Anatomy of a high efficiency high output electrostatic loadspeaker.

[Jazzman53]

The issue is, if you read articles on the web, that Mylar or its derivative have a low energy bond, meaning in my understanding, that they repel liquids on their surface. So it appears that even if the spray and other stuff is easy to apply, it won't last. The trick is to modify the surface to make it accept the coating. Of the two suitable liquids for home use to treat the surface is isopropyl alcohol or sodium hydroxide ( as in oven cleaner). Both etch the surface in preparation for the coating. I did not see how ML treats their surface, it's not shown in the video. The fact that their coating seem to evaporate more or less around ten years means that no surface treatment is used. The DW cells don't deteriorate because of surface coating going away, but because the high voltage creates pockets of corona almost all the time until there is a ground path to prevent the cell from biasing, or the area where the bias feeds the diaphragm attaches becomes so high in resistance.
I don't know what the actual ingredient that conducts in the various anti-static spray is. I looked at the coating from the seller in Australia, it is water based. I don't have any faith that it will last based on the chemical properties of the plastic. i read many years ago people used soap. Apparently this has a one year life. One thing I like about cell construction where the rivets are replaced with screws, you can take a cell apart unless its stuck in a frame surrounded by black corona dope, lol. The diaphragm on DW is only glued to one side of the cell frame. You separate the two frames and so you have access to it. After 40 years the surface resistivity is still intact. Mind you that the cell has not been exposed to any high voltage fields, but it shows that the coating chosen is sound (no pun intended).
My electrometer to measure surface conductivity.

I wonder what coating was used on the DW's.

So far, I have had no issues with Licron Crystal bonding to the Mylar. It's even difficult to physically scrape the dried coating off Mylar using my fingernail. Before I apply it, I solvent wipe the diaphragm with denatured alchohol to remove any fingerprints left by me handling the film.

Licron Crystal was designed as an ESD coating for plastic parts bins used to store ESD-sensitive electronics parts, so perhaps the manufacturer did their due diligence to ensure its bond strength to plastics. In any case they advertise it as having "superior adhesion to a variety of surfaces (glass, plastics, metals, etc...)" Of course, they would.

It's about 98% solvents, even including nitro-methane (not sure what that does but it's in there).

Anyway, it's not come off on any of my panel builds in the nine years or so that I've used it. However, it ain't cheap ($56 for 8oz spray, with shipping).

 

[ESLFan]

It was a carbon particle suspension in a oil based solvent. A solution you could silk screen on the Mylar. If you look at the picture of the diaphragm, you see a bunch of parallel lines. This is to prevent the charge from migrating sideways where the film is not attached to the frame. Spraying is always fraught with lack of control. You would have to mask the edges to prevent them being sprayed. You can see how little distortion the sheets has as the long edges don't distort. It is hard to describe the sound the make, except transparent could be one word.
Also if the front to back distance of diaphragm is not the same, you will get a bunch of second harmonic distortion. When you actually own a piece of hardware you can test it the way you like it and not how someone else wants it tested. DW published distortion numbers at 90 dB SPL, and in the DIYaudio forum someone actually ran a distortion test recently. Other than the bass, it is similar to headphone distortion.

Now that I have listened to the ML electromotion for quite a few hours I am pretty pleased but I would certainly say they are not in the same league.
I have some issues with female vocals sounding harsh. On DW they were just incredibly real. I am using different electronics now. Solid State Perraux SM2 preamp and Accurus power amp. Hooking up my Mosfet power amp which I thought was broken, but has a bad power switch. And my tube preamp as I had used before.

 

[Jazzman53]

Thanks for that info.

Charge on the diaphragm wants to migrate toward zones that are closest to a stator, and I'm beginning to see how the DW design uniquely mitigates charge migration.

If I'm interpreting the DW configuration correctly, attaching the diaphragm only at the top & bottom allows a more planar excursion, whereas a fully restrained diaphragm would become convex/concave with excursions. Thus; the stator-to-diaphragm distance (d/s) and resulting drive force remains relatively constant/linear in the width direction, and the striped coating further contributes to linearity by limiting the charge migration. It's quite ingenious.

