Why are we even dealing with diaphragm materials in a cone shape anymore? Not so big a deal with woofers and subs, since the depth of the cone is such a small percentage of wavelengths it carries.
But once something plays above 500 Hz or so, cone depth becomes a reasonable fraction of the wavelengths being carried, not to mention such issues as time smear, etc.
I have been told that the center of cone, with respect to depth, even shifts with frequency. That certainly cannot be good for imaging.
Technics came up with a brilliant solution with the SB series of flat face woofers some time ago, but has done nothing with it since.
http://www.diyaudio.com/forums/showthread.php?threadid=21321&perpage=15&highlight=&pagenumber=2
So unless you want to do it Technics' way, (and presumably pay them royalities), that leaves the filled-in cone. I know Cabasse had a model with a filled-in cone some time ago, but why aren't all high quality manufacturers coming up with them?
I tried filling in a cone of a speaker with that same soft foam stuff you use for weatherstripping-spray it on and it dries semi-hard. It made the frequency response worse. Not surprisingly.
But surely, with the thousands of materials available today, and more always coming down the pike, speaker designers can find a way to fill in the cone so the face of a mid is flat.
If filling in the cone with only one material won't work, how about a nice layer job of inexpensive materials cut into cone shape? The resonances can cancel each other out. Once glued together, a hole can be cut into the center-not puncturing the front-for ventilation purposes. Once the cone is made, you will not even need to have an outside diaphragm material-just the cone itelf would do, attached between the voice coil and the surround.
With expensive materials like Kevlar being used for diaphragm materials, it just seems to me that by now this is one problem that would have been solved. Does anybody have a good reason why it has not been?
But once something plays above 500 Hz or so, cone depth becomes a reasonable fraction of the wavelengths being carried, not to mention such issues as time smear, etc.
I have been told that the center of cone, with respect to depth, even shifts with frequency. That certainly cannot be good for imaging.
Technics came up with a brilliant solution with the SB series of flat face woofers some time ago, but has done nothing with it since.
http://www.diyaudio.com/forums/showthread.php?threadid=21321&perpage=15&highlight=&pagenumber=2
So unless you want to do it Technics' way, (and presumably pay them royalities), that leaves the filled-in cone. I know Cabasse had a model with a filled-in cone some time ago, but why aren't all high quality manufacturers coming up with them?
I tried filling in a cone of a speaker with that same soft foam stuff you use for weatherstripping-spray it on and it dries semi-hard. It made the frequency response worse. Not surprisingly.
But surely, with the thousands of materials available today, and more always coming down the pike, speaker designers can find a way to fill in the cone so the face of a mid is flat.
If filling in the cone with only one material won't work, how about a nice layer job of inexpensive materials cut into cone shape? The resonances can cancel each other out. Once glued together, a hole can be cut into the center-not puncturing the front-for ventilation purposes. Once the cone is made, you will not even need to have an outside diaphragm material-just the cone itelf would do, attached between the voice coil and the surround.
With expensive materials like Kevlar being used for diaphragm materials, it just seems to me that by now this is one problem that would have been solved. Does anybody have a good reason why it has not been?
The ratio of rigidity/weight is much much higher with a cone shape than with a flat shape. Even modern materials aren't rigid enough to make a flat speaker cone work well.
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Joined 2003
The only speakers I have seen with flat faces have been car subwoofers, such as the Phoenix Gold Titanium Elite. As far as I can tell, the Titanium elite uses a regular cone design, with a metal plate over the front. It also has 3 super-cool led's mounted on it 🙂
What about an inverted cone? It would have the same rigidity as a "concave" cone, wouldn't have sound bounce around on the inside, and would save some space (i.e. basket arms wouldn't have to be so long).
There are I believe actualy quite a few of the B & W speakers which use flat woofers in their designs, even as low down as the 600 series models. There ae also a number of older drivers before the Technics ones which were flat, in particular the KEF B139 which first came out back in the 70's I think.
I guess this may have been the one you were talking about Magura?
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Phase Technology's PC series has been using flat pistons for over 10 years now. If there really was something there, I figure somebody would have done it by now.
johninCR said:
I am not talking about taking a flat piece of material and driving it at it's center, which will result in flexing, (unless you do it like Technics). I am talking about a solid cone shape. The filled in cone will be more rigid than than a simple diaphragm, not less.
