If you bought the Tang Band W4-656SB driver, you did not make a mistake. PPM cone, die cast basket, and shielded magnet structure are all positives in the design. While it does not have the high frequency extension to qualify as a full-range driver and it does need bass augmentation below 95 Hz, it has the potential to be a high quality and high fidelity extended range driver.
In stock condition, it does have some problems. You can, however, improve its performance with a series of modifications simpler than my modifications for the W4-654S paper cone driver. Here is one way of improving the driver.
First, remove the dust cap. The dust cap is a major problem for this driver and I do not understand why TB uses dust caps. Even with their low detail measurement set-up, they have to be able to measure the huge 7 kHz peak in the response.
Next, replace the dust cap with a “phase” plug. These plugs are neither wave-guides nor phase correctors, but they are useful in regulating cone loading and adjusting response. I find the TB phase plug shape to be less than optimal, but with four-inch drivers (and larger) the response is less sensitive to changes in plug shape. I have included a photo of the wooden plug I used for this modification sequence. The plug is 1.5 inches long. The first .75 inches is just a cylinder, the second .75 is tapered. I have made plugs out of aluminum, wood, plastic (both machined and cast), plaster, and hard rubber. I have found that the shape is important; the material of construction is unimportant.
Next, lay down a thin bead of glue (GemTac works well) that is 1 to 1.5 mm in diameter, 6 mm in from the inside diameter of the surround. This stops the origin of a 7 kHz cone vibration mode. Unlike the W4-1052SA modification One, the glue circle does not cause a dip in the response in the 656SB driver. A second cone resonance remains at about 9kHz. I have yet to locate the attractor region of the cone that is the origin of this vibration mode.
Lastly, construct the three-component equalizer circuit. The component values are small and can be obtained inexpensively even when selecting high quality components.
There is a multitude of midrange drivers available. If, however, you wish to design a 2.5 or 2.1 way loudspeaker while pushing the crossover regions as far away from the midrange as possible, this is a desirable driver option.
Good designing,
Mark
In stock condition, it does have some problems. You can, however, improve its performance with a series of modifications simpler than my modifications for the W4-654S paper cone driver. Here is one way of improving the driver.
First, remove the dust cap. The dust cap is a major problem for this driver and I do not understand why TB uses dust caps. Even with their low detail measurement set-up, they have to be able to measure the huge 7 kHz peak in the response.
Next, replace the dust cap with a “phase” plug. These plugs are neither wave-guides nor phase correctors, but they are useful in regulating cone loading and adjusting response. I find the TB phase plug shape to be less than optimal, but with four-inch drivers (and larger) the response is less sensitive to changes in plug shape. I have included a photo of the wooden plug I used for this modification sequence. The plug is 1.5 inches long. The first .75 inches is just a cylinder, the second .75 is tapered. I have made plugs out of aluminum, wood, plastic (both machined and cast), plaster, and hard rubber. I have found that the shape is important; the material of construction is unimportant.
Next, lay down a thin bead of glue (GemTac works well) that is 1 to 1.5 mm in diameter, 6 mm in from the inside diameter of the surround. This stops the origin of a 7 kHz cone vibration mode. Unlike the W4-1052SA modification One, the glue circle does not cause a dip in the response in the 656SB driver. A second cone resonance remains at about 9kHz. I have yet to locate the attractor region of the cone that is the origin of this vibration mode.
Lastly, construct the three-component equalizer circuit. The component values are small and can be obtained inexpensively even when selecting high quality components.
There is a multitude of midrange drivers available. If, however, you wish to design a 2.5 or 2.1 way loudspeaker while pushing the crossover regions as far away from the midrange as possible, this is a desirable driver option.
Good designing,
Mark
An externally hosted image should be here but it was not working when we last tested it.
Mighty impressive R&D work on the TB driver Mark.
How is it to put a tweeter cone, like the ones on fostex drivers, on it? will it have any effect in the higher freq. range?
How do you find the "attractor region" for the given freq. is it just try and fail?
How did you calculate the notch filter?
How is it to put a tweeter cone, like the ones on fostex drivers, on it? will it have any effect in the higher freq. range?
How do you find the "attractor region" for the given freq. is it just try and fail?
How did you calculate the notch filter?
