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post #91 of 151

ARNAUD

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. 

 

 

 _______________________________________________________________________________

 

 

 

Nor do I know how much the stat diaphragms move and certainly it is less than a dynamic speaker.  However I recall that a number of stat systems use plastic spacers on the stators to minimize arcing, the first I encounter were the old B &W and I thought that Stax might have also done so.  This would seem to be done to physically stop the diaphragm from getting too close to the stators, thus implying  a fair bit of movement, at least at the center of the diaphragm.


Edited by edstrelow - 4/12/11 at 11:22pm
post #92 of 151

I've ordered the Stax SR-009 for five reasons:

1. Sound quality/realism may well be the best available for earphones.

2. The continuing threat of dollar devaluation/inflation - ‘get 'em while u can’ -- don't have enough cash to fill a wheelbarrow.  It can't happen here?

3. From watching a posted Japanese TV video, it appears that the new Stax SR-009 is truly more an "Open Air" flow design compared the SR-007 (I have SR-007 Omega MK1 and they can fell 'hot' over the ears, and also subject to diaphragm noise (crackling noises when moving head, etc. -- diaphragm movement against the stators due to pressure variation, lack of internal air flow/circulation with tight ear cup seal).

The lack of air circulation in my Omegas (the ear cups have relatively tight seal) often causes me some discomfort after an hour or so -- and it's worse in warm humid summer days.

In the Japanese Stax interview video, the circular electrostatic sound transducer element in the SR-009 appeared to be open in the center, as well as having additional open holes around the perifery.  So, I'm hoping/anticipating that the SR-009 will be much more comforable for hot humid summer days.

4. I’m getting the Smyth 'Realiser' processor which reportedly offers a very good multichannel soundstage recreation experience from headphones (Stax phones have been recommended by Smyth)

5.  Planning to downsize in retirement - move to smaller, lower cost of living housing where earphones might just have to be the primary sound source.  Large loudspeakers (especially multichannel) are no longer practical, & WAF.  I use headphones most of the time, even now - usually just more convenient to get the audio system up and running.

post #93 of 151

Subject:  Amplifier for SR-009 and electrostatic headphones in general.

Currently, I’m listening to my Omega SR-007 phones with a SRM-252.  IMO, for low & normal listening volume levels, the result is more than satisfactory. 

SR-009 is now on order.

The circuit topology and solid-state devices used are essentially the same as the SRM 323 amp (I have the schematic).  Mainly, what’s  different is the power supply, and the output stage bias – more voltage swing and current drive capability.  

An electrostatic transducer basically presents a capacitive load to an amplifier.  For a given sound pressure level, output drive current is proportional to frequency, or rate of change of voltage (I = C dv/dt). 

I feel that heroic output power capability (high current * voltage) provided by the far more expensive power amps is not really needed at normal listening levels (for me, anyway) – as long as the electrostatic amp behaves well with very low distortion at small to moderate voltage swings.  I’ve listened to tube (I have a Stax tube amp also) and solid state amps, and feel that the well-designed Stax SRM-323S should offer all the amp power  I need,  even for the SR-009 (yes, perhaps a radical opinion).   Even the lowly STAX SRM-252 amp is direct coupled, with no coupling caps in the path – IMO, a remarkably nice sounding design.  I understand that the SRM-323 is well regarded ...

I used to feel that tubes were somehow naturally better than solid state – not any more.  

I've read that solid state might be more compatible with the new SR-009 compared to the previous Omegas (initial listening impressions were posted, as I recall) 

post #94 of 151

Bill13,

 

It's hard to say if the SRM-323S has the power to drive the SR-009 well because Stax doesn't say anything about power in regards to their headphones or amps. There is no information about the power requirements for the headphones, and no information about the power output of the different amps.

 

For example, it's not even clear if the SRM-323S has more or less power than the SRM-007tA. The 323S can provide more voltage (400V vs. 340V), but there's no informatoin about the power.

 

Same with SRM-600 vs. SRM-007tA.

 

The problem with power is that it can vary based on the load, and my understanding is that Stax headphones provide a variable load throughout the frequency range, so you really need a power graph for each amp and an impedance graph for each pair of headphones...

 

It's pretty hard to make an informed choice in this area.

