I was curious about the effect of slicing and coating a speaker cone in a similar way ScanSpeak do.
So here you go. Original driver, measured 80dB @ 30cm (at least according to my phone SPL meter).
Now we slice and varnish! Varnish used was two part Sayerlack TLL3097.
I'm amazed the results are so damn similar before and after such brutal slaughter of the driver!
So here you go. Original driver, measured 80dB @ 30cm (at least according to my phone SPL meter).
Now we slice and varnish! Varnish used was two part Sayerlack TLL3097.
I'm amazed the results are so damn similar before and after such brutal slaughter of the driver!
Attachments
Nice experiment. Try overlaying the results and observing them on a smaller vertical scale, as a 90 dB scale easily hides 1 dB differences.
Slicing can be done to alter the cone resonance modes. Where to slice, depends on the mode shapes, which you can find with a Finite Element study. It also matters what you do with the slices. If you glue the edges together with a stiff glue, I think you basically undo the slicing. Scan Speak uses a flexible glue that adds damping to the modes. I do not know if the slicing has a significant effect. The cone is also coated, which can be done to dampen these modes as well.
Slicing can be done to alter the cone resonance modes. Where to slice, depends on the mode shapes, which you can find with a Finite Element study. It also matters what you do with the slices. If you glue the edges together with a stiff glue, I think you basically undo the slicing. Scan Speak uses a flexible glue that adds damping to the modes. I do not know if the slicing has a significant effect. The cone is also coated, which can be done to dampen these modes as well.
Overlaid, the differences are within measurement tolerance and noise.
I do know that the main breakups are happening around 1-2cm from the outer edge of the cone. I put the mic very close to 'scan' the cone surface.
Polyurethane has pretty high damping, hence use in performance suspension bushings for cars. Although there are of course many types of polyurethane. As I said to my friend when discussing this earlier, I'm sure we could alter things so the slice has some bigger effect, however the results here are so tiny given what I did to the cone, I don't think there is a lot to gain.
I do know that the main breakups are happening around 1-2cm from the outer edge of the cone. I put the mic very close to 'scan' the cone surface.
Polyurethane has pretty high damping, hence use in performance suspension bushings for cars. Although there are of course many types of polyurethane. As I said to my friend when discussing this earlier, I'm sure we could alter things so the slice has some bigger effect, however the results here are so tiny given what I did to the cone, I don't think there is a lot to gain.
I suspect damage to surround or spider that has been repaired would have more effect, but certainly this paper type the cone itself seems quite resilient.
I'm thinking to try a two coatings (I've got a pair of woofers to sacrifice) to see what happens with that 5KHz break-up. Any recommendations?
I was curious about SBR Styrene Butadiene Co-polymer Latex but I know it is quite liquid. I wonder if I can thicken it by boiling off or something... EDIT: Reading about liquid latex for costmetics it can apparently be thickened with fumed silica, which I happen to know has very high self damping properties
I'm thinking to try a two coatings (I've got a pair of woofers to sacrifice) to see what happens with that 5KHz break-up. Any recommendations?
I was curious about SBR Styrene Butadiene Co-polymer Latex but I know it is quite liquid. I wonder if I can thicken it by boiling off or something... EDIT: Reading about liquid latex for costmetics it can apparently be thickened with fumed silica, which I happen to know has very high self damping properties
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I have used artist "dope" on some cones and to great effect on the dust caps ( aluminum) of my FE 85's Of course doping adds mass, so it has a lot of effects. I played with some cheap Silver Flute and some Mark drivers for various mode management hacks. Good success adding phase plugs. Not so much on the cones. If you have access to laser inferomerty and can test to see the modes, them knowing what to attack may be easier. People like Scan Speak can and do. There were several papers to AES on this subject in the '70's. Go search the AES archives.
Going wayback, I remember thin balsa strips set in RTV on some cheap cone. I figured out, I should just buy a better driver. A 5K breakup is better handled by selecting an appropriate crossover. If you have used many Dayton RS drivers, you have had to master that. I did want a lower Fs on one aluminum driver and a coating of fabric paint around the edge did help a little as I could use a shallow but lower crossover.
Tenson, Poly is used on car bushings by kiddie racers who don't know better as it is stiffer than rubber giving better control, and slick enough to last a little while. NOT because it has any dampening features. It has a little more shock absorbing than metal in a real race car, and way too much for a street car. There are a few places where it works OK, TC rods and sway bar end bushings for example. One will get around the track on FAT a lot quicker if they used the poly bushing money for an hour of professional instruction.
Going wayback, I remember thin balsa strips set in RTV on some cheap cone. I figured out, I should just buy a better driver. A 5K breakup is better handled by selecting an appropriate crossover. If you have used many Dayton RS drivers, you have had to master that. I did want a lower Fs on one aluminum driver and a coating of fabric paint around the edge did help a little as I could use a shallow but lower crossover.
Tenson, Poly is used on car bushings by kiddie racers who don't know better as it is stiffer than rubber giving better control, and slick enough to last a little while. NOT because it has any dampening features. It has a little more shock absorbing than metal in a real race car, and way too much for a street car. There are a few places where it works OK, TC rods and sway bar end bushings for example. One will get around the track on FAT a lot quicker if they used the poly bushing money for an hour of professional instruction.
I agree. If you repeat the experiment, Tenson, I suggest a flexible sealant/adhesive.
