|7th May 2014, 07:48 PM||#1|
New build questions
Thanks to all of the seasoned builders and new builders for their interesting and informative posts. I've been reading quite a bit over the last week or so and I'm keen to get building. (Couldn't help ordering a bit of Mylar C)
Perhaps it's useful for me to give some background for the build I'd like before I start firing questions away.
Ideally I'd like:
To get down to 350hz
Use a dynamic mid/bass driver (pre-assembled) for low frequencies
Have the ESLs on my desk for near field monitoring
Possibly extend dispersion
Use a software crossover - I make music and mix music so feel optimistic about this bit.
My build is quite strongly based on the info on Charlie/Jazzman's, but many more comments have been extremely important: Jer, Calvin, Bolsterst (in no particular order!!)
Onwards to my questions:
Coating the stators acts as an insulator correct? Presumably this coating if expertly applied stops electric shocks on touch. So what comes out of the stators? (I plan to use a grill/stretched material to stop my two year old coming near the stators)
I get the impression that only one side of the membrane is coated. Why only one side and doesn't the membrane also act as an insulator?
How far does the membrane move when in use?
On that note I get the impression that the diaphragm supports are put on the stators- should these be less than the d/s spacing?
Smaller is better for me. What is the relationship between area, width and height in terms of audio quality and dispersion? Or succinctly will 1.2M/50" x 300mm/12" (or 2 x 150mm/6" panels based on next point) get me down to 350hz?
What are your thoughts on a 2xflat panel design per speaker, with the 2 flat panels angled at say, 20 degrees. (Curved is looking like too much of a challenge for a first project.)
Will a 70 watts per channel into 4Ω do the job? (based on Electrics using Calvin's and Charlies efforts Jazzman's DIY Electrostatic Loudspeaker Page: The Electronics Package)
Also I read the wire wound resistor after the amp might be better upgraded?
I've got a few more questions which are relational to the square root of ignorance!!
Thanks for your patience.
|8th May 2014, 12:07 AM||#2|
Join Date: Dec 2012
Location: Redondo Beach, CA
The low frequency cutoff is a function of a few things:
1) Tensioning the diaphragm makes for a "drumhead" type of resonance. The smaller the drumhead for the same tension, the higher the resonant frequency. The higher the tension for the same size panel, the higher the frequency. You need to be sure you cross over plenty above the resonance. I'd suggest a couple of octaves unless you have a real steep rolloff.
2) The saturation of the step-up transformers provide another low frequency limit. These transformers are meant for 50-60Hz operation at 50VA typically. Higher VA or lower frequencies will cause them to go into saturation.
3) Diaphragm excursion is limited by d/s. To produce sufficient SPL at low frequencies, you need larger d/s or a larger radiating area.
As for curved vs flat stators or a physically angled stator, I have opted for a segmented stator to achieve greater dispersion. The vise-tight sweet spot in a single flat stator was too restrictive for me.
I have put together an illustrated guide as to how I built my segmented ESLs here:
Segmented Electrostatic Speaker
|8th May 2014, 01:25 AM||#3|
Join Date: Feb 2008
Location: Savannah, GA
|8th May 2014, 02:03 AM||#4|
Join Date: Feb 2008
Location: Savannah, GA
Deciding which options to go with is always anguishing. And you have a lot of options.
Syborg's project is pretty awesome and his write up is excellent as well.
I have no experience with smaller panels so I won't advise you on those.
Our friend Jer has experimented extensively with smaller wire-stator panels and I expect he will jump in with advice on their roll off and associated crossover requirements.
Since the diaphragm coating must be applied AFTER tensioning, it's generally not practical (and fortunately not necessary) to coat both surfaces. The polyester diaphragm is an insulator but it's so thin the electrical field strength passes right thru it practically undiminished.
I would not advise using 2 angled flat panels, as this would certainly produce an on-axis dead spot. However, 3 flat panels with the outer ones slightly angled would likely work OK. Also, I don't think curved perf metal panels would be as difficult as you think.
