Oh yeah, and I have one weird Leak speaker that has a flat cone, which seems to be made out of something like polystyrene. The label has come off the box so I don't know what it is, but it looks pretty '70s. Sounds alright, but a bit muddy. It has really peculiar tweeters as well. They have what looks like thick fabric over them.
Cabasse had a filled in cone of expanded polystyrene, (Styrofoam). A short article on them said that other manufacturers had tried filling the cone with Styrofoam, but got resonance problems. However, Cabasse had found a way to deal with those.
Cabasse still makes some flattish mid drivers. Slightly convex, (middle higher than the edges), in shape. So they must like the idea.
I suspect the problem is finding a filling material that does not resonate in the frequencies the speaker will be carrying.
The idea of those expanded material flats encased in a hard coating, (aluminum, magnesium, etc) is to make the filling material so stiff that resonances are either eliminated or the frequency of resonance is driven up higher than the frequencies the speaker will be used for.
Checking out various metal finishing forums to see about plating aluminum or magnesium onto plastic. No luck so far, but there seems to be a consensus that copper plating is best for beginners in plating anyway. One guy copper plated a leaf with no problem. Hmm, if I make the copper plating thin enough, it still might be useful to coat the expanded material.
Cabasse still makes some flattish mid drivers. Slightly convex, (middle higher than the edges), in shape. So they must like the idea.
I suspect the problem is finding a filling material that does not resonate in the frequencies the speaker will be carrying.
The idea of those expanded material flats encased in a hard coating, (aluminum, magnesium, etc) is to make the filling material so stiff that resonances are either eliminated or the frequency of resonance is driven up higher than the frequencies the speaker will be used for.
Checking out various metal finishing forums to see about plating aluminum or magnesium onto plastic. No luck so far, but there seems to be a consensus that copper plating is best for beginners in plating anyway. One guy copper plated a leaf with no problem. Hmm, if I make the copper plating thin enough, it still might be useful to coat the expanded material.
If you're serious about designing a flat cone, I think a sandwich of pre-impregnated carbon fiber cloth and a thin layer of aluminum foam would do the trick.
CF/Al foam/CF/voice coil former
http://www.cymat.com/Cymat_Foam_Products.htm
CF/Al foam/CF/voice coil former
http://www.cymat.com/Cymat_Foam_Products.htm
Kelticwizard
Have you done any testing yet?
i have found a fairy light stiff material of about 3mm thickness.
it would be about 1.6 grams for a 3 inch diameter.
Its Alu on top and bottom and a fairly hard foam in between.
I think its PUR. You could Stack 2 or 3 of these with smaller diameters to make it thicker. I will have to find out where we get it. It looks like refridgerator insulation.
That alu foam looks WAY too heavy.
Coolin
Have you done any testing yet?
i have found a fairy light stiff material of about 3mm thickness.
it would be about 1.6 grams for a 3 inch diameter.
Its Alu on top and bottom and a fairly hard foam in between.
I think its PUR. You could Stack 2 or 3 of these with smaller diameters to make it thicker. I will have to find out where we get it. It looks like refridgerator insulation.
That alu foam looks WAY too heavy.
Coolin
Coolin:
Haven't started yet. To be honest, ths sounds like a project that might take a couple of months.
First, I have to get the plating down right-which material, etc.
It occurs to me that just gluing aluminum foil on the outside of the flats could be beneficial, since when a piece flexes, the outside etge has to stretch. A sheet of aluminum foil glued outside will help to prevent this, thereby possibly raisng the frequency of resonance without plating. Still, I am going to investigate plating some more before tearing into it.
I will look up PUR material on the net and see what they say. It sure looks like a good candidate for what I am trying to do. If you can look it up or tell me where it is available, that would be so much the better.
Thanks.
Haven't started yet. To be honest, ths sounds like a project that might take a couple of months.
First, I have to get the plating down right-which material, etc.
It occurs to me that just gluing aluminum foil on the outside of the flats could be beneficial, since when a piece flexes, the outside etge has to stretch. A sheet of aluminum foil glued outside will help to prevent this, thereby possibly raisng the frequency of resonance without plating. Still, I am going to investigate plating some more before tearing into it.
I will look up PUR material on the net and see what they say. It sure looks like a good candidate for what I am trying to do. If you can look it up or tell me where it is available, that would be so much the better.
Thanks.
454:
Thanks for the link. I have decided to try the expanded material covered by aluminum foil or something else first. This is because some time ago I read Don Barlow's article about making a sandwich cone. Although Barlow made a traditional cone aout of his sanwich material, the idea of flat pieces grew out of that. So i will be concentrating on that first.
However, I am definitely keeping this aluminum foam in mind. If the flat pieces don't look like they can be made to work properly, I will definitely give this aluminum foam a try.
