[AmarokCZ]

dude_500: the blue line is definately not sealed, there must be some leak, a large one!
I'm using the same film as you were (2um) and with two dust covers my bass frequency response is flat just like yours with 6um (even flatter). Just look at the SR-009 measurements: free-air resonance is ~170Hz but when sealed the frequency response is flat (except the ~40Hz step).
 
Here's my response (2um diaphragm, two dust covers, driver in wooden earcup, leatherette earpads, little bit of damping on the back side of driver, bias 580V), finally with calibrated mic:

 
As you can see the bass is great even at 20Hz, so I think you must have some huge leak somewhere.

 

[chinsettawong]

So, do you guys like 6 microns Mylar or not?  

 
I bet you can give it a bit more tension and it will be stable at 600V and the bass will be very good too.
 
Not putting a sweat screen isn't a good idea.  You probably can only do that in the dry seasons.
 
Wachara C.

 

[AmarokCZ]

I'd like to ask what's the benefit of 6um Mylar to 2um one?

 

[chinsettawong]

6um Mylar is supposed to give better bass than 2um one.  But for some reasons, dude_500 haven't found that to be true.
 
As for me, 3um is already a lot better bass than 2um.  But 6um isn't very clear winner of 3um.
 
Wachara C.

 

[AmarokCZ]

Quote:

But for some reasons, dude_500 haven't found that to be true.

I think he did! Now with 6um he got response flat to ~30Hz and with 2um it was flat only to 60Hz (and there was bump at ~80Hz).
For me the 2um is great and I can't imagine it could be better.

 

[dude_500]

I do get more bass with 6-micron, but only with no sweat screens. Increased tension a little bit (about 30%) to ensure stability, and also built new 6-micron sweat screen to see how that does. 
 
Severe bass roll-off with sweat screen, non without. Both times pushed hard into the cushion, definitely sealing in both tests. Results are highly repeatable.
 
 

 
 
So, I guess I'll just have to see what happens with no sweat screen, unless anyone has ideas about it. I've tried 2 micron with no tension, low tension, high tension, and no tension with 6 micron and high tension with 6 micron. It all destroys the bass.
 
 
Overall, my favorite sound thus far is no sweat screen, 6-micron.

 

[khbaur330162]

Quote:

Anyone got idea what's causing the sharp change in response near 30Hz? (same thing is on responses of SR-009 measured by arnaud)

 
Quote:

I can't comment anything about the FR curves.  I just don't know anything about them, unfortunately.  

 
Wachara C.

 
http://www.innerfidelity.com/content/skullcandys-director-electrical-acoustical-engineering-dr-tetsuro-oishi-visits-innerfidelit-0
 
This might be of some help.

 

[arnaud]

Quote:

I do get more bass with 6-micron, but only with no sweat screens. Increased tension a little bit (about 30%) to ensure stability, and also built new 6-micron sweat screen to see how that does. 
 
Severe bass roll-off with sweat screen, non without. Both times pushed hard into the cushion, definitely sealing in both tests. Results are highly repeatable.
 
 

 
 
So, I guess I'll just have to see what happens with no sweat screen, unless anyone has ideas about it. I've tried 2 micron with no tension, low tension, high tension, and no tension with 6 micron and high tension with 6 micron. It all destroys the bass.
 
 
Overall, my favorite sound thus far is no sweat screen, 6-micron.

 
It looks like your sweat screen is as much tensioned as the diaphragm and that you get coupling between the two membranes (double slope for the roll off at LF). Depending on how lucky you are with the free air resonance frequency of both the diaphragm and the sweat screen (which acts like a passive radiator), you seem to be getting a bump before the roll off (similar to a poorly aligned bass-reflex speaker).
 
I'd be interested to see a summary of the comparisons between the various thicknesses and tensioning. But I guess a key point when you're doing the comparisons is ensure all configurations have the same free air resonance, else all subjective impressions are likely more due to the tensioning than change in material. Theoretically, a thicker / heavier diaphragm should roll of at HF, which does not seem to be visible in your graphs? Maybe this belief is a bit "overrated" and a result of years of Stax marketing

 

[arnaud]

Quote:

So a few things... first off, I had one of the drivers mounted upside-down in my headphones, which was leading to the awful sound. I can't stand phase-reversed channels!
 
