Why do some woofers have a fully concave inner surface, ala the Peerless Nomex woofers that I have:
While others have a convex inner surface, a "bubble" in the center, ala the Scan Speak Revelator midwoofer?
An externally hosted image should be here but it was not working when we last tested it.
While others have a convex inner surface, a "bubble" in the center, ala the Scan Speak Revelator midwoofer?
An externally hosted image should be here but it was not working when we last tested it.
Member
Joined 2003
Technical term...dustcap.
Sometimes it is only cosmetic, sometimes it helps with some frequency response, off-axis response, power compression...really depends on the driver, engineers likely try a driver with both and see what measures best.
IMO, I think most dustcaps are not optimal. They are attached to the cone, when their best location would be to attach directly to the voice coil, such as many Fostex drivers, MarkAudio, and Eminence beta8 are done.
I suppose the size of the dust cap will also affect the driver performance, speaker design is made of compromises, what you see is usually a combination of what the marketing department thinks looks pretty, and what the engineering department thinks performs well.
Maybe I am just talking out of my A...who knows.
Sometimes it is only cosmetic, sometimes it helps with some frequency response, off-axis response, power compression...really depends on the driver, engineers likely try a driver with both and see what measures best.
IMO, I think most dustcaps are not optimal. They are attached to the cone, when their best location would be to attach directly to the voice coil, such as many Fostex drivers, MarkAudio, and Eminence beta8 are done.
I suppose the size of the dust cap will also affect the driver performance, speaker design is made of compromises, what you see is usually a combination of what the marketing department thinks looks pretty, and what the engineering department thinks performs well.
Maybe I am just talking out of my A...who knows.
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A quick re-read of the "Cook-Book" tells me that the HF is radiated from the centre of the driver and that the dust cover can have a definite effect on the quality of the higher frequencies.
Vifa used to use a soft dust cover on small woofers and mid-bass drivers and a rough textured coating on their dedicated mid-ranges, M-11 comes to mind
Vifa used to use a soft dust cover on small woofers and mid-bass drivers and a rough textured coating on their dedicated mid-ranges, M-11 comes to mind
So dust caps are cosmetic and tend to be an engineering compromise? It would seem that the Scan Speak would not use one, if that were the case, since it performs so well in tests. Also, if you're gonna plop something into the center of the driver, wouldn't a phase plug be a much better aesthetic solution, which also has better engineering payoff too?
The inverted dustcap thing is pretty rarely an improvement for wideband drivers. In that case I think it's usually done more for the "Ooo neato!" effect rather than better response. Inverted can reinforce the cone over a wider gluing interface, maybe why it's seen a lot on higher power woofers.
Phase plug forfeits the cone reinforcement and the coil cooling pump effect of the dustcap, again not a real good tradeoff for very high output.
Phase plug forfeits the cone reinforcement and the coil cooling pump effect of the dustcap, again not a real good tradeoff for very high output.
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Speakers of this genre are often purchased based on looks, so looking different is a selling point.
TAD drivers are the best looking speakers that I have ever seen, but they perform the same as all the rest. They just look a lot better. The looks net an additional $2000 per driver in some cases. Worth doing I suppose.
Member
Joined 2003
Earl, looks are a more important factor in this "genre" when compared to high sensitivity pro-audio drivers, but not the sole reason to purchase, that's for sure.
Tyson, I think you misunderstood me. The dust cap itself is not an engineering compromise nor purely cosmetic, but the entire speaker is a combination of compromises. The choice of the dust cap is one of which to balance the compromises to create a good performing loudspeaker. Because speakers are made by companies, part of the design choice is undoubtedly a combination of cosmetic appearance as well as acoustic performance.
Phase plugs are along the same lines, however a phase plug attached directly to the pole piece will affect the motor, so part of the choice to use or not to use a phase plug may come from the motor design, among other things.
Peerless exclusive speakers have a phase plug, but they did not completely remove the dust cap, just put a hole in it. There are a couple possible reasons for this:
-removing the dust cap affected frequency response in an unwanted manner
-cosmetic consistency between models of the same product line
-added mass necessary to obtain desired T/S parameters
Who knows, the voice coil former comes up to the dust cap on these speakers, if the dust cap were not there, the voice coil former could be made shorter, reducing weight further. Maybe something to do with the moving mass, or power handling...Lots of possibilities for the choices made that resulted in the final product.
Tyson, I think you misunderstood me. The dust cap itself is not an engineering compromise nor purely cosmetic, but the entire speaker is a combination of compromises. The choice of the dust cap is one of which to balance the compromises to create a good performing loudspeaker. Because speakers are made by companies, part of the design choice is undoubtedly a combination of cosmetic appearance as well as acoustic performance.
