The weight of nuthun
Ok you math masters out there. Here is what I can come up with for the weight of the foam I'm going to use for the core of the diaphram. It's 28kg/metre^3 or 0.000036 grams/cm^3 Not a hell of a lot. Where I run into fun is trying to find a formula to calculate the surface area of a curved cone. The rest is easy!!
If I knew that then we could have a diaphram mass using RH's weight for the carbon fiber epoxy.
RH don't think that 14.6 psi is weak. ( by the way that number is only good at sea level ) I regularily snapped off backer boards when I started vacuum clamping. It's gradual to be sure but adds up to 2102 ponds/ft^2
As a reference only I found a site last night that lists a whole bunch of driver parts. speakerbits.com
The prices will knock you out but there is some idea as to what is available. I checked in the LIS book and the old places that I knew of don't have web sites. I'm also trying to find some thermally bondable CCA rectangular wire ( any help on this one would be much appreciated ) as we are not going to get anyone to roll us a few voice coils for free when there is no real market potential. What we need is some that are reasonable in price and ready made. We are looking at 6 per driver and a winding height of how high???? Motor gurus take over. If I can get the wire again I'll happily wind them. It's just a pain in the but to set it all up!
As for spiders I don't think that it will work with normal spiders. Six inches is a long way to flex something that is in the shape of a ring. as a crude test take a strip of paper and try to hold one end and lift it at a reasonable height while the end is fixed. Then add your pole piece diameter and proper pleats and tell me what you come up with. A full piece of paper will ( 11" ) will give most of the excursion that you would need. But when you fold up some pleats you end up needing about 14". Multiply that by two and add 4 and you end up with a pretty big spider. I'm not saying that number is cast in concrete ( 32" ) but I'm pretty sure it's not out by that much. Probable around 24 to 28" in diameter. Definitley not standard fair.
MArk
Ok you math masters out there. Here is what I can come up with for the weight of the foam I'm going to use for the core of the diaphram. It's 28kg/metre^3 or 0.000036 grams/cm^3 Not a hell of a lot. Where I run into fun is trying to find a formula to calculate the surface area of a curved cone. The rest is easy!!
If I knew that then we could have a diaphram mass using RH's weight for the carbon fiber epoxy.
RH don't think that 14.6 psi is weak. ( by the way that number is only good at sea level ) I regularily snapped off backer boards when I started vacuum clamping. It's gradual to be sure but adds up to 2102 ponds/ft^2
As a reference only I found a site last night that lists a whole bunch of driver parts. speakerbits.com
The prices will knock you out but there is some idea as to what is available. I checked in the LIS book and the old places that I knew of don't have web sites. I'm also trying to find some thermally bondable CCA rectangular wire ( any help on this one would be much appreciated ) as we are not going to get anyone to roll us a few voice coils for free when there is no real market potential. What we need is some that are reasonable in price and ready made. We are looking at 6 per driver and a winding height of how high???? Motor gurus take over. If I can get the wire again I'll happily wind them. It's just a pain in the but to set it all up!
As for spiders I don't think that it will work with normal spiders. Six inches is a long way to flex something that is in the shape of a ring. as a crude test take a strip of paper and try to hold one end and lift it at a reasonable height while the end is fixed. Then add your pole piece diameter and proper pleats and tell me what you come up with. A full piece of paper will ( 11" ) will give most of the excursion that you would need. But when you fold up some pleats you end up needing about 14". Multiply that by two and add 4 and you end up with a pretty big spider. I'm not saying that number is cast in concrete ( 32" ) but I'm pretty sure it's not out by that much. Probable around 24 to 28" in diameter. Definitley not standard fair.
MArk
Of course atmospheric pressure isn't trivial... it's enough to crush most containers when evacuated. 🙂
Area of a cone = pi × r × (r + sqrt(r^2 + h^2))
Area of a cone = pi × r × (r + sqrt(r^2 + h^2))
Are we on the straight and level or are you throwing me a curve???