Member
Joined 2004
Outstanding Mark! I bought four of these when P.E. started carrying TangBand a couple of years ago. These do not seem to be available anymore. I have been listening to a pair driven fullrange for a couple of years in a rear horn loading cabinet and a Dayton PT-2 tweeter helping fill in the upper registers (2nd order xover @3 KHz). You are right, This TB does not have the top end as supplied and also needs augmentation in the bottom. I ended up using a 6.5" and 8" Dayton woofer run face to face isobaric in the hole in the rear horn originally contemplated for a second TB W4-656. They are run flat out in parallel with the TB no crossover. The net result is very good. I want to try your mod.
I originally wanted to try to use this folded horn cabinet with the W4-656 driver alone as a sort of poor man's Lowther or Fostex. Maybe with your mod I still can.
Can Weldbond (the white universal glue that looks like white wood glue wet and dries clear) be used to damp the cone?
Do you plan to experiment with adding a wizzer to increase the top end capability?
I originally wanted to try to use this folded horn cabinet with the W4-656 driver alone as a sort of poor man's Lowther or Fostex. Maybe with your mod I still can.
Can Weldbond (the white universal glue that looks like white wood glue wet and dries clear) be used to damp the cone?
Do you plan to experiment with adding a wizzer to increase the top end capability?
Attachments
rcavictim said:
Thanx -- watch for the advert in the Vendor's Bazaar...
I have a set of pictures taken for just such a page... they will go up on this page which has a preliminary description
http://www.planet10-hifi.com/pp-install.html
dave
Lots of questions.... I will try to address them all in this one post.
First, the glue. I am not familiar with WeldBond glue. The species of glue is called "aliphatic." If it is water soluble, dries clear, and remains flexible it is in the same glue species. I can even give you a detailed chemical recipe for the glue, but that won't help.
The glues vary by water content and adhesion. Some hold to the poly much better than others. The GemTac holds the best of any of the commerical glues I have tried. The WeldBond, if it remains flexible, will work. How easily it can be pulled off the poly I cannot say.
I don't understand the part of your message about not available anymore? I just checked and the W4-656 is listed on the Parts Express Website and is stated as in stock. I bought mine a little more than a month ago during one of their regular sales.
In other postings I have declared my allegiance to transient coherence. Whizzers are antithetical to transient coherence and resonance control. In my world, the frequency extension provided by whizzers is an illusion and they are all terribly destructive to sound reproduction accuracy. Just as I have taken off the dust cap, if this driver had a whizzer, I would take it off too.
An analogy to a whizzer would be adding a bell to the system. Attach a tiny little clapper to the voice coil and when the voice coil moves the clapper strikes the bell. The system now has more high frequency content. The new high frequency content is created in response to the signal applied to voice coil but it is not a reproduction of the applied signal. It is new and added to the sound.
Second, I would say inexpensive and not cheap. There is nothing cheap about the performance after modification.
Third, Dave, there are so many topics this will apply to, but length and diameter are both important. You can shim your plugs to the 1.5 in spec, but I believe the Fostex uses a 20 mm voice coil and the Tang Band 656SB uses a 25 or 26 mm coil former. It will be impossible to shim the diameter. Your profile seems to be closer to the TB shape than mine. I like a slightly flatter tip with a larger radius near the terminal end. The possibility for innuendo is endless.
Vinnie, thanks for the last two questions. These are great questions for a diy forum. It is classical R&D: empirical research. If my modeling is correct and cone breakup is chaotic, then it will defy simple predictive formulas. Still, there are regions of order within apparent chaos. For example, in four-inch drivers res problems below 10 kHz are always outside edge problems. Above 10 kHz and the triggers are always between half way and inner third. The same corrective techniques do not work for every cone and every material. Aliphatic glue rings won't do a thing on paper (or banana paper). Here it is a matter of matching material mechanical impedances.
I have been working with material resonance problems for so long that I use what academics call an expert system. I have learned about 100 questions to ask when presented with a material resonance problem. I really don't have to think about it very much. I view the data and I make predictions. I found the 7 kHz cone trigger on the second try. My first attempt was at 4mm in and it turned out to be at 6 mm in. The changes in the response to the 4mm ring told me where I had to go. If you go to an analytic chemist to identify a compound, talk to a physicist about the welding properties of an elemental metal, or a medical doctor about diagnosing a disease, the process is the same. You may have to do this a thousand times before you will be as good at it as I am, but it is within anyone's capabilities. You just need to learn the appropriate 100 questions of material science so well that you don't have to think about them anymore. Not only do I know this academically, but also I can testify that this is the way physicists work. I was hanging around a materials joining think tank and sitting in a physicist's office one day when a call came in asking about the oxidation byproducts of welding a particular metal. He just looked at the periodic table on his wall and said, " your metal is in the same column as titanium and so you can expect a similar oxidation spectrum to welding titanium."
