Just weight
I surfed and found the weight of the styrofoam I will be using. Hold on to your seats gents. 28kg/cubic metre. or about .000036 grams /cubic centimetre. Not much. A cone will weigh not a lot. I have to break out the old math texts and figure out the volume of a cone. But it won't be a perfect cone just a hyperbolic curve staring at the voice coil junction and then out to about 24" overall height will be 3" or about 75mm. Now to crunch numbers and drive the last few hairs out of the top of my head. Wheres the asperin!
Mark
I surfed and found the weight of the styrofoam I will be using. Hold on to your seats gents. 28kg/cubic metre. or about .000036 grams /cubic centimetre. Not much. A cone will weigh not a lot. I have to break out the old math texts and figure out the volume of a cone. But it won't be a perfect cone just a hyperbolic curve staring at the voice coil junction and then out to about 24" overall height will be 3" or about 75mm. Now to crunch numbers and drive the last few hairs out of the top of my head. Wheres the asperin!
Mark
Honestly, I'm not ashamed to say I'm a relative newbie at the XBL^2 designing aspect of the game... but I've at least got the toolsetsBill F. said:
, I understand how XBL^2 does work, and this would be a great exercise for sure. I honestly don't know, that's just my imagination going "there must be a way.... there must be a way...Bill F. said:
I haven't prototyped it... and honestly, I don't know if they could mold something like that... at least without a seam one way or the other. Hmm.
But, as with the half roll surround, there seems to always be geometry opposing a non-pistonic movement... I would think, anyway.
That's a very interesting thought then...Bill F. said:
Because my other question was going to be "how would the excursion capability of the tube vary from the excursion capability of a half-roll surround of the same dimensions (as half of your tube illustration).
The inflated-adjustability is an interesting concept to ponder, for sure...
As is the essentially adjustable VAS of the sub... wonder if it would be too dramatic though.
I suppose it could be a function of the material/thickness of the "innertube" material.
I wonder too, about the effective shape of the KMS curve, if it would result in (because of the rising air pressure in the tube at higher excursions a more parabolic, or linear KMS curve shape...
...and if THAT would also be adjustable as a function of the material that the tube is made out of.
Something to think about as I'm sleeping (since it's after 1am here and I'm going to have to wake up and shovel about a foot of snow to get my wife out in the morning... and I really don't want to think about that...
Re: Hello gentlemen
Still pondering and making sure it would seem to effectively prevent rocking...
...honestly I'm not sure we even care, because we can take care of that by the rear suspension...
), then we can solve this very easily...
Dual spiders, with a space measured in inches between them.
The old "brute force" technique to preventing rocking.
And for that matter, if we are already of the train of thought that would be thinking like this:
If we can effectively control cone rocking motions via the rear suspension (that's 'catch' number one)...
Then why not simply take a look at other high-stroke pistonic devices for inspiration?
The car piston comes to mind, instantly.
No "surround" needed there.
In fact, it doesn't even use a rear "suspension" to ensure linear, rock-free behavior.
What would prevent us from literally creating a piston, in a 'bore', with 'piston rings' (of a low-friction variety, like Delrin or Teflon) to perform effective sealing?
Don't get too hung up on the concept that the surround makes for an effective seal, separating that back energy from the front... mostly the cone itself does that.
In fact, subwoofers like the Phoenix Gold Cyclone even have a gap, effectively, where some small amount of leakage could occur as the diaphragm swings back and forth.
It's still one of the most remarkably efficient subwoofers in the world (by nearly a factor of ten!).
Just something to promote a little thinking...
So many people have already voiced their concerns at the high-power that's going to be required to effectively throw the Parthenon to realize it's excursion potential, and the amount of heat that would be likely to generate, and of course the amount of heat required to destabilize Neodymium...
Interesting thoughts... but 40 grade Neo seems relatively inexpensive... what are the trade-offs?
Does it become more, or less heat-tolerant as magnetic strength increases?
