivers have no bearing here.  While amps like the BHSE and T2 are massively over spec for the job at hand it is nothing like driving a headphone from a 300W amp. 
 

Birgir, thanks for your detailed explanation. Just like jagzal, it will take some more effort for me to digest. On the mechanical side, I think we have some miscommunication in regards to vocabulary. When you say the diaphragm doesn't "move", I believe you are contrasting against traditional piston-type eletrodynamic transducer that produces sound through movement allowed by the spider and suspension. Indeed, the diaphragm is tight like a drum but, as you mentioned, vibration must be induced to produce some sound... So much so that Chu Moy in his introduction mentions one of the drawbacks of reducing the spacer thickness (to increase efficiency) is potential contact of the stators by the diaphragm.
 
Actually, the diaphragm is so thin that it can't have that much stiffness even though the membrane is pretensioned. It also does have a mass and as Chu Moy writes, in that mechanical sense it still very much is a spring / mass / damper type of oscillating system. What is neat though is since the input mechanical force is uniformly distributed over the surface of the membrane, I guess the resonances of the presstressed membrane are much less of an issue than the breakup modes of an electrodynamic cone.
 
I know this is probably clear to you but to clear out any misconception with anyone: the pretensioning of the membrane does not free it up from mechanical behavior. It still has modes (just look at the patterns of sand on the surface of the drum when you shake it at various frequencies) and from what I read on Chu Moy's summary the resonance frequency of very first so called "pumping" mode (with maximum amplitude at the center of the  diaphragm) determines the low frequency limit of the transducer.
 
However, in the end, indeed if only the stator has really changed (I was under the impression from the interview though that they changed the membrane and did not want to go into detail as to the optimal thickness), then probably there's no so much difference on the mechanical side (well indeed apart from the stator rigidity).

 

[spritzer]

Like I said, the diaphragm vibrates only, it doesn't move like a piston.  The D/S gap (i.e. the distance from the diaphragm to the stator) and its relationship with the bias voltage has everything to do with the breakdown voltage of the atmosphere (around 100V/mill), the diaphragm moving isn't a factor here.  That doesn't mean the diaphragm can't move but not simply by using the weak electrostatic force, you need some external force to do that.  For instance, the HE90 works just fine as it is but push on the earcup with it on your head and you'll be scared half to death by the sounds it makes. 
 
As with anything in the world, the diaphragm has a resonant frequency and that is very much a factor in the over all sound.  How you can tame this resonance is not that easy but airdamping plays a bit part with the SR-007.  It's also one of the reasons why 1um film or thinner isn't always a good idea. 

 

[edstrelow]

 
Quote:

Let's start off with one thing, the diaphragm doesn't move and it certainly doesn't flab around as it is tight as a drum.  The sound is produced by vibrating the very taught diaphragm.  If the diaphragm would move at all then the ultra low distortion figures would quickly disappear and be replaced by horn levels.  What we have is a reactive driver which is essentially a capacitor so any similarities to resistance based drivers have no bearing here.  While amps like the BHSE and T2 are massively over spec for the job at hand it is nothing like driving a headphone from a 300W amp. 
 
 

 


Quote:

Birgir, thanks for your detailed explanation. Just like jagzal, it will take some more effort for me to digest. On the mechanical side, I think we have some miscommunication in regards to vocabulary. When you say the diaphragm doesn't "move", I believe you are contrasting against traditional piston-type eletrodynamic transducer that produces sound through movement allowed by the spider and suspension. Indeed, the diaphragm is tight like a drum but, as you mentioned, vibration must be induced to produce some sound... So much so that Chu Moy in his introduction mentions one of the drawbacks of reducing the spacer thickness (to increase efficiency) is potential contact of the stators by the diaphragm.
 
Actually, the diaphragm is so thin that it can't have that much stiffness even though the membrane is pretensioned. It also does have a mass and as Chu Moy writes, in that mechanical sense it still very much is a spring / mass / damper type of oscillating system. What is neat though is since the input mechanical force is uniformly distributed over the surface of the membrane, I guess the resonances of the presstressed membrane are much less of an issue than the breakup modes of an electrodynamic cone.
 
I know this is probably clear to you but to clear out any misconception with anyone: the pretensioning of the membrane does not free it up from mechanical behavior. It still has modes (just look at the patterns of sand on the surface of the drum when you shake it at various frequencies) and from what I read on Chu Moy's summary the resonance frequency of very first so called "pumping" mode (with maximum amplitude at the center of the  diaphragm) determines the low frequency limit of the transducer.
 
However, in the end, indeed if only the stator has really changed (I was under the impression from the interview though that they changed the membrane and did not want to go into detail as to the optimal thickness), then probably there's no so much difference on the mechanical side (well indeed apart from the stator rigidity).

Indeed!  
 
If  an electrostatic diaphragm doesn't move towards and away from the stators, there wouldn''t be  much worry about arcing or the need to increase the spacing of the stators with higher bias voltage.
 
