Bill F. said:
That's a very good question, and was considered. I unfortunately can't say why yet until the Parthanon is released.
Man I can't wait. I do like your idea as well. It reminds me of the high roll surround like the one used in the ID Max. But yours gets rid of the puckering problem.
Magura,
You are right that this innertube system would require regular adjustment of the inflation. Not only do innertubes leak, their enclosed volume also changes with temperature and atmospheric pressure.
I guess this idea would only be acceptable to tweakers (like me ) who don't mind fiddling with their gear to keep it running correctly.
As for the rollers holding up, I don't see the forces as being that great, though heat tolerance could possibly be an issue. I suspect a decent little cartridge bearing inside a silicone-rubber wheel would survive ok...
I'm not saying this innertube/roller idea is the only way to execute this high-excursion suspension. It's just the best I could come up with off the cuff that combines the following critical ingredients (If there's another system that would do it better, then let's talk about it! )
1. Long excursion potential
2. Axial return force (to return the VC to dead center at zero signal)
3. Stiff radial centering of both the diaphragm and the VC (to keep the coil from touching down)
4. No significant static friction (as with a sliding piston)
5. An airtight seal between the front and rear waves.
6. Relative simplicity/cheapness (c'mon folks, this is DIY)
7. There may be others I'm not thinking of right now...
You are right that this innertube system would require regular adjustment of the inflation. Not only do innertubes leak, their enclosed volume also changes with temperature and atmospheric pressure.
I guess this idea would only be acceptable to tweakers (like me
) who don't mind fiddling with their gear to keep it running correctly.As for the rollers holding up, I don't see the forces as being that great, though heat tolerance could possibly be an issue. I suspect a decent little cartridge bearing inside a silicone-rubber wheel would survive ok...
I'm not saying this innertube/roller idea is the only way to execute this high-excursion suspension. It's just the best I could come up with off the cuff that combines the following critical ingredients (If there's another system that would do it better, then let's talk about it!
)1. Long excursion potential
2. Axial return force (to return the VC to dead center at zero signal)
3. Stiff radial centering of both the diaphragm and the VC (to keep the coil from touching down)
4. No significant static friction (as with a sliding piston)
5. An airtight seal between the front and rear waves.
6. Relative simplicity/cheapness (c'mon folks, this is DIY
)7. There may be others I'm not thinking of right now...
Bill F. said:Magura,
You are right that this innertube system would require regular adjustment of the inflation. Not only do innertubes leak, their enclosed volume also changes with temperature and atmospheric pressure.
I guess this idea would only be acceptable to tweakers (like me
As for the rollers holding up, I don't see the forces as being that great, though heat tolerance could possibly be an issue. I suspect a decent little cartridge bearing inside a silicone-rubber wheel would survive ok...
The innertube system with air is very sensitive to temperature changes, actually come to think of it, it cant be airfilled for that single reason. It must be foam filled. The difference from cold to warm speaker...cold / warm day, is huge in pressure matters.
The reason for the rollers not holding up is not the forces, but the osciliation speed...no ordinary ball bearing can do that, especially since we cant preload the bearings, then it turns into a 100% no-go.
Magura
Magura,
I guess I don't share your pessimism about the bearings. I could be wrong, but I don't believe rapid acceleration/deceleration is damaging to a bearing. I believe the only thing that significantly affects performance WRT acceleration is the bearing/wheel system's rotational momentum. IOW, if a the wheel/bearing system has too much rotational momentum for a given acceleration, it will overcome the static friction at the wheel's point of contact and "skid" on the inside of the former. Even if this does happen (which I don't see as likely with a small bearing/wheel), it wouldn't really stress the bearing, though I guess enough skidding could wear down the wheel.
Regarding the idea of filling the innertube suspension with foam, unless I misunderstand what you mean, I believe that would rob it of its freedom to roll since it needs to deform without much resistance to do so.
Again, I could be wrong, but I don't expect the innertube inflation to fluctuate wildly with reasonable barometric shifts or a few degrees of temperature shift. I may be going out on a limb here, but I'm just guessing that checking the inflation of your DIY Parthenonesque Super-Sup at most twice a week would be plenty adequate.
I guess I don't share your pessimism about the bearings. I could be wrong, but I don't believe rapid acceleration/deceleration is damaging to a bearing. I believe the only thing that significantly affects performance WRT acceleration is the bearing/wheel system's rotational momentum. IOW, if a the wheel/bearing system has too much rotational momentum for a given acceleration, it will overcome the static friction at the wheel's point of contact and "skid" on the inside of the former. Even if this does happen (which I don't see as likely with a small bearing/wheel), it wouldn't really stress the bearing, though I guess enough skidding could wear down the wheel.
Regarding the idea of filling the innertube suspension with foam, unless I misunderstand what you mean, I believe that would rob it of its freedom to roll since it needs to deform without much resistance to do so.