That's essentially what mine was, if you scroll back for my diagram.mwmkravchenko said:
Still pondering and making sure it would seem to effectively prevent rocking...
...honestly I'm not sure we even care, because we can take care of that by the rear suspension...
If we don't care about the mounting depth on this thing (and my god... how COULD we?mwmkravchenko said:
), then we can solve this very easily...Dual spiders, with a space measured in inches between them.
The old "brute force" technique to preventing rocking.
And for that matter, if we are already of the train of thought that would be thinking like this:
...then why even necessitate a front suspension at all?mwmkravchenko said:
If we can effectively control cone rocking motions via the rear suspension (that's 'catch' number one)...
Then why not simply take a look at other high-stroke pistonic devices for inspiration?
The car piston comes to mind, instantly.
No "surround" needed there.
In fact, it doesn't even use a rear "suspension" to ensure linear, rock-free behavior.
What would prevent us from literally creating a piston, in a 'bore', with 'piston rings' (of a low-friction variety, like Delrin or Teflon) to perform effective sealing?
Don't get too hung up on the concept that the surround makes for an effective seal, separating that back energy from the front... mostly the cone itself does that.
In fact, subwoofers like the Phoenix Gold Cyclone even have a gap, effectively, where some small amount of leakage could occur as the diaphragm swings back and forth.
It's still one of the most remarkably efficient subwoofers in the world (by nearly a factor of ten!).
Just something to promote a little thinking...
Any more detail on this?mwmkravchenko said:
So many people have already voiced their concerns at the high-power that's going to be required to effectively throw the Parthenon to realize it's excursion potential, and the amount of heat that would be likely to generate, and of course the amount of heat required to destabilize Neodymium...
Interesting thoughts... but 40 grade Neo seems relatively inexpensive... what are the trade-offs?
Does it become more, or less heat-tolerant as magnetic strength increases?
Now wait just a minute.
A while ago I remember reading about a competition car audio driver that had what they called a "field-replaceable voice coil", which actually meant that nothing in the driver was glued--everything was held together by gaskets and screws, and the voice coil former was hugely longer than necessary, in order to fit all the hardware.
I suspect that if we used a non-flat spider *on each end of the voice coil* in conjunction with something just as commonplace for the cone suspension, we could handle the lateral motion alright, and prevent the premature destruction of our woofer.
Balancing this with the super-high-excursion goal, however, might not be so pretty! I think the biggest advantage here is that we can have a very large spider attached to the voice coil (at either end) much more acceptably than a huge surround on the cone! (People don't like large surrounds on the cone, I've noticed.)
Here, look at this:
http://www.codrive.com/tech.htm
A while ago I remember reading about a competition car audio driver that had what they called a "field-replaceable voice coil", which actually meant that nothing in the driver was glued--everything was held together by gaskets and screws, and the voice coil former was hugely longer than necessary, in order to fit all the hardware.
I suspect that if we used a non-flat spider *on each end of the voice coil* in conjunction with something just as commonplace for the cone suspension, we could handle the lateral motion alright, and prevent the premature destruction of our woofer.
Balancing this with the super-high-excursion goal, however, might not be so pretty! I think the biggest advantage here is that we can have a very large spider attached to the voice coil (at either end) much more acceptably than a huge surround on the cone! (People don't like large surrounds on the cone, I've noticed.)
Here, look at this:
http://www.codrive.com/tech.htm
Id go for the suspensionless idea as well....it sounds like something much easier to actually succeed with.....and the spider in the voicecoils is perhaps also not a bad idea.
I like the sound of not gluing things together, the possibillity to take the whole thing apart is very appealing.
The cone though must be made of either kevlar or carbon fibre....its cheap easy to shape and reliable. The dampening can be adjusted by making a sandwich construction, and choosing the right material for the dampener.
Magura
I like the sound of not gluing things together, the possibillity to take the whole thing apart is very appealing.