I recommend the following product which is non-shrinking and permanently flexible:
https://www.halfords.com/motoring/p...nville-black-silicone-sealant-40g-173867.html
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If you are trying to get rid of breakups at higher frequencies, i suggest to experiment with phase plug removal
See, higher frequencies comes more directly from voice coil, and if there is no phase plug, they cancel
Phase plug extends high frequencies guiding them out front
Midranges i used, which had almost no breakups, had just soft cloth as dust cap
Hard dust cap, metalic like in old full range speakers, does the oposite
See what response you get with vs without phase plug
Just a suggestion
See, higher frequencies comes more directly from voice coil, and if there is no phase plug, they cancel
Phase plug extends high frequencies guiding them out front
Midranges i used, which had almost no breakups, had just soft cloth as dust cap
Hard dust cap, metalic like in old full range speakers, does the oposite
See what response you get with vs without phase plug
Just a suggestion
Reminded me of my first speaker box I built.
Was bolting up the speaker with spanner on nut and screwdriver on the screw head.
Slipped and screwdriver went straight through the cone !
Managed to pull cone back into the hole and super glued it.
Worked ok for many years after that but lesson learned.
The rock band the Kinks used slashed speakers to get a more abrasive sound.
Was bolting up the speaker with spanner on nut and screwdriver on the screw head.
Slipped and screwdriver went straight through the cone !
Managed to pull cone back into the hole and super glued it.
Worked ok for many years after that but lesson learned.
The rock band the Kinks used slashed speakers to get a more abrasive sound.
There is another thread about this topic:
https://www.diyaudio.com/community/threads/sbacoustics-slit-cone-poor-mans-revelator.331983/
https://www.diyaudio.com/community/threads/sbacoustics-slit-cone-poor-mans-revelator.331983/
I bet that slicing or similar "treatments" will give "better" results with larger pulp/paper cones. Aluminiium is the most problematic material, but slicing/glue would not work...
Here is link to my experiment with glued-on felt pads - reversible method that works with alu as well!
https://photos.app.goo.gl/VYG73N6d57gKfLz27
Here is link to my experiment with glued-on felt pads - reversible method that works with alu as well!
https://photos.app.goo.gl/VYG73N6d57gKfLz27
Curious. Any difference with shape? Normal "bullets", some flat plugs, some with exotic looking but unknown if any science slots.
Your observation follows what I found on the FE 85's.
I suspect there is something to the opening angle of the crevice between the phase plug and cone, but a bulbous phase plug becomes obstructive and the "horn" this creates points away from the listener.
The point on the tip of the phase plug helps the wavefront separate from the tip rather than form a standing wave node like on dustcaps with a large radius. Sort of like Fostex drivers with pointed dustcaps although according to them it seems to be more about vibrations of the dustcap itself than it's affect on the wavefront. A dustcap below it's breakup modes behaves more like a plane radiator with beaming whereas a phase plug or pointed dustcap produces less of a planar wave.
For similar reasons a phase plug should probably be longer than it is wide, to minimize circumferential standing waves.
That said, phase plug geometry seems to be fairly forgiving and the effect of these details might be tiny compared to the ragged response you can expect in affordable fullrange drivers. Perhaps that is why I have never seen a detailed discussion on phase plugs.
I suppose a conical dustcap could be configured like a Walsh driver with the taper matching the speed of sound in the cap to the speed of sound radially outward, but I don't know if the radiation pattern would be an advantage.
The point on the tip of the phase plug helps the wavefront separate from the tip rather than form a standing wave node like on dustcaps with a large radius. Sort of like Fostex drivers with pointed dustcaps although according to them it seems to be more about vibrations of the dustcap itself than it's affect on the wavefront. A dustcap below it's breakup modes behaves more like a plane radiator with beaming whereas a phase plug or pointed dustcap produces less of a planar wave.
For similar reasons a phase plug should probably be longer than it is wide, to minimize circumferential standing waves.
That said, phase plug geometry seems to be fairly forgiving and the effect of these details might be tiny compared to the ragged response you can expect in affordable fullrange drivers. Perhaps that is why I have never seen a detailed discussion on phase plugs.
I suppose a conical dustcap could be configured like a Walsh driver with the taper matching the speed of sound in the cap to the speed of sound radially outward, but I don't know if the radiation pattern would be an advantage.
Thank you! Your experiment proves very well that anyone who advocates such treatment simply spreads snake oil BS, unless he's in need for an ugly looking driver.
You're lucky as you're capable of doing proper measurements. But what about the vast majority that isn't - and whom advices like these most probably adresses?
Best regards!
You're lucky as you're capable of doing proper measurements. But what about the vast majority that isn't - and whom advices like these most probably adresses?
Best regards!
Stuff to think about. I played with them ( carved from wood) as I detected really bad breakup on the dust-cap. They also reduce Sd which can be significant on smaller drivers. I guess they also limit the VC diameter.
I don;t remember seeing a paper on them in the old AES speaker anthology
Walsh had some clever ideas, but they never really took off. Ohm and Infinity was about it. Modern manufacturing processes may make the transition zones more predictable.
It may have made a measurable difference if Tenson had introduced some compliance between the cone segments instead of simply welding them back together - repairing the damage in effect.
I certainly don't advocate slicing up one's speaker cones. However, since this is intended as an experiment, other variables warrant investigation - in the interests of science!
I certainly don't advocate slicing up one's speaker cones. However, since this is intended as an experiment, other variables warrant investigation - in the interests of science!
Honourware REW and the mic in your laptop would work just fine for this kind of comparative or iterative (and most other kinds of) measurement (except absolute measurements below 100 Hz). Try it.
B.