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Old 11th April 2010, 09:18 PM   #1
bentl is offline bentl  Norway
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Default Stator size/frequency range

Hi,

I have built 1 stator made of perforated, powder coated steel plates, d/s = 2 mm and stator size is 1000mm X 350mm. Spacers are sectioned in 4 sections of 250X350mm

I find the size impractical, and using steel stators gives some challenges when it comes to insulation, fastening to supports etc. Gluing the diaphragm is also a challenge - it requires a slow-curing glue that will glue to spacers and diaphragm.

I have designed a new stator in standard A4 (297X210mm) that will be made out of lexan, and coated with a conductive coating on the inner side.

I will make 6-10 of these stators and make an array, electrically connected in parallel.

My question is, how will this affect frequency response? The new stators will be about the same size as one section of the big stator, but total size of 4-5 of these panels will be larger.

Thanks for any input!


Regards,

Bent
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Old 11th April 2010, 10:38 PM   #2
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Hi Bent,

stator dimensions affect the frequency range in two ways:

1 - The smallest dimension sets the frequency at which bass roll-off starts, due to cancellation of the back & front waves. You only get more bass if you put two 'stacks' of modular panels right next to each other side-by-side.

2 - The panel area determines the capacitance, and this affects the frequency range insofar as a larger panel presents a lower reactance to your amplifier at high frequencies.

Making the panel area higher, but not wider, is a good thing. It does not extend low frequencies but gives you more max SPL. It also makes your speaker work more like a line source, which means that the SPL will not decay so fast with increasing listening distance.

To sum it up: if you make N panel modules, you have two options:

1 - Try to keep the smallest dimension big, to get more bass --> make your panels more or less square.
2 - Strive for a line source to get better SPL at your listening position and to minimize room interaction --> make narrow floor-to-ceiling panels.
3 - Make another N modules + amps and do both

HTH
Kenneth
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Old 26th April 2010, 10:25 AM   #3
bentl is offline bentl  Norway
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Default Stator conductive coating

Hi,

the plastic stators will be machined this week, and I am looking into what conductive coating to use on the stators, and what to insulate the conductive coating with.

As conductive coating I plan to use Graphite Dry Lubrication, a spray on graphite that dries and forms a uniform and wear-safe layer. I am unsure about the electrical properties for this product.

As insulation for preventing arching, I will apply layers of acrylic clear coating. An alternative is spray-on circuit board insulation.

A4_stator_1.jpg

The stator is 49% open, 4mm thick and made of a rigid lexan-type plastic.

Any suggestions on other products that will serve the purpose and is easily obtainable and DIY-friendly?

Regards,

Bent

Last edited by bentl; 26th April 2010 at 10:34 AM.
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Old 26th April 2010, 02:32 PM   #4
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Hi Bentl,

Your idea is very interesting. However, I'm not sure if your 4 mm plastic will be too thick. I have been thinking of making the stators out of PCB. Since it is conductive on one side and non-conductive on the other side, it will be quite safe for making stators.

Wachara C.
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Old 26th April 2010, 06:25 PM   #5
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I have been doing much research on stator coatings lately.
I have found that clear spray acrylic is probably the best choice to use with around 1,5kv/mil breakdown factor with the exception of super corona dope wich claims a breakdown factor of 3.1kv/mil and 4kv/mil if oven cured.
Don't use a paint with any pigment as I had used white and had found the even the thickest areas conducted more than than the thinnest areas did around 5kv and above.
I think I remember reading that black may have been a better choice but white was what I had on hand at the time.
I've been toying with the idea of using a coat or few of a gray primer using talc as a pigment or use a white using titanium oxide or dioxide(each sucsessively having a higher dielectric constant) and then sealing with several coats of clear to get the desired thickness and insulating factor.
This procedure may work to raise the dielectric constant ,slightly or even significantly, and posibily raising efficiancy.
I am still in the process of sorting out my elctronics issues, amplifier is one and and getting my bias supply to maintain a constant voltage over 8kv with a load is the other.
Once these issues are ironed out I will start building some new panels again to investigate different stator coatings in more detail. jer
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Old 26th April 2010, 07:02 PM   #6
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I am curious,Bentl,as to why you have chosen a graphite based material to use as a stator?
You can get many different types sprayable metal coatings such as copper or nickel and such.
Although you can get graphite coatings with a very low resistance, my only concern is the adhesive ability to the insulative coating and stator base material might not be very good and could seperate when flexed, while handling. jer
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Old 26th April 2010, 08:20 PM   #7
bentl is offline bentl  Norway
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Hi, I am going to test graphite - as it contains little else than graphite which I know is conductive and adheres to smooth surfaces very well.

I have also bought copper- and silverloaded spray paint, but I am not so sure if this will work very well. (theese are normal spary-paints, not designet specially to be conductive)

I will make a test with all coatings, just take a sheet of plastic and add a row of connectors on two oposite ends. Then mask of identical strips and apply coating over 2 connectors with each coating and measure conductivity/resistance to see. Then add clear coat to see if that messes ut things.

I will also test zinc spray used to repair galvanic zinc coatings to see if that works.

Testing will commence on sunday (due to a disturbing element called work..)

Regards
Bent
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Old 26th April 2010, 08:45 PM   #8
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Hey Bentl,

if you use graphite stators they should be of sufficiently low resistance, otherwise you'll get weird HF response. But I'm curious about the results!

Kenneth
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Old 27th April 2010, 09:51 AM   #9
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Hi Bentl,

I've tried zinc spray, and it didn't work. I couldn't measure its conductivity using a simple digital multimeter.

Wachara C.
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Old 27th April 2010, 10:57 AM   #10
bentl is offline bentl  Norway
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Hi Wachara

I guess there is different types of zinc spray; I know there are types are conductive which can be applied and then arch-weld or spotweld through it.

But, I will start testing with graphite spray, copper spray and nickel spray to see how it works.

The zinc spray that I have in mind is 98,7% zinc, and should be conductive. But there will be 1,3% adhesives, which may or man not work as an insulation.

I will post the test results during the weekend, and hopefully have a few complete ESL elements assembled during next week.



Quote:
Originally Posted by chinsettawong View Post
Hi Bentl,

I've tried zinc spray, and it didn't work. I couldn't measure its conductivity using a simple digital multimeter.

Wachara C.
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