The cone though must be made of either kevlar or carbon fibre....its cheap easy to shape and reliable. The dampening can be adjusted by making a sandwich construction, and choosing the right material for the dampener.
Magura
OK, here's my thoughts about this.
Bill, I like your innertube surround/suspension. It has a lot of good things about it. One that hasn't been mentioned is that the change in volume as the tube distorts can actually be leveraged to provide an axial restoring force past a certain excursion. In that way, it mimics the suspension characteristics of a spider/surround design. Still, I think in practice it will be too difficult to control compliance, linearity, and excursion using off-the-shelf tubes. Throw in leakage, temperature, and altitude complications, and I think a different route should be pursued.
I really like the idea of a central rod with a linear bearing for radial centering control. Linear bearings on ground rods are very common in a wide variety of machinery, and they work very well. I think Magura might be correct about the ability of ball bearings (whether radial or linear) to handle the accelerations required, but something like the Frelon impregnated aluminum mentioned previously might work out nicely. I've used these linear bushings in the past, and they are quiet and fairly low in friction when aligned properly. A longish central rod in the middle of the former with adequately spaced linear bushings could provide all the rocking and radial control you need.
If you really want to make this complicated, the same type of NeFeB magnets used for the motor can be used to make some really, really slick linear bearings with essentially zero friction and excellent alignment and centering characteristics. Might really cause a problem with the motor and suspension fields interacting though. ??
Now for a suspension. Once you have a central rod and bushings, is there a way of further using that structure to provide the basis of a linear suspension? Standard coil springs and/or elastic bands would be pretty easy to use for a suspension, and the force/displacement curve would be linear, but is that what is typically referred to as a "linear" suspension? (my assumption is that you want the suspension force to be constant over a wide range of motion, not linear to the displacement... please clarify this for me). If not, and this is going into rambling here, how difficult would it be to use the multi-gap XBL^2 architecture to make a non-linear motor that complements a non-linear suspension? i.e., a higher motor strength at the extremes of excursion than at the centered position?
In any case, the central rod provides a nice attachment point for a variety of axial suspension ideas, and we should be able to come up with something that works. All that is left for the surround to do is provide a seal, and that could well be left as just a small non-contacting gap with minimal leakage. (I don't think a true "piston" design complete with sliding sealing rings would work due to fairly high static and dynamic friction... besides, anyone want to pay for a precision machined 24"+ metallic bore/basket and piston/cone? Don't think so ).
I work as a mechanical engineer, and have plenty of experience in both material science and mechanism design, so maybe I can come up with more suspension ideas as some of the gaps in my knowledge are filled in. At the very least, I can conjure up some quick solid models of the leading ideas to help others visualize the concepts.
Bill, I like your innertube surround/suspension. It has a lot of good things about it. One that hasn't been mentioned is that the change in volume as the tube distorts can actually be leveraged to provide an axial restoring force past a certain excursion. In that way, it mimics the suspension characteristics of a spider/surround design. Still, I think in practice it will be too difficult to control compliance, linearity, and excursion using off-the-shelf tubes. Throw in leakage, temperature, and altitude complications, and I think a different route should be pursued.
I really like the idea of a central rod with a linear bearing for radial centering control. Linear bearings on ground rods are very common in a wide variety of machinery, and they work very well. I think Magura might be correct about the ability of ball bearings (whether radial or linear) to handle the accelerations required, but something like the Frelon impregnated aluminum mentioned previously might work out nicely. I've used these linear bushings in the past, and they are quiet and fairly low in friction when aligned properly. A longish central rod in the middle of the former with adequately spaced linear bushings could provide all the rocking and radial control you need.
If you really want to make this complicated, the same type of NeFeB magnets used for the motor can be used to make some really, really slick linear bearings with essentially zero friction and excellent alignment and centering characteristics. Might really cause a problem with the motor and suspension fields interacting though. ??
