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Old 23rd September 2012, 04:19 AM   #61
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Custom fabrication would cost even more!!!!

That is why it is called DIY!

He,he,he,he can't get any more custom than that !!!!!

jer
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Old 23rd September 2012, 05:21 AM   #62
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I thought about custom fabrication but didn't follow thru on getting a price. One of the past projects at work required that we furnish perfed panels for a strainer assembly. can't remember what they were straining. in any case, my ears perked up because i was thinking that not only could there be a border but that there might be a meaningful scheme where the perfs ranged in size from the center to the outer edge of the panel. possibly a way to affect dispersion, damping... who knows?
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Old 24th September 2012, 04:38 PM   #63
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This site looks interesting. Too late for this particular build, but in the future...
Metalex | Perforated Metal | Perforated Metal Applications
Anyone ever use these guys?
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Old 24th September 2012, 04:51 PM   #64
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This pattern seems to be the best one,

.156" X .188" STAGGERED 62%

Should anyone inquire to them for a quote.

By the time you have it coated the open area will drop down to the 50% to 40% range.

jer

Last edited by geraldfryjr; 24th September 2012 at 04:58 PM.
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Old 26th September 2012, 04:29 PM   #65
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Quote:
Originally Posted by geraldfryjr View Post
Yes, that is a very good general rule of thumb.
Especially for diagphram widths larger than say 5 to 6 inchs.
However this rule quickly runs into practical considerations as the panel gets wider than say 9" or more.

The lowest frequency of operation must be taken into account as well.
As not too run out of room for large excursions at the lower frequency's of operation.

There was a good chart that I knew of that suggested the minimum D/S as per lowest frequency of operation.
However I am having a difficult time trying to find it on the web or the original document has been modified since and no longer has the data that I am looking for.
I do have it in my archives somewhere though.

Even with my little panel with a width of 3.25" and aprox. D/S ratio of 1:45 I have been able to clip the diagphram into the stator at Frequency's lower than about 200Hz to 250Hz even with a spacing of .072" (+/- .003").
Even more so when I hit the resonate frequency of the diagphram of about 70hz to 90hz.

May I add that this much excursion for my little 3.25" X 9.75" diagphram is quite very loud!!

A 1mm spacing may be good if you are planning on crossing over at a rather high frequency of say 1Khz or even 1.5Khz or higher and definitely if it was intended to be strictly a tweeter panel.
IMHO .0625" or as Charlie had mentioned a spacing of 1.5mm to 2mm is a very good place to start and should be good for those peaks at around 300Hz.

Remember that the excursion doubles for every octave lower in order to produce the same SPL as the starting fundmental.

Here is a very good read on the subject although it pertains mostly to headphone drivers,

HeadWize - Project: Notes on DIY Electrostatic Headphones by Chu Moy

And here is a much more detailed version as well just scroll back to page 138 for the beginning,

Loudspeaker and Headphone Handbook - Google Books

And here as well,

Audio and Hi-Fi Handbook - Ian Robertson Sinclair - Google Books

This is a very good thread that had touched on the subject as well,

Hybrid ESL, suitable x-over frequency?

The last time I was able to run my little panel I found that I got about +/- 30 degrees of usable dispersion off of the center.
And at about 45 degrees off the center there was noticeable drop off of the high frequency's as expected.

Enjoy !!

jer


I must correct myself.

The excursion quadruples for every octave lower for the same SPL.
Here is a nice little calculator that helps determine SPL's for a given displacment(Xmax) vs frequency.
this calculator assumes a monopole or Closed box/IB (Infinite Baffle).
Just convert your total surface area into driver diameter.

Piston Excursion calculator

According to the calculator my little panel was doing 114.5 db at 300Hz clipping into the stators !!!
Very Very loud as I remember as I didn't have an SPL meter at the time. He,he,he,he

jer

Last edited by geraldfryjr; 26th September 2012 at 04:43 PM.
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Old 26th September 2012, 05:14 PM   #66
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One more correction that I just noticed,

The program compensates for 83% of the driver diameter due to the surround.
Multiplying your surface area by 1.17 will adjust for this.

This also raised my predicted SPL by nearly 3db at 117.2db and is more like what I remember.

Have fun !!!

jer
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Old 26th September 2012, 05:30 PM   #67
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What was the d/s spacing on your little panel doing 114.5 db?
Is the first touch of a diaphragm to a stator a failure event requiring a rebuild?

Also, funny how I am seeing perforated metal in so many places now. I noticed the 2' x 2' ceiling vent where I work might make a good stator, albeit more squarish than is typical.
Still, if you could be OK with the shape, they are only $25 each and don't need much additional prep.
Air vents, AC Vents, Ac Diffusers, Air Return, AC Return part way down the page on the left.
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Old 26th September 2012, 05:56 PM   #68
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I had it about .072" to .075" (1.6mm to 1.8mm) D/S.

I detected the stator clipping with a micropone and you could hear it as well.

Ahhh,ha,ha,ha,ha,ha, You have the bug now !!!
Everything you see your gonna think about "Hey, I could use that to build an ESL!!! ".

I use window screen and plastic lighting grate (egg crate) and I have even made some out of gift Credit cards,wire,PCB material and aluminium foil, almost anything can be used!!!
My very first one was made out of a piece of perforated aluminium soffit material and this worked great except the open area was quite low and restricted the sound too much.

The failure and demise of my little panels was the failure of stator coating pushing in excess of 25kv p-p across them.
This was the first time it had burst into flames and I was able to repair it, But sadly not the second time around.

jer

Last edited by geraldfryjr; 26th September 2012 at 06:12 PM.
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Old 28th September 2012, 12:30 AM   #69
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Got the Mylar today! Time to get serious...
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Old 28th September 2012, 01:21 AM   #70
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Quote:
Originally Posted by Shaunman View Post
What was the d/s spacing on your little panel doing 114.5 db?
Is the first touch of a diaphragm to a stator a failure event requiring a rebuild?
I think not.... I'm sure the nasty transient pop I've heard on occasion at high volume was due to my subwoofer acoustically coupling to the diaphragm and driving it into a stator; momentarily discharging the diaphragm. So far no apparent damage, though. Burning holes in the diaphragm has practically no effect but I suppose if it happened repeatedly at the same location, the arcing could burn thru the stator coating and that would be a problem. I think one advantage to using a high-resistance coating on the diaphragm is that it can't then pass enough current to sustain a really hot arc to the stator.... just speculating but it sounds logical to me.

Last edited by CharlieM; 28th September 2012 at 01:40 AM.
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