 

post #95 of 151

 

By the way, I agree with you on low volume. Differences between amps in general diminish significantly at low volume. This applies to amps for both dynamic and electrostatic headphones (and also speaker amps for that matter).

 

The thing is that low volume is really the only safe way to listen to headphones, so in reality high-volume performance matters a lot less than one would imagine...

 

post #96 of 151

 


Quote:
Originally Posted by Bill13 View Post

I've ordered the Stax SR-009

 

Good choice, I'll do the same at some point...

 

Quote:
Originally Posted by Bill13 View Post

4. I’m getting the Smyth 'Realiser' processor which reportedly offers a very good multichannel soundstage recreation experience from headphones (Stax phones have been recommended by Smyth)

 

Ah, that is also in my purchase pipeline! Kind of would like to see a v2 with digital inputs and without head tracking unit though.

 

Quote:
Originally Posted by edstrelow View Post

Nor do I know how much the stat diaphragms move and certainly it is less than a dynamic speaker.  However I recall that a number of stat systems use plastic spacers on the stators to minimize arcing, the first I encounter were the old B &W and I thought that Stax might have also done so.  This would seem to be done to physically stop the diaphragm from getting too close to the stators, thus implying  a fair bit of movement, at least at the center of the diaphragm.


I wonder if the center opening on the stators is just for that?? You'd expect max displacement at the center of the diaphragm and this could enable a smaller spacing between the stators while preventing contact! Maybe it's a stupid idea though ;).

 

post #97 of 151

Hi all,

 

Where did you ordered/pre-ordered your SR-009? Your local/national Stax dealer or some Japanese online shops?

Stocks seem limited and the first batch is probably already gone.
 

I have a Realiser and it is really fantastic. I recommend it for surround movies and surround music/live, but don't really see the point at reproducing a stereo environment, unless you don't like headphone sound style. I went to L.A. to do measurement at AIX (music mixing studio) and Mi Casa(bluray mixing studio).

I originally used the bundled Stax 202, now I am using a HE6 and I am looking forward the SR-009, it should be even better.

 

post #98 of 151

Pre-ordered SR-009 USA dealer Elusivedisk - full list price - sure, USA dealer price bothers me, but am afraid of Price Japan dealer {for example}  which adds 5% to quote in addition to doubts about factory warranty and service.   I understand from Elusivedisk that they already have about 14 pre-orders for the SR-009.

 

Some Smyth Realiser users like the HE-6, but my feeling is that the Stax SR-009 should be state-of-the-art for electrostatic fans.

 

You can estimate the relative drive capability of the STAX SRM 323 into the load presented by the Stax SR-009 amplifier drive scales linearly as a function spec'd capacitive load compared to the SR-303:

SRM-323 spec: Frequency Response: DC to 60,000Hz with SR-303 (Stax SR303 spec = 120 picofarad capacitance including the cable; ~100 dB sens); High Frequency Distortion: Max. 0.01% (with 1kHz, 100V r.m.s. output).

SR-009 spec: Capacitance: 110pF (including cable)
Impedance 145kohm (including cable at 10kHz)
Sound pressure sensitivity 101dB / input 100Vr.m.s / 1kHz

So, it's reasonable to say that the 303 & 009 present about same cap load to an amp with approx. same drive sensitivity.

If amp drives the SR303 OK, then it's logical to say that SRM 323 amp will be fine with the new SR-009.

IMO, If I wanted to blast my ears with loud sounds, then the ears would distort before the amp would - so I think.

 

So, I believe that there is sufficient information to estimate what the SRM-323S can do into the SR-009 -- just by doing the math.

 

I did debate whether to get the HE-6 phones, but continue to be an electrostic fan.

 

Bill13
 

post #99 of 151

The other thing that is a little shady about PJ is that they won't disclose where they are buying their units from...meaning that it might not even be from an authorized dealer.

post #100 of 151
Quote:
Originally Posted by Bill13 View Post

 

IMO, If I wanted to blast my ears with loud sounds, then the ears would distort before the amp would - so I think.

 

 


 

I'd be more worried about hearing damage at high volume (or even moderate volume on long listening sessions). Low volume is the way to go in my opinion if you want to keep your hearing in top shape.