Thanks. 🙂
Thanks for the link. I have decided to try the expanded material covered by aluminum foil or something else first. This is because some time ago I read Don Barlow's article about making a sandwich cone. Although Barlow made a traditional cone aout of his sanwich material, the idea of flat pieces grew out of that. So i will be concentrating on that first.
However, I am definitely keeping this aluminum foam in mind. If the flat pieces don't look like they can be made to work properly, I will definitely give this aluminum foam a try.
Thanks. 🙂
Filling Cones
Wonder if any manufacturer has started playing with Aerogel yet? Any DIY members from NASA please stand up.
Wonder if any manufacturer has started playing with Aerogel yet? Any DIY members from NASA please stand up.
Flypig:
Audax has been making aerogel cones for years-the entire AP line is aerogel, I believe.
As for aerogel for making filled in cones, I don't know of anyone, but who knows.
It was suggested here, but so far all I see available comes in rolls, so it does not seem to be a stiff material.
I do believe there are stiff aerogels, but I just haven't run across them on the internet.
Audax has been making aerogel cones for years-the entire AP line is aerogel, I believe.
As for aerogel for making filled in cones, I don't know of anyone, but who knows.
It was suggested here, but so far all I see available comes in rolls, so it does not seem to be a stiff material.
I do believe there are stiff aerogels, but I just haven't run across them on the internet.
Another reason why speakers they don't have flat/rigid cones is that you deliberately need some decoupling of the center of the woofer from the edge.
This way the center of the driver is free to move in small motions for the higher frequencies, but as the frequency gets lower in the driver's operational range, the driver becomes more stiff.
You can especially see how this is done deliberately in cheap paper full range car speakers. The area around the whizzer cone has been embossed to make the paper thinner. Some of these also have annular folds in the speaker cone, which permits the decoupling but helps keep the motion more linear.
BTW, I noticed 20 years ago that the cheap $10 full ranges sounded better then than all but the very best $100 buck two-way and three-way car speakers. If you couldn't afford the good speakers, you were BETTER off with some of the cheapest. They weren't terribly durable, but they sounded OK. So this decoupling works even on cheap speakers, even though you would think this is a strange idea.
The advantages of having the center of the driver move independently of the outside of the driver are:
1. Better rolloff characteristics. Since the piston area is effectively decrease as the frequency goes up, the driver stays more linear in response.
2. Better dispersion characteristics. Again, the diameter of the piston are stays smaller than the characteristic wavelength of the emitted sound, so it doesn't beam a flat wave with poor dispersion.
The main tradeoff for this lack of cone rigidity is that there are probably a few frequency modes that cause standing waves in the cone instead of the desired decoupling. Designer take care of these with carefully spaced annular rings and controlling the curvature of the driver in ways that they tend to cancel themselves out over a wide range of frequencies.
This is probably one of the reasons why paper or coated paper woofers have such good sound, even though more modern materials are stronger and more rigid. Paper is actually a pretty good material for this because it is pretty well damped, it is stiff but not TOO stiff.
A good designer can take advantage of more modern materials and still get good sound. But this excessive stiffness is probably the reason why most aluminum woofers have rather bad breakup modes. They are so stiff that they "ring" rather than permit the decoupling.
This way the center of the driver is free to move in small motions for the higher frequencies, but as the frequency gets lower in the driver's operational range, the driver becomes more stiff.
You can especially see how this is done deliberately in cheap paper full range car speakers. The area around the whizzer cone has been embossed to make the paper thinner. Some of these also have annular folds in the speaker cone, which permits the decoupling but helps keep the motion more linear.
BTW, I noticed 20 years ago that the cheap $10 full ranges sounded better then than all but the very best $100 buck two-way and three-way car speakers. If you couldn't afford the good speakers, you were BETTER off with some of the cheapest. They weren't terribly durable, but they sounded OK. So this decoupling works even on cheap speakers, even though you would think this is a strange idea.
The advantages of having the center of the driver move independently of the outside of the driver are:
1. Better rolloff characteristics. Since the piston area is effectively decrease as the frequency goes up, the driver stays more linear in response.
2. Better dispersion characteristics. Again, the diameter of the piston are stays smaller than the characteristic wavelength of the emitted sound, so it doesn't beam a flat wave with poor dispersion.
The main tradeoff for this lack of cone rigidity is that there are probably a few frequency modes that cause standing waves in the cone instead of the desired decoupling. Designer take care of these with carefully spaced annular rings and controlling the curvature of the driver in ways that they tend to cancel themselves out over a wide range of frequencies.
This is probably one of the reasons why paper or coated paper woofers have such good sound, even though more modern materials are stronger and more rigid. Paper is actually a pretty good material for this because it is pretty well damped, it is stiff but not TOO stiff.
A good designer can take advantage of more modern materials and still get good sound. But this excessive stiffness is probably the reason why most aluminum woofers have rather bad breakup modes. They are so stiff that they "ring" rather than permit the decoupling.