Round wire stators should be less prone to arcing than perf metal stators because they have no sharp edges to focus corona. So if you opt for perf metal, you will need to do a very good job on the coatings.... at least 10 mils coating thickness. The coating hopefully is sufficient to prevent easy conduction into a body touching them but coatings are not perfect insulators (if they were, the driving electric field would not be able to penetrate thru the coatings to react against and move the diaphragm to make sound).
Good luck with your project!
|8th May 2014, 03:37 AM||#5|
Join Date: Feb 2008
Nearfield Desktop ESL's is right up my ally!!!
I have been designing these type of ESL's on and off for the last 10 years.
Here are a few threads on my designs and the latest one (using TIG rod) is setup for electrical segmentation although I have not tested it yet.
My First set used a very simple and cheap method using plain ole' window screen and it impressed me so much that I have stuck with this design since I started in this hobby in 1994.
I have yet to build a large ESL but it is on my things to do soon.
I plan on starting a new tutorial on my method of using window screen soon as I have refined that method since the very first models I made back in 1994.
I will try to answer some of questions the best I can,
Getting down to 350Hz or so is quite possible, But, this is about the limit you can go with our current method of using a Toroid power transformer in reverse unless you use more of them.
This is a another whole discussion and there are many threads on this and here is one where I test a Antek AN(AS) 1206 showing the limits and parameters of this transformer as it is the DIY choice so far do to cost.
Do Stay Away from the Shielded versions (AS-xxxx) as these are prone for failure as I have shown in that thread.
The sad part is that Antek as discontinued the non shield version of transfomer's that we use, But not to worry there are several ways to get around this.
If you want something better then it is possible to wind one up from scratch and maybe even cost less with more performance......Providing you have to patient's to wind about 2000 to 5000 turns of 32gauge wire neatly and with no overlaps!
The width of the panel for a non-segmented stator determines the horizontal dispersion as I explain in the segmented version thread.
The diaphragm width of my ESL's is typically about 3".
This gives me approximately 15 to 30 degrees of dispersion from off each side of the center.
This is enough for nearfield and works great in the Farfield axis as you can imagine too.
Much Much better than my original 8" X 22" panels did.
Although the wider panel did give a nicer low end extension, The beaming was atrocious compared to the little panels.
This was okay since I was planning for a hybrid system anyhow.
The other thing that works against you is dipole cancelation.
There are several ways to combat this one is Equalization and the other is to increase the front to back distance using some kind of baffle.
I have found that this can raise the low end slope by as much as 3db!
Displacement is the key to low end performance as mentioned by Syborg increasing the Excursion and/or increasing the surface area.
The D/S I used on my first builds was about .075" or so and it worked well.
My new build is set at 1.85 and I will be experimenting with that once I get around to testing it.
Therefore a D/S spacing of 1.5mm to 2 mm is a good starting point for frequency's that low using a narrow panel.
If you want a wider panel such as 8" or so then be prepared to go as high as 3/32" (.090" or 2mm to 3.5mm), YMMV !!
As you halve the frequency the Diaphragm requires 4 times the excursion to maintain the same SPL.
The larger the D/S is you need to compensate this by using higher voltages.
Every thing is a compromise!!
I have found that every time you double the voltages you increase the efficiency by 6db.
The easiest thing to do is to increase the bias voltage, I suggest not to go any higher than 7Kv if you have a really good stator coating.
I have gotten as high as 12Kv or so but thing get really shakey and unstable as the stator coating is at its limits of breakdown at this point.
When I started out I was using only about 2Kv to 3.5Kv and this worked very good as well and sound great, I was so amazed at the sound.
Then I started pushing every thing to an extreme and I found the about 7.5Kz is the most any one should try and go and even that is high.
You can however go higher if you wish to experiment as I have, But, It won't be reliable at those kind of levels and is something that I Do Not Suggest for the Newcomer.
I have been nailed by my 14Kv supply many times and the last time I had it set to about 10Kv and I am lucky to still be here typing this stuff!!
I had accidentally brushed the bias feed wire and got nailed by 10KV!!!
Luckily I do practice the one hand in your pocket method when messing with such high voltages!!
However at a normal bias of 5Kv to 7Kv I am able to handle the panel and move it around at will, Providing that I don't touch an exposed wire or one of the sandwiching bolts that holds my design together since I had added a charge ring to it.