Now for a suspension. Once you have a central rod and bushings, is there a way of further using that structure to provide the basis of a linear suspension? Standard coil springs and/or elastic bands would be pretty easy to use for a suspension, and the force/displacement curve would be linear, but is that what is typically referred to as a "linear" suspension? (my assumption is that you want the suspension force to be constant over a wide range of motion, not linear to the displacement... please clarify this for me). If not, and this is going into rambling here, how difficult would it be to use the multi-gap XBL^2 architecture to make a non-linear motor that complements a non-linear suspension? i.e., a higher motor strength at the extremes of excursion than at the centered position?
In any case, the central rod provides a nice attachment point for a variety of axial suspension ideas, and we should be able to come up with something that works. All that is left for the surround to do is provide a seal, and that could well be left as just a small non-contacting gap with minimal leakage. (I don't think a true "piston" design complete with sliding sealing rings would work due to fairly high static and dynamic friction... besides, anyone want to pay for a precision machined 24"+ metallic bore/basket and piston/cone? Don't think so
).I work as a mechanical engineer, and have plenty of experience in both material science and mechanism design, so maybe I can come up with more suspension ideas as some of the gaps in my knowledge are filled in. At the very least, I can conjure up some quick solid models of the leading ideas to help others visualize the concepts.
I think you are thinking of the MTX RFL. It even came with a replacement cone unit.... it wasn't just the coil.Nappylady said:
Cheaper than replacing a whole sub though... Car audio competition guys are BRUTAL I tell you... shoving 8,000 watts into a sub rated around 1000 for the sake of a momentary "bass fart"
I had one guy send me back one of my woofers, all apologetic...
He had built a very high-tune SPL box (basically, these guys find the resonant peak of their interior, build a huge ported box tuned to that frequency - to minimize excursion / maximize output at that frequency, and just burp that frequency), and as he was tweaking (at full output), he inadvertantly put on a 20hz track.
Oops.
He was very straightforward with me, so I reconed it for him and sent it back for nothing essentially... I appreciate honesty.
But it did have me wishing that our subs had some field-replacable system like that... I hate reconing.
But getting back on topic...
What would our benefit be here? Ease of swapping out, if we find we've made a mistake?
I like the idea, but in the same sense, I'd be concerned, because we are talking about SUCH high excursions, I'd be afraid that there will be too much tugging on the surround/suspension landing points to be able to do something like that...
And, if we use your idea for the spider on each end of the former (which I like even better, due to the superior control), we almost couldn't do that anyway... how do you recone a sub that's got a spider on each side of a top plate(s) gap?
I think we'll find a unique solution to the surround (possibly even elimination.Nappylady said:
)Consider that the JL Audio W7 subwoofer has been DUMAX verified at around 50mm of decently flat KMS (one way), with a pretty normal diameter spider.
No doubt 80mm can be accomplished, and tooling up spiders isn't all that expensive or difficult ultimately.
I might be able to help out with that (unless someone can think of a way to truly DIY a spider fabrication).
If we have a build-house do it for us, another benefit is we'll end up with 20 or 30 of them at least, if we do need to revisit the cone unit later down the road.
And with that, I'm off to pack and catch a flight to Las Vegas for the CES show...
...so unfortunately I won't be able to reply to this thread until I get back on the 12th.
But I'll definitely be thinking about it... as I'm checking out (and photographing, and taking mental notes) the Adire Parthenon and Resonant Engineering XMX uber-drivers.
Maybe I can get Dan Wiggins and Chris Brunhaver (and maybe even David Hyre) over to my hotel again for a little hanging out... all are great guys.
I'll run this idea by them, see what they think of it.
Not that I'll be anxious to leave Las Vegas or CES, but I'm looking forward to coming back and seeing what's up with this thread!
See you all then!
...so unfortunately I won't be able to reply to this thread until I get back on the 12th.