Straight sided cone or curved cone Mr. RH ???
I've known of a formula for a straight cone for some time . It's the curved one that is causing me the problems.
RH what's your name????
Mark
Straight sided cone or curved cone Mr. RH ???
I've known of a formula for a straight cone for some time . It's the curved one that is causing me the problems.
RH what's your name????
Mark
Richard Hosch
The most straightforward way to find the area of a given revolved surface is to integrate the expression defining the curve over the limits applicable.
For instance, take a curve defined as y = x^2 for the area bounded by 0<x<1.
The area is the integral from 0 to 1 of (2*pi*y*ds)
where ds = sqrt(1+((dy/dx)^2)dx
So for this case, dy/dx = 2x and (dy/dx)^2 = 4x^2, thus ds = sqrt(1+4x)dx. The integral would then be 2*pi*INT[0,1](x^2)(4x^2)dx.
That probably doesn't help much. Wish there was an easy way to insert mathematical expressions. 🙁
The most straightforward way to find the area of a given revolved surface is to integrate the expression defining the curve over the limits applicable.
For instance, take a curve defined as y = x^2 for the area bounded by 0<x<1.
The area is the integral from 0 to 1 of (2*pi*y*ds)
where ds = sqrt(1+((dy/dx)^2)dx
So for this case, dy/dx = 2x and (dy/dx)^2 = 4x^2, thus ds = sqrt(1+4x)dx. The integral would then be 2*pi*INT[0,1](x^2)(4x^2)dx.
That probably doesn't help much. Wish there was an easy way to insert mathematical expressions. 🙁
Former thoughts
When talking about a 4" VC we literally mean the ID of the coil right? Just need confirmation that we're not talking about a 4" former ID, or pole piece OD, or top plate ID, or even the VC OD.
And what's the likely material for the former? Aluminium? And the ball park thickness 1mm? 3mm? (perhaps weight as well)? What temperatures should it be able to withstand? (I'm assessing the feasibility of using my plastics contacts)
When talking about a 4" VC we literally mean the ID of the coil right? Just need confirmation that we're not talking about a 4" former ID, or pole piece OD, or top plate ID, or even the VC OD.
And what's the likely material for the former? Aluminium? And the ball park thickness 1mm? 3mm? (perhaps weight as well)? What temperatures should it be able to withstand? (I'm assessing the feasibility of using my plastics contacts)
It all depends on
The former must either match an existing coil or be made to our specs. If we can find ready made coils cheap enough then we will match their I.D. and the pole piece must be sized accordingly to provide clearance. If we are making it from scatch then it will be designed to clear the pole piece with enough clearance to not rub on it. Probably about 3 to 4 mm. So allthough I cannot give you a clear cut answer it can serve as a guideline.
As for the material. Aluminum is good from a strength viewpoint. But the thickness should be 0.5mm or even less. A rigid cylinder can sustain quite a bit of compression.
As for plastics I've seen Kapton, glass fiber, paper all used as formers. Our particular problem is the length needed for a double diaphram. It is not normal! We are looking for 6+6+(for excursion) +2+2 for decent clearance plus extensions to fasten to the diaphram of 2 to 3" per end so what 22". Definitely not a trivial length of voicecoil former. So we don't want something that is heavy. And my beer can idea is up in smoke because of not thinking about how long it needed to be. ( Nuts, no noble reason to drink beer )
Since no one is throwing in their hand to figure out the surface area of a curved baffle I'm going to sharpen my pencil, break out my old calculus books and sharpen my pencil.
Mark
The former must either match an existing coil or be made to our specs. If we can find ready made coils cheap enough then we will match their I.D. and the pole piece must be sized accordingly to provide clearance. If we are making it from scatch then it will be designed to clear the pole piece with enough clearance to not rub on it. Probably about 3 to 4 mm. So allthough I cannot give you a clear cut answer it can serve as a guideline.
