Tang Band uses neodymium magnets that are already coated with a conductive and non magnetic metal. In addition, they glue a second coated neodymium on top of the steel disc that defines the gap height on the pole piece. Because of the extra magnet and thus extended pole piece, a faraday ring will not do much. Also, since the aluminum plug is already conductive and non magnetic, it should work as well as copper. In sum, attempts to retrofit a faraday ring will be of little value.
Mark
Here is an update to the Tang Band W4-656SB modification. While I am including a link to the graph section of that modification, the accompanying text is still in its own thread.
I am trying to more precise reproduction accuracy, and that means going after vibration structures that are smaller and even more chaotic. The more you strive for that last little bit, the more precise the modification must be.
In this update, I try to minimize the remaining 9 kHz peak and to minimize a 4 kHz vibration structure that is visible only in the decay spectrum. Both structures are trickier than the 7 kHz structure with more complex cone motion.
Six narrow glue arcs are required to minimize the two vibration structures. Each glue ring is formed from a 1 mm diameter bead of Gem Tac glue. The 4 kHz structure is handled by three arcs three mm in from the inside radius of the surround. Each arc is 3 cm in. The mounting holes are uses as reference points to center the arcs. The longer arc should be between the two shorter arcs.
The nine kHz peak is handled by one glue arc 11 mm in from the inside radius of the surround. This glue arc is 3.5 cm in length. This center of this glue arc is marked by the remaining mounting hole. The last two glue arcs are 12 mm in from the inside radius of the surround and each is 2 cm in length.
Just to make a point of the arbitrary nature of plus or minus ratings, with mod two, holding to the plus or minus zone of mod one, the driver has a bandwidth of 72 to 14 kHz. If, however, we base the plus or minus range to the new driver response, then the modification driver will have a bandwidth of 68 to 15 kHz. This is shown in the mod one to two comparison graph by the dark purple offset range band.
Good designing and good building,
Mark
The mod one graphs and photo:
I am trying to more precise reproduction accuracy, and that means going after vibration structures that are smaller and even more chaotic. The more you strive for that last little bit, the more precise the modification must be.
In this update, I try to minimize the remaining 9 kHz peak and to minimize a 4 kHz vibration structure that is visible only in the decay spectrum. Both structures are trickier than the 7 kHz structure with more complex cone motion.
Six narrow glue arcs are required to minimize the two vibration structures. Each glue ring is formed from a 1 mm diameter bead of Gem Tac glue. The 4 kHz structure is handled by three arcs three mm in from the inside radius of the surround. Each arc is 3 cm in. The mounting holes are uses as reference points to center the arcs. The longer arc should be between the two shorter arcs.
The nine kHz peak is handled by one glue arc 11 mm in from the inside radius of the surround. This glue arc is 3.5 cm in length. This center of this glue arc is marked by the remaining mounting hole. The last two glue arcs are 12 mm in from the inside radius of the surround and each is 2 cm in length.
Just to make a point of the arbitrary nature of plus or minus ratings, with mod two, holding to the plus or minus zone of mod one, the driver has a bandwidth of 72 to 14 kHz. If, however, we base the plus or minus range to the new driver response, then the modification driver will have a bandwidth of 68 to 15 kHz. This is shown in the mod one to two comparison graph by the dark purple offset range band.
Good designing and good building,
Mark
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The mod one graphs and photo:
An externally hosted image should be here but it was not working when we last tested it.
When I responded with the below, I assumed the question referred to the W3-881S.
I now recognize the possibility that it might have referenced the W4-656SB. The magnetic circuit design of the 656 is more conventional. It would be better served by a faraday ring (field modulation/eddy current control), but to optimize the corrective technique you have to get inside the gap and not be above it. Hard to do on an already assembled driver. Field strength drops quickly outside of the gap. In this low flux environment, I am uncertain of the possible gains of a shorted turn technique.
Instead, I suggest using bass augmentation and thus holding the extended range driver to within its Xmax.