But I'll definitely be thinking about it... as I'm checking out (and photographing, and taking mental notes
) the Adire Parthenon and Resonant Engineering XMX uber-drivers. Maybe I can get Dan Wiggins and Chris Brunhaver (and maybe even David Hyre) over to my hotel again for a little hanging out... all are great guys.
I'll run this idea by them, see what they think of it.
Not that I'll be anxious to leave Las Vegas or CES, but I'm looking forward to coming back and seeing what's up with this thread!
See you all then!
BTW...the basket should be either fibre or metal.
We need something we can know the resonanse frequency of...im sure that it would be easier to make it of carbon fibre anyway.
Its also a matter of strength and weight+ aerodynamics. We will encounter a problem if we dont take into account that an awfull lot of air have to pass through the basket, and the fact that it will have to carry a huge motor.
Magura
We need something we can know the resonanse frequency of...im sure that it would be easier to make it of carbon fibre anyway.
Its also a matter of strength and weight+ aerodynamics. We will encounter a problem if we dont take into account that an awfull lot of air have to pass through the basket, and the fact that it will have to carry a huge motor.
Magura
Perspective is everything
On the subject of composite this and that.
Many things that we have in everyday use are allready composites. A multiple ply birch plywood when you apply the same testing as your carbon fibre composites sits right up there with them. There is no need to try to hang a monster motor structure on a basket. Hell this motor will be in the 60 to eighty pound range ( 28 to 36 kg) It is the otherway around that the driver will be held up by the motor.
I just did a search on the availability of neo rod magnets to make the inner quide rod an true magnetic bearing. They exist and one site gives away their constuction method. With a properly placed set of rings we could have an almost perfect linear bearing. Next to no contact!!
Maqua I like the idea of making a sandwich cone. And your idea of using some composite is indeed good. So whynot combine the two. Construct a foam cone core using the hot wire method and then overlay it with a fibreglass skin. Heck even an polyester resin (fibreglass resin or epoxy) skin would significantly increase it's stiffness.
A note taken is the ease of assembly and disassemly. Fasteners or mechanical joints are the thoughts that come to mind. Like a twist lock dovetail and such.
One thing or two I guess still bother me. The multiple gaps make sense to me. Energizing the top plates look feasable. The pole piece on the other hand has to be in saturation at certain points as well. How much metal are we talking about?? What diameter.
We can calculate with a fair degree of certainty what the voice coil and former will weigh. I have found castable rubber that could be used to make surrounds. It could be setup in a two part rotary mold and we could get any shape that our heart desired including ears to mount it mechanically. If I can vary the orientation of the mold evenly enough I could even mold a proper custom innertube. Not bad for a wood chipper!! It's available locally. I have material to make a basket in stock. ( let me try it out maqua and then you can shoot it down when it doesn't work or sing praises if it does. I have done allot of aluminum casting in the past, it's just that I am not setup for it right now and a mold could be taken of a good wood pattern in the first place YES? ) No problem there. I have talked to my friend about the machining ( how much machining is the real question now )
This disscussion has been going on as if the motor structure is a done deal and we have only to control the savage beast to do our bidding. Is this the case??
I think that to a great degree the beginnings of some nifty experiments are coming to fruition. I need to make some drawings and put them up for comment as destructive oops constructive criticisim.
Iam happy to get the ball going on the basket front. Out of my pocket. If we get the motor structure finalised then I can check what I have in stock. I feel very comfortable paying for the castable rubber as well. the cone again is not the end of the world to pay for. I just have to get a heavy duty 5 volt power supply at my local computer recycler ( in the 100s of amps not an AT supply I'm not that stupid ) and I'll be ready to cut out the foam core. I have both epoxy and fiber glass resin and i know one of them will not eat up the foam. The rest if there is any we will have to come to when there are components to put together!
I have a buddy who has a digital camera so I could take some pics and show whats up.
Does anybody have any spare time that they could give me???
Mark
On the subject of composite this and that.