 
I turned down my bias and went back to 6-micron to try them out again, now they're stable (about 450V bias vs. 600). They sounded about the same as the last week of listening on the 2 micron. 
 
Randomly, I thought let's take off the sweat screens (I still just don't like the concept of them being there). Within seconds, I was absolutely blown away. Felt like I was being kicked in the face by the low bass.
 
Blue - 6 micron with sweat screen (sealed)
Green - 6 micron without sweat screen (sealed)
Red - 6 micron without sweat screen (a few inches away, unsealed)
 
 

 
So, it looks like I have free-air resonance at 100hz, and sealed it pulls it down to an incredible 30hz. 
 
 
6-microns it is! I'm going to sit back and enjoy the sheer beauty.

 
Do you have the 6 micron WITH sweat screen (a few inches away, unsealed) ? Curious to see the free air resonance frequency of that one...

 

[chinsettawong]

Ok, I think that we can now confirm that the sweat screen tames down the bass somewhat.  Perhaps its' time to look into what better material is suit for this purpose.  Stax uses a different material for all it's sweat screens.  The material is really thin and fragile.  It has some wrinkles on the surface.  What it is, even Spritzer doesn't know.  

 
I have a quick and simple idea.  If we really don't want to use a sweat screen, then maybe we can swap the direction of the energized Mylar to facing outward.  That way the humidity in the cup won't affect the diaphragm so much.  Let's try it.
 
Another idea is to make the double diaphragms design.  We encapsulate the energized sides of the diaphragm in the middle.  The two diaphragms serve as protective diaphragms on either side.  We need to make a special bias ring that would gives the bias voltage to both diaphragms. Let's say make it using a thin sheet of copper of 0.1 mm.  This idea sounds rather funny, but I've actually tried it.  At that time, I just did it for fun and didn't think about not using the sweat screen.  The sound was pretty nice.  I was hoping to gain a bit of efficiency from using two diaphragms, but that wasn't the case.  The idea was from an ESL expert who whispered softly to me.  

 
Wachara C.

 

[chinsettawong]

By the way, we can also try playing with the distance of the sweat screen and the diaphragm.  I'm not sure if we move the screen further away from the diaphragm will cause any better or worse effect.  What do you guys think?
 
Wachara C.

 

[AmarokCZ]

dude_500: The response on the last picture you posted is now with good seal because there is no visible resonance (unlike the previous one). What's the tension of the sweat screens? It seems to be high and it's causing the roll-off (I've been there). This is the reason why I'm not using Mylar for sweat screen (I already wrote here that the sweat screen must have low youngs modulus or must be similar to the Stax sweat screens).
khbaur330162: thanks for the helpful link! The good thing is that this "spring effect" gets almost canceled with good seal (see my frequency response at the top of this page). If you look at my response on the top of the page, there seems to be the "Voice Coil Wobble" at ~500Hz, so I guess that has nothing to do with coil (from what I can tell it't also caused by the same "spring")
EDIT: chinsettawong: I tried it, but the effect of diaphragm-sweat screen distance is small. 

 

[ujamerstand]

I don't know what stax uses for their dust screen, but from this post, they seem to slowly hand rub the material (for a staggering 30 hours?!) to add folds into the film.

 

[dude_500]

Quote:

 
I have a quick and simple idea.  If we really don't want to use a sweat screen, then maybe we can swap the direction of the energized Mylar to facing outward.  That way the humidity in the cup won't affect the diaphragm so much.  Let's try it.

 
I have always been careful in my designs to have the charged side facing outwards, for exactly this reason. After wearing after a shower, I have seen the entire diaphragms covered with visible condensation on the inside from water in my hair evaporating, it had no impact on performance. And since it's condensation, it's pure water and will just evaporate away in time leaving nothing behind. Time can only tell if it would work in the long term, though.
 
I'm mainly worried about hair grease building up from the few hairs that penetrate the stator. If one were bald or had extremely short hair, I see no reason why you would need a sweat cover. Even evaporated sweat should be pure water.

 

[AmarokCZ]

Quote:

If one were bald or had extremely short hair, I see no reason why you would need a sweat cover.

I see a reason - short hair gets between stator and diaphragm. Only way to get it out is disassembling the driver.