 

As to power requirements - I think Stax is keeping that area completely fuzzy on purpose, and I find that pretty frustrating.

 

post #101 of 151
Lately I been liking my 4070s more than my Omega twos. I think they are deeper and smoother. I like my headphones the way I like my women; what can I say.
post #102 of 151

Error correction:

In my above post regarding Stax specs for earphones, I typed "SR-303" when the correct earphone model number should have been 'SR-307'.  Sorry for the error.

 

Regarding load capacitance and sensitivity the newer Stax Lamda series: SR-207, 307, 407 and 507 - -  all specs are roughly the same (same "sound element" for the Lamdas) - The SR-407 and 507 have slightly less capacitance (10 pf lower) due to lower cable capacitance.  

 

 

In general the lower the total capacitive load presented to the amp, the easier to drive the phones to intolerable loudness at extremely high frequencies.  However, your hearing health may be endangered when pushing the amp at high volumes -- as 'visualguy' pointed out. 

 

 

BTW, Adding an extension cable may tend to slightly reduce the maximum high frequency voltage swing that a smaller electrostatic amp can deliver, but I understand that it's very difficult to hear any treble reduction, even at loud volumes, when using a Stax extension cable.

post #103 of 151

Bill13, you should look into post #53 in regard to your calculated assumption about drive capabilty of the SRM323 and SR009:

Quote:
Originally Posted by spritzer View Post

The new drivers are more sensitive (says so right there in the spec sheet though the difference is tiny) but when has that ever had anything to do with how easy a transducer is to drive?  We are still dealing with the same 66K to 66M load of the other Omegas so why is the SR-007 harder to drive than the SR-Omega when it is indeed more sensitive?  Thinner diaphragm means you need a better amp to control it but I guess these new drivers could be able to defy Ohm's law...

 

As for "In regards to amplification, sometimes less is more you know", how the hell does that apply to the 727? 

 

I defintley lack your technical expretise but i do know that gain doesn't equate to amp's drive/sound quality, Just volume level.  
 

 


 

 
post #104 of 151

Amarphael, I looked at previous postings here, including post 53.

 

I am not saying that the 'sound elements' in any of the current Stax Lambda phones & SR-009 are relatively easier (or harder) to drive.

They all are about the same 'ease of drive', if you will.  I go by the laws of physics when I say this.   I will try to explain.

Engineering wise, it's reasonable to say that 'ease of drive' is proportional to total earphone load capacitance, the frequency, and rated sensitivity of the electrostatic transducer (SPL Vs. RMS voltage spec). "Ease of drive” is directly proportional to the 'sound element' capacitance because the current that the amp must supply to the load is a function of frequency: i =C dv/dt. So, the amplifier power required for a given voltage swing (Vrms ~ SPL) increases linearly with frequency (or current into the capacitor increases directly with the amp output voltage slew rate, if you prefer that terminology).

Since Stax has reduced the sound element diaphragm thickness to a mere 1.35 u, for audible frequencies, f=ma, the acceleration of the diaphragm is affected by the mass of the air around it.  

So, the way I see it, comparing 'ease of drive' between the various current Stax earphones isn't all that relevant.  Current Stax earphones are all roughly about the same drive difficulty, or ‘ease’ to drive (they have same 1.35 u diaphragm, and essentially the same SPL sensitivity vs. frequency spec, and present roughly  the same fixed capacitance load).  Also, all use the same polarizing voltage (580V, implying about the same stator spacing).

 

Since SPL output is about the same, we can assume that sound element efficiencies are actually about the same.  In my view, Stax has not dramatically changed the basic design/physics – only refined the implementation (for example, Lambda resin mounting, engineering materials, etc.).

When you say “gain”, what do you mean?  Do you mean earphone SPL sensitivity for a given applied voltage swing?   -- Gain is not relevant to ‘ease of drive’ (?)

 

BTW, when I said I made an error about the SR-303 vs. the newer Lambdas (SR-207 thru SR-507), it was not a technical error (SR-303 has similar design parameters), but only that I intended to discuss the newer Lambdas.

Bill13

post #105 of 151
How will or does the recent Japanese Earthquake and Sunami effect the Stax Corporations ability to finish and deliver orders? Are they affected in any way?
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