A few people asked: "you made a Isobaric planar , why?". I try to explain it in this video :) don't laugh at my drawing skills or writing skills :) they do not exist. its a miracle this ended up on the paper !
good concept! The less air between the membranes, the better. It would surprise me if would work for mid and high. This is excellent for the low end, what typically the weak spot is for foil. Hope this works out, at some point you need a product.
Between the membranes I used a porous damping material. This more effectively lowers the resonant frequency and reduces the time delay between the front and rear membranes.
well it would damp the main resonance , but would increase the delay between the foils, since i believe you slow down the air when damping. then again the distance foil to foil is not a problem at these low frequencies its out of phase above serveral Khz, so no problem for low end.
Great explanation. It's been many years since I studied physics, but I recall the magnetic field strength drops with 1/ distance^2 or maybe for a long slender magnet 1 / distance, but I'm grasping at straws. Of course you've done FEM modeling, so you know better than I. It is very interesting as the motor gets stronger at the limits, the opposite of traditional woofer coil leaving the gap. A speaker suspension tends to get stiffer at the limits, so the motor getting stronger with excursion will compensate for the suspension getting stiffer. Pretty interesting. If you were to cut the driver in two with half the magnets on each side, it would be the same as two panels back to back, so that looks to me exactly like an open baffle isobaric configuration. I don't know. Mark said he is happy to have a zoom call with you. Hopefully he has emailed you.
Thank you ! well it does have similarities to an isobaric for sure. but the main benefit half the enclosure is not a thing here and i use one motor to drive both. about suspension im sure something similar happens here, but in this case the suspension on both increases with excursion both ways. inward and outwards so im not sure. i think damping and the air in between has room to play around with. since i am not sure yet what would be better. for the driver
@@joppepeelen If you have any digital EQ available, I find that using the Linkwitz transform (2nd order asymmetrical shelf filter) is very good at producing the desired response electronically even with a slightly high Q woofer systems. It sort of seems too good to be true, but I use it all the time now. I really want to build a pair of these panels. I need to find the source for the thin foil and Kapton for the diaphragm.
This is nothing like a normal driver isobaric coupling, where you (almost) double MMS and halve Vas while keeping the air loaded area constant. The reason your Fs (main resonance) goes up in frequency is that your MMS (total weight of membrane including air load) is LOWER for a coupled membrane1+membrane2 than if either membrane was acting by itself. The air mass that is between the membranes shares its' load between both. The MMS (total driver acoustic mass) is totally dominated by air load in an elctrostatic or planar driver, while it's almost completely dominated by actual cone assembly mass (not airload) in a normal driver.... Two membranes standing alone have total air mass loaded area of 4 surfaces x the surface size, a couple pair only have two-point-something (2.5?) x the surface area. If you had zero losses (nothing but a thin air gap) between the membranes you would get half the air mass load. Now you don't get a perfect halving since you have flow resistance and other things lowering that "sharing" capability. What's happening with the Helmholtz resonance between the membranes (through the magnet gaps) is extremely hard to say. You have a LOT of unsupported area of foil between the coil tracks, and a lot of air volume - so at least some of the pressure goes there in stead of being converted into air movement. It's pushing the un-driven foil out (relative to the coil going "in") on larger excursions. I've used slot venting in cardoid modified normal speakers, and slots/vents that are this short/narrow are pretty hard to model. It takes some experimentation to tune what leakage you get.
thanks for the explaination ! i agree the coils should be wider. and i normally do, but in this case i wanted as much output. and the next foils will have more coil, since i think its importand to have it driven more uniform over its width ! about the leakage there is not much right now but the question is do i need leakage >? if so where do i get it from :) maybe some holes in the magnet frame to the outside world. but they have to be big to let all the air trough. without scuffing etc
@@joppepeelen :) I meant that how the air in the magnet gaps behave compared to if the volume between the membranes was fully "open" was hard to say :) I would bet that you have some secondary resonance around 700-1500Hz caused by interaction between the volume of air between the membrane (the 'box') and the magnet gaps (the 'ports')... That's what I saw with slots with about that size. I don't think you want much leakage to the outside in this case - I did, when experimenting with rear pressure leakage to get midrange directivity control. Different thing altogether. But actually, having a few very small pressure venting holes to allow for some (very slow) pressure equalization if you transport the driver or something like that would be a good idea. Especially if you make something like this that's meant to last for a few years of use. In a compression driver you solve that airgap/slot resonance by keeping the trapped air volume extremely low. Typically a compression driver dome has less than a mm of physical room to move, meaning that the volume of air between the dome and the slotted phase plug isn't really large enough to trigger a Helmholtz resonance
For other applications isobaric was used because you could put the driver's in a box half the size of a single driver and get the same output as a larger box. I think you should try a box.
hmm yeah and that might be true in this case although io doubt it :) but its not the reason for making the thing. since it adds indeed other benefits that isobaric does not have. or at least should not have :)
@@joppepeelen Think of it this way: you have two membranes with separate voice coils that use the same magnets. As you pointed out in you explanation, the field strength for the front membrane drops as it moves outward, but since the membrane on the back is also moving in the same direction, the field strength for that coil is increasing. If you maintain a constant pressure (isobaric) between the membranes, they will tend to couple with one another better, so as the rear membrane pushes forward it will also push the front membrane with it, and linearize the field strength. Same as the front membrane moves backwards, it helps push the rear membrane with it, but only if the space between the membranes is sealed. The main reason cone drivers are set up in an isobaric configuration is to reduce the enclosure size. The idea that orienting them cone to cone to reduce distortion is mostly a red herring. The distortion reduction you get is barely measurable and certainly not audible. What isobaric for cone drivers does is make them more like modern drivers that are designed for smaller boxes.
As with an isobaric driver, a mass of the membrane is doubled. So, you have two resonance frequencies: a single, lighter membrane (actually these are two frequencies cause membranes are slightly different, and so a tension), and doubled, heavy, composite single one. The easier an air moves through a grid with magnets, the more the second resonance plays. The tighter holes are the more role have two higher resonances. What is in a between I don't know -)
well i dont know either :) i am not even sure yet if the air is something i want... or not i can imagine it can be nice if the air is free to move. and not been compressed by a piece of damping it encounters. so i might need to make one that is leaky somehow... although i am afraid it will have scuffing like closed speakers with a leak :)
yes as one of these much smaller ones it might... but what if these where twice the size. and 4 or 5 mm xmax instead of 6 ? besides that it is not using metal. making construction rather easy :) no jigs no glueing (might need some but at least it will stay put :))
When do isobaric woofers the air space between the drivers must be perfectly air tight. Play 50hz and if the output drops over time then pressure is building up between the membranes.
its not better then a push pull, i never said so :) it is better for my wallet ! and fingers. the idea is its better then a single ended. while i spend far less money on magnets and even steel. having to put 2 steel plates a 25 euro together with 180 magnets.. is not a nice choir. and well cost much more. you never wonder why most are single ended when it comes to low end ?
