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Old 18th May 2017, 06:23 PM   #21
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lupi View Post
Hello everyone
Wrinex, you can use a stroboscopic method to determine if it is a membrane self-resonance problem. I use it when I have similar problems with my tapes and I can always see what's wrong, if the displacements are big enough to be visible. Then correcting the problem is another matter, but at least I know it depends
i dont have a strobe
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Old 19th May 2017, 02:12 AM   #22
ICG is offline ICG  Germany
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Originally Posted by kevinkr View Post
I can't imagine linear excursion is much over a mm pp.. (Question, I don't know)

I lived with various Magnepans for almost a decade and remember excursion was extremely limited. (And they did not need to move much to couple either)
These drivers usually have less than 0,5mm linear excursion.

Quote:
Originally Posted by WrineX View Post
For this panel excursion limit was 1.6mm (one way) almost as much as a full blown SMGA. with 1,8mm (3.6 pp). just what i had around in terms of spacers
No, that's wrong. That's the maximum distance the membrane can physically move, the distortion starts waaaay lower. The surround/suspension (well, if you want to call it that) allows hardly any excursion. Since the movement on the edge is very limited it means the more excursion you force onto the driver, the more the foil has to stretch.
But that means at the same time that the membrane does not work with the whole surface fully, it's only partitially moving, which gives you the the first part of the distortions, this part of distortion is mostly non-linear. That also means, larger spacers are definitely not the solution.
With rising frequency the excursion becomes smaller. You can see that on your slowmotion video and I'm sure you've noticed yourself visually the excursion becomes a lot lower with rising frequencies.

And the second thing is, it's excursion is bending it a lot. That means the bending stretches the foil and like pulling on a rubber band, the more you stretch it, the happier it will oscillate and there is the second source of distortions. And the more it changes in shape, the less it behaves like the originally intended 'capacitor foil' of the concept.

To sum that up, excursion is the main problem. Since you can't increase the linear excursion (or only marginally), you either have to limit the power (=excursion) or you have to increase the size of the panel (a lot).

Quote:
Originally Posted by WrineX View Post
trick is go big and with allot of tension on the foil so it seems, the lower it is the more crap it looks.
Well, you might want to reconsider that one though.
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Old 19th May 2017, 09:02 AM   #23
WrineX is offline WrineX  Netherlands
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Yeah bigger is lower distortion an yes iT niveau mostly in the middle, about the tension you ever tapped a smga ? Tension is really really high. To get a res of 55 hz with such huge panel you have to increase tension quit allot. I agree that using bigger spacers does not solve it, it never was my intention to do so but it was just what I had laying around for a bigger panel 5 times the surface area of the small one (the one in the slowmo)
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Old 19th May 2017, 09:44 AM   #24
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by WrineX View Post
Yeah bigger is lower distortion an yes iT niveau mostly in the middle, about the tension you ever tapped a smga ? Tension is really really high. To get a res of 55 hz with such huge panel you have to increase tension quit allot. I agree that using bigger spacers does not solve it, it never was my intention to do so but it was just what I had laying around for a bigger panel 5 times the surface area of the small one (the one in the slowmo)

damned i was to late to edit it

Thanks for Chipping in ICG

About the tension you ever tapped a smga ? Tension is really really high. To get a res of ~55 hz with such huge panel you have to increase tension quit allot.

I agree that using bigger spacers does not solve it (i never said i would btw), it never was my intention to do so but it was just what I had laying around for a bigger panel 5 times the surface area of the small one (the one in the slowmo is the big one)
why is my excursion limit of 1.8mm on the SMGA wrong ? i just say thats the limit i dont say it is the linear excursion.

one other weird thing would be when you bend it (when playing a 50 hz for instance) the resonance should go up to at the max peak wonder how that looks.

But most of these problems should occur in a ESL to , at least all the physics about it being a drum and foil not moving like a piston etc. still never had the same weird sounding distortion with an esl

Last edited by WrineX; 19th May 2017 at 09:55 AM.
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Old 19th May 2017, 12:20 PM   #25
lowmass is offline lowmass  United States
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The esl is typically enough less mass that the air load alone can supress these resonances a little better, not completly but better.

I have never gotten a small panel like what your doing to work well at elevated volume below about 500 Hz. The mechanical properties of the system are very non linear if you move a small area film too far.

The resonances below about 700 hz are often spread out somewhat on larger panels like Maggie with some varied tunning in the form of different tensions from one end to other and or carfully placed clamps.

In the Apogee design these resonances are spread out some by varied tension,varied diaphragm width, AND some corrogations. All these tuned till u get the desired response.

I have made a bunch of diaphragm copies of the Apogee design and maggie design and can tell u the Apogee design is better at dealing with these resonances. The corrugations in particular go a long way to making a better panel but there size is critical.
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Old 19th May 2017, 02:01 PM   #26
WrineX is offline WrineX  Netherlands
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Yeah lowmass the Maggie looks so simpel aparantly iT is all but easy to get iT to work proper.

Well must see what happend with the 680 X 280 mm panel if i stretch iT hard enough, right now the panel from the slowmotion, is to low in res.

What i want to clearify , i never intended to make a small panel that would work from 100 hz to 20khz , i just hoped to first make some small scale tests. But it looks like it does not work this way. I hope the middle size panel from the slowmo gives a better inside. I wanted to make a bass panel twice the size that would keep an esl midrange tweeter company

To make an esl more affordable and give it a bit more oempf without screwing up the polar pattern to much.
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Old 19th May 2017, 06:56 PM   #27
lowmass is offline lowmass  United States
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yep good perf is a system of balances. The "art" of all this is knowing each well enough to make the best judgment as to wich ones and how much of each to work into the design.

The Maggies are quite simple really BUT in its simplicity they have still had to manage each tune able part until they got an overall acceptable perf. There simply is no such thing as " no compromise" design. Fundamentally thats not the real world. This is where hard work and trial and error comes in. Pure science and engineering takes a back seat at this point. Kind of like "voicing" a speaker, in the end our knowledge is limited and we have to manipulate everything to a good end.
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Old 19th May 2017, 10:59 PM   #28
lupi is offline lupi  Italy
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Quote:
Originally Posted by WrineX View Post
i dont have a strobe
I do not even have a real strobe. Simply connect a led with a series resistance to a pulse generator and voilą a strobe
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Old 21st May 2017, 06:21 PM   #29
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lupi View Post
I do not even have a real strobe. Simply connect a led with a series resistance to a pulse generator and voilą a strobe
That's a good idea !! Thank you , you then tune the strobe until it hits the resonance ?
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Old 22nd May 2017, 01:20 AM   #30
lupi is offline lupi  Italy
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Originally Posted by WrineX View Post
That's a good idea !! Thank you , you then tune the strobe until it hits the resonance ?
If you tune it at the same speaker frequency, you will see the membrane stop. It is best to tune to 0.5 / 1 Hz more or less so that you see the membrane moving slowly. The pulse width must be short with respect to the period: from 1/20 to 1/100 it's okay
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