Aerogel is light but doesn't have enough stiffness to significantly add to the structure. Might as well just use air. 😉
Geewhiz:
Well, you might well be right. But I wonder if this "advantage" of controlled decoupling is not really just a way of saying that since the outer edge of the cone is unsupported, we are bound to get breakup modes, so let's carefully select our cone material to make the breakup as smooth as possible?
I would like to see what happens with a flat cone that does not break up, at least in the frequency range for which it is intended.
I think speaker design might have fallen into a rut here. First they design the cone shape because in the 1920's they did not have the materials to make a diaphragm better. The cone shape works well enough so that the industry concentrated on refining it instead of replacing it with something better.
I am going to give a shot to seeing what happens with flat stiff cone.
People are building their spakers with sloped fronts for a reason. They would not have to do that if the mid diaphragm is flat.
Well, you might well be right. But I wonder if this "advantage" of controlled decoupling is not really just a way of saying that since the outer edge of the cone is unsupported, we are bound to get breakup modes, so let's carefully select our cone material to make the breakup as smooth as possible?
I would like to see what happens with a flat cone that does not break up, at least in the frequency range for which it is intended.
I think speaker design might have fallen into a rut here. First they design the cone shape because in the 1920's they did not have the materials to make a diaphragm better. The cone shape works well enough so that the industry concentrated on refining it instead of replacing it with something better.
I am going to give a shot to seeing what happens with flat stiff cone.
People are building their spakers with sloped fronts for a reason. They would not have to do that if the mid diaphragm is flat.
RHosch said:
Great idea!!
I'll investigate using a balloon or an inflated plasitc bag glued to the voice coil and attached to the surround. Might prove interesting. 😉
Seriously, I have not actually seen aerogel, only pictures on the web. So I am holding out hope that there is a form of it that is non-flexible.
I still think you guys are barking up the wrong tree.
What I'm talking about is not "controlled breakup". You are not getting breakup when the center of the speaker is moving independently of the outer edge, especially when such motion is a deliberate design decision.
Breakup is when the motion gets out of control due to resonances. Aerogel may be a way for Audax to create a light, but flexible cone, but with good damping characteristics because as the gel flexes, the embedded air gets squished around in the pores of gel, creating a considerable amount of damping.
I have seen some mid 80s infinity speakers with the airbag method; these were poly drivers and you could clearly see thru the polymer that they had two layers, presumably they were air tight. It did look really kewl and high tech.
The probably got a fairly rigid piston action with the driver. I'm sure they still flexed to some degree tho.
But the speakers didn't sound all that great either, possibly because of the beaming effects I mentioned, the tendency of such a driver to have a steep rise in response with increasing frequency, making them a bear to correct to flat response.
My current bass/mid drivers are the GR-Research 5.5 inch coated paper driver.
You'd be surprised at the good articulate, fast bass, the clean midrange. Later I will handle the extreme low bass below 55hz with a subwoofer.
Because the driver is heavily coated paper and has a very precisely controlled curve to the shape, they get a very controlled flex of the driver with increasing frequency and extremely flat response.
Sloped fronts are merely a design decision. You can use a sloped front to direct the sound upward into the room, and to correct time misalignments of the crossover.
They also look kewl. My speakers have sloped side, by Dannie Ritchie (the owner GR-Research) suggest that I didn't mess around with sloping the fronts since the crossover for my speakers is time-aligned for a flat front box. He didn't thinkk that sloped sides would make much of a difference as long as I kept the volume of the box correct, which I did.
*****
If you want to make a cone more rigid with a very small amount of extra weight, I'd try those cans of polyurethane construction foam.
First, build a cardboard form that almost touches the cone everwhere. You may want to first fill the inside of your form with the foam and let it dry so that the form is very rigid.
You could spray paint the cardboard several times and dry it very good so it isn't porous. If you are in more of a hurry, a duct-tape surface can work pretty good too.
Coat the surface with some mold release compound. If you don't have any, I would guess that non-water-based car wax would probably work pretty good. I would also guess that liquid clothes softener would work pretty good too, but use a few layers and let it dry.
Then spray the foam on to the surface of the form an put it on the surface of the speaker. You proably will have to put some sort of weight on it. The form should be designed so that excess foam can vent somewhere.
After all of this, I doubt if you would like the results. You may get a bit better bass, but it will come at the expense of frequency response. The extra mass will lower the tuning and reduce the efficiency and motor control of the driver.
What I'm talking about is not "controlled breakup". You are not getting breakup when the center of the speaker is moving independently of the outer edge, especially when such motion is a deliberate design decision.
Breakup is when the motion gets out of control due to resonances. Aerogel may be a way for Audax to create a light, but flexible cone, but with good damping characteristics because as the gel flexes, the embedded air gets squished around in the pores of gel, creating a considerable amount of damping.