The same applies to designing res networks. I have a multi page flip chart of standard component value resonant frequencies. I know the Q limits of the charts and I just flip through them until I find the values I want to use for the shape and frequency of problem I plan to correct. I have the tables in html format and could post them to my Web site if anyone is interested or would find them useful. You could print them and make your own design flip chart. Just let me know.
Lastly, maybe one of you can help me. I have identified a common characteristic of all four-inch cone drivers. Regardless of Fs or enclosure, the output begins to fall at 95 Hz and is minus 3 db by around 72 Hz. I have tried infinite baffle, ported, and sealed enclosures of different sizes and tunings and nothing will change this roll-off. I have not reached expert level yet with transmission line or horn loaded enclosure designs. If this is a physical limitation caused by the falling mechanical impedance of the cone to air coupling, then I do not know if transmission line or horn loading will solve the problem, or if you can fluid couple multiple drivers to make the combined cones act as if they were larger. Would anyone be willing to help me complete this aspect of the R&D? This is relevant to one of you because if my hypothesis is correct, then equalization will not work.
Mark
First, the glue. I am not familiar with WeldBond glue. The species of glue is called "aliphatic." If it is water soluble, dries clear, and remains flexible it is in the same glue species. I can even give you a detailed chemical recipe for the glue, but that won't help.
The glues vary by water content and adhesion. Some hold to the poly much better than others. The GemTac holds the best of any of the commerical glues I have tried. The WeldBond, if it remains flexible, will work. How easily it can be pulled off the poly I cannot say.
I don't understand the part of your message about not available anymore? I just checked and the W4-656 is listed on the Parts Express Website and is stated as in stock. I bought mine a little more than a month ago during one of their regular sales.
In other postings I have declared my allegiance to transient coherence. Whizzers are antithetical to transient coherence and resonance control. In my world, the frequency extension provided by whizzers is an illusion and they are all terribly destructive to sound reproduction accuracy. Just as I have taken off the dust cap, if this driver had a whizzer, I would take it off too.
An analogy to a whizzer would be adding a bell to the system. Attach a tiny little clapper to the voice coil and when the voice coil moves the clapper strikes the bell. The system now has more high frequency content. The new high frequency content is created in response to the signal applied to voice coil but it is not a reproduction of the applied signal. It is new and added to the sound.
Second, I would say inexpensive and not cheap. There is nothing cheap about the performance after modification.
Third, Dave, there are so many topics this will apply to, but length and diameter are both important. You can shim your plugs to the 1.5 in spec, but I believe the Fostex uses a 20 mm voice coil and the Tang Band 656SB uses a 25 or 26 mm coil former. It will be impossible to shim the diameter. Your profile seems to be closer to the TB shape than mine. I like a slightly flatter tip with a larger radius near the terminal end. The possibility for innuendo is endless.
Vinnie, thanks for the last two questions. These are great questions for a diy forum. It is classical R&D: empirical research. If my modeling is correct and cone breakup is chaotic, then it will defy simple predictive formulas. Still, there are regions of order within apparent chaos. For example, in four-inch drivers res problems below 10 kHz are always outside edge problems. Above 10 kHz and the triggers are always between half way and inner third. The same corrective techniques do not work for every cone and every material. Aliphatic glue rings won't do a thing on paper (or banana paper). Here it is a matter of matching material mechanical impedances.
I have been working with material resonance problems for so long that I use what academics call an expert system. I have learned about 100 questions to ask when presented with a material resonance problem. I really don't have to think about it very much. I view the data and I make predictions. I found the 7 kHz cone trigger on the second try. My first attempt was at 4mm in and it turned out to be at 6 mm in. The changes in the response to the 4mm ring told me where I had to go. If you go to an analytic chemist to identify a compound, talk to a physicist about the welding properties of an elemental metal, or a medical doctor about diagnosing a disease, the process is the same. You may have to do this a thousand times before you will be as good at it as I am, but it is within anyone's capabilities. You just need to learn the appropriate 100 questions of material science so well that you don't have to think about them anymore. Not only do I know this academically, but also I can testify that this is the way physicists work. I was hanging around a materials joining think tank and sitting in a physicist's office one day when a call came in asking about the oxidation byproducts of welding a particular metal. He just looked at the periodic table on his wall and said, " your metal is in the same column as titanium and so you can expect a similar oxidation spectrum to welding titanium."
