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Old 4th July 2006, 01:11 PM   #1
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Question ESL Contruction, material for separation diafragm to stators

Hi, in the moment i work in constructions the my ESL. What material recomends for separation diafragms to stators... What spesor correct spesor.

My pannel 125x25 cms, the diafragm is a mylar 12um..



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Old 6th July 2006, 09:46 PM   #2
Bazukaz is offline Bazukaz  Lithuania
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Hi,
You can use many types of plastic - like plexiglass , PVC , textolyte. For sure , the best is to use material with low permeability.High permeability plastics will increase panels capacitance more.

Regards,
Lukas.
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Old 6th July 2006, 10:34 PM   #3
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What spesor recomend. i have a acrilic 10mm
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Old 7th July 2006, 01:47 AM   #4
BillH is offline BillH  United States
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Hi, pmscompany.

Acrylic is good. The thickness depends on how low a frequency you want the ESLs to play.

Here's an example of different frequency and spacer thicknesses:
10Hz------10mm
100Hz------1mm
1000Hz---0.1mm

There is a tradeoff, though. Your bias voltage is proportional to the spacer thickness. Thicker spacers=more voltage.

My ESLs are have a spacing of 1.4mm and run at about 3500 volts bias voltage.
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Old 7th July 2006, 06:07 AM   #5
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Default 10mm acrilic

Hi,
i think 10mm is too mutch.
If you build the speaker with this thickness you need several kilovolts, around 35Kv total (bias + audio).
How do you go to buy the transformer?
Even if you make a series/parallel connection of more transformer, the road is complex.
If you wont a good bass response, you can make your speaker whit 4 mm insulator thikness and have around 50Hz bass response.
remember with 4mm you must have max 10Kv total voltage.
5Kv bias and 2Kv rms ( 5 Kv peak to peak) audio voltage.
With this voltage don't forget the corona spray (insulator) on the out side of the stators....


good bye and good work.............

.........marco italian esl constructor!
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Old 7th July 2006, 03:50 PM   #6
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Hi, my pannel 225-20Khz frecuence responce, 1500v EHT two toroidal 50va, 230 secundary and 6v primary.

- Saludos
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Old 7th July 2006, 09:11 PM   #7
Bazukaz is offline Bazukaz  Lithuania
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Hi,
Remember - efficiency and stator spacing relation is quadratic , i.e if you double the spacer thickness the output power will drop 4 times.
So , for 10mm spacers the output power will be 100 times less compared to 1mm spacers , assuming the drive voltage is the same !

Regards,
Lukas.
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Old 8th July 2006, 10:43 AM   #8
maudio is offline maudio  Netherlands
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For spacers any plastic should do. I build the stator frames from trespa using the same material as spacers.

About spacing: It all comes down to matching the spacing to available drive voltage and lowest frequency that must be reproduced. Higher frequencies mean more drive voltage from the transformers before core saturation kicks in, while spacing can be made smaller increasing sensitivity. At some point there is an optimum where combined panel sensitivity and available drive voltage at the lowest freq result in maximum possible stroke.

2 x 6v/230v toroids will give a max drive voltage of only around 500V rms @ 50 hz before core saturation kicks in. 500V rms = 1.4 kV peaktopeak. But the max output voltage of the trannies increases in a linear way with freq so at 200 hz you'll have 5.6kV peaktopeak. With the 225 hz crossoverpoint the transformers output will be more than enough.

For fullrange (>40hz) panels, my personal rule-of-thumb is that 2....2.5 mm (membrame to stator) is about the maximum spacing that is usable. Only up till this spacing you can reach full stroke using normal transformers and amplifiers (talking about 8-10 kV peak drive and 4-5 kV bias). Anything larger will require much more drive voltage than can be raised resulting in reduced instead of increased output. For instance, a panel with 4 mm spacing might end up with a max stroke of less then a mm, because of lack of drive voltage.

Seen the output of your transformers and the 225 hz lowest freq I would chose spacing around 1...1.5 mm. Anything less than a mm is difficult because of tolerances.

Try tensioning the mylar as tight as possible, will allow for more bias and better sensitivity. This is the key to high output. I think you should use much more than 1500V EHT.
Btw I think 12 um is a bit heavy for a panel running up till 20 khz. You'd be better of using 4 or 6 um.

Good luck!
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Old 11th July 2006, 10:22 AM   #9
Calvin is offline Calvin  Germany
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Default material

Hi,

choose the material after needed parameters/dimensions, price and availability.
Depending on the construction the spacers have to fullfill an electrical task and an mechanical task.
For example with most wire-Stators the spacers build a frame that has to take serious mechanical stress, whereas with perforated metal sheets the only mechanical task is to provide for the d/s and to withstand the tearing force of the diaphragm.

You can find tables for different materials at many suppliers websites.
Of major importance are the insulative values and the permeability (epsilon(r)). The first should be higher than ~20kV/mm and the second as low as possible (1 beeing the theoretically lowest value)
But keep in mind, that those values count for pure material. PVC for example can be used very well in pure (white) form, since its a commonly used, cheap material that can be glued well. But You might be offered filled/coloured PVC. Stay away from black versions and be aware of grey versions since those might use carbon.
(As a general guide, be cautious with black materials in any way when HV is involved!)
Acrylic is useable too but You have to check for constant thickness. This can vary unacceptably!

Since flashovers are often found in closest proximity to the spacers the spacers should preferrably made of a material that doesn´t creep and doesn´t build carbon tracks.
Another useful feature is hydrophobic behaviour. Over the time dust, smoke and humidity tend to build up a conductive film on every surface. Hydrophobic materials like silicones prevent the built of this moisterous film.

An excellent material can be simple Silicone since it has outstanding insulative parameters, a low permeability and can function as a flexible glue. As long as the mechanical task allows for the use of silicone this is a cheap but excellent solution. It can be used with perforated metal sheets.
When You need mechanical strength, PVC, Acrylic and Trespa are better, but You might still combine materials for a better overall result. (for example using PVC or acrylic for an outer frame and silicone as damping pads and as an sealant of the outer and inner rims of the plastic-frame.

jauu
Calvin
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