I have seen some mid 80s infinity speakers with the airbag method; these were poly drivers and you could clearly see thru the polymer that they had two layers, presumably they were air tight. It did look really kewl and high tech.
The probably got a fairly rigid piston action with the driver. I'm sure they still flexed to some degree tho.
But the speakers didn't sound all that great either, possibly because of the beaming effects I mentioned, the tendency of such a driver to have a steep rise in response with increasing frequency, making them a bear to correct to flat response.
My current bass/mid drivers are the GR-Research 5.5 inch coated paper driver.
You'd be surprised at the good articulate, fast bass, the clean midrange. Later I will handle the extreme low bass below 55hz with a subwoofer.
Because the driver is heavily coated paper and has a very precisely controlled curve to the shape, they get a very controlled flex of the driver with increasing frequency and extremely flat response.
Sloped fronts are merely a design decision. You can use a sloped front to direct the sound upward into the room, and to correct time misalignments of the crossover.
They also look kewl. My speakers have sloped side, by Dannie Ritchie (the owner GR-Research) suggest that I didn't mess around with sloping the fronts since the crossover for my speakers is time-aligned for a flat front box. He didn't thinkk that sloped sides would make much of a difference as long as I kept the volume of the box correct, which I did.
*****
If you want to make a cone more rigid with a very small amount of extra weight, I'd try those cans of polyurethane construction foam.
First, build a cardboard form that almost touches the cone everwhere. You may want to first fill the inside of your form with the foam and let it dry so that the form is very rigid.
You could spray paint the cardboard several times and dry it very good so it isn't porous. If you are in more of a hurry, a duct-tape surface can work pretty good too.
Coat the surface with some mold release compound. If you don't have any, I would guess that non-water-based car wax would probably work pretty good. I would also guess that liquid clothes softener would work pretty good too, but use a few layers and let it dry.
Then spray the foam on to the surface of the form an put it on the surface of the speaker. You proably will have to put some sort of weight on it. The form should be designed so that excess foam can vent somewhere.
After all of this, I doubt if you would like the results. You may get a bit better bass, but it will come at the expense of frequency response. The extra mass will lower the tuning and reduce the efficiency and motor control of the driver.
PUR
I think This PUR foam is a great idea !!
Why not spray it directly on the cone and get a good bond.
The only problem is getting the flat front afterwards. You dont want to compress the material because that will increase the mass because it cant expand fully. It can be cut or machined pretty easy though. The weight will increase quite a bit though.
If i remember correctly something like 500 grams expands to 10 or so liters so thats not too bad at all.
Coolin
geewhizbang said:
I think This PUR foam is a great idea !!
Why not spray it directly on the cone and get a good bond.
The only problem is getting the flat front afterwards. You dont want to compress the material because that will increase the mass because it cant expand fully. It can be cut or machined pretty easy though. The weight will increase quite a bit though.
If i remember correctly something like 500 grams expands to 10 or so liters so thats not too bad at all.
Coolin
Im not sure what the weight is but i found a bottle of 500 ml that expands to 24 liter. I think that weight includes the gasses that will expell it from the can, so it will be even less.
This stuff is so light......What if you made the front of the cone hemispherical, you might be able to improve or prevent beaming !
Also once hard you could also drill holes at strategic places to reduce weight even more. As long as you keep the depth of the holes axisymetrical.
Does the phase change when the mass is increased?. That means the time alignment with the other drivers will change.
For the first experimentors -->IF you have it all lined up that aspect will get worse. If you dont it might get better.
Also the filling um of the cone itself will also move the acoustic center forward.
Coolin
This stuff is so light......What if you made the front of the cone hemispherical, you might be able to improve or prevent beaming !
Also once hard you could also drill holes at strategic places to reduce weight even more. As long as you keep the depth of the holes axisymetrical.
Does the phase change when the mass is increased?. That means the time alignment with the other drivers will change.
For the first experimentors -->IF you have it all lined up that aspect will get worse. If you dont it might get better.
Also the filling um of the cone itself will also move the acoustic center forward.
Coolin
If you want to be more precise about it, gorilla glue is the same thing.
Measure a controlled amount with a spoon, and add a specific amount of water to it. You can do tests first with a similar sized peice of cardboard until you get the volume of foam that you want.
I still think you need a weighted mold to keep the coating aligned with the cone. You probably should have some styrofoam blocks on the INSIDE wedged between the basket and the cone as well.
Measure a controlled amount with a spoon, and add a specific amount of water to it. You can do tests first with a similar sized peice of cardboard until you get the volume of foam that you want.
I still think you need a weighted mold to keep the coating aligned with the cone. You probably should have some styrofoam blocks on the INSIDE wedged between the basket and the cone as well.
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