The air has to be got moving somehow. If I understand Spritzer's explanation he thinks the diaphragm operates by jiggling in place, something like the Heil Air Motion driver.

 

[ast]

Quote:

Have ordered one from sofmap yesterday. Hope I can get it at the same day of release and have my friend shipped to me.
 

So you prefer sofmap to PriceJapan, as the latter seems have better price?

 

[wink]

 
Quote:

Wanna buy the Stax sr009, should I?  
 

Any true head-fier would not need to ask this question - They'd just buy them.................

 

[rzy6cn]

So you prefer sofmap to PriceJapan, as the latter seems have better price?

I have friend in Japan who is a VIP of sofmap. So I get back:

368000*0.11=40800 points when I purchase the headphone. These points can be used as sofmap credit which I can spend afterwards anyway.

In other words, in fact I paid : 368000-40800=327200 yen (exclude shipping) for the headphone.

For PriceJapan I have to pay 309800*1.05(5% service fee) =325290 which is merely the same of sofmap. And if I want to pay by paypal I have to pay 3.9% surcharge to pricejapan...

However PriceJapan mentioned: "Please understand that it is Not clear how long days we need to get it after your order and payment. ( One month or longer may be needed.)"

In order to get the order more quickly I choose sofmap, at least I can get it just after it released and also get full warranty.

Although PriceJapan is reliable (in the sense that they will ship your item), but I'm unsure about the channel they got it and sofmap is more reliable in my opinion.

 

[kiertijai]

For PriceJapan I have to pay 309800*1.05(5% service fee) =325290 which is merely the same of sofmap. And if I want to pay by paypal I have to pay 3.9% surcharge to pricejapan...

However PriceJapan mentioned: "Please understand that it is Not clear how long days we need to get it after your order and payment. ( One month or longer may be needed.)"

In order to get the order more quickly I choose sofmap, at least I can get it just after it released and also get full warranty.

Although PriceJapan is reliable (in the sense that they will ship your item), but I'm unsure about the channel they got it and sofmap is more reliable in my opinion 
 
 
In Pricejapan,  they also allow you to do the wire transfer so that you don't have to pay the full paypal fee of 4% .  From Thailand you will have to pay around 40$
for wire transfer for both parties.  Doing wire transfer to your friend you also have to pay for the wire transfer fee. Again the difference is not much,  the more important
is the timing of delivery.  Another good thing of pricejapan is that you don't have to pay the full amount but pay only for the down payment of 1000$.  Your deal is also a good
deal, however other may not have your channel of sofmap.
 
I have asked another party : japonicamarket , Yoshiyuki Sensei said that the first shipment was sold out  from all sites in Japan that he tried to contact even  Fujiya Avic.
So I think even from sofmap, it has to be the second shipment which will be around middle of May to early June.  I hope pricejapan will be able to get the second shipment.

 

[rzy6cn]

For PriceJapan I have to pay 309800*1.05(5% service fee) =325290 which is merely the same of sofmap. And if I want to pay by paypal I have to pay 3.9% surcharge to pricejapan...

However PriceJapan mentioned: "Please understand that it is Not clear how long days we need to get it after your order and payment. ( One month or longer may be needed.)"

In order to get the order more quickly I choose sofmap, at least I can get it just after it released and also get full warranty.

Although PriceJapan is reliable (in the sense that they will ship your item), but I'm unsure about the channel they got it and sofmap is more reliable in my opinion 
 
 
In Pricejapan,  they also allow you to do the wire transfer so that you don't have to pay the full paypal fee of 4% .  From Thailand you will have to pay around 40$
for wire transfer for both parties.  Doing wire transfer to your friend you also have to pay for the wire transfer fee. Again the difference is not much,  the more important
is the timing of delivery.  Another good thing of pricejapan is that you don't have to pay the full amount but pay only for the down payment of 1000$.  Your deal is also a good
deal, however other may not have your channel of sofmap.
 
I have asked another party : japonicamarket , Yoshiyuki Sensei said that the first shipment was sold out  from all sites in Japan that he tried to contact even  Fujiya Avic.
So I think even from sofmap, it has to be the second shipment which will be around middle of May to early June.  I hope pricejapan will be able to get the second shipment.

The transfer fee also included in the PriceJapan's payment, they have already count it in so you did not see the currency exchange surcharge. However it is actually there if you try to do a quote on PriceJapan and calculate the exchange rate, you will understand.

I actually ordered from Sofmap at the first day it release the pre-order page. Sofmap is one of the biggest consumer electronics and anime accessories distributor in Japan. I can hardly believe that they can not get the 1st batch stock. Sofmap's price is the most expensive if not count the points in. So I hope that I can get the 1st batch lol.

 

[kiertijai]

I actually ordered from Sofmap at the first day it release the pre-order page. Sofmap is one of the biggest consumer electronics and anime accessories distributor in Japan. I can hardly believe that they can not get the 1st batch stock. Sofmap's price is the most expensive if not count the points in. So I hope that I can get the 1st batch lol 
 
I do hope that you can get that in the first batch, please share your impression on the SR009