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Old 6th November 2005, 08:17 PM   #11
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Location: Calgary on the Bow
Default interesting information!

Calvin: thanks for the interesting heads up on your findings with curved panels. I think that the key with curved panels is in the stretching process of the diaphragm. Curved panels do present the diy builder with more complex jigs and I suppose a longer slower learning curve. My thoughts about vertical segmentation were directed toward helping to minimize the expanse of unclamped diaphragm (and so stability)as well as to help reduce the difference between front to back stator thickness. It seems that this issue (assuming we don't ask the panel to make bass(a good idea anyway)) is not the problem that I would have thought given your findings and that is very good to know for those who want to buld curved panels.
I would be interested to know what amount of curve you find is possible and also approx. how much linear travel you think that the diaphragm has with such a curve? Do you think that the diaphragm is stable to as much as one stator thickness peak to peak in a panel that you build? This is probably hard to establish but I would be interested in you estimate. What is the approximate area of one of your panels and how low do you drive them?
I very much appreciate you providing this information and the opportunity that such discussions afford. Being able to learn from others experience is of enormous value to diy builders. Given your personal experience with curved ESL could you comment on how much wider you feel that the sweet spot is with a curver stator versus a flat panel of the same dimension and also do you believe that the sweet spot with a curved panel is as good as that of a flat panel? Thank for your comments and thoughts. Best regards Moray James.
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Old 7th November 2005, 07:45 AM   #12
Calvin is offline Calvin  Germany
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Default curves

Hi,

stretching is indeed the keyword. With curved panels imo only mechanical stretching is senseful. I prefer a tension that gives a Fs well above 100Hz,which is way above whats possible with thermal stretching. You canīt really expect curved panels to produce bass (neither can You with flat panels. Its more of a pronounced resonance and a suck-out in the lower mids than real bass). So diaphragm/stator distance should be kept as small as needed for the supposed frequency range to give maximum efficiency. Design for highest efficiency! Itīs much better to match efficiency to a woofer by using a lower transformer ratio than anything else! Donīt expect to get much lower than 200Hz, even with panels of considerable width.
A streching jig is quite easy to build, because You only need the variability in vertical direction. My frame works for flat panels as well as curved ones. Its just an stable outer frame to which variabel inner elements are connected. These Elements can be īpulledī outside by threaded rods and nuts. The diaphragm is glued to the inner elements with double side sticky tape. To change between flat and curved style I just change the flat vertical elements against curved ones that have identical curvature as the panels stator. I use just a slight degree of curvature. 20° to 30°. The dispersion broadens up a bit but not very much. Directivity is still very high, but the panels play a bit more pleasant when casual listening. Higher degrees of curvature will make stretching and installation of the diaphragm harder and it wonīt really give drastically better dispersion figures. The big advantage of the curvature is a higher mechanical rigidity of the stators, which leads to less resonance, less rattle and a optically very pleasing appearance without the need for additional supporting structures.

With regard to diaphragm stability I can only add my personal experiences. One of my panels is sized 25x125cm with a d/s of 1.0mm to the front and 1.1mm to the back. Horizontal spacers are added app. every 80mm. The diaphragm is stretched very hard and lenghtened thereby by app. 2%. When glued to the spacers this gives a resonance of app 150Hz. This provides for excellent stability. As a worst case test I played tracks from Cincinnatti Pops CDs fullrange(!). My Rotel 980, that can push out more than 300W blew its fuse, but the panel worked flawlessly and stable without the diaphragm touching the stator once. For the intended frequency range well above 200Hz You have plenty of stability headroom left.
Even though You have to correct for the falling frequency response -due to phase cancellation- between app. 200Hz and 600Hz with an equalizing filter.
The German manufacurer PAS, who sell similar panels for PA uses claims for a panel of this size (but with 1.5mm d/s) an frequency range of 180-20.000Hz, crossover point of 200Hz@24dB/oct, an efficiency of 90dB/2.83V/4m and a peak SPL of 113dB/4m@3%THD.

jauu
Calvin
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Old 13th November 2005, 02:59 PM   #13
OlafZ is offline OlafZ  Germany
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Default similar challenge to me

Hi,

very interesting thread to me, since I decided to replace the foil of my ML Sequel's.
I already removed the old ones. It was not so easy, I didn't use any sover for the glue and of course the original membran got damaged by this action, but anyway I'm going to replace.
I realized ML seemd to use some graphit stuff as conductment agent, like some black powder (applied on an atomar level, haha).
I'll use EC coating and thinner foils.

I would like to renew all, or least the white double-sided sticky tape around the inner side of the panels, but unfortunately I didn't find a supplier. Maybe someone here can provide me informations regarding this.

Eventually I'll reuse the old tape (It's still sticky).

Hello Calvin,
your rig for tensioning the foil sounds very interesting. I tried to do by hands, but i'ts not the right way. It's not doable accurately enough.
I would like to contact you personaly, since I live next to you.
Feel free to contact me by pm, I would be very glad.

Olaf
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