Again, I could be wrong, but I don't expect the innertube inflation to fluctuate wildly with reasonable barometric shifts or a few degrees of temperature shift. I may be going out on a limb here, but I'm just guessing that checking the inflation of your DIY Parthenonesque Super-Sup at most twice a week would be plenty adequate.
The problem of the ballbearings isnt the skidding between the roller and the former, but the skidding between the balls and the raceways. Thats surely gonna kill the bearings very fast. The issue is the weight of the balls VS. the friction between the balls and the raceways. Its very hard to overcome without preload of the bearings. With preload the problem can be reduced by using ceramic balls, since they are about a third of the weight of steel balls.
You are not facing the need to adjust the pressure twice a week, but every time prior to using the speaker. If a very soft type of foam is used, i believe the properties of the assembly would be close to the inflated assembly, but without the issues of pressure changes or air loss.
Magura
You are not facing the need to adjust the pressure twice a week, but every time prior to using the speaker. If a very soft type of foam is used, i believe the properties of the assembly would be close to the inflated assembly, but without the issues of pressure changes or air loss.
Magura
The inner tube concept is really quite clever I'd say (who is he? they are saying the Arbitor of Clever? 
)
And it works by rolling, which should have low resistance and large excursion. For that reason the foam filling won't work.
It is similar to bearings using flexible bands.
Bands are also used to drive those super pro subwoofers whose cones are attached by bands around the shaft of a stepper motor, another design to keep in mind while working on this project. Anyone remember what that company is? Servo Drive? or something. I'll bet they had to solve a lot of problems you are discussiong....
)And it works by rolling, which should have low resistance and large excursion. For that reason the foam filling won't work.
It is similar to bearings using flexible bands.
Bands are also used to drive those super pro subwoofers whose cones are attached by bands around the shaft of a stepper motor, another design to keep in mind while working on this project. Anyone remember what that company is? Servo Drive? or something. I'll bet they had to solve a lot of problems you are discussiong....
I guess i should introduce myself, since this thread requires a little backgroung knowledge about the participants
Im a toolmaker in diecasting, ive been studying ballbearing engineering rather intensive during the last 10 years. I have been working with composites in many different applications.
At last ive been working for Dynaudio and 2 of their sub contractors, so i have an idea about some of what this takes.....not that dynaudio were like an open book, they were more like nasa or fort knox
Magura
Im a toolmaker in diecasting, ive been studying ballbearing engineering rather intensive during the last 10 years. I have been working with composites in many different applications.
At last ive been working for Dynaudio and 2 of their sub contractors, so i have an idea about some of what this takes.....not that dynaudio were like an open book, they were more like nasa or fort knox
Magura
Variac said:
The foam filling wouldnt change anything but the resistance, since it would roll with the tube. Resistance is already an issue built in by the concept of rolling a tube.....i would expect the difference in resistance between air and foam filling to be insignificant....if detectable at all.
Magura
Magura,
I hadn't thought about how the balls could slide on the races--good point. (This is an example of why the broad-based, knowlegable input of this public forum is so nice. ) In light of that, I'd propose substituting bushings with small-diameter shafts and self-lubrication to minimize static friction. Probably would be cheaper, too.
Back to the foam idea, it isn't the foams ability to deform that I'm worried about, it's how it handles the inevitable shearing motion at the center of the tube.
Variac,
My mental simulation differs from yours... But only empirical experimentation will tell.
Here's an idea for a suspension test rig:
Get two straight-sided buckets, one very large, and one at least 4" smaller in diameter. Get an appropriately-sized innertube, partially inflate it, and glue it to the outside of the smaller bucket about 4-5" from the bottom. (You should first drill a hole for the inflation stem to pass through the bucket wall.) After the glue has set, run another bead of glue around the inside of the larger bucket, about 4-5 inches from the top. Using spacers, place the smaller bucket upside down in the larger one, line the tube up with the fresh glue, and inflate it untill it compresses the bead. (You'll probably need to use wax paper or some other means of controlling the spread of the glue to create a narrow narrow, clean adhesion.) When it's dry, you'll have a fine suspension test mule.
I hadn't thought about how the balls could slide on the races--good point. (This is an example of why the broad-based, knowlegable input of this public forum is so nice.
) In light of that, I'd propose substituting bushings with small-diameter shafts and self-lubrication to minimize static friction. Probably would be cheaper, too.Back to the foam idea, it isn't the foams ability to deform that I'm worried about, it's how it handles the inevitable shearing motion at the center of the tube.
Variac,
My mental simulation differs from yours... But only empirical experimentation will tell.