Thank you all for your answers.
I appreciate the references to the few speakers that do have filled in cones.
However, I wonder why by now all quality speakers do not have them.
Common sense tells you that sound coming from a flat source is bound to be better than one coming from an irregularly shaped one. And with all the effort to slope baffles and align the sound sources lately, it seems incredible that we still are dealing with a cone shaped radiator. Especially since the acoustic center of the depth of the cone apparently varies with frequency.
I appreciate the references to the few speakers that do have filled in cones.
However, I wonder why by now all quality speakers do not have them.
Common sense tells you that sound coming from a flat source is bound to be better than one coming from an irregularly shaped one. And with all the effort to slope baffles and align the sound sources lately, it seems incredible that we still are dealing with a cone shaped radiator. Especially since the acoustic center of the depth of the cone apparently varies with frequency.
Well common sense is implemented by many vendors - the trick is to drive the flat membrane over its whole surface ....
Stax, Martin Logan, Infinity, Quad, etc. etc.
they just happen to not utilize an ordinary coil ;-)
/
Stax, Martin Logan, Infinity, Quad, etc. etc.
they just happen to not utilize an ordinary coil ;-)
/
Well, it just seems hard to achieve reasonable efficiency with this "filled in" design. The volume of material which makes up the cone is likely 20-100s times the volume of a comparable unfilled cone. It probably needs a lot less strength, but I would guess weight would still be high and efficiency low.
If you mean an "empty" cone which is simply a disc on top of a conventional cone driver, I think the flexing problem is still severe.
If you mean an "empty" cone which is simply a disc on top of a conventional cone driver, I think the flexing problem is still severe.
"Cones" is actually a misnomer, most have curved profiles which
adds stiffness in the circumferential direction at the cost of losing
some radial stiffness you get with a pure cone.
Young's modulus, mass per unit stiffness is an issue, and the
cones profile can be used to adjust midrange response.
Filled cones, with flat fronts have very poor midrange performance.
🙂 sreten.
adds stiffness in the circumferential direction at the cost of losing
some radial stiffness you get with a pure cone.
Young's modulus, mass per unit stiffness is an issue, and the
cones profile can be used to adjust midrange response.
Filled cones, with flat fronts have very poor midrange performance.
🙂 sreten.
sreten said:
Would that be due to resonances of the filling material or some other reason?
I would think that when the cavity of the cone is a fair percentage of the wavelength being carried, you are bound to have smearing.
TNT said:
You found me out!! 🙂
Yes, I do wonder if at least part of the difference between "normal" speakers and electrostatic/ribbon speakers, (in the ESL/ribbons' favor), is the irregualrly shaped radiating surface of those "normal" speakers.
It doesn't make much difference if the depth of the cone is minisucle compared to the wavelengths being generated, but in the midrange the depth is a fairly big percentage of those wavelengths.
SY said:
Two 5" midranges from Peerless had Mms of 5.7 and 7.9 grams respectively.
While that precludes concrete or solid wood, there must be a whole host of materials which can be made to make a 4" cone and be within that limit.
Back in the sixties or seventies, British designer Don Barlow made a cone out of Styrofoam and glued strips of aluminum foil on it. It was not a filled cone, but it certainly made the walls of the cone thicker. It certainly improved the stiffness of the cone, with excellent results for the frequency response.
He wrote it up in the Journal of The Audio Engineering Society. I can Email it to anyone who wants.
Among other ideas, I am wondering why they cannot take some sheets of various expanded materials, put them one atop one another, cut a cone out of the combo, then cover or even plate each individual sheet with aluminum/magnesium to add stiffness to each one. Then glue them together to make a solid cone.
Just one idea. But the point is, I do believe that several materials can be combined to make a fairly non resonant solid cone that would meet weight requirements and make a flat front.
And I believe a flat front should result in superior reproduction, assuming resonance problems are controlled.
kelticwizard said:
In the absence of cone breakup, why? I'm hoping that someone with a good understanding of the physics will explain this. My intuition is that the sum contribution of the cone motion nets out the contribution of the disparate "point sources" which are at different depths. The z-axis acoustic point of origin may move with frequency, but this is simply phase shift and not "time smearing" or some interferance effect.
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