The same applies to designing res networks. I have a multi page flip chart of standard component value resonant frequencies. I know the Q limits of the charts and I just flip through them until I find the values I want to use for the shape and frequency of problem I plan to correct. I have the tables in html format and could post them to my Web site if anyone is interested or would find them useful. You could print them and make your own design flip chart. Just let me know.
Lastly, maybe one of you can help me. I have identified a common characteristic of all four-inch cone drivers. Regardless of Fs or enclosure, the output begins to fall at 95 Hz and is minus 3 db by around 72 Hz. I have tried infinite baffle, ported, and sealed enclosures of different sizes and tunings and nothing will change this roll-off. I have not reached expert level yet with transmission line or horn loaded enclosure designs. If this is a physical limitation caused by the falling mechanical impedance of the cone to air coupling, then I do not know if transmission line or horn loading will solve the problem, or if you can fluid couple multiple drivers to make the combined cones act as if they were larger. Would anyone be willing to help me complete this aspect of the R&D? This is relevant to one of you because if my hypothesis is correct, then equalization will not work.
Mark
RCAVICTIM,
Was your question for me and the TB or Dave and the Fostex?
If it was for the TB, don't use a heat gun. The adhesion to the poly is not that great. There are two easy ways to get off the dust cap. The first way is to take the exacto knife and going under the outside edge begin to fold back the dust cap edge. By the time you are half way around the edge you can just pop the cap off.
The second way is to cut the center of the dust cap out, then run the tip under the remaining lip to cut the remaining ring. Then just grab one end and peel off the dustcap ring.
I usually use the first technique only because I like to remove the dust caps undamaged. The second way is easier and pretty much fool proof.
Mark
Was your question for me and the TB or Dave and the Fostex?
If it was for the TB, don't use a heat gun. The adhesion to the poly is not that great. There are two easy ways to get off the dust cap. The first way is to take the exacto knife and going under the outside edge begin to fold back the dust cap edge. By the time you are half way around the edge you can just pop the cap off.
The second way is to cut the center of the dust cap out, then run the tip under the remaining lip to cut the remaining ring. Then just grab one end and peel off the dustcap ring.
I usually use the first technique only because I like to remove the dust caps undamaged. The second way is easier and pretty much fool proof.
Mark
Thanks for all your work Mark.
I have a pair of 656s in modified Fostex Back horns which work OK.
I haven't measured their response to know if the bass is much better than you have seen in a ported box, but I think they are going deeper than 95hz...
I'll try these mods. and see if I can't them to sound very good...
Jason.
I have a pair of 656s in modified Fostex Back horns which work OK.
I haven't measured their response to know if the bass is much better than you have seen in a ported box, but I think they are going deeper than 95hz...
I'll try these mods. and see if I can't them to sound very good...
Jason.
MarkMcK said:
Mark,
Yes my Q's were for you. Thanx for the info. The Weldbond glue does have the properties you described. I tried a couple of beads on some smooth polypropelene sheet I have in stock in natural color yesterday and today one dried bead although nice and flexible, peeled off. There was nothing but atmospheric air pressure holding it to the poly it seemed. It appears that surface roughness is the only binding mechanism that will make this glue adhere to polypropelene. The rear surface of the TB cone is much rougher than the front but applying a bead to the back would be somewhat difficult because of restricted access working against ham-handedness. Any comments about the effectiveness of applying the glue to the back of the cone from a sonic perspective?
I see that PartsExpress does still list this driver but I was recalling that I had noticed it disappear I thought from the TangBand website some time ago. Maybe I was mistaken.
Your thoughts about the wizzer cone made sense. I am wondering if there is some other shape of bullet that would better create a horn loading to the innermost portion of a small loudspeaker cone to work better than the traditional wizzer and also give HF boost over a common bullet (which I understand is doing other things like eliminating the resonant chamber previously formed by the dustcap, and more).