I was able to detect Diaphragm to stator clipping once I got to and below about 200Hz with my setup but that was at very extreme voltage levels and SPL's (+110db).
I was using about +5Kv of bias if not more and about 20Kv to 25Kv p-p across the startors.
I was using my crown DC300A to power them during those tests.
Since then I have a much more accurate way of measuring the voltages precisely.
I had it running under these conditions for about 10 to 15 minutes until the stress caused the coating to fail and the panel met its final demise (caught fire a few times), You may have already read about that.
But, Those are very extreme conditions and were only meant for experimentation and to see where exactly the breaking point was so that I knew what and where it was in order to not go there for a more reliable operation.
Under normal conditions I was using a small amp as well, a Awia 80watt that is very finicky.
It did perform well, and I was able to get great sound (+90db) with only a 5Vp signal into about 1:160 step up ratio and 7Kv of bias with my little panel (3.25" x 9.75").
I would get well over +105db with only a 20Vpeak signal at 1 meter.
You can only imagine the levels at my listening distance of 1/3 to 1/2 of that.
I use heat to tension my diaphragms and it works well for the smaller widths but can be a bit difficult to get enough tension if you plan on a wider panel, but it is possible.
It is the only method I use at the moment.
I can get a consistent resonance of about 70Hz to 90hz when I replace a diaphragm.
This is mainly from lots of practice but it is not at all difficult to do.
Typically you want to keep your crossover frequency at least two times above this resonate frequency.
I tried messing with VST digital crossovers for a short time but I was not happy with the results but I will explore this more at a later time.
I just used the filters on my mixer for a crossover and I will be making a proper analog filter on my next build as this will be the one that will be a permanent build for everyday use.
This has been a long time process of experimentation to find what works and what doesn't, while trying to find the cheapest way to make these things.
The performance I have gotten up to this point has been phenomenal!!!
And to think that when I started out, I could barely use the very same panel as a headphone driver!!!
I have tried multi-panel configurations and it works, but it is tedious to get them angled just right to be seemless.
20 degrees is quite a bit much and 7 degrees is about what you will find that works okay.
This is only feasible for larger taller array and I find it if no benefit to the smaller desktop version.
I have fancied the idea of making a curved Desktop version as I think that this might work very well for the smaller panel without the issues of the larger curved panels.
Curved vs Flat is a worn out debate, But I do think it is a cost effective solution for a smaller panel compared to the segmented version I have already made.
Obtaining the slightly expensive HV resistors is the only reason I have not finished the build yet.
Not to mention how bulky they are, and trying to conceal them in such a small and compact design.
The resistors alone are about 10 to 20 times the cost of the panels alone!!
I have not given up on the idea, I am just slow at it as it is just a hobby for me.
Lately, I have been focusing more of my energy on transformer designs and a preamp and parallel chipamp system to power them in a nice compact case.
Not to mention the DD amp designs that I have been contemplating, But that is another subject.
I have been more pressured to do a new build (and finish it) lately because I need something good too do mixdown's on for an up coming recording project.
In my thread on the latest build you should be able to find all of the software I use to predict the performance of an ESL from Excursion to Dispersion.
If you have any questions at all do feel free to ask!!!
It is a lot to try and soak in at once!!!!
Cheers and Good luck on your venture in to this wonderful technology!!!
P.S. Nice Build Syborg, I like it a lot!!!
Last edited by geraldfryjr; 8th May 2014 at 03:55 AM.
|8th May 2014, 05:24 PM||#6|
Join Date: Dec 2012
Location: Redondo Beach, CA
If you are not looking for room-filling sound, then a small, narrow panel may just do the trick for you, as Jer has pointed out above. The narrower the panel, the better the dispersion. Certainly fine for a desktop monitor set.
The second set of panels I ever built were a small 4" x 18" size, perf metal, flat set (see photo). The resonant frequency of the panel was 127Hz, so I crossed it over at 360Hz to good effect. With a d/s of 0.063 and a bias of 2.7KV it worked well for a small monitor set, but wasn't quite what I wanted for a main set. I'm not as adventurous as Jer with the bias voltages, but ran this one up to about 4.5KV before seeing some corona discharge.
