ESL Panel construction?

[CharlieM]

I will give you my opinions but I would seek other opinions as well:

Originally Posted by markusA

Will I need the frame? Is the frame important?

A flat panel would be quite wimpy and would definitely need a supporting frame. A curved panel would be substantially more rigid but I can't imagine it being strong enough to resist flexing and deformation when handling it so I would use a frame with a curved panel as well.

It will add mass, rigidity and it might change resonance behavior as well.
Yes, all of those things-- but I assure you it will sound wonderful. I think resonance in the panel is not a good thing and a frame can help beneficially dampen that resonance

The panels will be 165x25cm (160x20cm actual active membrane area).
I'll be using 1.0mm Rv 3-4 perf steel stators.

The perf you mentioned should work well. You're panels are large so will surely yield high output but they will also have fairly high capacitance-- it would probably be OK but I'm not positive about that and too much capacitance will pull down the treble response and makes a harder load for an amp (the tranny type and step-up ratio plays into that as well). Calvin has far more experience than I do with capacitance issues so I would certainly ask his advice before committing to that panel size.

3M 1.6x25mm VHB tape (I'm considering 1.1mm thickness)
(25mm 5962 or 5952 since the stators will be powdercoated)
I'm not decided on the additional tape spacers needed, width and orientation will depend on the thickness of the tape.

I would definitely go with 1.6 mm tape for the spacers, no matter the panel coating thickness. My view is this: In a perfect world where stators are always perfectly straight and diaphragms retain perfect tension, 1 mm of d/s (diaphragm to stator spacing) might be fine provided that the distance between support spacers does not exceed 100x d/s (70-100x d/s is the Cookbook guidline). However, I have yet to see perfectly straight and true stators, even after straightening. Also, even though you will have separate woofers for the bass, the bass notes in the room will push the diaphragms to larger excursions than the signals fed to the stators. Roger Sanders's Cookbook recommends .070" minimum d/s and I think he's not far off the mark with that so I go with .062 (1.6mm) spacers.

I'll try to run them as low as possible (hybrid) without compromising the audiable qualities to badly. X-over <300Hz I think? Exactly how low depends on the final result and I won't know that until the panels are built.

A 24/db/oct crossover @ 300 hz would be fine but I would not go higher or much lower. Mine is currently set to 270hz (lower is certainly doable but you then need more EQ on the panels to compensate the dipole phase-cancellation so it's a matter of diminishing returns).

Will the vibrations be large enough to warrant a frame?
For vibration alone, probably not, but I would use a frame anyway for structural rigidity.

And now back to the original question.
I could do it without the extra holes but holes will make a better solution I think.
I need 2 holes for M8 screws on each side (L/R) for each panel. The stands will be mounted near the floor so the holes will need to be located a few inches above floor level.

Since I would use VHB tape to assemble and secure the panels together and also place the panel in a support frame, screws and added holes would not be needed.

[markusA]

Thanks for the detailed response.
My initial thoughts were 1.6mm spacers and a frame so your advice is kind of already the default plan.
I guess I'm just exploring another option.

A 1mm steel sheet is indeed very flimsy, I was thinking the layered build with tape would transfer any bending motion/force into shear forces making the construction stiff.
Yoy're probably right, a frame is probably the way to go.

(Swedish terminology might not translate 100%, if I'm saying strange things please tell me and I'll try to find the correct words.)

[markusA]

I might just add a little side note...
It was the free samples of 1.1mm (43mil) VHB that got me thinking if it would be a viable option to go with the smaller d/s spacing. (I got a couple of sample rolls to try out the product...)

[markusA]

This 30 minute rule for editing posts is a nuisance. :P
Coating will be approx 6mil.

[CharlieM]

Originally Posted by markusA

I might just add a little side note...
It was the free samples of 1.1mm (43mil) VHB that got me thinking if it would be a viable option to go with the smaller d/s spacing. (I got a couple of sample rolls to try out the product...)

As I said in my earlier post, I think you should seek other opinions, not just mine.

Since I have not personally built an ESL with d/s spacing smaller than .062" (1.6mm) I can't say for sure that 1.1 mm spacing would create problems, provided that the distance between support spacers is within the 70-100x d/s guideline per Roger Sanders' ESL Cookbook (which also recommends .070" minimum [about 1.6mm] d/s spacing).

It is correct to say that closer spacing gives higher efficiency because the strength of the electrostatic force falls off quadratically with distance. So, for a given power input, 1.1 d/s would yield significantly higher efficiency, within the smaller space provided for the diaphragm to move in. The question then becomes at what point and loudness the diaphragm would be driven into the stators-- and I can't answer that question.

I will stick with my recommendation of 1.6 mm d/s for the reasons given in my earlier post. I can say with certainty that 1.6 mm d/s will give no problems in a hybrid panel and will yield good output too. This I know because my 30.5cm x 122cm panels with 1.6 mm d/s will play louder than I can stand to listen.

One more thing, your 25cm x 165cm panels are only about 12% larger than mine so I'm thinking their 12% higher capacitance would likely not be a problem. (of course, if you use the smaller 1.1 mm d/s, the capacitance would then be substantially higher). Again, I would ask Calvin's opinion on your panels size/capacitance and d/s spacing.

[markusA]

Let's hope Calvin joins in then.

[bentoronto]

What's the downside to bigger spacing? Voltage is cheap but burning holes in your diaphragms sure isn't. If it is a conflict between engineering design perfection versus plain good sense, it really shouldn't be hard to decide.

[markusA]

In my case here the 1.6mm (0.062") option is the default option. It's tried and true.
If 1.1mm (0.045") were an option it would make my life easier.
Inter-Spacer distance would be more optimal, I already have tape lying around, due to lower voltage demands a direct drive amplifier might be an option later on.

Active diapraghragm width will be 200mm.
Recommended inter-spacer distance is 70-100 x d/s spacing -> either 116-160mm or 77-110mm. Running a spacer down the centerline with 1.6mm d/s spacing would put me outside the recommended interval forcing me to go with horizontal spacers insted. -> Not as good for the active radiating area. -> possibly loosing efficiency/sensitivity?
Voltage requirements estimate 1.6kVrms vs 1.1kVrms. 3.1kVpp might be doable with a fairly simple OTL tube amplifier. I said might... I'm just keeping my options open at this point. 4.5kVpp is a harder nut to crack.

So I guess there are some incentives for me to explore the small d/s route.
If it's just a plain and simple bad idea I'll drop it and not look back, but abandoning it just because it's not the normal way of doing things just isn't my style.

[SM7UYJ]

markusA:
I would go with the 1.6mm spacers!
I use 2mm for my midpanel and 1mm for the tweeterpanels in my ESL-hybrids.
It will be a compromise as you want to cross over to your woffer as low as possible => the need off larger d/s, small d/s => lower EHT, transformers etc. as you previous stated. With 1.6mm d/s you should have no problem getting your XO below 300Hz!

Roger

[Calvin]

Hi,

1.1mm is good for a maximum SPL-value of 110dB@4m for f>200Hz with my small panel.
Sounds sufficient eyyh? Gives any bass a good run for the money.

jauu
Calvin