OK it's time to start the winter project. I'm thinking about building Acoustat model 3's starting from scratch. I want the speakers to be right at 7 feet tall so i'm planing on making the panels 9x36 inches and stacking .Now the problem, where can you get the 2x4 egg crate light defuses in 1/2 inch thickness. While they were common years ago no one seems to carry them now, and the ones I have found are around $25 each.
The common thickness is now .375 inch and I don't think that this would be stiff enough to build from... Any Ideas.
The common thickness is now .375 inch and I don't think that this would be stiff enough to build from... Any Ideas.
3/8" is a better thickness for what it is worth you will get less of a resonant tunnel. You can get either thickness if you want and if you really want to do a top quality forget the styrene versions and order the acrylic ones but be fore warned they are not cheap. Double stacked Acoustats are 7' 10" base included. Best regards Moray James.
The Local stores used to carry it about 10 years ago then they changed.
I went to get a new sheet to match the one I had and found the thickness had changed as well as the size of the squares, But the overall size is exactly the same.
I had found the good stuff at one time for about $32 for a 4' X 8' sheets but you had to by a whole case of 10 or so.
I still use it today for building smaller panels, My 8.5" wide panels did tend to bow out from the tension of the Mylar, So some extra support may be needed, but nothing seemed to effect they way they sounded overall.
The only difference in my construction method is that I use window screen as the stator material.
Because of the bowing issue I haven't built a larger panel yet, So my main focus is on panels less than about 4" to 6" wide using the material.
FWIW
jer
I went to get a new sheet to match the one I had and found the thickness had changed as well as the size of the squares, But the overall size is exactly the same.
I had found the good stuff at one time for about $32 for a 4' X 8' sheets but you had to by a whole case of 10 or so.
I still use it today for building smaller panels, My 8.5" wide panels did tend to bow out from the tension of the Mylar, So some extra support may be needed, but nothing seemed to effect they way they sounded overall.
The only difference in my construction method is that I use window screen as the stator material.
Because of the bowing issue I haven't built a larger panel yet, So my main focus is on panels less than about 4" to 6" wide using the material.
FWIW
jer
The original louvers used by Acoustat were made by Paragon Molding. At the time, several manufacturers made similar louvers, but they were not identical, and due to slight variations in the spacing, they would not work with Acoustat's 'combs' used at the ends of the panel. (These 'combs' , a custom-molded part, provided the 'hooks' necessary to loop the stator wire back and forth.)
Be aware that some louvers (at least appear to) have a metallized coating on the plastic, and for obvious reasons these should be avoided.
I think the AudioCircuit website still has a sequence of photos I provided showing the assembly sequence of the Acoustat panel. If you can't find them there, I can probably re-post here (but it is quite a few photos).
Good luck with your project. There are many more issues involved besides the louvers, so when you get to that point, feel free to pick my brain.
Here's the link to the Acoustat panel assembly photos mentioned in my last post. Sure does bring back some fond memories.
Acoustat article: Acoustat factory photo tour
Acoustat article: Acoustat factory photo tour
looks like jim had it going on back in the day.........an those were the days of Acoustat........dont for get to bow the louvers..........An let us all know when you get the coating figerout??
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And more than double the mass? Hmmm.
The real answer is doing a surface treatment of thin polyester film (Saran is even better, but tougher to find these days- my last ESL build used Clysar) before coating. A corona or plasma treater is optimal, and one can improvise that with a Tesla coil. With a sufficiently high surface energy (40 dynes), it's easy to paint on a good, stable coating; there are quite a few commercial PTF resistor coatings that will work fine. I used a thinned version of Acheson 423, a carbon-black-loaded vinyl composition, but I don't know what's around these days. The membrane switch industry uses lots of this sort of stuff, so something equivalent will be findable.
Making your own coating will be problematic without good dispersion equipment to obtain a consistent conductivity with no hot spots. Most of us don't have three roll mills or homogenizers.
The real answer is doing a surface treatment of thin polyester film (Saran is even better, but tougher to find these days- my last ESL build used Clysar) before coating. A corona or plasma treater is optimal, and one can improvise that with a Tesla coil. With a sufficiently high surface energy (40 dynes), it's easy to paint on a good, stable coating; there are quite a few commercial PTF resistor coatings that will work fine. I used a thinned version of Acheson 423, a carbon-black-loaded vinyl composition, but I don't know what's around these days. The membrane switch industry uses lots of this sort of stuff, so something equivalent will be findable.
Making your own coating will be problematic without good dispersion equipment to obtain a consistent conductivity with no hot spots. Most of us don't have three roll mills or homogenizers.
Getting the conductive coating right is probably the hardest part of building your own ESL. I see several problems with using contact cement: 1) it will probably add significant moving mass to the diaphragm; 2) it will be very messy to work with; and 3) contact cement remains tacky essentially forever, and therefore will attact dust (which, in turn, will eventually cause unwanted ionization and even arcing).
Keep in mind that the goal is to have a highly-resistive coating, so as to keep as close as possible to the theory of constant-charge operation.
Many different methods have been tried for ESL conductive coating, many of which are documented here at DIYAudio. Most of them have one or more problems with performance and/or long-term stability. I do think that Acoustat's success had much to do with their proprietary coating, which yielded very consistent results and extreme long-term reliability. Many years of experimenting and many dollars were spent on developing that compound. Even if I could share the ingredients with you (which I don't have) the equipment necessary to create it is way beyond the scope of DIY'ers.
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