I am thinking of a form of ring horn with the traditional bullet in the center (like the looks of a bullet tweeter). There would be a necessary space between the input plate of the horn and the speaker diaphragm to allow for low frequency excursion but nevertheless there would be a high pressure zone (I suspect) built up in this area that might be useful on the input end of a small exponential horn. The bullet and pole piece could be used to support the entire structure. Something to try on my lathe maybe.
That the glue peels off is not a bad thing. Even the Gem-Tac will peel off. It just takes more effort than with the weaker glues. Even with the weakest of these glues, there is some adhesion beyond mere air pressure. I have never been able to delaminate even the weakest glues with cone accelerations, they just don't control the vibration mode triggers as well.
You can glue the backsides of the cones. Works just as well as front side gluing. As you say, it is just a much more difficult task to apply it smoothly and evenly and so I don't make that the preferred way of application.
About your short horn loading... Why do the high frequencies roll-off? In part it is because of the voice coil (both mass and inductance). You can never recover this loss with any cone or cone loading modifications or structures. Still, if cone losses are involved, then changes in loading can make for differences. Yet this is a very complex and sensitive mechanism we are trying to alter. Just as I am stopping the triggers of vibration modes with modifications of spring rate and mass to very small areas of the cones, other changes can set off other vibration modes that did not previously exist.
I don't know when Dave starting thinking about modifiying the Fostex, but I do know what I posted before he started talking about it. That modification also involved replacing a dust cap with a plug. Yet this replacement was just one part of an integrated design. If all I had done was to replace the dust cap with a plug, the performance would have become worse. In my example the dust cap was causing unit-to-unit variability, but was also stopping a rather nasty cone vibration mode. Removing the dust cap released this mode and installing a plug did not damp it. Because my design was integrated, I used other techniques to control the vibration and replace the function provided by the original dust cap.
I am afraid that I know more about the design and performance of the Fostex than this forum's Fostex modifiers do. The dust cap is serving specific functions in Fostex's integrated design. A plug does not replace these functions.
In sum, I encourage you to generate ideas and to try them out. You just need to have a means of documenting the changes you make to see if you are improving the performance or just making it different.
Good designing,
Mark
You can glue the backsides of the cones. Works just as well as front side gluing. As you say, it is just a much more difficult task to apply it smoothly and evenly and so I don't make that the preferred way of application.
About your short horn loading... Why do the high frequencies roll-off? In part it is because of the voice coil (both mass and inductance). You can never recover this loss with any cone or cone loading modifications or structures. Still, if cone losses are involved, then changes in loading can make for differences. Yet this is a very complex and sensitive mechanism we are trying to alter. Just as I am stopping the triggers of vibration modes with modifications of spring rate and mass to very small areas of the cones, other changes can set off other vibration modes that did not previously exist.
I don't know when Dave starting thinking about modifiying the Fostex, but I do know what I posted before he started talking about it. That modification also involved replacing a dust cap with a plug. Yet this replacement was just one part of an integrated design. If all I had done was to replace the dust cap with a plug, the performance would have become worse. In my example the dust cap was causing unit-to-unit variability, but was also stopping a rather nasty cone vibration mode. Removing the dust cap released this mode and installing a plug did not damp it. Because my design was integrated, I used other techniques to control the vibration and replace the function provided by the original dust cap.
I am afraid that I know more about the design and performance of the Fostex than this forum's Fostex modifiers do. The dust cap is serving specific functions in Fostex's integrated design. A plug does not replace these functions.
In sum, I encourage you to generate ideas and to try them out. You just need to have a means of documenting the changes you make to see if you are improving the performance or just making it different.
Good designing,
Mark
MarkMcK said:
Since i started getting into Fostex -- my RS 1197s were 1st -- about 4 years ago, but i've been modifying drivers since the late 70s -- nothing as well detailed as Mark thou...
Never actually had my hands on an "official" Fostex to mod it, just siblings like the RS 40-1197 and the Foster "FE103A" variants. I do know without a doubt that an FE103A can be tweaked to outperform a stock FE108 Sigma, the FE108ES is breaking in.
dave
Mark wrote:
Please post the tables, they sounds like a very useful format for that information.
I found this thread while searching for information on shielded A/V drivers. It seems common for them to have a small anomoly or two in the phase response, with corresponding effects in frequency response.
Can anyone explain this phenomenon, and/or offer suggestions for reducing the effects?
