Has anybody made an ELS headphone?

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Hi JonusKarud,

The design you pointed to was actually what I had in mind. If I were to use a double sided PCB in the middle, then I only need 3 pieces of stators to work with a double diaphragms design. I can do that easily. I agree with you that it will take some experiments to actually find out if the theory works. I will find the time to experiment with this design. :)

Wachara C.
 
Hi Wachara,
if you´re going to try the three stator design, theres a whole bunch of things you can experiment with! For example, connect the outer stator to ground via a 47-200k resistor so that the outer membrane is low pass limited to 1000 Hz. You can also try to give the two membranes slightly different mounting tensions, as I had better (cleaner and tighter) sound when I did this in my experiments.

Now I'm so inspired I must take up my experiments again! I'm thinking of something like a double membrane wire stator Jecklin Float EarSpeaker!
 
Hi,

the 3-layer membrane would yield two layers of film and a layer of conductive adhesive in between. Think of a double sided PCB, where the two copper surfaces represent the film and the core material (FR4 or alike) represents the conductive adhesive.
The two film layers would shield the core layer against environmental influences like humiduity or sratch resistance. Leakage could be reduced, since there´d always be an insulating layer between the conductive core and the outside world. The films would also function as an additional insulating layer which allows for an increased flashover treshold.
Though beeing very thin films the flashover treshold of the film could reach a couple hundred volts.

So its a totally different thing as a 3-stator-ESL.
A different tension of the films is not needed. The close mechanical coupling of the two membranes lead to a beghaviour as if it were just one membrane. So the mechanical tension ofthe films is connected in series, which leads to a reduced overall tension, hence lower Fs. Since the Fs of HPs easily ranges around 100Hz the reduction in Fs may well be responsible for the improved bass response.
This is simialar to the Fs reduction caused by the increased weight of a 3-layer membrane.

jauu
Calvin
 
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I still can't figure out how a sandwiched diaphragm would outperform a single layer. When you glue them together, they become one. So what's the difference compared with a thicker Mylar. I understand that by sandwiching, you get a better weather shield. But for sound, I really doubt it.

However, with a triple stators and 2 diaphragms design, I think it can improve the sound pressure. It will probably make the sound louder and bass deeper. Don't you think?

Wachara C.
 
Hi,

there are several, methods to improve bass response. One of which is to use a heavier and thicker membrane. This is what Stax has done with the C32. They could have achieved the same result with a coated and equally thick mono-membrane. But besides the acoustic response, safety and longevity aspects have to be dealt with and may have been the decisive points to choose the sandwich membrane over a mono-membrane.

2nd answer is yes.

jauu
Calvin
 
I've finished my 3 stators and double diaphragms electrostatic headphones. Here are some pictures:

The front and back stators are made of single sided 1 mm PCB. The middle stator is made of 1.5 MM double sided PCB.

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I use 0.5 mm plastic rings as spacers, 1 mm singe sided PCB ring for gluing the dust protective diaphragm on, and 2 mm foam rings as damper rings to eliminate the possible vibration.

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The unneeded copper on the PCB is chemically etched away. The copper side is spray painted with white and the other side with black.

DSC_0887.jpg


The enclosures are routed to shape similar to the dimensions of those of Stax Lambda series.

DSC_0883.jpg


I utilize a cable from KOSS ESP950 extension cord. Thanks Matt. :)

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This is with the dust protective diaphragm on.

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And this is with the 2 mm foam ring on.

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Putting everything together, this is how they look like. The ear pads are replacement pads from ESP950. Again, thanks to Matt. ;)

DSC_0897.jpg
 
There are a lot more works involved in making this pair of headphones. They sound pretty nice. However, I thought I could get a lot more bass out of them, but for some reasons I couldn't get much more. I'm thinking that I might have put too much tension on the diaphragm. :(

Comparing these to my older ones, I much prefer the former oval shape ones. Even though the 3 stators and double diaphragm yield better efficiency, but for the kind of music I mostly listen to, I prefer my older pair.

It's a fun project though.

Wachara C.
 
Hi JonasKarud,

The bias voltage goes to the center wire which is solder to a copper adhesive tape that I taped it from the back side to the front of the middle stator. This gives bias voltage to both diaphragms

The left wire is connected to the back stator and top side of middle stator. The right wire is connected to the top stator and back side of the middle stator. This is like putting two complete sets of ESL in series of one another. :)

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I also make a connector that is compatible with a Stax Pro series. :)

DSC_0901.jpg


Wachara C.
 
Okey, Wachara.

This means that you will have two opposite voltage swings on each side of the double sided middle stator.

There's a very high capacitance between the two copper layers of the middle stator , which will drain the drive transformer/transistors/tubes on (especially high frequency) power.

As I see it, You are much better of with one membrane with positive bias and one with negative bias.
The two outer stators are then connected to ground, and both the layers on the middle stator gets the signal.
 
Hi JonasKarud,

That's a very interesting idea. Do you mean to say that I should try making the two diaphragms work only half of the signal - one plus signal and one negative signal?
Doing so will require 5 wires. It's something that I can't do it right now. :(

Thanks for sharing the idea. I will try to source the wires and try later.

Wachara C.
 
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