As for the material. Aluminum is good from a strength viewpoint. But the thickness should be 0.5mm or even less. A rigid cylinder can sustain quite a bit of compression.
As for plastics I've seen Kapton, glass fiber, paper all used as formers. Our particular problem is the length needed for a double diaphram. It is not normal! We are looking for 6+6+(for excursion) +2+2 for decent clearance plus extensions to fasten to the diaphram of 2 to 3" per end so what 22". Definitely not a trivial length of voicecoil former. So we don't want something that is heavy. And my beer can idea is up in smoke because of not thinking about how long it needed to be. ( Nuts, no noble reason to drink beer )
Since no one is throwing in their hand to figure out the surface area of a curved baffle I'm going to sharpen my pencil, break out my old calculus books and sharpen my pencil.
Mark
If you give me some idea of the curve you have in mind, I'll work through the calculus for you. Have we settled on a diameter (36")? What depth for the cone? How large of a central hole (4")?
So... define the function that describes the cone, and I'll return the surface area. Still, surface area only does so much... you still need to know the thickness of skins and core, which should ideally be set by structural analysis of the diaphram.
So... define the function that describes the cone, and I'll return the surface area. Still, surface area only does so much... you still need to know the thickness of skins and core, which should ideally be set by structural analysis of the diaphram.
It's all greek to me!!
OK Richard here goes. A tractrix curve. Start the curve 3 or 4 inches in from the outside edge and complete it at the 4" diameter allowing at least an inch or 1 1/2" of straight area to afix the voice coil former. Sort of making a pipe at the area that the former must be bonded. So the diaphram curve will not be 36 inches in diameter but more like 28" with a 4" hole in the middle. Make it 6" deep. I'm guessing that you will have to fit a curve to the dimensions. If you work with a 3D surface modeler it will be easy. I only have 2D at work and it is not set up to calculate surface ares automatically. The surface area is a basis to figure out the rest. Once we have it the thickness and mass calculations are childs play. You know that! We then need Carbon fiber mass which is easy to get. You allready gave a spec for carbon/epoxy. I have a mass for the foam core. A voice coil former can be easily guessed at for weight. Once we have moving mass then a motor design to achieve what we want will make more sense.
If you have the capability to model stresses in a diphram then start with the core thickness of 6mm ( 1/4" ) Layer what is required on the inside and outside. I'd be guessing that two layers laid up at a 45 degree angle or what ever you sugest would be a beginning.
As someone who does not work in this field ( composites ) I stand aside and listen to those with experience. If it makes sense then I won't argue!!
Mark
OK Richard here goes. A tractrix curve. Start the curve 3 or 4 inches in from the outside edge and complete it at the 4" diameter allowing at least an inch or 1 1/2" of straight area to afix the voice coil former. Sort of making a pipe at the area that the former must be bonded. So the diaphram curve will not be 36 inches in diameter but more like 28" with a 4" hole in the middle. Make it 6" deep. I'm guessing that you will have to fit a curve to the dimensions. If you work with a 3D surface modeler it will be easy. I only have 2D at work and it is not set up to calculate surface ares automatically. The surface area is a basis to figure out the rest. Once we have it the thickness and mass calculations are childs play. You know that! We then need Carbon fiber mass which is easy to get. You allready gave a spec for carbon/epoxy. I have a mass for the foam core. A voice coil former can be easily guessed at for weight. Once we have moving mass then a motor design to achieve what we want will make more sense.
If you have the capability to model stresses in a diphram then start with the core thickness of 6mm ( 1/4" ) Layer what is required on the inside and outside. I'd be guessing that two layers laid up at a 45 degree angle or what ever you sugest would be a beginning.
As someone who does not work in this field ( composites ) I stand aside and listen to those with experience. If it makes sense then I won't argue!!
Mark
Re: It all depends on
But...
Are we looking to figure out the surface area for weight calculation purposes?
If we do a cone, do we even need to do a sandwich construction?