Tim
Please post the tables, they sounds like a very useful format for that information.
I found this thread while searching for information on shielded A/V drivers. It seems common for them to have a small anomoly or two in the phase response, with corresponding effects in frequency response.
Can anyone explain this phenomenon, and/or offer suggestions for reducing the effects?
Tim
Since I made that offer, I discovered that Speaker Workshop (the free testing and design program) has a notch filter calculator. I have tested it and it works quite well.
One thing about small signal phase response, it generally follows the bode plot frequency response. When you correct for the vibration mode frequency response problems, the phase problems go away too. It is impossible to separate the two in signal driver performance because they are just one phenomenon.
Other than determining where the cone vibration modes are and then squashing them (figurative use of language), there is no universal way to correct for either the frequency response or the phase problems in drivers.
Some will fall to electrical prefiltering, others to mechanical modifications of the cones. It is, however, a case by case determination as to which is which.
Perhaps you would consider one of the modified TB shielded four-inch drivers. With a sub woofer, both detailed here will produce excellent results and performance.
Mark
One thing about small signal phase response, it generally follows the bode plot frequency response. When you correct for the vibration mode frequency response problems, the phase problems go away too. It is impossible to separate the two in signal driver performance because they are just one phenomenon.
Other than determining where the cone vibration modes are and then squashing them (figurative use of language), there is no universal way to correct for either the frequency response or the phase problems in drivers.
Some will fall to electrical prefiltering, others to mechanical modifications of the cones. It is, however, a case by case determination as to which is which.
Perhaps you would consider one of the modified TB shielded four-inch drivers. With a sub woofer, both detailed here will produce excellent results and performance.
Mark
MarkMcK wrote:
Thanks for the response, Mark.
I should have deduced that phase response would follow frequency response.
Maybe it's my imagination, or maybe I'm jumping to conclusions here. But, I've noticed a significant bump/dip in frequency response of most shielded drivers in the 1-2kHz region. I *assumed* it was related to shielding.
I guess it's time to look back over some graphs to validate my observation before questioning further.
The specific drivers in question are little Bravox 3". Cheapies purchased from PE just for miscellaneous use. I'm going to stick a couple in the ceiling in the laundry room and kitchen, driven by whatever I can come up with. They're not worth a lot of effort in this application. However, I do have a few extras for later use in whatever comes along.
And thanks for the tip on Speaker Workshop.
Tim
Thanks for the response, Mark.
I should have deduced that phase response would follow frequency response.
Maybe it's my imagination, or maybe I'm jumping to conclusions here. But, I've noticed a significant bump/dip in frequency response of most shielded drivers in the 1-2kHz region. I *assumed* it was related to shielding.
I guess it's time to look back over some graphs to validate my observation before questioning further.
The specific drivers in question are little Bravox 3". Cheapies purchased from PE just for miscellaneous use. I'm going to stick a couple in the ceiling in the laundry room and kitchen, driven by whatever I can come up with. They're not worth a lot of effort in this application. However, I do have a few extras for later use in whatever comes along.
And thanks for the tip on Speaker Workshop.
Tim
With the region of interest being one to two kHz, the most likely explanation is back side bounce off the basket/magnet structure propogating through the cone. Shows up in the mid to late decay response. Not much can be done to correct this relatively small and generally acoustically benign (as compared to other problems in the bandpass).
Good luck with the Bravox three-inchers,
Mark
Good luck with the Bravox three-inchers,
Mark
Chris8sirhC:
I purchased a few of those as well. Looked good for cheapie projects for the kids computer and such.
Did you check out the projects page for this driver?PE Buyout
The stamped basket and tall gasket remind me of ultra-cheap automotive OEM replacement speakers I used years ago.
Anyway the page mentions awful basket ringing to be damped, suggests cone doping and making a hole in the dust cap. There are several projects listed, some with filter details.
Tim
I purchased a few of those as well. Looked good for cheapie projects for the kids computer and such.
Did you check out the projects page for this driver?PE Buyout
The stamped basket and tall gasket remind me of ultra-cheap automotive OEM replacement speakers I used years ago.
Anyway the page mentions awful basket ringing to be damped, suggests cone doping and making a hole in the dust cap. There are several projects listed, some with filter details.