Please do not over simplify the motor circuit variables. There is some complex stuff going on here that I do not believe is well understood. While some have documented benefits of copper shorting rings, they have done so in conjunction with other changed variables (T-pole for example) and produce results that are complicated and not always obviously a product of either inductance reduction or field modulation.
If you are building a driver from scratch, then magnetic circuit performance is a viable design consideration. When working with already assembled and charged magnetic circuits, I would hold operating conditions to minimize magnetic circuit problems and concentrate on the variables I can (and should) control.
Still, in the case of the W4-656SB, there is an experiment that can be conducted by shortening the plug length and using a copper ring spacer to bring the total assembly back to 1.5 inches. In this case, the only variable in play is the copper faraday ring sitting just in front of the gap. If the diameter of the plug and ring match, then any differences in response (transient response, frequency response, or distortion) can, with a high degree of certainty, be assigned to the presence of the shorting ring. Anyone want to conduct the experiment?
Good designing and good building,
Mark
Removing dust cap from polypropylene cones
The question was asked earlier about how I was able to remove the dust cap so cleanly. I did not really understand this question. Low terperature hot melt glue always comes off of polypropylene relatively easily and always cleanly.
To me, the obvious answer to the question was that I do it by following the sequence of steps provided in the post on the W3-881S. 1. Cut off the dome portion of the dust cap using an Xacto knife. Using just the tip and holding the side of the blade parallel to the cone surface, cut at the juncture of the dome and dust cap rim. 2. With the cutting edge of the blade pointing away from the cone, slip the tip under the remaining dust cap rim (easy to do, very little resistance. Then move the knife away from the cone slicing through the dust cap rim. 3. Grip one end of the dust cap rim and pull, peeling it away from the cone. 4. If any glue remains on the cone, use thumb or finger to rub it into a ball and then pluck it from the cone surface.
Still, in case the question was really a request for clarification about the step, I have gone to the considerable trouble of providing a pictorial guide that I now include here.
There might be one complication about ambient temperature. If the temperature is about 72 degrees, in my experience, the glue always adheres better to the dust cap material than it does to the PPM cone. Somewhere about 80 degrees F, maybe about 85, the glue does sometimes separate from the dust cap and stay on the cone. If it does, just use your thumb or finger to rub the glue. It will ball up and can be pulled off.
I hope this helps. If not, if you can restate the question and provide a little more detail I might be able to provide more responsive information.
Good designing and good building,
Mark
The question was asked earlier about how I was able to remove the dust cap so cleanly. I did not really understand this question. Low terperature hot melt glue always comes off of polypropylene relatively easily and always cleanly.
To me, the obvious answer to the question was that I do it by following the sequence of steps provided in the post on the W3-881S. 1. Cut off the dome portion of the dust cap using an Xacto knife. Using just the tip and holding the side of the blade parallel to the cone surface, cut at the juncture of the dome and dust cap rim. 2. With the cutting edge of the blade pointing away from the cone, slip the tip under the remaining dust cap rim (easy to do, very little resistance. Then move the knife away from the cone slicing through the dust cap rim. 3. Grip one end of the dust cap rim and pull, peeling it away from the cone. 4. If any glue remains on the cone, use thumb or finger to rub it into a ball and then pluck it from the cone surface.
Still, in case the question was really a request for clarification about the step, I have gone to the considerable trouble of providing a pictorial guide that I now include here.
There might be one complication about ambient temperature. If the temperature is about 72 degrees, in my experience, the glue always adheres better to the dust cap material than it does to the PPM cone. Somewhere about 80 degrees F, maybe about 85, the glue does sometimes separate from the dust cap and stay on the cone. If it does, just use your thumb or finger to rub the glue. It will ball up and can be pulled off.
I hope this helps. If not, if you can restate the question and provide a little more detail I might be able to provide more responsive information.
Good designing and good building,
Mark
An externally hosted image should be here but it was not working when we last tested it.
There is great potential in having frequencies from mid bass to mid treble reproduced by one coherent driver. The TB W4-656SB, when modified, is one great performer over this bandwidth. Indeed, while the W4-1052SA has more high frequency extension than the W4-656SB, from mid bass to mid treble, the W4-656SB is the better performer.
