[chinsettawong]

Quote:

 
But isn't sitting on your desk or suspended an inch away from your ears with no earpads or damping practically the same thing? I know every electrostat I've ever made sounds pretty bad when held an inch away from sealing

 
Please remember that size does matter.
You've got to try listen to a pair of good fullrange ESL. 

 
Wachara C.

 

[chinsettawong]

I played around with bicycle inner tire diphragm tensioning method again yesterday.  The diameter of this jig was 400 mm, and I stretched the diaphragm to 1%.  Apparently 1% was too much.  I'll try 0.5 and 0.75% next time.
 

 

 
 

 

 

[arnaud]

What an interesting way to apply the tensioning wachara!! This seems so much cleaner method than the discrete weights.

 

[spritzer]

I love that last picture... 

 
"You want tension..?  I'll give you tension...  "

 

[chinsettawong]

Quote:

What an interesting way to apply the tensioning wachara!! This seems so much cleaner method than the discrete weights.

 
It's actually a pretty good and easy tensioning method.  Once you get the right tension amount, you can repeat the same tension again and again with ease.  However, it wastes too much material.  
 
 
Quote:

I love that last picture... 

 
"You want tension..?  I'll give you tension...  "

 

 
Too much tension isn't good.  With these diaphragms, what I hear is that the dynamic and bass aren't as good.  Tomorrow, if time allows, I'll try 0.5% or 0.75% tension (2 or 3 mm) and will report back.  By the way, the Mylar I used was 3.5 micron.
 
Wachara C.

 

[chinsettawong]

I made a smaller jig today.  I made a stupid mistake again by tensioning the diaphragm to 1% elongation(2 mm on this one is about 1%).  So I had the same result as the last ones.
 

 

 

 
Well, I had to redo them again.  For this second time, I tensioned the diaphragm to 1 mm (0.5%) and they're better.  They sound very nice and stable now.
 
If you guys want to try this technique, 0.4%-0.5% elongation on the 3.5 micron diaphragm seems to be right on target.
 
Wachara C.

 

[wakibaki]

I just bought a 4 inch embroidery hoop:-
 
http://www.ebay.co.uk/itm/Elbesee-Wooden-Cross-Stitch-Embroidery-Hoop-Choice-of-Sizes/160923561289?_trksid=p2045573.m2102&_trkparms=aid%3D555003%26algo%3DPW.CAT%26ao%3D1%26asc%3D16548%26meid%3D477708376818621753%26pid%3D100034%26prg%3D7839%26rk%3D4%26rkt%3D4%26
 
I was going to use it to tension some very fine wire mesh I bought to attach to a spider-type stator, but I guess it can be used for a tensioning jig for the diaphragm too.
 
I still haven't got my CNC machine to cut the stator and diaphragm spacers yet, there were some problems with the electronics that I didn't get fixed before I went into hospital for surgery and I've been feeling a bit down 'cause I've started on chemotherapy. I'm still very interested in this project though, and I'm working on PCBs for a very straightforward amplifier I've designed using depletion-mode mosfets. The amp has a very low component count and cost and is intended to run off a 12V AC wallwart.
 
w

 

[chinsettawong]

Hi Wakibaki,

Wishing you a speedy recovery. I'm very much looking forward to seeing your new amp.

About the wire mesh stator, believe it or not, I've bought the similar hoop that you bought and intended to do the same. But I haven't done it yet.

Good luck.

Wachara C.

 

[chinsettawong]

I've got some updates on the inner tire tensioning jig method that I'm using.  Apprently, 1% elongation on Mylar is too much.  Since the elongation is so little using this small jig that it's very difficult to measure, I've found a new way to identify the right tension amount.  This time I purposely make some wrinkles on the Mylar.  I've found out that if you tension Mylar enough, all the wrinkles would be gone.  But when you see all the wrinkles are gone, the tension is too much already.  So, I tension the Mylar until the point where the wrinkles are almost gone, and this is what I get.
 

 
Notice the wrinkles on the Mylar.
 

 
This is before I pump the air into the tube.
 

 
This is after I've pumped in some air and the wrinkles on Mylar are almost gone.  The elongation is so small that it's very difficult to determine the right amount by observing these lines.
 

 
These are what I get.  Still the tension is just a little too much, but it's not too bad. 
 
Wachara C.
 
 
 
 
 
 

 

[shipsupt]

Just a question out of pure curiosity... how much tension are you putting into the material?  Do you need to pump the tire up to a pressure like it was being used on a bicycle, or is it just getting slightly inflated?

 

[chinsettawong]

That's a question that I'm trying to find an answer myself.  At the very beginning, I was aiming for 1% elongation.  Then it was too much.  Anything less than 1% would be very difficult to make an accurate measurement.  If I have to guess now, I would say 0.3-0.5% elongation should be just right.  
 
You can't really look at how much pressure you're putting into the tire, since you don't really put in that much at all. 
 
Wachara C.

 

[shipsupt]

Quote:

You can't really look at how much pressure you're putting into the tire, since you don't really put in that much at all. 
 
Wachara C.

 
That's exactly what I was wondering.  Thanks.
 
This thread is always fun to read!

 

[arnaud]

Wachara, you've always been making your transducers like this? I mean gluing the tensioned mylar to the spacers rather than one of the stators.

Reason I ask this is that I don't imagine how such kind od spacer cam hold it's shape unless it's like 2mm thick aluminum ...

This current spacer looks like copper, but is it different from usual or you typical 1mm PCB?

 

[chinsettawong]

A little warping isn't a problem.  When I put everything together, I use plastic screws to hold them in place, and the spacer will be flat.  
 
The spacer is my usual 0.5 mm PCB. 
 
The trick is really to get the best suitable tension.  It's not so easy, but let's try.
 
Wachara C.

 

[Salm0n]

Hey guys, sorry for a somewhat off topic post, but I can't think of anywhere better to post this question.
I'm building a set of planars from scratch, parts are in the post, but I'm unsure as to how I should mount the mylar diaphragm to the frame holding the magnets. I was thinking about just using epoxy, but I dont know a lot about glues. What method(s) do you use for attaching the mylar?