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Old 4th January 2012, 01:36 AM   #501
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It's highly questionable to use resonance frequency to estimate mass attached. What is the air mass attached?
400X microscope costs around $30.
If this is too much for you:
Can't you just bring your coated film to the store and check microscope they are selling...
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Old 4th January 2012, 11:39 AM   #502
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@alexberg: I don't know if you are replying to me, but the method I posted has nothing to do with resonance. (my panels don't resonate at 18kHz :P)

It uses the phase-lag/damping behaviour which a membrane has on a sound-wave. As you see in the formula only the mass is included, not something like a stiffness-factor. For resonance you need both!

For a lot of people this method means no extra cost at all (if you have an old oscilloscope somewhere)! And it's also possible to study the behaviour of other parts of the loudspeaker this way. (like for example the effect of the stator, a layer of cloth for or damping material)
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Old 4th January 2012, 01:55 PM   #503
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I agree, for resonance you need both.
Nevertheless, that is NOT easier/simple/cheaper to arrange then find a microscope.
What about HF stripe 2..5 cm wide, which is usually made of really thin film?
Do not we need the membrane dims to be >> wavelength to escape diffraction?
Secondly, you do not need to make sizable membrane... mounted on a frame just a little painted flake
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Old 4th January 2012, 03:17 PM   #504
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I just used a painted flake... But you can also measure the weight of a membrane which is mounted.
As long as the piece of diaphragm is larger than +/-3 times the wavelength (5cm) this will be all right.
It also has the advantage of directly measuring the the weight, so you don't have to know the density of the dried coating.

Off course there are disadvantages, a measurement probably takes more time than a measurement with a microscope and the precision might not be as good as with a microscope.

(I'm not saying everybody should use this method, but it's nice to have several methods to measure something)
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Old 5th January 2012, 07:54 AM   #505
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I use a highly accurate Mettler milligram balance for measuring mass (it has a 0,1 mg reading). From the measured mass of part of the Mylar the total moving mass of the esl can be extrapolated. From the difference with/without coating the mass of the coating can be measured as well.
The total moving mass of an exl easily exceeds that of a dynamic tweeter by the way.
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Old 5th January 2012, 09:39 AM   #506
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I wish I had that equipment

The moving mass is around 0.5g-1.0g for a 0.1 by 1m ESL unit. That doesn't seem to be much to me... How much is it for a dynamic tweeter?

But in practice it's not that much of a problem. A dynamic tweeters has a much larger excursion. A tweeters surface area is 4cm^2, the surface area of an ESL is easily 100x larger. So the dynamic tweeter has to move sqrt(100)=10 times as much, so it has to be 10^2=100 times lighter than the diaphragm to have the same amount of kinetic energy.
I guess it is heavier than 10mg...
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Old 5th January 2012, 12:23 PM   #507
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The moving mass of the scanspeak tweeter revelator D2905/990000 is stated as 0,45 gram.
Still there are many people who claim that the esl is much lighter than a dynamic speaker and therefor offers superior speed.
(Ofcourse you can't compare the two only by their mass as the radiating surface and the driving forces are completely different, that's another story.)
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Old 5th January 2012, 03:15 PM   #508
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An ESL can have as much excursion as a dynamic driver can if not more,Considering that I have reached the the excursion limits of my 3.25" wide panels with a D/S of .075" starting around 150hz to 200hz.
The total area of that panel is 204.435cm^2 (3.25" X 9.75").
Although I don't yet have a good scale I am sure that the mass is much less than .45 grams.
I use a .25 mil (6um) mylar with the Licron Crystal on my panels.

Just for what it is worth.

jer
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Old 6th January 2012, 12:55 PM   #509
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Quote:
Originally Posted by geraldfryjr View Post
An ESL can have as much excursion as a dynamic driver can if not more,Considering that I have reached the the excursion limits of my 3.25" wide panels with a D/S of .075" starting around 150hz to 200hz.
The total area of that panel is 204.435cm^2 (3.25" X 9.75").
Although I don't yet have a good scale I am sure that the mass is much less than .45 grams.
I use a .25 mil (6um) mylar with the Licron Crystal on my panels.

Just for what it is worth.

jer
That will be true in case of your relatively small panels, but a modest fullrange will have more moving mass than the scanspeak (e.g. several grams as zweetvoetjes already mentioned).
B.t.w. I expect the ' speed' being independent on the size of the ESL-film as both the driving force and the mass are directly proportional to the size of the film and cancel in Newton's equation.
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Old 6th January 2012, 02:36 PM   #510
fperra is offline fperra  United States
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Quote:
Originally Posted by MJ Dijkstra View Post
The moving mass of the scanspeak tweeter revelator D2905/990000 is stated as 0,45 gram.
Still there are many people who claim that the esl is much lighter than a dynamic speaker and therefor offers superior speed.
(Ofcourse you can't compare the two only by their mass as the radiating surface and the driving forces are completely different, that's another story.)
Can the D2905 play full range down to 300hz? No. If you want to compare a MC tweeter mass to an electrostatic, wouldn't it be a better comparison to compare the mass of equal radiating area, or at least compare the MC to a true ELS tweeter?
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