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Some interesting findings about Stax electrostatic stators
Some interesting findings about Stax electrostatic stators
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Old 26th September 2011, 06:26 AM   #11
Calvin is offline Calvin  Germany
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its the trasducers proximity to the ear channel that boosts the bass up to sufficient levels. Measured free-air the amplitude response probably shows a falling response below ~100Hz. So even for low bass-frequencies the excursion may remain small, especially with a such a large transducer as the Stax.
The array of small dots allows for a distribution of resonances and lower Qs of these and secures a proper d/s. The diaphragm movement on a macroscopic level is closer to translatory than bowed. This should also allow for higher possible SPLs.
Manufacturing -even if we donīt know the howto yet- was probabely much easier and cheaper than glueing multiple spacer dots and results in smaller dots, hence less īdeadī capacitance/diaphragm area.

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Old 26th September 2011, 05:00 PM   #12
geraldfryjr is offline geraldfryjr  United States
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That was my next question "if those are supports for the Diagphram ot not ?" if so then I understand the design.

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Old 26th September 2011, 07:17 PM   #13
lcsaszar is offline lcsaszar  Hungary
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They prevent the diaphragm from sticking to the stators at high SPL (clipping).
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Old 27th September 2011, 04:29 AM   #14
chinsettawong is offline chinsettawong  Thailand
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I'll try putting some silicone dots on the diaphragm and see if it will make any difference in sound. I agree with Calvin that this is a lot easier to do than making the micro spikes.

On the other hands, I do not think that these spikes actually touch the diaphragm. I agree with Oshifis that they are there only to prevent the diaphragm sticking to the stator. I've actually tried to tension my diaphragm using mechanical tension and hand stretch tension techniques. Mechanical tension tends to be too much for these headphones as the bass isn't as good. When I do hand stretch tension, it's a lot better. So, with low diaphragm tension and spacer to diaphragm width ratio of 1:143, my guess is that these spikes help the diaphragm sticking to the stators.

Wachara C.
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Old 27th September 2011, 07:58 AM   #15
MJ Dijkstra is offline MJ Dijkstra  Netherlands
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If the spikes won't touch the Mylar than I think you would hear a rattling sound at higher levels when the Mylar starts to touch the spikes. So these spikes must always touch the Mylar ( and otherwise they could be simply omitted).
While silicon dots offer some great insulation I wonder what these spikes can offer at this point. Of course the voltage requirements are much lower
I own some stax myself for several years and these things work great
drs M.J. Dijkstra
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Old 27th September 2011, 08:31 AM   #16
chinsettawong is offline chinsettawong  Thailand
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I've just opened up the driver again to check if the spikes touch the diaphragm, and no, they don't. I wish I have a tool to measure the height of these spikes.

Wachara C.
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Old 27th September 2011, 02:18 PM   #17
Nevod is offline Nevod  Russian Federation
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Very clever things they are..
Usually when diaphragm hits the stators, there is still lot of unused displacement - often about half of what is achieved when all the diaphragm hits the stators.

Standard support points which touch the diaphragm increase resonance frequency at same tension level, but they do allow to reduce tension and still not touch the stators.

These supports both do not increase resonance frequency and allow reduced tension. When the diaphragm deflects too much it first hits the supports, which seem to be round so this does not produce sound, and is mechanically divided into regions. So in the conditions where with an conventional stator a diaphragm would hit the stators at center of the driver, while it would barely move at edges, with such a dotted stator there would be the whole diaphragm would be deflected almost equally while not touching stators anywhere.

That's how I see it. Would be a PITA to diy though, sadly.
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Old 27th September 2011, 03:53 PM   #18
bobnick is offline bobnick
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Originally Posted by chinsettawong View Post
I wish I have a tool to measure the height of these spikes.

Wachara C.

You can often make measuring devices from stuff around the house. For example, you can make shims from pieces of paper stacking then up until they are the same height. For instance, you could measure the height of a ream of paper and then divide by 500 to find the height of a single sheet. Also you could use the geometry of triangles to "amplify" the height to an easily measurable level.

Umm, but don't you have a CNC machine? Couldn't you make a set of gauges like a small inverted U?

As to the purpose of the spikes, I don't know. But independent of what their purpose is, they will introduce non-linear behaviour to the membrane resulting in something akin to soft limiting - so distortion as high deflection. It would be different if they always touched the diaphragm.

I do not know about them stopping the membrane from sticking to the diaphragm due to electrically generated negative compliance. All I have read has put the mechanical compliance of the membrane due to tension quite high. Whether it is as high as the 3.5 ratio used by Quad, I do not know. Has anyone on the forum experienced a membrane sticking to a stator in Stax phones under normal circumstances - at any level? It would be noticable because the sound would cut out. Of course, this argument could be shot down if you find this particular model is aberrant. Will it be a future design feature or a dead end?

Also, from the photo you supplied, the stator design should preclude the diaphragm being influenced by the thin film behaviour of the air trapped between the membrane and the stator so that one is out.

I can't see how they would affect the behaviour of the primary membrane resonance (apart from the non-linear bit) as this is purely a function of mass, compliance, and damping none of which is altered, at least at reasonable deflections. As to the higher order modes in the membrane, even if the spikes could affect them, I hope the modal deflections are not large enough to contact the spikes - that would be really bad.

Nope, short of tracking down the designer and making him talk, I don't think you will ever know for certain. Another Stax mystery!

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Old 2nd October 2011, 09:45 AM   #19
210 is offline 210  Germany
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Regards Wachara! Very interesting spikes. No spikes between the outer three holes/rows, and in the middle row they are three holes apart, else just two. Maybe the spikes do a little disloading of the diaphragm when touched. Could you measure the resistance between spikes and stator with a multimeter (probably in the megaohm range) ?
You know that's it: receive and transmit (Peter Gabriel
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Old 2nd October 2011, 04:16 PM   #20
chinsettawong is offline chinsettawong  Thailand
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Hi 210,

The Stators are coated with powder coating, I think. I don't have a high voltage resistance meter on hand. So, sorry about that.

I've been thinking about these spikes. Will they be beneficial if we were to put them on full range electrostatic speaker stators?

Wachara C.
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