Here's an idea for a suspension test rig:
Get two straight-sided buckets, one very large, and one at least 4" smaller in diameter. Get an appropriately-sized innertube, partially inflate it, and glue it to the outside of the smaller bucket about 4-5" from the bottom. (You should first drill a hole for the inflation stem to pass through the bucket wall.) After the glue has set, run another bead of glue around the inside of the larger bucket, about 4-5 inches from the top. Using spacers, place the smaller bucket upside down in the larger one, line the tube up with the fresh glue, and inflate it untill it compresses the bead. (You'll probably need to use wax paper or some other means of controlling the spread of the glue to create a narrow narrow, clean adhesion.) When it's dry, you'll have a fine suspension test mule.
Bill F. said:Magura,
I hadn't thought about how the balls could slide on the races--good point. (This is an example of why the broad-based, knowlegable input of this public forum is so nice.
Id propose a sliding bearing on a rod in the center of the motor. Its possible to get very low friction using the right bearing configuration, and its something thats actually do-able in real life. If done like that, the air gap can be minimized.
The idea with small rollers looks good on paper, but is almost impossible to make on DIY basis.
Magura
Hi Everybody!
Great thread!
I like the idea with the tube.
And I think I could accept to repump some air every or so in order to achieve the coorect pressure.
But I am not sure if the tube would be the right thing to adjust the suspension with tube. Wouldn't we get a very nonlinear behaviour? If I am right normally the spider dominates the value of the spring.
Another point: How can we guarantee that the voice coild does not touch the pole plates without making the gap very large. I fact I feel that this will require very precise mechanical work!
Looking forward to get a perfect set of instructions for a xxl-excursion diy-driver.....
Markus
Great thread!
I like the idea with the tube.
And I think I could accept to repump some air every or so in order to achieve the coorect pressure.
But I am not sure if the tube would be the right thing to adjust the suspension with tube. Wouldn't we get a very nonlinear behaviour? If I am right normally the spider dominates the value of the spring.
Another point: How can we guarantee that the voice coild does not touch the pole plates without making the gap very large. I fact I feel that this will require very precise mechanical work!
Looking forward to get a perfect set of instructions for a xxl-excursion diy-driver.....
Markus
Humm. I think something like a frame on both front and back with the cone inbetween would work, that way the front edge of the VC former has a hard mount and a crude physical barier to keep the cone from flying in your face. This seems like it would be easier to keep everything linier as well, kind of like Volt drivers except with a basket on the rear as well.
http://ldsg.snippets.org/graphics/volt/R4504pic-opt.jpg
http://ldsg.snippets.org/graphics/volt/R4504pic-opt.jpg
Hello gentlemen
I'm away for a while and the ideas are coming up like mushrooms. On some of your posts I may make these observations.
Diameter must be determined
How BIG?? Round Please
Cone will be made of styrofoam untill some one comes up with a cheaper, stiffer alternative. I'll figure out the mass of the stuff tomorrow.
Power handling will be a relationship of the diaphram mass plus the former and associated masses real and instataneous.
(someone who is better at complex math has to take care of this one. We can all talk it through but there has to be a final theoretical goal.)
Basket will be of bent laminated birch ply. I don't want to argue about much else on this one. It is very stiff relatively easy to machine and relatively stable. And since this is an experiment.
CHEAP!!!!!
Motor structure idea looks good on paper. Any modeling of the beast? At what flux density? What kind of material? Note that 1008 steel is very diffucult to get in North America. The last custom driver that I made used a continuous cast silicone iron. It wasn't cheap but it could support the flux densities that we were shooting for.
The surround is a fluid work in progress. Nice ideas are coming up. No one has thought of a multiple roll surround yet?
The A#1 Primo problem is the stablilty of the coil/former. Without this worked out there is no point in going anywhere with this effort.
Maqua and Bill have the same line of thought that I have on the subject.
A central rod that will serve as a guide on the voice coil former.
Disclosure of the fine print.
I am not a certified machinist. BUt I do know my way around a machine shop. I have a friend that is a tool and die maker and I have permission to use his shop as long as I don't break anything. LOL Any direction from those who are more experienced will be most welcome (maqua)
I am not an acredited electrical engineer.
I am a skilled cabinet maker not of kitchens but the real stuff furniture and complex millwork.
And I am the most dogged stuborn son of a motherless dog when I want to get something done. That's what got me into doing audio and has kept me there for almost twenty years. Not that I fail to be open to good ideas. I just like to get things I'm interested in done.
This project can be done!
So we need a low friction bushing to fit onto a central shaft. I have seen teflon impregnated aluminum bushings ( frelon I think) but his is a little above my present knowledge. I understand what we need as do most of us. Rapid movement with as little noise as possible and with the least friction as possible.
An air bearing may be the ultimate. But I must confess that I know not how to constuct such a widget. Nor do we want a franken woofer with al sorts of apendages and tubes to keep it alive. It may be possible to use the considerable amount of air that could be pumped by the diaphram for our intended purpose of keeping it on centre. Maybe not toss that one around.