In case you were holding off on the W4-656SB because you do not have a lathe to make the phase plugs, here is an inexpensive and fairly easy alternative for only a minor decrease in the performance.
Go to a hobby or fabric/crafts store. I bought my supplies at Jo Anns (I could be wrong about how you spell the name). I bought two packages of wood shapes at .98 US dollars each (98 cents each). I bought one package of 1 inch wood discs, and one package containing three one inch by 1 and 1/8 inch wooden flower pots. Stack and glue four of the discs, and add one inverted flower pot to the top of the stack.
The machining on these wood novelties is not precise. You need to hold the maximum diameter to no more than 24 mm. Some of the novelties are under that diameter and most are slightly over. The part of the plug that is likely to be too large in diameter is not particularly important for performance as long as the voice coil can move freely. You do not have to have this portion perfectly round.
You can sand the base of this inexpensive plug by hand, just make sure that the largest diameter is no more than 24 mm. With 100 grit sand paper, it should take no more than 2 minutes of sanding per plug.
I have included a photo of the parts for one plug and a completed plug. I have also included a graph comparing the frequency spectra of the machined plug and the flower pot plug. Of course, all of the mod 2 changes should be made to the cone and you should use the mod 2 prefilter.
Good designing and good building,
Mark
In case you were holding off on the W4-656SB because you do not have a lathe to make the phase plugs, here is an inexpensive and fairly easy alternative for only a minor decrease in the performance.
Go to a hobby or fabric/crafts store. I bought my supplies at Jo Anns (I could be wrong about how you spell the name). I bought two packages of wood shapes at .98 US dollars each (98 cents each). I bought one package of 1 inch wood discs, and one package containing three one inch by 1 and 1/8 inch wooden flower pots. Stack and glue four of the discs, and add one inverted flower pot to the top of the stack.
The machining on these wood novelties is not precise. You need to hold the maximum diameter to no more than 24 mm. Some of the novelties are under that diameter and most are slightly over. The part of the plug that is likely to be too large in diameter is not particularly important for performance as long as the voice coil can move freely. You do not have to have this portion perfectly round.
You can sand the base of this inexpensive plug by hand, just make sure that the largest diameter is no more than 24 mm. With 100 grit sand paper, it should take no more than 2 minutes of sanding per plug.
I have included a photo of the parts for one plug and a completed plug. I have also included a graph comparing the frequency spectra of the machined plug and the flower pot plug. Of course, all of the mod 2 changes should be made to the cone and you should use the mod 2 prefilter.
Good designing and good building,
Mark
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Mark,
In my own case I am not 'holding off' on making phase plugs for my TB W4-656's for lack of a lathe. I do have a metal machine shop and show a solid aluminum phase plug I made for another driver as an experiment a few years ago. I am eager to experiment with these TangBands but am very preoccupied on another major loudspeaker project at the moment and want to wait on the TB until I have adequate computer based testing capabilities set up to 'see' what is going on like you can.
Rob
In my own case I am not 'holding off' on making phase plugs for my TB W4-656's for lack of a lathe. I do have a metal machine shop and show a solid aluminum phase plug I made for another driver as an experiment a few years ago. I am eager to experiment with these TangBands but am very preoccupied on another major loudspeaker project at the moment and want to wait on the TB until I have adequate computer based testing capabilities set up to 'see' what is going on like you can.
Rob
Attachments
Rob,
I saw your announcement in another thread that you were ready to go commerical. My congratulations.
My flower pot plug was not aimed at the professionals in the forum. Rather, I was trying to come up with something that would not require a diyer to buy from anyone or buy machining equipment to join in the fun.
It was also a subversive way to demonstrate variable tolerance in a four-inch driver. While three-inch drivers are extremely sensitive, by the time you get to 6.5 inch diameter, plugs are of little use in altering performance.
Mark
I saw your announcement in another thread that you were ready to go commerical. My congratulations.
My flower pot plug was not aimed at the professionals in the forum. Rather, I was trying to come up with something that would not require a diyer to buy from anyone or buy machining equipment to join in the fun.