Many things that we have in everyday use are allready composites. A multiple ply birch plywood when you apply the same testing as your carbon fibre composites sits right up there with them. There is no need to try to hang a monster motor structure on a basket. Hell this motor will be in the 60 to eighty pound range ( 28 to 36 kg) It is the otherway around that the driver will be held up by the motor.
I just did a search on the availability of neo rod magnets to make the inner quide rod an true magnetic bearing. They exist and one site gives away their constuction method. With a properly placed set of rings we could have an almost perfect linear bearing. Next to no contact!!
Maqua I like the idea of making a sandwich cone. And your idea of using some composite is indeed good. So whynot combine the two. Construct a foam cone core using the hot wire method and then overlay it with a fibreglass skin. Heck even an polyester resin (fibreglass resin or epoxy) skin would significantly increase it's stiffness.
A note taken is the ease of assembly and disassemly. Fasteners or mechanical joints are the thoughts that come to mind. Like a twist lock dovetail and such.
One thing or two I guess still bother me. The multiple gaps make sense to me. Energizing the top plates look feasable. The pole piece on the other hand has to be in saturation at certain points as well. How much metal are we talking about?? What diameter.
We can calculate with a fair degree of certainty what the voice coil and former will weigh. I have found castable rubber that could be used to make surrounds. It could be setup in a two part rotary mold and we could get any shape that our heart desired including ears to mount it mechanically. If I can vary the orientation of the mold evenly enough I could even mold a proper custom innertube. Not bad for a wood chipper!! It's available locally. I have material to make a basket in stock. ( let me try it out maqua and then you can shoot it down when it doesn't work or sing praises if it does. I have done allot of aluminum casting in the past, it's just that I am not setup for it right now and a mold could be taken of a good wood pattern in the first place YES? ) No problem there. I have talked to my friend about the machining ( how much machining is the real question now )
This disscussion has been going on as if the motor structure is a done deal and we have only to control the savage beast to do our bidding. Is this the case??
I think that to a great degree the beginnings of some nifty experiments are coming to fruition. I need to make some drawings and put them up for comment as destructive oops constructive criticisim.
Iam happy to get the ball going on the basket front. Out of my pocket. If we get the motor structure finalised then I can check what I have in stock. I feel very comfortable paying for the castable rubber as well. the cone again is not the end of the world to pay for. I just have to get a heavy duty 5 volt power supply at my local computer recycler ( in the 100s of amps not an AT supply I'm not that stupid ) and I'll be ready to cut out the foam core. I have both epoxy and fiber glass resin and i know one of them will not eat up the foam. The rest if there is any we will have to come to when there are components to put together!
I have a buddy who has a digital camera so I could take some pics and show whats up.
Does anybody have any spare time that they could give me???
Mark
To begin with the cone:
There is no reason to not use carbon fibre for the cone, its cheap and available anywhere. You cant make a cone by making the foam core first, the foam core would absorb waaay too much epoxy....almost like a sponge. Besides that, the carbon must be wetted with epoxy, and then put under pressure to get any structural streingth. That is don by making the two carbon cones and then gluing them on to the foam core.
If carbon fibre is a problem to obtain in canada (i find it hard to believe it should be) i can help you out.
The basket is no big issue for a test setup (material vise i mean), the reason i pointed out carbon (or glass) fibre, is that if you want to make more than one, its much easier....and we sure know its not gonna be all that easy to make from wood.
If you havnt got a lot of experience, dont be afraid of it....its a very gratefull material, cheap and easy to work with.
Magura
There is no reason to not use carbon fibre for the cone, its cheap and available anywhere. You cant make a cone by making the foam core first, the foam core would absorb waaay too much epoxy....almost like a sponge. Besides that, the carbon must be wetted with epoxy, and then put under pressure to get any structural streingth. That is don by making the two carbon cones and then gluing them on to the foam core.
If carbon fibre is a problem to obtain in canada (i find it hard to believe it should be) i can help you out.