 

[ESLFan]

I found out what the vocal issues were. Unrelated to the speakers. I was playing a record and seems the cartridge was not sounding right when i compared the CD to the record. I checked the tracking force and the anti skating, Those were right on. The only thing left was the VTA. So the easy way to adjust it quickly was to add another felt map on top of the platter. Bingo! Now on the LP the female vocal sounded the same as on the CD. The LP/CD I was using is Laura Branigan "Self Control". The first two songs. The voice has been recorded quite forward and I found this to be quite a good test for phono cartridge and power amplifier into a demanding speaker.
I use a CD player from Pioneer Elite line: PD-65 feeding a S.M.L SU-9 DAC. I have a choice of a SS or tube preamp for phono.

 

[ESLFan]

I don't think it would be too hard to make a DW cell even without the special stator casting. You need to make a jig where you can bend the edges of the stators outward to control the electric field. Then attach some supports to them and create the bridge to tie them to the outer frame. As I measured the ML electromotion panel's capacitance, I get 1100 pF. Ten DW cells are 600 pF and are a much larger active area. Now since the ML gap is smaller, each time you half it you double the capacitance, so the higher capacitance makes sense, and to prevent a high frequency short to the amplifer, you lower the step-up transformer ratio. With 1100 pF you would use between 50:1 and 75:1, add some series resistance to increase the impedance, maybe using a thinner wire gauge in the windings, may do the trick.
@Jazzman53. How did you create the extra resistance you mention in the description of your speaker?
The method of applying the conductive layer with a comb of q-tips if you don't have silkscreeing equipment handy is quite doable.

 

[Jazzman53]

@Jazzman53. How did you create the extra resistance you mention in the description of your speaker?

Segmentation:

The load the amp sees from an unsegmented panel would be predominantly capacitive, as the only resistance would be the transformer's small winding resistance and whatever series resistor might have been added on the primary side (typically 1 Ohm).

My wire panel is electrically segmented, with its (15) segments driven in series thru an RC transmission line.

So; in addition to the 1-Ohm series resistor in front of the transformers, the segmentation resistors on the secondary side render the load the amp sees predominantly resistive.

I can't tell you what my panel's resistance and capacitance actually are. However, based on the technical paper by physicist/ESL guru Dr. Rod White (a.k.a golfnut @diyAudio), from which my panel design is based on, it's capacitance should be about 1/20th that of an unsegmented panel of similar area and spacing.

I can't post that paper here (its copywrited) but I can reference the thread below, which was posted by that paper's author. See near the end of the post where it describes a segmented line source panel.

https://www.diyaudio.com/community/...ormer-requirements.393531/page-2#post-7222598

 

[Russr]

First, thanks very much for posting this thread; fascinating stuff.


The latest remix in Atmos is spectacular. I have the 5.1 SACD, and the Monoliths get the transients perfectly. The panels seem to have little resonance internally. But the mount to the frame is another thing, and at 400Hz to 700Hz, there are some resonances that I need to dampen with something I can fit between frame and panel.

Referencing the chimes on Dark Side of the Moon...
I always thought Alan Parsons produced Dark side, but it seems he was a sound engineer. Most of the whacky, high quality effects were products of his fertile mind. Apparently he was not aware that he could ask for a "slice of the pie", and was making a fairly low hourly rate at the time... so he did not pursue further collaborations with Floyd

 

[ESLFan]

Yeah, he was an amazing sound engineer and also produced many albums of his own as the Allan parson project. I have most ofd those LPs. They always sounded good on my equipent.
@Jazzman53 Thanks for the info.

 

[ESLFan]

Russ Knotts is a good resource for repairs. I took my set of Prodigy panels to him.

He looks like a competant guy. The typical problem with physically big and heavy speakers is the transportation cost. Nowadays it seems particulary high, even shipping a big amp can cost over a $100, I can't imagine the freight for 200# of speakers. There are between 8 and 10 cells in each and you could remove them all, which is a terribly laborous job.

 

[ESLFan]

I carefully looked at the cells again and the diasphragm material is attached on all 4 sides. Sorry about the previous mis-information.