It was also a subversive way to demonstrate variable tolerance in a four-inch driver. While three-inch drivers are extremely sensitive, by the time you get to 6.5 inch diameter, plugs are of little use in altering performance.
Mark
Thanx Mark,
As far as going commercial I have over two years in dedicated speaker R&D behind me now and feel that I am close to a product, have prototyped some really fine speakers but feel they are too labour intensive to mass produce so my R&D continues. I do not want to compete with big box store junk or a price point. I only want to offer something that is really good, in the limited quantities that a small shop can supply an exclusive marketplace. I am most fortunate to own a 3500 sq. ft. commercial building with 10 foot ceilings in which I can manufacture.
Your observation about phase plugs losing effectiveness in larger sizes should be leaked to those manufacturers and buyers of the 12" woofers with the huge phase plugs.
As far as going commercial I have over two years in dedicated speaker R&D behind me now and feel that I am close to a product, have prototyped some really fine speakers but feel they are too labour intensive to mass produce so my R&D continues. I do not want to compete with big box store junk or a price point. I only want to offer something that is really good, in the limited quantities that a small shop can supply an exclusive marketplace. I am most fortunate to own a 3500 sq. ft. commercial building with 10 foot ceilings in which I can manufacture.
Your observation about phase plugs losing effectiveness in larger sizes should be leaked to those manufacturers and buyers of the 12" woofers with the huge phase plugs.
How similar is the 656 to the 657?
The spec sheets look very similar. Frequency response appears close, they both have the same peak at 7k (according to TB). 656 is rated for slightly more power and has a 1g higher moving mass.
Just wondering because the 657 already has a phase plug. But the cone material is aluminum. I dont know if you like aluminum at all. I assume it "rings" at a certain frequency so maybe its not usable as high as the 656.
Just curious
thanks
The spec sheets look very similar. Frequency response appears close, they both have the same peak at 7k (according to TB). 656 is rated for slightly more power and has a 1g higher moving mass.
Just wondering because the 657 already has a phase plug. But the cone material is aluminum. I dont know if you like aluminum at all. I assume it "rings" at a certain frequency so maybe its not usable as high as the 656.
Just curious
thanks
thomas 997,
I am curious about your interest in the 657. With the manufacturer's specs so close to that of the 656, why would you be interested in the metal 657?
In reply to your questions, all driver cone or diaphragm materials suffer from unintended vibration modes that mess up sound reproduction.
Metal cones, like cones of all other materials have vibration modes. Metal, however, has a very different mechanical impedance than plastic. In fact, it is much closer to the paper we use than it is to the plastics.
Metal and paper both suffer from very high Q vibration modes. Each can be changed, just as I have been doing with the TB PPM cones. It is just that it is more difficult to stop the vibration mode triggers/attractors in either paper or metal. While I can and have modified both paper and metal, the techniques require much more work, technology, access to materials, ability to shape materials, and so on than does PPM. So, for the modifications I provide, I tend to stay away from those materials. Just look at the relative complexity of the 654 and the 656 modifications included in this thread.
While I know that there is a strand of thought out there that you can just coat metal with tar, or hobby glues, or rare and expensive Australian varnish, I also know how ineffective all of those techniques are. I also know that applying beads of glue (as I do on PPM) does nothing for metal, even when you have correctly identified the attractor or trigger for the vibration mode.
So, from my perspective, while the stats provided by TB make the drivers seem similar, they are not. If I were to test the AL cone driver, I would also expect it to measure much different than the stock 656 regardless of what TB may imply. Sorry, just one of the pitfalls of non standard testing.
The process of controlling the vibrations in metal is much more difficult to pull off in terms of access to materials and precision in fabrication and application. There has to be a compelling advantage to metal to make it worth working with. I have found such an advantage to using metals in composites. To date, however, I can neither hear nor measure such an advantage in pure metal cones or diaphragms.
Mark
I am curious about your interest in the 657. With the manufacturer's specs so close to that of the 656, why would you be interested in the metal 657?