The basket is no big issue for a test setup (material vise i mean), the reason i pointed out carbon (or glass) fibre, is that if you want to make more than one, its much easier....and we sure know its not gonna be all that easy to make from wood.
If you havnt got a lot of experience, dont be afraid of it....its a very gratefull material, cheap and easy to work with.
Magura
Yep and Yepp yep
I'm with you on the ease of foam. I don't even have to hot wire it. It can be machined with a router and a contour jig. No big deal. Carbon fibre doesn't scare me it's just I've never worked with it before. The only thing that bothers me is the potential cost. The learning curve would be eased by someone ( maybe maqua ) who was familiar with the stuff. I'm a quick study when it comes to learning things. I have vacuum facilities so i can apply allot of pressure to get a smooth surface and eliminate bubbles. As for the foam absorbing the epoxy. Not a chance. This is a rigid closed cell ( actually microscopic closed cell ) foam. Almost no absorbsion. The magnets could be sourced from a couple of surplus places. I put up a couple of links on the other parthenon thread where I started all this mess with Bill. The magnets are amazingly cheap.
I'm still thinking over whether or not a good magnetic linear bearing could be fabricated. It need only repel the cone assembly and keep it in a stasis and then dampen the cone as it gets to the extremes of it's excursion. Maybe to pie in the sky or maybe a stroke of genius. ( pun intended )
The wood work is not dead simple but not hard. A form is required and a series of layers of 3mm ply is laid and glued up. It forms a composite structure. If you choose the glue carefully it can be a very strong but light weight rib in a basket structure. The ribs can be drilled and tapped ( yes tapped maqua it's actually stronger to use a machine screw in a close grained wood then a wood screw ) and the ribs can be bolted to a ring that would support the surround. The interior could again be set into a block and bolted to the motor structure.
I tend to build things with a hand drawn sketch, a lot of thought and disscussion with people whose opinion I trust and then go to it. This job could benefit from some cad drawings for some of the jigs and fixtures as well as the layout of the basket spokes. But nothing to hard.
Mark
I'm with you on the ease of foam. I don't even have to hot wire it. It can be machined with a router and a contour jig. No big deal. Carbon fibre doesn't scare me it's just I've never worked with it before. The only thing that bothers me is the potential cost. The learning curve would be eased by someone ( maybe maqua ) who was familiar with the stuff. I'm a quick study when it comes to learning things. I have vacuum facilities so i can apply allot of pressure to get a smooth surface and eliminate bubbles. As for the foam absorbing the epoxy. Not a chance. This is a rigid closed cell ( actually microscopic closed cell ) foam. Almost no absorbsion. The magnets could be sourced from a couple of surplus places. I put up a couple of links on the other parthenon thread where I started all this mess with Bill. The magnets are amazingly cheap.
I'm still thinking over whether or not a good magnetic linear bearing could be fabricated. It need only repel the cone assembly and keep it in a stasis and then dampen the cone as it gets to the extremes of it's excursion. Maybe to pie in the sky or maybe a stroke of genius. ( pun intended )
The wood work is not dead simple but not hard. A form is required and a series of layers of 3mm ply is laid and glued up. It forms a composite structure. If you choose the glue carefully it can be a very strong but light weight rib in a basket structure. The ribs can be drilled and tapped ( yes tapped maqua it's actually stronger to use a machine screw in a close grained wood then a wood screw ) and the ribs can be bolted to a ring that would support the surround. The interior could again be set into a block and bolted to the motor structure.
I tend to build things with a hand drawn sketch, a lot of thought and disscussion with people whose opinion I trust and then go to it. This job could benefit from some cad drawings for some of the jigs and fixtures as well as the layout of the basket spokes. But nothing to hard.
