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Old 15th May 2017, 08:07 PM   #11
lowmass is offline lowmass  United States
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wen u say closed more distort than open...

How much more distortion and how "closed" is it really?

small diaphragms are much more suseptable to quality control issues like not perfect flatness, not perfect tension etc.

sooo some of the difference u see between your open and more closed units could be just diaphragm tension differences.

A big diaphragm has quite a bit more elasticity and can be tensioned more evenly.

Again just thinkin out loud so really not sure
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Old 15th May 2017, 09:08 PM   #12
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lowmass View Post
wen u say closed more distort than open...

How much more distortion and how "closed" is it really?

small diaphragms are much more suseptable to quality control issues like not perfect flatness, not perfect tension etc.

sooo some of the difference u see between your open and more closed units could be just diaphragm tension differences.

A big diaphragm has quite a bit more elasticity and can be tensioned more evenly.

Again just thinkin out loud so really not sure


Ok its like this.

Panel 1
magnets are 9.5mm wide then a 1mm gap. of this one mm gap +-90% is open

so around 9% total open area, downside is the panel is 4mm thick and not made of metal compare to the 1 mm perforated sheet.


panel 2 only 40 percent of the 1mm gap is open so around 4% total open area. even lower since holes dont always line up from perf sheet.


both are not that much. a magnepan comes in at around 10% i believe of total open area.

Those maggies are not as simple as they look
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Old 16th May 2017, 02:34 AM   #13
lowmass is offline lowmass  United States
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hmmm I see yes that is a low open area%. My notes tell me anything below about 12% open is well damped.
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Old 16th May 2017, 02:41 AM   #14
golfnut is offline golfnut  New Zealand
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Impulse response suggests 150 Hz resonance to me. If so damping with a tightly tensioned cloth over the panel might help to lower the Q.
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Old 16th May 2017, 11:08 AM   #15
lowmass is offline lowmass  United States
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WrineX , can u go into more detail on the design

1- exact length width of diaphragm( dont include frame)
2- material and thickness of film
3- thickness of foil
4- width of foil traces
5- width of undriven film between traces
6- tensioning method
7- type and approx thickness of adhesive


At the moment I am leaning a bit to the idea that its a small panel and thus will has some serious issues below about 700 hz unless it is very carfully tensioned and the diaphragm itself very carfully manufactured. Just a guess at this point however and need more info
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Old 16th May 2017, 02:33 PM   #16
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lowmass View Post
WrineX , can u go into more detail on the design

1- exact length width of diaphragm( dont include frame)
2- material and thickness of film
3- thickness of foil
4- width of foil traces
5- width of undriven film between traces
6- tensioning method
7- type and approx thickness of adhesive


At the moment I am leaning a bit to the idea that its a small panel and thus will has some serious issues below about 700 hz unless it is very carfully tensioned and the diaphragm itself very carfully manufactured. Just a guess at this point however and need more info
I have to lookup the the size of the panel when im home. i can awnser a few already

2. Mylar 12 micron (chosen for low end duty)
3. I used wire on this panel. diameter 0.31mm aluminium magnet wire (i also used 40 micron 5mm alu tape)
4.if foil is used 5mm or 3. in these measurements only wire was used as used on magnepan.
5. undriven area approx 9.5 mm the width or the magnet (also like magnepan although they used 1/4 inch magnet)
6. by hand (not something i would use in the final models)
7.adhesive used for wires and mylar 3M 30nF contaxct adhesive as used by magnepan.


something i would like to try , but is allot of work but cutting my magnets down 3.8mm (i already did several meters i made a jig for it and works perfectly but lose some of the magnet in the process) and decrease undriven area and as well expand open area on the metal plate by adding more magnets i create more magnet gaps. for strength i might need to use push pull but we will see.




By the way in other posts i was shooting for the high frequency extend, this is another topic and i used other materials like etched foils and such, this topic was mainly about the distortion in the lower department.

Last edited by WrineX; 16th May 2017 at 02:36 PM.
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Old 16th May 2017, 08:03 PM   #17
lowmass is offline lowmass  United States
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hmmm well there are a bunch of things going on with those materials that would make a small panel very difficult IMO. 12 micron film is quite stiff and can be hard to tension evenly on a small diaphragm frame. Remember the Maggies may use similar stuff BUT there much longer dimension will likley give a better result. Also the undriven area and the mechanical properties of stiff riggid wire in a short distance(small diaphragm)

I would try some thinner film , 6 micron or less and foil with full width traces. When I was working small diaphragms I would actually put the foil traces for say a 6 inch by 6 inch diaphragm on a film that was about 18 inches square. I would tension on an 15 inch square frame by hand . Then just lay the whole thing down on the 6 by 6 frame. This gave even tension in that small area in center.
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Old 16th May 2017, 08:17 PM   #18
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lowmass View Post
hmmm well there are a bunch of things going on with those materials that would make a small panel very difficult IMO. 12 micron film is quite stiff and can be hard to tension evenly on a small diaphragm frame. Remember the Maggies may use similar stuff BUT there much longer dimension will likley give a better result. Also the undriven area and the mechanical properties of stiff riggid wire in a short distance(small diaphragm)

I would try some thinner film , 6 micron or less and foil with full width traces. When I was working small diaphragms I would actually put the foil traces for say a 6 inch by 6 inch diaphragm on a film that was about 18 inches square. I would tension on an 15 inch square frame by hand . Then just lay the whole thing down on the 6 by 6 frame. This gave even tension in that small area in center.
Thanks ! lowmass. well i tried foil on smaller panels as well as etched and results are the same. one thing is clear the bigger you go the less pronounced the problem is overall. but this could be because of the reason of less excursion so it does not tell much. i really need to try the smaller magnets to see any difference , changing from 12 to 6 micron did not change anything. i tried this one
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Old 16th May 2017, 09:59 PM   #19
lowmass is offline lowmass  United States
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ok yea not surprised.

yes size matters a great deal with larger excursions.
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Old 17th May 2017, 01:49 AM   #20
lupi is offline lupi  Italy
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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
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