In reply to your questions, all driver cone or diaphragm materials suffer from unintended vibration modes that mess up sound reproduction.
Metal cones, like cones of all other materials have vibration modes. Metal, however, has a very different mechanical impedance than plastic. In fact, it is much closer to the paper we use than it is to the plastics.
Metal and paper both suffer from very high Q vibration modes. Each can be changed, just as I have been doing with the TB PPM cones. It is just that it is more difficult to stop the vibration mode triggers/attractors in either paper or metal. While I can and have modified both paper and metal, the techniques require much more work, technology, access to materials, ability to shape materials, and so on than does PPM. So, for the modifications I provide, I tend to stay away from those materials. Just look at the relative complexity of the 654 and the 656 modifications included in this thread.
While I know that there is a strand of thought out there that you can just coat metal with tar, or hobby glues, or rare and expensive Australian varnish, I also know how ineffective all of those techniques are. I also know that applying beads of glue (as I do on PPM) does nothing for metal, even when you have correctly identified the attractor or trigger for the vibration mode.
So, from my perspective, while the stats provided by TB make the drivers seem similar, they are not. If I were to test the AL cone driver, I would also expect it to measure much different than the stock 656 regardless of what TB may imply. Sorry, just one of the pitfalls of non standard testing.
The process of controlling the vibrations in metal is much more difficult to pull off in terms of access to materials and precision in fabrication and application. There has to be a compelling advantage to metal to make it worth working with. I have found such an advantage to using metals in composites. To date, however, I can neither hear nor measure such an advantage in pure metal cones or diaphragms.
Mark
I believe somewhere in this thread I indicated I would announce when the brick and mortar modification article for the TB W3-881S became available.
It will be published in AudioXpress December of 2004. Volume 35, No. 12.
Either the glue mod (provided in this thread) or the dimple mod will create a driver of super performance.
Good designing and good building,
Mark
It will be published in AudioXpress December of 2004. Volume 35, No. 12.
Either the glue mod (provided in this thread) or the dimple mod will create a driver of super performance.
Good designing and good building,
Mark
Thanks.
Just curious because that is what I have bought
I can see how it would be hard to work with the metal cone, as you say.
I have tried to do some testing of my own, but my equipment is not good enough. Even with no input I get a fair bit of bass response, which interferes with the measurements.
Just curious because that is what I have bought
I can see how it would be hard to work with the metal cone, as you say.
I have tried to do some testing of my own, but my equipment is not good enough. Even with no input I get a fair bit of bass response, which interferes with the measurements.
Just wanted to quickly update this project and to make one clarification.
I have stopped supporting the 654 paper cone modification on my Web site. The performance of the 657 is equal to or better and requires much less work. I fear that the complexity of the 654 mod may have been somewhat intimidating.
Also, I now have posted a wooden dowel "phase" plug modication for the W3-881S driver. This rationalizes the price to performance ratio at three price points of 3-inch drivers.
Otherwise, everything is the same. This is because there isn't anything better. And now the clarification. I received a e-mail that included a lot of stuff, but one of the items was that the drivers I work with were "sow's ears" that I turned "into silk purses."
Wrong! If you have read my AudioXpress article on modifying the TB W3-881S you know that I chose that driver only after an exhausting review of 3-inch drivers. None of the drivers I provide modifications for are "sow's ears" in stock condition. Instead, they are the only drivers showing much potential. Indeed, they often already outperform other drivers for accuracy. I just make them much better.
I guess there is one last update. On the driver testing section of my Web site I now post performance evaluations of three Fostex drivers. I don't identify the drivers on the Web site, but they are the FE87E, FE103E, and FE126E. As stock units, the TBs outperform the Fostex drivers. They are more accurate and faithful reproducers of the signal you feed them. (They also sound better to my ear and they cost less). The Tang Band drivers I modify may already be silk purses in stock condition. Once modified, however, they are definitely upscale silk purses.
