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Wanna buy the Stax sr009, should I? - Page 6

post #76 of 151

Well well well... I was actually in line with Fujiya Avic but I walked out of the pre-order list tonight... Too much money right now, I will wait until the fall or Christmas. Until then, I will live vicariously through the early adopters!

post #77 of 151
Quote:
Originally Posted by arnaud View Post

Well well well... I was actually in line with Fujiya Avic but I walked out of the pre-order list tonight... Too much money right now, I will wait until the fall or Christmas. Until then, I will live vicariously through the early adopters!


I suppose it is better to wait Fujiya-Avic 2nd hand ones.

There are always someone who tried once and do not feel comfortable with the headphone and directly sell it back to Fujiya or list on yahoo auction. In this case the headphone will be in as new condition which you can snap a bargain lol.
post #78 of 151

Yes indeed, that's what I am thinking ;). It has happened with each and every one of the previous headphones releases (HD800, T1, Edition 10 ...), it should be not different this time. Especially with the large change in tonality when driven from Stax amp, it's bound to bother some people who were used to the dark sound of the underpowered O2...
 

Quote:
Originally Posted by rzy6cn View Post



Quote:
Originally Posted by arnaud View Post

Well well well... I was actually in line with Fujiya Avic but I walked out of the pre-order list tonight... Too much money right now, I will wait until the fall or Christmas. Until then, I will live vicariously through the early adopters!




I suppose it is better to wait Fujiya-Avic 2nd hand ones.

There are always someone who tried once and do not feel comfortable with the headphone and directly sell it back to Fujiya or list on yahoo auction. In this case the headphone will be in as new condition which you can snap a bargain lol.


 

post #79 of 151
Quote:
Originally Posted by edstrelow View Post

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.


The film vibrates, it doesn't move, that's how the air is excited. 

 

The arcing is due to too much voltage, roughly double the bias voltage appearing on the stators and a spark being generated. 

 

post #80 of 151
Quote:
Originally Posted by spritzer View Post




The film vibrates, it doesn't move, that's how the air is excited. 

 

The arcing is due to too much voltage, roughly double the bias voltage appearing on the stators and a spark being generated. 

 



Isn't vibration movement?

 

The issue appears to whether or not the diaphragm moves more or less as a whole, i.e. like a piston. The alternative seems to be some kind of complicated  pattern where different parts of the diaphragm move differently.

 

post #81 of 151
Quote:
Originally Posted by edstrelow View Post





Isn't vibration movement?

 

The issue appears to whether or not the diaphragm moves more or less as a whole, i.e. like a piston. The alternative seems to be some kind of complicated  pattern where different parts of the diaphragm move differently.

 


 

Hi Ed,

 

I believe that Birgir is trying to express that basically the motion of the membrane is really small even in comparison to the height of the spacer. Oppositely, an electro-dynamic type transducer is supposed to have a much larger displacement range, in hopefully "piston" fashion. The truth is that any membrane has so-called breakup modes, where the surface no longer moves uniformly. These "modes" are basically the result of interaction of waves that are being reflected off the boundary of the cone.

 

Think of a wave like the ripples on a calm lake when you through a stone, the wave moves outward in circular shape. When it reaches an edge, it will reflect back. In a finite size structure, you get these waves reflecting off the edges and interacting which leads to the establishment of "modes". Each mode has an associated "resonance frequency", that is if you excited the structure at that frequency and can observe the vibration on the surface, you will see exactly the shape of that mode. I have pasted a link here to illustrate the modes of a circular disk: http://paws.kettering.edu/~drussell/Demos/MembraneCircle/Circle.html

 

At low frequency, any cone will behave like a piston. At some higher frequency, it will have the first mode (1,0 in the link above), higher order modes will occur as you move up in frequency. Ideally, you want the cone to have no resonances in the audio range and behave effectively like a piston. It is seldom the case so people pay attention to the damping of the material / surround / spider (or the air layer in front / back of the membrane in the case of electrostatic driver) in order to limit the effect of the resonance on the acoustic response (peaks and valleys, change in the phase). Fundamentally, the resonance frequency of a mode is proportional to the bending stiffness of the cone and inversely proportional to its surface mass. So, the stiffer and lighter the better. Accessorily, the lighter the cone, the higher the frequency its response will start to roll-off, which in the time domain will translate into very quick transient response.

 

For a stax electrostatic transducer, the membrane is very thin and low mass. Its stiffness comes from the tensioning as it's basically a thin sheet of plastic as is... It isn't allowed to move like a piston (what birgir is trying to explain) so basically it's movement is regulated by the frequency at which the first mode (1,0 above) occurs and the tensioning of the membrane. This first mode is the one causing the largest displacement (at the center of the membrane) and I thought it could be an issue (contact with the stator under high SPL or if the spacer is too thin) as referenced in cmoy's explanation. But from what birgir is saying, actually it isn't. I don't have any idea how much displacement you get for say reaching 100dB at the ear for the size and thickness / stiffness of diaphragm.

 

One thing I mentioned in a previous message is that the advantage of the electrostatic transducer is that the force is applied uniformly on the whole surface. Because of this, ( I believe ) the effects of the resonances (the modes) are much less visible than when they occur on a traditional electrodynamic transducer with the forces applied on the rim of the voice coil.


Edited by arnaud - 4/9/11 at 5:14am
post #82 of 151
Thread Starter 

Wow you guys like to discuss alot on technical aspect of things. To me ,simply just.....it either sounds good or not.

post #83 of 151
Quote:
Originally Posted by hentai View Post

Wow you guys like to discuss alot on technical aspect of things. To me ,simply just.....it either sounds good or not.