😕
I actually never took calc, so I'm at a loss for that, sorry! 😀mwmkravchenko said:
But...
Are we looking to figure out the surface area for weight calculation purposes?
If we do a cone, do we even need to do a sandwich construction?
😕
I'm not exactly sure what function defines a "tractrix" curve, but I'll look it up and see what I find. Otherwise, it sounds like some form of ellipsoid will suit most of the requirements.
geolemon - much of the stiffness of composites comes through sandwich construction. That form of geometric stiffening is, IMO, a better approach than simple conical or curved conical geometries. Not only do you increase the system stiffness, but you also increase the local stiffness of any one point on the cone. That means increased plate buckling resistance and higher local modes... walla, higher cone breakup frequencies. May not matter much in a sub though.
My question is the corrallary to yours... if we use sandwich construction, do we even need to do a cone? 🙂
geolemon - much of the stiffness of composites comes through sandwich construction. That form of geometric stiffening is, IMO, a better approach than simple conical or curved conical geometries. Not only do you increase the system stiffness, but you also increase the local stiffness of any one point on the cone. That means increased plate buckling resistance and higher local modes... walla, higher cone breakup frequencies. May not matter much in a sub though.
My question is the corrallary to yours... if we use sandwich construction, do we even need to do a cone? 🙂
http://melhuish.org/audio/tractrixcalc.html
http://melhuish.org/audio/hornshape.html
Woah.Collaboration between many people! all the best,i hope for success!
im hoping for high eff-not that i can ever get one LOL...87db/1watt monster? might as well build a 20hz 999Litre basshorn 🙂
Cheers
😀
http://melhuish.org/audio/hornshape.html
Woah.Collaboration between many people! all the best,i hope for success!
im hoping for high eff-not that i can ever get one LOL...87db/1watt monster? might as well build a 20hz 999Litre basshorn 🙂
Cheers
😀
Vikash posted:
The pole we used was 2.914" OD (this was for a 3" voice coil). For a 4" nominal unit, I'd look at 3.91" OD of the pole. The ID of the former would be 4"; the OD of the former is typically 4.075" (20 GA material with Kapton and spun lace over it), then the wire lays up on top of that. Figure a total ID on the top plate of ~4.35" or so (0.175" wide gap).
Temperatures - I'd like to see 200 deg C capability, since that's what most voice coil glues can handle. I'd rather the voice coil delaminate than the former melt to the driver. A lot easier to fix...😉
Dan Wiggins
Adire Audio
The pole we used was 2.914" OD (this was for a 3" voice coil). For a 4" nominal unit, I'd look at 3.91" OD of the pole. The ID of the former would be 4"; the OD of the former is typically 4.075" (20 GA material with Kapton and spun lace over it), then the wire lays up on top of that. Figure a total ID on the top plate of ~4.35" or so (0.175" wide gap).
Temperatures - I'd like to see 200 deg C capability, since that's what most voice coil glues can handle. I'd rather the voice coil delaminate than the former melt to the driver. A lot easier to fix...😉
Dan Wiggins
Adire Audio
I've had trouble understanding those dimensions Dan, so I've drawn a quick scaled diagram of the pole/former/vc/tp based on your 4" nominal figures.
A couple of observations that weren't obvious to me before:
The VC is centred in the gap, and so there is unequal spacing on either side of the former. I figue that if the inside gap is large enough to avoid former scraping then the outside gap can be reduced too (more flux potential). But I guess there's a superseding reason (if I have interpreted the dimensions correctly) to having the VC dead centre in the gap?
Secondly, the gap is 0.22" wide by your figures, but I think you may have been working in radius? (which would give a gap width more akin to your designs: > 11mm)
What glue can you use to hold the VC? I have some Styrenated Alkyd Varnish rated class H (180oC) lying around, but not sure of its applicability to any VC winding (big or small)
A couple of observations that weren't obvious to me before:
The VC is centred in the gap, and so there is unequal spacing on either side of the former. I figue that if the inside gap is large enough to avoid former scraping then the outside gap can be reduced too (more flux potential). But I guess there's a superseding reason (if I have interpreted the dimensions correctly) to having the VC dead centre in the gap?