Now, I may criticize TB (and in my world that criticism is valid), but I do this only in preparation for improving the performance. That I criticize them does not mean that the particular units I work with are not as good as others (especially true of the 871). Indeed, they are equal to or better than and they have the potential to become significantly better.
Good designing and good building,
Mark
I have stopped supporting the 654 paper cone modification on my Web site. The performance of the 657 is equal to or better and requires much less work. I fear that the complexity of the 654 mod may have been somewhat intimidating.
Also, I now have posted a wooden dowel "phase" plug modication for the W3-881S driver. This rationalizes the price to performance ratio at three price points of 3-inch drivers.
Otherwise, everything is the same. This is because there isn't anything better. And now the clarification. I received a e-mail that included a lot of stuff, but one of the items was that the drivers I work with were "sow's ears" that I turned "into silk purses."
Wrong! If you have read my AudioXpress article on modifying the TB W3-881S you know that I chose that driver only after an exhausting review of 3-inch drivers. None of the drivers I provide modifications for are "sow's ears" in stock condition. Instead, they are the only drivers showing much potential. Indeed, they often already outperform other drivers for accuracy. I just make them much better.
I guess there is one last update. On the driver testing section of my Web site I now post performance evaluations of three Fostex drivers. I don't identify the drivers on the Web site, but they are the FE87E, FE103E, and FE126E. As stock units, the TBs outperform the Fostex drivers. They are more accurate and faithful reproducers of the signal you feed them. (They also sound better to my ear and they cost less). The Tang Band drivers I modify may already be silk purses in stock condition. Once modified, however, they are definitely upscale silk purses.
Now, I may criticize TB (and in my world that criticism is valid), but I do this only in preparation for improving the performance. That I criticize them does not mean that the particular units I work with are not as good as others (especially true of the 871). Indeed, they are equal to or better than and they have the potential to become significantly better.
Good designing and good building,
Mark
Sorry to be the bearer of bad news but the W3-881S driver has been replaced by the inferior W3-881SD. I have been testing the "SD" this week and it is different in several significant ways. There are two new vibration modes in the SD. One is centered at 17.5 kHz. The new modes make the driver more smeared in reproducing transients and reduce clarity.
The 881S modifications will not work with the 881SD. It is a different driver.
PE may have sent you SD drivers instead of the 881S drivers you ordered. They are clearly marked as SD on the Tang Band boxes even if the difference is noted nowhere else.
Good designing and good building,
Mark
The 881S modifications will not work with the 881SD. It is a different driver.
PE may have sent you SD drivers instead of the 881S drivers you ordered. They are clearly marked as SD on the Tang Band boxes even if the difference is noted nowhere else.
Good designing and good building,
Mark
Hi Mark,
Thank you for posting an update. This is an absolutely fascinating thread for me. It was not until close to the end (The AudioXpress reference) that I realized it was an old thread that had been updated. Do you do any distortion testing like Mark K http://206.13.113.199/ncdiyaudio/mark/Testing/testing.htm does here?
Also, do you measure the (driver) behavior off-axis? I saw mainly on-axis at your site (which are much improved from stock form of the drivers
). Your Mad.6T looks especially interesting to me. It may be the driver I have long been looking for. They are still available correct?
What are your thoughts on the TB W2-880SC (PPM cone+available at PE) as a driver intended for use above, say 400hz ?
Do you see any uses for a driver that small? I do for a very specific application.
Thank you.
Cheers,
AJ
Thank you for posting an update. This is an absolutely fascinating thread for me. It was not until close to the end (The AudioXpress reference) that I realized it was an old thread that had been updated. Do you do any distortion testing like Mark K http://206.13.113.199/ncdiyaudio/mark/Testing/testing.htm does here?
Also, do you measure the (driver) behavior off-axis? I saw mainly on-axis at your site (which are much improved from stock form of the drivers
). Your Mad.6T looks especially interesting to me. It may be the driver I have long been looking for. They are still available correct?What are your thoughts on the TB W2-880SC (PPM cone+available at PE) as a driver intended for use above, say 400hz ?
Do you see any uses for a driver that small? I do for a very specific application.
Thank you.
Cheers,
AJ
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