I still want to try some more to get the EPDM rubber working with a non solid alu as backing.
I'm thinking of trying to make a combination of the following:
With just enough width of the red supports to keep the membrane from being squeezed.
And for the record, when I say solid backing membrane, I mean 14 um soild alu + kapton + coils on the other side of the kapton, like this:
Or another interesting option:
What if I do a coaxial membrane with both? solid on the outer coil, gap on the inner coil. The solid outer coild naturally falls off more, and the gapped inner coil shoud help smooth out the response. If I also add wool yarn it will dampen the outer coil making the inner more impactful. And even more so if I also drive it coaxially and add a lowpass filter to the outer coil. Might also be interesting to also test adding a notch filter @ 300 hz for the inner coil.
I'm thinking of trying to make a combination of the following:
With just enough width of the red supports to keep the membrane from being squeezed.
And for the record, when I say solid backing membrane, I mean 14 um soild alu + kapton + coils on the other side of the kapton, like this:
Or another interesting option:
What if I do a coaxial membrane with both? solid on the outer coil, gap on the inner coil. The solid outer coild naturally falls off more, and the gapped inner coil shoud help smooth out the response. If I also add wool yarn it will dampen the outer coil making the inner more impactful. And even more so if I also drive it coaxially and add a lowpass filter to the outer coil. Might also be interesting to also test adding a notch filter @ 300 hz for the inner coil.
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Hmm, if the coaxial performance would be roughly equal to both of these but at the same time, the outer green coil falls off naturally at 8 khz and stays 3-5 dB below the gapped red membrane so with some wool yarn on the outer holes, there might not be any need for driving the membrane coaxially to additionally reduce the level of the outer coil.
EDIT: I used the wrong measurement, oops! Driving it coaxially might be needed after all.
EDIT: I used the wrong measurement, oops! Driving it coaxially might be needed after all.
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I too am confused of why the EPDM has worse top end response above 10 khz. And if we knew why, maybe there was some fix that could be done to mitigate it.Yes, but EPDM seems not to support the same response in the high frequency... I wonder why...
//
First I wanted to see if I could use the EPDM rubber but with the top end smoothness of the foam. A solid membrane is too stiff and has the dips I want to avoid, but a gapped membrane where there are gaps around the traces is not stiff enough along the corrugations which causes a huge distortion spike at 300 hz, which is no good.
So my thought was, what if I, instead of having a solid fill, use a ladder shaped fill + EPDM rubber?
i was just drawing up an idea had for some time , dual sided foil, but i shifted the back coil (it has 1 trace less) so it overlaps the other front coil. this way you get you covered foil, without wasting output on weight.
The Brownish and Yellow strip in the midlle are the spot the connection will be soldered trough the membrane to the other coil. nice thing about it, it makes the connection points on the outer sides of the coil , i used this in my bass panels 2 years ago. i now wanted to try it on a midrange carver style tweeter.
the 2 coils are here next to eacht other but will overlay so the whole foil will be covered with coil, but only in the middle of the magnet there is a filler piece
its gone be a rather wide foil, and my hopes are since it has alu all over, it might hold its shape horizontally good enough to make them this wide.. 🙂 fingers crossed, it has to bridge 6 cm beteen the support foams.
downside is making 2 coils and laminate them.... but you where doing that already anyhow 🙂
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minor changes might as well the reason for the differences ? i mean its even hard to line it up the same way everytime, or put the 2 halves together without it pushing it to one way more then the other (if closer to the magnet top end goes up).. what i nodiced is ad the foil on one frame. the other frame add the foam and put it foam down on a table (with some weight on it). it will compress the foam temporarilly , then put them together and it wont be pushing towards the mangnets... i bet if you do this with both, the foil might end up at the spot you had in mind ! maybe even use temperature to increase the time you have to line up the ribbon/foil (cold)I too am confused of why the EPDM has worse top end response above 10 khz. And if we knew why, maybe there was some fix that could be done to mitigate it.
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I just realized something, a parameter which I haven't really accounted for that may or may not be significant:
My traces, which in some cases have 2 traces or 1 trace, but in all later cases they are very narrow compared to the whole membrane. Of a 55 mm wide membrane, only 12 mm is covered by the coils. Hence they apply more pressure per mm2 compared to traditional membranes where the coils are much wider and cover more of the membrane, and if there is problems with bowing of the membrane, then my gut feeling tells me that such narrow force application should make everything worse. Especially since the 12 um kapton which fills the gap has to do a lot of heavy lifting, probably too much since it is obviously not as stiff as aluminum.