Tim
The 49 cents clearance driver (not really a buy out) uses a paper vc former and a paper cone. It handles only 5 watts RMS and has a tight suspension with an over 100 Hz Fs. These are all bad things in driver performance. And last, you do not want to know how they perform acoustically.
The techniques suitable for controlling vibration modes in paper are not simple or easy. Adding glues to the cone does not work, whether as glue rings or glue coatings. You can get an idea of the difficulty modifying paper cones with my W4-654 modification (a thread on this Web site and on my own Web site).
In contrast, I am amazed by all the things people do to drivers that do not improve the performance. These include damping baskets, punching small holes in dust caps, and coating paper or metal cones.
Let us look at damping stamped metal baskets. While the baskets do ring when unmounted, mounting them to a wooden baffle will damp the basket more effectively than any hydrocarbon based tar or caulk substance applied to the surface of the basket. The wood of the baffle is a much better mechanical impedance match than any of the compounds people are using for coating the baskets. Even the special damping sheets designed for car panels and such are largely ineffective because of the small area of the metal baskets. Besides, people can do things like coating the basket on their own. They do not need my help for that. And unless they really mess up, while they do no good, damping the baskets (separate from properly mounting them) does no harm.
These seem to be ideas that are rationalized more by their simplicity and ease of application than increasing acoustic performance.
Unlike damping baskets and the copper "phase" plugs I am developing for the 656 and other drivers, coating paper and metal cones and punching small holes in dust caps cause harm while doing no good. They make a difference in the performance, it just that it is now worse.
As for the 871, yes, with difficulty it can be improved. While there are lots of people using and talking about the 871, I believe it has several troubling acoustic reproduction problems other than the 18 kHz cone vibration mode. If that is the driver you have to use instead of most other midrange and tweeter combinations, that is fine. It will outperform the vast majority of midrange/tweeter or woofer/tweeter combinations. Compared to those, it is a good choice for the next step toward greater transient coherence.
In contrast, with the modifications I have posted for free for the W3-881S I do not see any reason to modify the 871. The modified 881S outperforms the 871, is easy to modify, and it sounds better when all is done. With the 881 being inexpensive and readily available, there has to be a compelling reason to redesign a poorer performing metal or paper coned driver. So far, I have not seen that reason. Still, I am open to being convinced by some compelling reason.
Good designing and good building,
Mark
The techniques suitable for controlling vibration modes in paper are not simple or easy. Adding glues to the cone does not work, whether as glue rings or glue coatings. You can get an idea of the difficulty modifying paper cones with my W4-654 modification (a thread on this Web site and on my own Web site).
In contrast, I am amazed by all the things people do to drivers that do not improve the performance. These include damping baskets, punching small holes in dust caps, and coating paper or metal cones.
Let us look at damping stamped metal baskets. While the baskets do ring when unmounted, mounting them to a wooden baffle will damp the basket more effectively than any hydrocarbon based tar or caulk substance applied to the surface of the basket. The wood of the baffle is a much better mechanical impedance match than any of the compounds people are using for coating the baskets. Even the special damping sheets designed for car panels and such are largely ineffective because of the small area of the metal baskets. Besides, people can do things like coating the basket on their own. They do not need my help for that. And unless they really mess up, while they do no good, damping the baskets (separate from properly mounting them) does no harm.
These seem to be ideas that are rationalized more by their simplicity and ease of application than increasing acoustic performance.
Unlike damping baskets and the copper "phase" plugs I am developing for the 656 and other drivers, coating paper and metal cones and punching small holes in dust caps cause harm while doing no good. They make a difference in the performance, it just that it is now worse.
As for the 871, yes, with difficulty it can be improved. While there are lots of people using and talking about the 871, I believe it has several troubling acoustic reproduction problems other than the 18 kHz cone vibration mode. If that is the driver you have to use instead of most other midrange and tweeter combinations, that is fine. It will outperform the vast majority of midrange/tweeter or woofer/tweeter combinations. Compared to those, it is a good choice for the next step toward greater transient coherence.
In contrast, with the modifications I have posted for free for the W3-881S I do not see any reason to modify the 871. The modified 881S outperforms the 871, is easy to modify, and it sounds better when all is done. With the 881 being inexpensive and readily available, there has to be a compelling reason to redesign a poorer performing metal or paper coned driver. So far, I have not seen that reason. Still, I am open to being convinced by some compelling reason.
Good designing and good building,
Mark
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