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Building an Electrostatic Speaker
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue Apr 26, 2011 5:18 am    Post subject: Reply with quote


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Tom,

Yes, normally the HV-supply to bias the membrane is set to a fixed value and cannot be changed, in the case of the 3mm spacing for the ESL-1 and ESL-0.5 it is around 1800V. The customer liked to be able to play around with it a bit so I made it variable.

The step-up transformers I just ordered are for the audio signal and the outputs are connected to the front and back stators.

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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue May 03, 2011 6:37 pm    Post subject: Reply with quote

The perforated metal arrived today, I will post some pictures later. Now I have to deburr them some more before they can go to the powder coater.
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Tom.W



Joined: 09 Mar 2006
Posts: 6539



PostLink    Posted: Tue May 03, 2011 7:59 pm    Post subject: Reply with quote

beun wrote:
The perforated metal arrived today, I will post some pictures later. Now I have to deburr them some more before they can go to the powder coater.


What method do you use ?
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue May 03, 2011 8:17 pm    Post subject: Reply with quote

What I have now looks like a round Scotch pad that is mounted on a drill. Depending on the life of that thing I may have to use a flap wheel.
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Tom.W



Joined: 09 Mar 2006
Posts: 6539



PostLink    Posted: Wed May 04, 2011 2:50 am    Post subject: Reply with quote

Well I must say this has been an interesting thread ! Smile
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Wed May 04, 2011 4:54 am    Post subject: Reply with quote

It is going to be a lot more interesting when I am finally going to put it together. I am also working on an update of the high voltage supply and I made an initial layout of the PCB.

Most of my time now is spent on getting ready for the 2011 Lone Star Audio Fest on 13th-15th of may at the Park Central Embassy Suites in Dallas, TX. Together with the customer that I am doing this built for we have been doing some experiments to better control the panel resonance and the measurements show we have made progress. If anyone is interested I can post the results.

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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Thu May 05, 2011 10:06 pm    Post subject: Reply with quote

I am starting to order the South American Rosewood veneer and I managed to score a 2'x8' piece for only $25. This is great to be used for edge banding and mostly hidden spots. I will order the big sheet(s) later. I still have to figure out how much I actually need.
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Sun May 08, 2011 2:22 am    Post subject: Reply with quote

I have been a bit busy today and started to put a nice curve on the front of the base. To do so I glued a piece of lexan in the desired curve on the wood with some epoxy glue.



After drying I then used the miter saw for some rough cutting and the router with a trim bit to remove the wood until I have curve that is flush with the lexan strip.



After removing the strip and sanding off the epoxy glue I then copy this to three other wood pieces. Tonight I will stack two of these pieces on top to create the base.

I also finally took a picture of the perforated metal. The shop did a really nice job, also with the deburring it actually feels nice and smooth.


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Tom.W



Joined: 09 Mar 2006
Posts: 6539



PostLink    Posted: Sun May 08, 2011 6:15 pm    Post subject: Reply with quote

beun wrote:
It is going to be a lot more interesting when I am finally going to put it together. I am also working on an update of the high voltage supply and I made an initial layout of the PCB.

Most of my time now is spent on getting ready for the 2011 Lone Star Audio Fest on 13th-15th of may at the Park Central Embassy Suites in Dallas, TX. Together with the customer that I am doing this built for we have been doing some experiments to better control the panel resonance and the measurements show we have made progress. If anyone is interested I can post the results.



Please do ! Thumbs Up
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Mon May 09, 2011 4:26 pm    Post subject: Reply with quote

Ok, so here it is: the first frequency response is of the original ESL-0.5 with graduated vertical spacers only, narrower at the center and getting wider at the edges.



As you can see there is a visible major peaking of the frequency response at about 70Hz which is probably actually not that bad since the sub-woofer crossover frequency is supposed to be somewhere between 80 and 100Hz. There are also some minor peaks because of the purposely unequal distance in the spacers

The next response is of the same speaker but now there are additional horizontal spacers that divide up the vertical strip in 7 horizontal bands that get exponentially larger towards the bottom.



It is obvious that the resonance is now spread out over a much larger frequency range thereby reducing its peak by about 10dB or so. A subwoofer cross-over frequency of 80-100Hz will still be a very good choice.

Now a word of warning about the measurements, they are totally uncalibrated and the absolute vertical scale is meaningless. I took the measurements in the largest room I have using the audio output of a cheap netbook, I am pretty sure that its headphone output doesn't quite go all the way to 20KHz. The microphone used was a Dayton audio measurement electret from Parts-Express and again I used it uncalibrated, the microphone amplifier is a Blue Icicle and I don't know its exact frequency response nor do they publish a response curve.

The idea to use logarithmically sized spacers is not new by the way, it has been done by Soundlab a long time ago, but then again it is better to copy a good idea than to design a bad one.

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Last edited by beun on Tue May 10, 2011 12:46 pm; edited 1 time in total
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue May 10, 2011 5:58 am    Post subject: Reply with quote

Some more info on the variable HV-supply. I think I have the schematic finished and the first cut of the PCB is finished as well. The output voltage has two ranges: 1.8kV - 3.5kV and 3.5kV - 7kV. For the original design with the metalized membrane the 1.8kV setting should really be the only one used, the rest is for experimentation purposes only.


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HV_VAR.pdf
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue May 17, 2011 3:40 am    Post subject: Reply with quote

I got notification today that the transformers shipped, they ship from Canada so it may take a while.
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Tue May 17, 2011 4:30 pm    Post subject: Reply with quote

Another quick update, I just ordered the remaining two sheets of Rosewood veneer, I should get it in a week. With the veneer I already have I will start the edge banding.
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Thu May 19, 2011 9:39 pm    Post subject: Reply with quote

Well, my usual powder coater has ceased to be full service so I am on the lookout for a new one. This might take a few days.
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Tom.W



Joined: 09 Mar 2006
Posts: 6539



PostLink    Posted: Fri May 20, 2011 5:58 am    Post subject: Reply with quote

beun wrote:
Well, my usual powder coater has ceased to be full service so I am on the lookout for a new one. This might take a few days.



What ...Too much work ?

http://www.custompowdercoating.com/



Wink
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Fri May 20, 2011 1:31 pm    Post subject: Reply with quote

Well, not quite he went through a rough patch during the downturn. Thanks for the link, I already contacted these guys and am working on a few others.
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garyfritz



Joined: 08 Apr 2006
Posts: 7733
Location: Fort Collins, CO


PostLink    Posted: Fri May 20, 2011 1:50 pm    Post subject: Reply with quote

Man. Seeing what you go through to build these things, I gotta believe you're doing it for fun and not for profit!!
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Fri May 20, 2011 1:53 pm    Post subject: Reply with quote

Oh its for fun alright. For this reason I am not afraid to document everything, after reading this no-one in his right mind would want to do it himself. Just let me do it for you Very Happy
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beun



Joined: 28 Jun 2006
Posts: 664



PostLink    Posted: Fri May 20, 2011 5:37 pm    Post subject: Reply with quote

UPS just delivered the audio transformers at my door, of cause there was an extra $25 customs charge. I am not a lawyer but isn't that what NAFTA was for? Anyways this is how it looks, I unpacked one of them.



These are a lot bigger (about 6" diameter) than the old ones I used for the ESL-0.5, they look really good.

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Tom.W



Joined: 09 Mar 2006
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PostLink    Posted: Fri May 20, 2011 8:23 pm    Post subject: Reply with quote

How about the specs and the manufacturer ?
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