That might be at least one of the reasons for why the solid backed membrane performs well on the low end, because it spreads the force.
So what if we take this into account and go halfway in between the solid backed and the pure gapped membrane, by adding localized solid areas to spread the force.
A, has until now the only EPDM compatible membrane I have made without the 300 hz disortion peak.
B, has the distortion peak and maybe this because or made worse because the force is applied in a very narrow area, so the pressure is pretty high on the surrounding kapton to keep everything stiff. When more force is applied it makes sense that the kapton gives which might cause excessive distortion.
But what if I go with C, which takes the idea of the solid backing but instead uses it to spread the force from my narrow traces into a wider area.
D is a realization of C but extended to a complete membrane.
E would be the same but also connect the outer solid fill under the suspension with the outer coil to ensure there are no solid areas that are not connected to a driven coil. Thus, in theory, there should be far less bowing forces on the kapton, since all the solid parts are driven. But at the same time, the two inner coils are disconnected from the outer coils, which might allow them to, on very high frequencies, function like separate drivers allowing for the coaxial driving.
D would be going even further and also connecting the backing under the two inner coils since even if I go for coaxial coils, they will run the same signal anyway.
My traces, which in some cases have 2 traces or 1 trace, but in all later cases they are very narrow compared to the whole membrane. Of a 55 mm wide membrane, only 12 mm is covered by the coils. Hence they apply more pressure per mm2 compared to traditional membranes where the coils are much wider and cover more of the membrane, and if there is problems with bowing of the membrane, then my gut feeling tells me that such narrow force application should make everything worse. Especially since the 12 um kapton which fills the gap has to do a lot of heavy lifting, probably too much since it is obviously not as stiff as aluminum.
That might be at least one of the reasons for why the solid backed membrane performs well on the low end, because it spreads the force.
So what if we take this into account and go halfway in between the solid backed and the pure gapped membrane, by adding localized solid areas to spread the force.
A, has until now the only EPDM compatible membrane I have made without the 300 hz disortion peak.
B, has the distortion peak and maybe this because or made worse because the force is applied in a very narrow area, so the pressure is pretty high on the surrounding kapton to keep everything stiff. When more force is applied it makes sense that the kapton gives which might cause excessive distortion.
But what if I go with C, which takes the idea of the solid backing but instead uses it to spread the force from my narrow traces into a wider area.
D is a realization of C but extended to a complete membrane.
E would be the same but also connect the outer solid fill under the suspension with the outer coil to ensure there are no solid areas that are not connected to a driven coil. Thus, in theory, there should be far less bowing forces on the kapton, since all the solid parts are driven. But at the same time, the two inner coils are disconnected from the outer coils, which might allow them to, on very high frequencies, function like separate drivers allowing for the coaxial driving.
D would be going even further and also connecting the backing under the two inner coils since even if I go for coaxial coils, they will run the same signal anyway.
the thing i said above might do the things you mention above. no parts where there is no alu, while not wasting output on pure weight. if it works 🙂 ill see tomorrow , printing the the frames right now, and will cut some coils tomorrow.
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must say i curently do not use metal. so output is far less , but its a quick way to see what it does sort of 🙂
the thing i said above kind of do the things you mention above. no parts where there is no alu, while not wasting output on pure weight
That works, but then I have to have wider coils:
Your suggestion is closer to A, but even wider coils and overlapping on the rear to get around the kap in between the coils.
The problem with that solution, however, is that it requires the coils to be wide, which works great above 600 hz where the the linear movement required for high SPL is non existent. But below 600 hz, where the membrane needs to move significantly to achive the target SPL, the distortion skyrockets because the magnetic field is not linear over the whole coil width as shown in this post.
The differences are huge!
Here is the distortion of A
And the distortion of B
Interesting ! the distortion of A is a bit funky, i am not sure it has to do with the width of the conductor (been more linear), in A the rise in the rest of the harmonics besides 2e and 3e looks weirdly steep. picture B looks similar as i get in a single ended (same distortion profile) a single ended is less linear then a push pull width wider trace i think?