Secondly, the gap is 0.22" wide by your figures, but I think you may have been working in radius? (which would give a gap width more akin to your designs: > 11mm)
What glue can you use to hold the VC? I have some Styrenated Alkyd Varnish rated class H (180oC) lying around, but not sure of its applicability to any VC winding (big or small)
Attachments
Re: Re: It all depends on
My thinking is "no"...
But then again, on the other hand.. it depends on our priorities.
Efficiency? Seems that the cone is lighter.
Stiffness? The panel alone would seem to do it... but then again, as long as we are building it, adding some curvature wouldn't seem to hurt... although that would add a bit more mass still.
geolemon said:
RHosch said:
My thinking is "no"...
But then again, on the other hand.. it depends on our priorities.
Efficiency? Seems that the cone is lighter.
Stiffness? The panel alone would seem to do it... but then again, as long as we are building it, adding some curvature wouldn't seem to hurt... although that would add a bit more mass still.
Which is stiffer???
In all the work I've ever done a flat panel is not as stiff as a curved panel of same thickness. That is my basic arguement for making a curved diaphram.
A flat panel can be made stiff enough and if it is also light it is obviously easier to construct. I'd go for either if there was some good thinking behind them.
For bonding voicecoil wire think in terms of the adhesives ability to hold things together under heated conditions. An efficent driver is just about 1% efficient. So wher does the rest of the heat go?? It must be radiated by the coil and hopefully conducted away from it by the drivers structure. So ability to withstand heat is paramount.
In the same train of thought there are wires that are pretreated with a layer on top of the insulation that can be baked and form a fused coil. I've seen it as bondable wire in some catalogs. I'm trying to find some that doesn't come in a mile long roll. 🙂
Mark
In all the work I've ever done a flat panel is not as stiff as a curved panel of same thickness. That is my basic arguement for making a curved diaphram.
A flat panel can be made stiff enough and if it is also light it is obviously easier to construct. I'd go for either if there was some good thinking behind them.
For bonding voicecoil wire think in terms of the adhesives ability to hold things together under heated conditions. An efficent driver is just about 1% efficient. So wher does the rest of the heat go?? It must be radiated by the coil and hopefully conducted away from it by the drivers structure. So ability to withstand heat is paramount.
In the same train of thought there are wires that are pretreated with a layer on top of the insulation that can be baked and form a fused coil. I've seen it as bondable wire in some catalogs. I'm trying to find some that doesn't come in a mile long roll. 🙂
Mark
All mourn the cone is dead!!!
I thunk for a while. I've been in bed with a bad back so thunking is all I'm good for untill today.
Why make a complicated cone when it is a free air dipole???
DUH!!!!!
A flat diaphram is easy. It can be curved shoulg there arise a need. And the curve will not really change the surface area that much if any. So that great big idea off my chest and I calculated with my pencil and my handy dandy TI 89 that it should weigh in at around 950 grams for a 30" by 30" baffle that comprises a 6mm foam core ( available at sign shops ) and two layers of carbon fiber set in epoxy.
The start of the moving mass. Multiply it by two to get a dipole. A coil weight is in the works as is a former weight.
PLEASE WEIGHT
P.S.
If this thread goes on life support I'M STILL BUILDING THIS THING
Mark😀
I thunk for a while. I've been in bed with a bad back so thunking is all I'm good for untill today.
Why make a complicated cone when it is a free air dipole???
DUH!!!!!
A flat diaphram is easy. It can be curved shoulg there arise a need. And the curve will not really change the surface area that much if any. So that great big idea off my chest and I calculated with my pencil and my handy dandy TI 89 that it should weigh in at around 950 grams for a 30" by 30" baffle that comprises a 6mm foam core ( available at sign shops ) and two layers of carbon fiber set in epoxy.
