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Old 31st March 2007, 01:49 AM   #1
BillH is offline BillH  United States
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Default An ESL Experiment

I've been enjoying my DIY ESLs for several months now, but wanted to try a new ESL with a different purpose. Rather than doing a large panel I'd like to try something on a smaller scale.

For now there will only be one panel, a test mule to explore different construction techniques. A panel to answer some questions of mine and some others from the forum:

Can a smaller ESL produce acceptable volume levels?
Does a smaller curved panel help dispersion?
How do I tension a curved diaphragm?
Can the back wave be contained and still give good sound?

Here's an exploded view of the first concept. A curved stator with a wad of absorbent material and an 8" wide x 14-1/2" tall enclosure with 6" deep sides.
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File Type: jpg curved esl1.jpg (48.4 KB, 818 views)
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Old 31st March 2007, 02:05 AM   #2
BillH is offline BillH  United States
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Here's a photo of the stators. 7-1/2" wide, 14" tall, and a 5-1/2 radius roll.

They're 0.032" thick aluminum with 0.125" dia. x 0.156 staggered holes, about 50% open area. One of the things I learned from the first build was to cut the edges to minimize sharp points to keep down leakage. The stators were rough cut 1/4" oversize on all sides, patterned matched, and screwed together before cutting both at once to final size.

I made no attempt this time to smooth the burrs from punching and just rolled them with the best sides facing in.
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Old 31st March 2007, 02:36 AM   #3
BillH is offline BillH  United States
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I'm going to try double sided tape to hold everything together. My first thought is 0.020" thick, 1/2" wide 3M VHB.

Here's a rendering of a curved ESL on top of my woofers. That's all for now, I need to do some thinking about how to tension the diaphragm, how to connect the electricals, how far apart and where to put diaphragm supports, how to make a curved grille, where to run the wiring, and the list goes on
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Old 31st March 2007, 05:49 PM   #4
Few is offline Few  United States
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Thanks for the updates, BillH. I'll be interested to hear what you discover. My attempts quite awhile ago to use thin aluminum and 0.032" tape led to quite a few diaphragm/stator contact problems, but I was working with longer stators. Perhaps your more compact design will make it easier to maintain the gap.

Few
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Old 31st March 2007, 06:40 PM   #5
poynton is offline poynton  United Kingdom
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Hi.

See this ....

Help ! Please Identify My ESLs

Andy
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Old 31st March 2007, 09:25 PM   #6
BillH is offline BillH  United States
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Andy, while I can't help you identify them, they do look familiar. Have you tried to listen to them?

Few, the spacer configuration seems like the secret to keeping the diaphragm away from the stator. I'm considering four possibilities at the moment, shown below. Right now #2 and #4 look like the best way to maintain the curvature of the diaphragm. I like the idea of #4 to break up the resonances, but not sure if it would make any difference. In all cases the narrow dimension of the rectangular sections or largest dimension of the tapered sections is about 2", appropriate for a 0.020" spacer thickness.
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Old 31st March 2007, 10:44 PM   #7
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by BillH
Andy, while I can't help you identify them, they do look familiar. Have you tried to listen to them?

Yes. As good as my old QUADs ! (at least in the top end )

Andy
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Old 1st April 2007, 10:01 PM   #8
Few is offline Few  United States
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BillH,
I agree that your numbers 2 and 4 look the most promising. I wouldn't expect the vertical spacers in #1 and #3 to ensure a curved diaphragm. Doesn't the diaphragm curve have to match the stator curve, or am I confused about what you're doing?

Also, I should clarify what I meant in my previous post. When I made prototypes with the 0.032" thick spacers I followed the usual rule of thumb:

(spacer separation) < or = 100 x (diaphragm/stator gap)

(did I remember that correctly? it's been awhile...) In any case, the problem I encountered was that I could never completely avoid minor bends or kinks in the thin aluminum stator material. Those kinks didn't cause trouble with a 1/16" gap, but they caused major headaches with the 1/32" gap because there was so little room for error.

Don't get me wrong I'm certainly not trying to convince you to change your plans. I just didn't want to see your posts go unacknowledged and thought I'd toss in a description of my previous experience in case it was useful. In fact, I'm in the process of accumulating the materials for some panels with 0.040" (1 mm) gaps in spite of the trouble I described above. I'm going to use tensioned wire in the hope that I'll be able to keep things flatter.

Few
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Old 2nd April 2007, 09:46 AM   #9
Calvin is offline Calvin  Germany
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Hi,

Q and A
Q1: Yes, but only at elevated frequencies
Q2: Yes, curving broadens dispersion, but not much
Q3: Only in the īstraightī direction and best is imo with high tension
Q4: Yes, but Youīll probabely need a very deep and voluminous housing to eliminate back sound completely.