I don't mind tech talk, but in the end I always say, "Trust your ears." That is what counts.

 

I can't help you. I have been a Stax guy since 1975, and I love my SR-007mk2, but I have not heard the 009.


Edited by Clarkmc2 - 4/9/11 at 12:37pm
post #84 of 151
Quote:
Originally Posted by spritzer View Post


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. 

 

What makes you believe that a plate-loading choke makes no sense?
 

post #85 of 151
Quote:
Originally Posted by 98664c3yijh View Post



What makes you believe that a plate-loading choke makes no sense?
 


I'm also curious about this. A plate choke is a lot closer to a CCS than a resistor. Morgan Jones uses a center tapped plate choke for his "Electrostatic Beast" amp.

 

post #86 of 151

I think I know! They are heavy, expensive and usually ugly. And look much worse than

anodized designer heatsinks!

 

post #87 of 151

 

Very interesting.
 
Is there any impedance vs. frequency graph on electrostatic transducers? I cannot find one.
 
I thought that, although very high impedance occurs at low frequencies (see text below), it would not be a "swing", but a roll off from low frequencies to high frequencies, without peaks and dips in between. 
 
I know that current requirements are tough. But what would be worst, electrostatic transducer impedance across the frequency spectrum or a dynamic full-range speaker with several transducers and the companion crossover? I read that peaks and dips of impedance are worst to deal with, is that right?

 

 

Quote:
Vacuum Tubes & ES Headphones 
 
The drive requirements for an electrostatic headphone are lots of voltage but not that much current, a set of requirements that the vacuum tube meets readily. A power tube is not even required, as a 6SN7 or a 6BX7 can easily put out 250 volt peak voltage swings. 
 
But voltage is only half of the complete equation. Current is needed as well. This requirement is often overlooked, as a charged capacitor requires no current to maintain its charge. AC signals are altogether different. The higher the frequency, the more current will be needed, as the reactive impedance of the capacitance falls off with frequency. For example, a 1 mF capacitor represents about an 8,000 ohm impedance at 20 Hz, an 800 ohm impedance at 2,000 Hz, and an 8 ohm impedance at 20 kHz. 
 
To determine how much current will be needed to drive a set of electrostatic headphones, the required slew rate of the peak voltage swing at the highest frequency being reproduced must first be calculated:

 

   Slew Rate = (2¶FVp) / 1,000,000.
 

In this case, where 20 kHz is highest frequency and 500 volts is the peak voltage swing, 
 

   Slew Rate = (6.8 x 20,000 x 500) / 1,000,000
   Slew Rate = 62.8 volts per microsecond.

 

Think of slew rate as a measure of the steepness of the waveform at its sharpest slope. 
 

The next step is to measure the total capacitive load represented by the electrostatic headphone's stators and its cable. The Stax Lambda Pros come in at 130 pF stator to stator. Then this quantity is multiplied against the slew rate to reveal the needed amount of current to charge and discharge the capacitance at the desired frequency and voltage swing. 
 

  Current = SR x Capacitance. 
 

In this case, 
 

   Current = 62.8 x 0.00013
   Current  = 8.16 mA.

 

This may seem like a fairly trivial amount of current, but do not forget the 250 volt voltage swing and the high voltage power supply, which when multiplied against the current equals a fair amount of power. 
 

Once we have determined the peak current requirement, we can begin designing the amplifier.

 

The Tube CAD Journal - Electrostatic Headphone Tube Amplifiers - November 1999 - Volume 1 - Number 9 - page 2 


Edited by jgazal - 4/11/11 at 7:31pm
post #88 of 151
Quote:
Originally Posted by 98664c3yijh View Post

I think I know! They are heavy, expensive and usually ugly. And look much worse than

anodized designer heatsinks!

 


All true. But on the other hand, a choke has the ability to store energy and thus produce a voltage swing greater than its B+. Unlike a CCS, a choke doesn't waste half its supply voltage in waste heat. Some people feel that a CCS imparts a glare or harshness to the sonics of the amplifier. When a choke clips, it's gradual and often not even noticable. When a CCS clips, it's like a car running into a brick wall. There's rarely a correct simplistic answer in audio design. Almost everything involves trade-offs. And for the record, I would generally choose a CCS for this application.
 

 

post #89 of 151

Common Frank, everyone knows that in high-end audio, there is a perfectly inverse relationship between efficiency and sound quality! 
 

Quote:
Originally Posted by FrankCooter View Post

Unlike a CCS, a choke doesn't waste half its supply voltage in waste heat.


 

post #90 of 151
Quote:
Originally Posted by El_Doug View Post

Common Frank, everyone knows that in high-end audio, there is a perfectly inverse relationship between efficiency and sound quality! 
 



 


There is rather a great deal of idiocy...there are 187532788789745 more ways to idiotycally loose efficiency winning nothing than to loose it deliberately and win something. Look at the speaker idiocy in the 80's and the kW amps to drive that idiocy...that was high-end too...unfortunately.

 

jgazal: 20kHz is pretty low, 100kHz is more appropriate if you want to +/- ok reproduce the transients. Real-life sounds have no HF, try to hear something at 12-15kHz, they have transients. HF is a hi-fi artefact. More transistors in the signal path, more HF.

 

 

 

 

 

 


Edited by 98664c3yijh - 4/12/11 at 6:58am
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