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Old 21st March 2017, 01:15 AM   #431
bengel is offline bengel  United States
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Just a quick update....

So I took my heat gun to it and made a *big* difference.... dropped the resonance down to 114hz almost exactly. I get the most "visible" excitement at this frequency consistently across the membrane... there are other modes of excitement as well but this one is quite obvious.

The bad news is I burned a tiny hole in the membrane with the heat gun. I put a little piece of the tyvek tape over it. It is on the bottom and not terribly visible so I may just live with it. Haven't decided yet...

It appears there is less strain in the membrane just from the "rainbow" diffraction patterns I was seeing before under fluorescent light, they were all twisted....now they are fairly straight and less visible. I will try photographing it on the next one but suspect it will be difficult.

I will probably do my next panel the same way... I like the idea of going a little over with tension then heat treating it "anneal" it out. No idea at all if it makes any sonic difference, just seems like it should.

I did also want to note that I plan on covering my panels with silk screen for damping.
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Old 21st March 2017, 08:47 PM   #432
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Awesome, that's great news!
Also one hell of an "Aha!" moment for me, I had no idea...
New one in my book, and a game changer as far as I'm concerned.

If you're going to be covering these, I wouldn't let the burn bother me unless it affects the sound negatively..
Roll with it bengel, you're almost done, haha..

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Last edited by wreckingball; 21st March 2017 at 08:58 PM.
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Old 25th May 2017, 01:59 AM   #433
bengel is offline bengel  United States
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I'm back again for an update on my insanely long ESL project.... it sucks in that literally every weekend for the past 6+ months I've been busy with other projects....

At any rate.... onward.... so I managed get the diaphram on my second panel; after *several* attempts at stretching.... I did it the same way as my last one.

My excited resonance frequency was about 132hz right off the stretching jig (well, I did let it sit overnight). I applied a few rounds of heat treatment and got it down to about 124hz. I stopped as I was getting uncomfortable how long I was having to go over it with my heat gun on full blast.... I didn't want another hole.

So I have one at 114hz (as of my measurement a few months back) and one at 124hz... close enough I guess.

Also noteworthy, is I do have other modes of excitement under 124... like a big one (smaller than 124 though) around 65hz.... about an octave so kind of makes sense.

I have become a fan of heat treating after stretching. The one thing I cannot get a good picture of is the diffraction you see when you look at fluorescent light at a "glancing" angle across the diaphragm.

Before I heat treat, the rainbow patterns (for lack of a better word) are twisted, clumped etc... all across the membrane surface, after heat treatment they are pretty much straight up and down. I could be wrong, but this is telling me the tension of the diaphragm becomes more uniform after treatment. I have no idea if this has any impact sonically.

Next is coating.... electronics, then some more woodworking.
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Old 26th May 2017, 04:24 PM   #434
bengel is offline bengel  United States
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Got the coatings sprayed on... though I think I went a little overboard with the spray.

I tested both panels for resonance and they both come in right around 124hz after the coatings. Not sure why my older panel increased in resonance or if my testing method is sound but at least they are consistent between the 2.

Some largeish dust particles settled into the coating, should I remove them (if even possible)?
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Old 26th May 2017, 06:37 PM   #435
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I think the bigger particles will vibrate off during use and the smaller ones won't be enough to affect their sound or performance..
Someone else more knowledgable than I will probably chime in though, I'm guessing..

How much coating is leftover in the can? I used just under half a can for my 15"x60" curved panels, that's probably overkill too, but I wanted to make sure they had full coverage. (plus a bunch wound up on a foam brush I used to spread it out)

Congrats on getting getting closer to completion, any pics you could post up?
Maybe a pic of the dust too, so someone could form a better opinion?

Cheers
-Steve
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Last edited by wreckingball; 26th May 2017 at 06:40 PM.
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Old 26th May 2017, 06:49 PM   #436
bengel is offline bengel  United States
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I have about half also.... my panels are a bit smaller than yours so I probably *really* over did it :-).

I just sprayed until the "mist" look on the panel was gone. I probably should of tilted the panel around a bit instead.

Oh well, can't be worse than aluminiumized mylar :-)
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Old 29th May 2017, 02:48 AM   #437
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Quote:
Originally Posted by bengel View Post
Also noteworthy, is I do have other modes of excitement under 124... like a big one (smaller than 124 though) around 65hz.... about an octave so kind of makes sense.
Glad to hear you are still making progress, and closing in on completion.
I wonder if the 124Hz resonance is the lowest mode, and is just being excited by the 65Hz tone.
Were you ever able to get a microphone to measure the actual response? That would let you know for sure.

Quote:
Originally Posted by bengel View Post
Got the coatings sprayed on... though I think I went a little overboard with the spray.…Some largeish dust particles settled into the coating, should I remove them (if even possible)?
Fortunately even a thick coating of Licron Crystal adds little mass.
David Lucas ESL

I doubt the dust particles will cause any problem whatsoever.
But, if it bothers you, you can remove them with a Qtip dipped in acetone.
Then reapply a bit of Licron in the area with a modeling paint brush.
I’ve done it.
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Old 31st May 2017, 02:09 PM   #438
bengel is offline bengel  United States
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So finally got the panels together... Put the charging ring on and stuck them together.

It's worth noting that I used conductive adhesive copper tape and stuck the tape directly to the diaphragm coating (which does not go all the way to the edge).

Definitely not built to the tolerances/quality I would like them to be but hopefully they will sound good. I am concerned how accurate/consistent the d/s spacing is across the diaphragm given that hundredths of an inch matter :-).


I have not measured the resonance with a microphone setup. I kind of figured I've done all I can do with it anyways other than try to go lower and redo the diaphragm. I think in the long run, I will be better off with a bit higher tension/resonance anyways.


Here is a pic of the current state. Have some touch ups to do on the grid, though I may not bother as I plan to cover them with silk screen for damping.


Next on to the resistor bank. I would love to measure the capacitance of the panel to nail down the resistor values but I am not sure my meter is accurate enough or if it would be accurate anyways.
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