Using sheet metal You should keep in mind, that the edges of the sheets are the most probable points where flashovers occur.
My assumption is that cutting both sheets at once will be a nearly perfect provedure of creating a sparking stator!
I did the cutting separately for every sheet. The reason is as follows:
If You look at the pic You might notice that the rim is cut in a way that no sharp points are left. Since You canīt avoid the stamp like rim with usual hole patterns You should ensure that the sheet is cut in a way that the īleftover holesī at the rim are less than 50% their original area. More than 50% left and there will be very sharp pinpoints and sparking. This will work when You cut each sheet individually. Small tolerances in overall dimensions are acceptable, whereas early sparking renders the panel useless.
Secondly I used a good thick insulation of ~0.5mm thickness.
Thirdly I glued some clear thin tape around the rim, thereby assisting the insulation. Beeing of PVC or PP-material this is good for several 100V of stable insulation on its own.
Click the image to open in full size.

With curved stators (curved in the horizontal plane only!) Iīd suggest only the spacer pattern No.2
You might think of varying the distance between adjacent spacers a bit as ML did. Theoretically this should broaden the ground resonance peak and minimize itīs Q-factor, but in praxis I found no difference to a equidistanced spacer-stator. The rule of thumb of placing the spacers is 70:1...100:1 times the d/s depending on the mechanical tension Youīll use (higher tensioning force allows for higher ratio). Donīt go smaller, because of efficiency reasons and donīt go higher because of dynamical stability reasons.
Patterns like No.4 donīt avoid resonance problems but reduce efficiency because of a higher shunt capacitance.
Shunt capacitance is already the highest with simple sheet metal stators and is higher the smaller the panel īs area becomes.
Large and curved stators are in advantage against flat ones because You only need a lot of glue joint area in the (straight) direction of membrane tension (top and bottom rim). The width of the glue joint along the long sides can be considerably smaller since it takes no shearing stress.

As Few already said will it be difficult to create a perfectly flat or perfectly equally curved stator with sheet metal. As a result there is a lowest spacer thickness down to which the warps of the sheet donīt play such an important role. This seems to be ~1mm (0.04"). If You intend to manufacture smaller gaps You should have certain experience especially with curved designs and have prime material to start with.
The soft tapes of 3M -I like to use them very much, because of the ease of usage and their damping characteristics- underly tolerances of their own which are bigger than for e.g hard plastics. I assume this discloses them for gaps smaller than 1mm (best usage is ~1.5mm).
3M offers a VHB-tape thats specially intended for use with powdercoated surfaces. The 495x- and 595x-series are promising as glue joint and the 491x-series as clear spacers. You might think of using round or rectangle shaped silicon bands as horizontally orientated membrane spacers too.
When You use these tapes You should always be aware that You have just one shot to get the membrane precisely where You want it! You canīt correct for failures -like wrinkles- by heating the membrane after montage.
On the other hand montage becomes quite easy and quick, which is important since the glue joints of the membrane in the tensioning frame are stressed with high shearing forces.

So far so good
jauu
Calvin
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Old 2nd April 2007, 04:24 PM   #10
BillH is offline BillH  United States
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Hi, Few.

Quote:
Few writes: Doesn't the diaphragm curve have to match the stator curve
Yes, it does have to curve. More on that later.

Quote:
Few writes: (spacer separation) < or = 100 x (diaphragm/stator gap) (did I remember that correctly? it's been awhile...)
That's the rule of thumb I've been using, too.

Quote:
Few writes: In any case, the problem I encountered was that I could never completely avoid minor bends or kinks in the thin aluminum stator material.
I've got that problem, too. Dropping them makes it worse, as I found out yesterday.

Quote:
Few writes: I just didn't want to see your posts go unacknowledged and thought I'd toss in a description of my previous experience in case it was useful.
I appreciate all the help I can get, thanks for the advice.

Hi, Calvin.

Quote:
Calvin writes: My assumption is that cutting both sheets at once will be a nearly perfect provedure of creating a sparking stator!
I did it this way to make sure the patterns matched on both stators. My first build ended up with some stator pairs that had openings that didn't match front to back. I don't know if it matters, but this time I wanted them to match. After shearing to final size, I spent some time with a file and sandpaper to get rid of burrs.

Quote:
Calvin writes: If You intend to manufacture smaller gaps You should have certain experience especially with curved designs and have prime material to start with.
Yes, as I found out first hand. I've abandoned the curved stators after trying to mount the diaphragm. The diaphragm tension is critical on a curved ESL. Too much tension and it pulls in between the spacers-ruining the diaphragm to stator distance, too little tension and the diaphragm is wrinkled. There's just not enough room for error.

So the plan has changed, as it sometimes does. Curved stators are out and flat is in. I'm thinking of going with the same 7-1/2" x 14" finished size and using flat steel stators instead of aluminum for the extra stiffness. I liked the VHB tape, but on a small ESL like this it covers a relatively large surface area. I'm considering going back to stacked acrylic insulators with a small cross section.

I've put down the tools and taken a break to think about this for a day or two. The goal is to produce a small ESL hybrid that can be integrated with a woofer and used as close to the wall as possible. Ear splitting volume is not needed.

Today's question:

Should I split the panel into midrange and tweeter sections?
I did it on my last ESLs, but they suffer from a 'phasing' (lobing?) effect as I move left to right. A single section would be much easier to build, but the promise of a narrow tweeter section spreading the highs is tempting.
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