If the desired frequency range is 300Hz to 20kHz, I think it is very difficult to achieve good SPL and low distortion over the whole range with the same typa of membrane.
If you have a co-linear speaker membrane with the tweeter part to the side, it will be different sides depending left or right loadspeaker, can you then optimize the membrane parts for high and low SPL respectively?
You might even remove the magnet column in between, even make two separate membranes with suround insntead of the removed column.
It will be messy, I know.
(I'm currently going in the opposite direction; making one membrane instead of two, but your conclusions suggests that it might be the wrong way to go.)
If you have a co-linear speaker membrane with the tweeter part to the side, it will be different sides depending left or right loadspeaker, can you then optimize the membrane parts for high and low SPL respectively?
You might even remove the magnet column in between, even make two separate membranes with suround insntead of the removed column.
It will be messy, I know.
(I'm currently going in the opposite direction; making one membrane instead of two, but your conclusions suggests that it might be the wrong way to go.)
If you have a co-linear speaker membrane with the tweeter part to the side, it will be different sides depending left or right loadspeaker
My co linear membrane had the midtweeter in the middle, so it was symmetric left to right. And both coils had the same signal excel the absolute top end so SPL should not be impacted significantly.
Yes, I know. It was a suggestion to have it asymmetrical. Perhaps it is easier to optimize the different parts then.
Here a measurement of a single ended i made 30 minutes ago , with 2 extra magnets on the front.. weird idea but thats what it is. with overlapped coils 1.9mm wide covering the whole foil. single ended (magnet config) is less linear then the pp. but you dont see the 4th 5th 6th 7th etc harmonics sky rocket like in your measurement above A. mostly 3th and 2e , but in your test 3th and 2e where almost the same in both A and B, except the rest of the orders. so i think it might be something else.
By the way i added the outer magnets as well on this front, it will create more orders of dirtortion, so i asume in this design, the foam damping or how far that driven coil is from the foam screws things up, kind of makes sense, if you try to drive the coil at the sides where its forced by the foam to move as little as possible. res of this panel is 190hz and i used 6 dB to compensate the rolloff down low. if you would make it a line like you do , that should not be needed, depending on the length


By the way i added the outer magnets as well on this front, it will create more orders of dirtortion, so i asume in this design, the foam damping or how far that driven coil is from the foam screws things up, kind of makes sense, if you try to drive the coil at the sides where its forced by the foam to move as little as possible. res of this panel is 190hz and i used 6 dB to compensate the rolloff down low. if you would make it a line like you do , that should not be needed, depending on the length


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Here a measurement of a single ended i made 30 minutes ago , with 2 extra magnets on the front.. weird idea but thats what it is. with overlapped coils 1.9mm wide covering the whole foil. single ended (magnet config) is less linear then the pp. but you dont see the 4th 5th 6th 7th etc harmonics sky rocket like in your measurement above A. mostly 3th and 2e , but in your test 3th and 2e where almost the same in both A and B, except the rest of the orders. so i think it might be something else.
I realize i omitted some crutial information in my previous post about the distortion.
Wide traces can absolutely have low distortion, as long as I don't push the SPL at low frequencies, thus not pushing the xmax. But given that narrow traces does allow me to push the xmax far higher, it lets me cross far lower than otherwise possible.
OB, have you tried measuring from a different distance re: the HF dip when using EPDM?
Not really, all of my measurements with the EPDM have been at 60-100 cm distance, most of the times eyeballed and not exactly measured.
But even if the effect is less at another distance, the foam suspension driver is measured from the same place and mic placement, and since there is still a difference between the foam and the EPDM the effect seems to be real.
I have modeled a split backing membrane with option for coaxial drive in the middle. The idea is to try this out during the weekend with EPDM rubber suspension and see how it performs. The end goal is to remove the 300 hz distortion peak while at the same time improving top end response and making it more smooth.
My gut feeling tells me the best performance will be to have the coaxial coils in the middle. The outer coils, unless I add more cuts in the backing, are held down more by the suspension where the inner coils are now, in theory, a bit more free floating.
Yes, I know. It was a suggestion to have it asymmetrical. Perhaps it is easier to optimize the different parts then.
My gut feeling tells me the best performance will be to have the coaxial coils in the middle. The outer coils, unless I add more cuts in the backing, are held down more by the suspension where the inner coils are now, in theory, a bit more free floating.
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