Noob ESL builder looking for advice
Hi. I'm launching headlong into an ESL project for the first time. I really appreciate the wealth of knowledge here on diyAudio. Hopefully I can make higher quality loudspeakers through our forum discussions.
The project is two ESL panels, built on as reasonable a budget as I can manage. I am not looking for full range, and will add the lower end frequencies with a separate subwoofer.
I have a steel perf sheet on the way, which can yield panel sizes of either:
91 cm x 25 cm
101 cm x 22 cm
Is that so narrow a difference that I should just go with what looks best to me, or would the taller, skinnier version have a little better dispersion in the higher frequencies?
I want to go with the dual transformer design for stator step-up mentioned by Calvin, Jazzman, and others. Is there a good supplier for those right now? I tried Antek and Newark, they are sold out of the 6v version.
Many thanks in advance for the help!
It is Great to see a new ESL project getting started!!!
The difference of 3cm in width won't make a whole lot of difference in the dispersion pattern.
But what will/can make a difference is the width of the sections you choose to use.
2 or 3 sections is good for your width of material.
I would go with 2 sections.
Keep the middle spacer narrow if you can ( 1/4" to 3/8") as this will help to increase your radiating surface area to a maximum.
3 sections may be a bit narrow as each section would be only about 2 5/16" (6cm) wide.
This may limit your lower midrange response due to excursion limiting from being too narrow.
My little panel has a diagphram width of 3.75" and smallest I think I would go maybe even 3" unless it was made strictly for a tweeter section.
Vertical sections vs horizontal. I see ML using horizontal, which seems a necessary step with the arched stators. But a good number of the DIY planars have vertical sections.
What is the maximum safe section area? I will stretch the Mylar with a bicycle tube table. (Although, since I have never done that before, it will be interesting to figure out how to know when it it stretched "enough".) D/S spacing about 1mm.
For 6-micron film on a flat panel, I would stretch the film with a bike tube jig, to 1.5% elongation. Before stretching, I put reference marks on the film exactly 12" apart in the width dimension, then apply stretch until the marks are 12 3/16" apart for 1.5% elongation. I also recommend 1/16" d/s for a hybrid panel (that's about 1.5mm).
Yes, that is a very good general rule of thumb.
Especially for diagphram widths larger than say 5 to 6 inchs.
However this rule quickly runs into practical considerations as the panel gets wider than say 9" or more.
The lowest frequency of operation must be taken into account as well.
As not too run out of room for large excursions at the lower frequency's of operation.
There was a good chart that I knew of that suggested the minimum D/S as per lowest frequency of operation.
However I am having a difficult time trying to find it on the web or the original document has been modified since and no longer has the data that I am looking for.
I do have it in my archives somewhere though.
Even with my little panel with a width of 3.25" and aprox. D/S ratio of 1:45 I have been able to clip the diagphram into the stator at Frequency's lower than about 200Hz to 250Hz even with a spacing of .072" (+/- .003").
Even more so when I hit the resonate frequency of the diagphram of about 70hz to 90hz.
May I add that this much excursion for my little 3.25" X 9.75" diagphram is quite very loud!!
A 1mm spacing may be good if you are planning on crossing over at a rather high frequency of say 1Khz or even 1.5Khz or higher and definitely if it was intended to be strictly a tweeter panel.
IMHO .0625" or as Charlie had mentioned a spacing of 1.5mm to 2mm is a very good place to start and should be good for those peaks at around 300Hz.
Remember that the excursion doubles for every octave lower in order to produce the same SPL as the starting fundmental.
Here is a very good read on the subject although it pertains mostly to headphone drivers,
HeadWize - Project: Notes on DIY Electrostatic Headphones by Chu Moy
And here is a much more detailed version as well just scroll back to page 138 for the beginning,
Loudspeaker and Headphone Handbook - Google Books
And here as well,
Audio and Hi-Fi Handbook - Ian Robertson Sinclair - Google Books
This is a very good thread that had touched on the subject as well,
The last time I was able to run my little panel I found that I got about +/- 30 degrees of usable dispersion off of the center.
And at about 45 degrees off the center there was noticeable drop off of the high frequency's as expected.
Sorry I miss quoted my panels diagphram width of 3.75" in post #3 and should be read as 3.25".
Here is a link to Peter Walkers paper,
Excellent information--exactly what I was hoping for. This helps my design. :-)
I have the 6 micron film on the way from Asia. Metal should arrive today.
Since I am shooting for about 300 Hz as the crossover frequency, maybe 1.5 to 2mm is a better way to go, as you both suggest.
In the U.S., what stores carry the 3M double-stick in that thickness? Anyone know?
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