In your case, for a desktop set, they would be great. Charlie's page has everything you need to know to make a perf metal panel like this.
Don't be afraid to dive right in and experiment! A lot of the fun in DIY is trying new things and having the occasional epic fail.
Charlie and Jer - thank you for the kind words on my build! They do sound fantastic.
|8th May 2014, 07:02 PM||#7|
Join Date: Feb 2008
I have a Two piece's of 10"x 48" metal that Charlie had sent me.
I have finally decided to cut them in half lengthwise for a couple of Midranges for my Rockin' system since I can't seem to keep a dynamic drivers from burning up!!!
I hope to get those done by the end of the summer.
|8th May 2014, 09:31 PM||#8|
Thanks for the feedback. Much appreciated.
Syborg, I really like the use of the TIG. Charlie, nice explanation of insulation properties. Jer as per usual a thorough undertaking; looking forward to reading more about your desktops.
As Syborg suggests I think I'll dive in as soon as the currency flow permits. (Also as my wife suggested I should go and listen to a pair of ESLs!) I'm inclined to run with a design akin to Charlie's whilst incorporating some of Jer's suggestions on transformers and wider baffle.
There are still a few things I find a bit confusing:
The strips that run down (or across) the stator to support the membrane are the same thickness as the periphery strips. Doesn't this mean the strips reduce the effective size of the membrane?
I'm not hung up on this and will certainly take your word for it, but doesn't coating the membrane only on one side introduce an imbalance between the stators?
As a side topic, those with ESLs with very good directionality might well benefit from listening to Binaural recordings - google binaural barber for an interesting listen.
|8th May 2014, 09:40 PM||#9|
Wondered if you thought this might be a viable alternative to perforated steel, certainly looks cheaper per square area..
Fine Aluminium Wire Grill / Netting / Mesh - 3m x 50cm Roll | eBay
|8th May 2014, 10:30 PM||#10|
Join Date: Feb 2008
Location: Savannah, GA
For my 12" wide panels I use two support strips which segment the diaphragm into 3 independently-moving sections. While this reduces the effective radiating area, it's necessary for a couple of reasons: 1) The unsupported width of the diaphragm should never exceed 100 x the diaphragm-to-stator spacing (70-100 x d/s is the rule); otherwise the diaphragm will be easily driven to slap the stators at high volume and/or via acoustic coupling to any woofers anywhere in the room. I prefer to go conservative. 2) perf metal stators are never perfectly flat, thus d/s spacing is never constant--more support spacers with less span between them mitigates this problem by keeping the diaphragm more or less centered between the stators, even if they are not flat.
If you look at the panels sold by Just Real Music you will see that Russ uses more support spacers with shorter spans between them than most DIY'ers. And his bias supplies are typically not over 3Kv. It's obvious that Russ plays it safe with the bias and diaphragm supports-- opting to sacrifice a bit of efficiency and output for a more robust panel. I like this approach for larger panels like Russ builds and it's just smart business if you're going to sell them.
While coating the diaphragm only on one side is bound to produce some degree of asymmetry; believe me, it's so slight that you will never notice it.
The only practical way I can see to coating both sides would be to mount the diaphragm in a separate, independent frame, rather than bonding it to a stator (the easy way). There's also a downside to coating both surfaces if you use a thicker coating that adds significan mass, like Elvamide or some of the graphite paint emulsions. (Licron Crystal is very thin but most DIY coatings are not).
With regard to directionality, there's no free lunch: Wider, ultra-directional panels have wonderful slam and superior imaging at the expense of a miniscule "head in a vise" sweet spot. Whereas, narrow wide dispersion panels achieve a wider sweet spot at the expense giving up some slam and imaging.
I would love to build panels with segmented TIG rod stators like Syborgs, except rig it with a means to switch between segmented and non-segmented operation, such that I could flip a switch for a wider sweet spot when I have guests over and then switch back to a narrow sweet spot for superior slam and imaging when I'm alone and listening at their focal point. This intrigues me to no end but I am nearing retirement age with not much savings so I cant afford to indulge this hobby anymore except vicariously thru others via my blog page. At least I already have a pair of pretty great speakers.
Last edited by CharlieM; 8th May 2014 at 10:38 PM.
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