The start of the moving mass. Multiply it by two to get a dipole. A coil weight is in the works as is a former weight.
PLEASE WEIGHT
P.S.
If this thread goes on life support I'M STILL BUILDING THIS THING
Mark😀
lol... I'm still on board, just been busy lately.
Anyone wanna take a shot at coil weight? Bill? If not, I'll go back through the last couple of pages, see what the suggestions were for VC former diameter, thickness, and material and make an estimate.
Anyone wanna take a shot at coil weight? Bill? If not, I'll go back through the last couple of pages, see what the suggestions were for VC former diameter, thickness, and material and make an estimate.
Weight = Power????
The weight of the voice coil will depend on how high a power rating we will need. Not want but actually need. We all know that the driver will start to roll off in the bass. Beyond that point we will need to equalise at around 6db per octave. Depending where the knee is we may need a lot of juice. I think RH did a calc of where the diaphram will start to roll off. From here we have a 0 reference and an idea where we will have to start boosting!
As for the coil or coils proper. I've been thinking that a coil that is 7" long is going to be heavy ( Brain storms are common but generally benign ) There may be a way to cut down on the weight by using 6 coils that all cover a portion of the gaps all thre per side wired in series. Maybe not. My other brain storm is to the motor gurus ( small drizzle ) How about using rod shaped magnets to line the interior of a gap plate. Wouldn't it give a more uniform field strength??? I can get them cheap thats why I'm asking.
Ive been pluging in some of the numbers that we have into the DPC program. Short story we need more parameters.
I can get the coils figured out soon. If we stick with ribbon wire we will get a better BL product. Literally more turns in the gap than round wire. It is also bondable which means it can be coiled up, and then baked to form a self supporting coil. Neat. I tried some vendors for existing coils. I think that it will cost to much.
Hey anyone with access to CCAW send me an email. I need some!
I'm thinking that 22 to 24 guage will be enough to work. ( the equivalent circular mills in a ribbon of course ) It's not a high current rating but the duty cycle of most music is not going to tax this monster to much if we have a strong motor ( Calling Mr. Bill HELLLLLLOOOOOO )
OK enough belly Aching lets see who wakes up out of the woodwork and makes some comments. I know that RH is still with me ( thanks RH your swell )
LOL
Mark
The weight of the voice coil will depend on how high a power rating we will need. Not want but actually need. We all know that the driver will start to roll off in the bass. Beyond that point we will need to equalise at around 6db per octave. Depending where the knee is we may need a lot of juice. I think RH did a calc of where the diaphram will start to roll off. From here we have a 0 reference and an idea where we will have to start boosting!
As for the coil or coils proper. I've been thinking that a coil that is 7" long is going to be heavy ( Brain storms are common but generally benign ) There may be a way to cut down on the weight by using 6 coils that all cover a portion of the gaps all thre per side wired in series. Maybe not. My other brain storm is to the motor gurus ( small drizzle ) How about using rod shaped magnets to line the interior of a gap plate. Wouldn't it give a more uniform field strength??? I can get them cheap thats why I'm asking.
Ive been pluging in some of the numbers that we have into the DPC program. Short story we need more parameters.
I can get the coils figured out soon. If we stick with ribbon wire we will get a better BL product. Literally more turns in the gap than round wire. It is also bondable which means it can be coiled up, and then baked to form a self supporting coil. Neat. I tried some vendors for existing coils. I think that it will cost to much.
Hey anyone with access to CCAW send me an email. I need some!
I'm thinking that 22 to 24 guage will be enough to work. ( the equivalent circular mills in a ribbon of course ) It's not a high current rating but the duty cycle of most music is not going to tax this monster to much if we have a strong motor ( Calling Mr. Bill HELLLLLLOOOOOO )
OK enough belly Aching lets see who wakes up out of the woodwork and makes some comments. I know that RH is still with me ( thanks RH your swell )
LOL
Mark
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