Mark
Re: Yep and Yepp yep
The learning curve is not steep at all....if nessecery ill make a monkey see monkey do movie for you.....its btw a very easy task when you have vaccuum equipment, then you just throw the whole thing in a plastic bag and attach the bag to the vaccuum. If its to be real good, you put a piece of PE with holes punched by needles film over the wetted parts and throw a pair of old socks in the bag as well (to absorb as much epoxy as possible, the less epoxy in the finished product the better).
Id stick to a static bearing for the guidance, a simple rod/- bushing assembly is cheap, easy and reliable.
Magura
P.S. Maqua....is actually called Magura
I was wondering whom you meant, till i figured it had to be me
mwmkravchenko said:
The learning curve is not steep at all....if nessecery ill make a monkey see monkey do movie for you.....its btw a very easy task when you have vaccuum equipment, then you just throw the whole thing in a plastic bag and attach the bag to the vaccuum. If its to be real good, you put a piece of PE with holes punched by needles film over the wetted parts and throw a pair of old socks in the bag as well (to absorb as much epoxy as possible, the less epoxy in the finished product the better).
Id stick to a static bearing for the guidance, a simple rod/- bushing assembly is cheap, easy and reliable.
Magura
P.S. Maqua....is actually called Magura
I was wondering whom you meant, till i figured it had to be me
No offense intended Magura. I'm the worlds worst person for names.
A fairly heavy weight cloth would be fine since you are just making flat panels. 10 osy or heavier. Either epoxy or vinylester resin would be fine. Epoxy offers greater strength, but all we really care about is stiffness, and in that case the matrix used matters very little.
www.uscomposites.com is a good source for composite materials/resins/core materials.
How thick of a sandwich are you guys think of? If the foam gets very thick (more than about half an inch), then it certainly does become a structural element. A low shear strength material might actually shear on the neutral axis under high bending moments... and you can rest assured that 6+ inches of excursion at any reasonably high frequency will produce high accelerations that will no doubt try to bend the diaphram. I'd recommend looking at end grain balsa for a core of any sizeable thickness... it's cheaper than the high strength foams that would otherwise be required. Common polystyrene foam might not be up to the challenge. This of course also depends on how you load the diaphram. If a central rod is the only connection to the diaphram, the core could be a concern. If the load is spread by an "inner cone" or other similar structure, then the core is less of a concern. My assumption is that with a central rod, a central connection will be the simplest and cheapest.
Vacuum forming will reduce weight, if that is a goal, but it isn't absolutely necessary to make a strong laminate. If you don't use vacuum assist then the final laminate will be thicker for a given strength, but it will also be a bit stiffer for a given strength. If weight isn't a concern, then hand layup with a well wetted cloth would be just fine. The extra resin will only affect weight and stength... not stiffness, which is the primary characteristic that is desired in the sandwich skins.
www.uscomposites.com is a good source for composite materials/resins/core materials.
How thick of a sandwich are you guys think of? If the foam gets very thick (more than about half an inch), then it certainly does become a structural element. A low shear strength material might actually shear on the neutral axis under high bending moments... and you can rest assured that 6+ inches of excursion at any reasonably high frequency will produce high accelerations that will no doubt try to bend the diaphram. I'd recommend looking at end grain balsa for a core of any sizeable thickness... it's cheaper than the high strength foams that would otherwise be required. Common polystyrene foam might not be up to the challenge. This of course also depends on how you load the diaphram. If a central rod is the only connection to the diaphram, the core could be a concern. If the load is spread by an "inner cone" or other similar structure, then the core is less of a concern. My assumption is that with a central rod, a central connection will be the simplest and cheapest.
Vacuum forming will reduce weight, if that is a goal, but it isn't absolutely necessary to make a strong laminate. If you don't use vacuum assist then the final laminate will be thicker for a given strength, but it will also be a bit stiffer for a given strength. If weight isn't a concern, then hand layup with a well wetted cloth would be just fine. The extra resin will only affect weight and stength... not stiffness, which is the primary characteristic that is desired in the sandwich skins.
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