Returning to a well engineered long throw voicecoil in the disk drive. They used a central shaft and an engineered plastic bushing to keep the coil in it's proper place. I have teflon here in stock but is this the best or lowest friction product available?
(maqua do you know?) anyone else?
Bill can a description of the motor structure be started ie:
top plate, second and third plate thicknesses and overall diameter I.D. and O.D.
Length of voice coil composite and desired excursion +- ???
Diameter of pole piece.
Size of support posts.
Size and number of magnets needed to reach your required flux density.
Type Neo 30, 35, 40??????
They all support a different flux level and can operate at a different temperature.
Former material will greatly alter our overall inductance and therefore the frequecy response of the driver.
Are we using aluminum? It could be black anodised to be heat emissive. Kapton ( but where to get a suitable size and how to work the stuff ) Paper treated?
Number of turns on the coil? What wire diameter?
Does anyone out there have or has access to reverse spead d??
Most of the motor, and frequency response questions can be modeled there.
( I think I spelled it correctly it is a motor stucture and loudspeaker modeling program )
One more thing and it should have been first.
I stand in awe at some of your posts. A sharp bunch of cookies are being drawn to this thread. If we put our heads together we could make an earthquake or two
Mark
I'm away for a while and the ideas are coming up like mushrooms. On some of your posts I may make these observations.
Diameter must be determined
How BIG?? Round Please
Cone will be made of styrofoam untill some one comes up with a cheaper, stiffer alternative. I'll figure out the mass of the stuff tomorrow.
Power handling will be a relationship of the diaphram mass plus the former and associated masses real and instataneous.
(someone who is better at complex math has to take care of this one. We can all talk it through but there has to be a final theoretical goal.)
Basket will be of bent laminated birch ply. I don't want to argue about much else on this one. It is very stiff relatively easy to machine and relatively stable. And since this is an experiment.
CHEAP!!!!!
Motor structure idea looks good on paper. Any modeling of the beast? At what flux density? What kind of material? Note that 1008 steel is very diffucult to get in North America. The last custom driver that I made used a continuous cast silicone iron. It wasn't cheap but it could support the flux densities that we were shooting for.
The surround is a fluid work in progress. Nice ideas are coming up. No one has thought of a multiple roll surround yet?
The A#1 Primo problem is the stablilty of the coil/former. Without this worked out there is no point in going anywhere with this effort.
Maqua and Bill have the same line of thought that I have on the subject.
A central rod that will serve as a guide on the voice coil former.
Disclosure of the fine print.
I am not a certified machinist. BUt I do know my way around a machine shop. I have a friend that is a tool and die maker and I have permission to use his shop as long as I don't break anything. LOL Any direction from those who are more experienced will be most welcome (maqua)
I am not an acredited electrical engineer.
I am a skilled cabinet maker not of kitchens but the real stuff furniture and complex millwork.
And I am the most dogged stuborn son of a motherless dog when I want to get something done. That's what got me into doing audio and has kept me there for almost twenty years. Not that I fail to be open to good ideas. I just like to get things I'm interested in done.
This project can be done!
So we need a low friction bushing to fit onto a central shaft. I have seen teflon impregnated aluminum bushings ( frelon I think) but his is a little above my present knowledge. I understand what we need as do most of us. Rapid movement with as little noise as possible and with the least friction as possible.
An air bearing may be the ultimate. But I must confess that I know not how to constuct such a widget. Nor do we want a franken woofer with al sorts of apendages and tubes to keep it alive. It may be possible to use the considerable amount of air that could be pumped by the diaphram for our intended purpose of keeping it on centre. Maybe not toss that one around.
Returning to a well engineered long throw voicecoil in the disk drive. They used a central shaft and an engineered plastic bushing to keep the coil in it's proper place. I have teflon here in stock but is this the best or lowest friction product available?
(maqua do you know?) anyone else?
Bill can a description of the motor structure be started ie:
top plate, second and third plate thicknesses and overall diameter I.D. and O.D.
Length of voice coil composite and desired excursion +- ???
Diameter of pole piece.
Size of support posts.
Size and number of magnets needed to reach your required flux density.
Type Neo 30, 35, 40??????
They all support a different flux level and can operate at a different temperature.
Former material will greatly alter our overall inductance and therefore the frequecy response of the driver.
Are we using aluminum? It could be black anodised to be heat emissive. Kapton ( but where to get a suitable size and how to work the stuff ) Paper treated?
Number of turns on the coil? What wire diameter?
Does anyone out there have or has access to reverse spead d??
Most of the motor, and frequency response questions can be modeled there.
( I think I spelled it correctly it is a motor stucture and loudspeaker modeling program )
One more thing and it should have been first.
I stand in awe at some of your posts. A sharp bunch of cookies are being drawn to this thread. If we put our heads together we could make an earthquake or two
Mark
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