Phase plugs are along the same lines, however a phase plug attached directly to the pole piece will affect the motor, so part of the choice to use or not to use a phase plug may come from the motor design, among other things.
Peerless exclusive speakers have a phase plug, but they did not completely remove the dust cap, just put a hole in it. There are a couple possible reasons for this:
-removing the dust cap affected frequency response in an unwanted manner
-cosmetic consistency between models of the same product line
-added mass necessary to obtain desired T/S parameters
Who knows, the voice coil former comes up to the dust cap on these speakers, if the dust cap were not there, the voice coil former could be made shorter, reducing weight further. Maybe something to do with the moving mass, or power handling...Lots of possibilities for the choices made that resulted in the final product.
I think some of the larger-than-VC dust caps have some degree of structure enhancement to the cones. Such a cap tends to be solid materials and shaped flatter. On where it joint the cone (somewhere between VC and surround) makes another support to fight against the distortion of the cone shape. I guess the overall stiffness contributed by this would probably larger than thickening the cone itself.
This should be another effective factor to 'tune' the breakup behavior.
Ref: Eminence Lab12, 18sound 6ND430 ....
This should be another effective factor to 'tune' the breakup behavior.
Ref: Eminence Lab12, 18sound 6ND430 ....
The inverted dust cap may limit high frequency responce. The reason I say that is I rember looking at the frequency responce of a 7" Dynaudio driver with an inverted dust cap ( realy the cone and dust cap were one piece) and a Focal tweeter with
an inverted dome. The Dynaudio was fine to about 2.8k then started a verry steep
roaloff the Focal tweeter was fine to about 18k then also started a verry steep roaloff. In both cases the roaloff looked steeper than 24db/oct.
an inverted dome. The Dynaudio was fine to about 2.8k then started a verry steep
roaloff the Focal tweeter was fine to about 18k then also started a verry steep roaloff. In both cases the roaloff looked steeper than 24db/oct.
The dustcap has two mainfunctions. To prevent dust to reach the voicecoilgap (DUH!) and to help the coil to stay round when the electric forces wants to bend it.
But i cant see any reason why the shape of the dustcap has any sonical difference below a couple of KHz (where the heightdifference of the cap is equal or bigger than a wavelength) and i cant imagine that this difference would be so large either.
JBL 2123 a 10inch midrange driver, also has reversed dustcap.
But i cant see any reason why the shape of the dustcap has any sonical difference below a couple of KHz (where the heightdifference of the cap is equal or bigger than a wavelength) and i cant imagine that this difference would be so large either.
JBL 2123 a 10inch midrange driver, also has reversed dustcap.
Hi,
Well I've been watching this thread from the beginning but didn't comment for various reasons !
Anyways although you folks have talked bout the dust caps in a generic manner not much has been said bout it in actual tech wise.
Yes the basic duty of the dust cap is to avoid dust but its not merely for that alone !
When we see various dust caps in use we only think of it as mentioned earlier !
But here are some other facts of it !
1) A dust cap type can depend on the type of the cone for more then one reason
A) Type of cone,as in the material of the cone ( many types of cones are made of certain polymers where sticking the dust cap is not easy and special glues are to used which in itself will add certain quality to the sound and also to weight of the cone)
B) Again different types of cones have different "Cone Break-Ups" to reduce the effects of it one may choose a particular type of Dust cap,say a big dimple one as opposed to a small and almost flat one for particular cone depending its Break-Up region/point !
C) As said above the cone material has certain weight (called Mass) which relates to sound quality,so when a driver is developed with a heaver cone then to reduce the further weight a small light weight cap is used (also the glue used although little will as said above adds its weight ) so when the cone itself is weighed in milligrams or grams each drop of glue and each gram of dustcap adds to the overall mass !
2) Dust caps as mentioned by Electroaudio depends on the driver as the he said bout dustcap being equal or more of the wave length being reproduced by the driver, So if its woofer its of different type as opposed to a Midbass, Am famous example is that of B&W where in all their woofers you see that the dust caps are almost as big as the cone itself !!
3) Material choice of the dustcaps sometimes depend on the Voice Coil and motor design,if a VC is made of normal material instead of high temperature one,in those designs to keep it cool one may use a cloth or fabric dust cap to allow the Air circulation but block the dust from entering !
4) Size of the dust cap again as said above depends on the type of driver !
5) there are 1000 more such tiny little details which dictates the type of dustcap,which will take a toll on this forum server if I or we start to point one by one !! but one last point I'll add is, as said in the beginning of the thread its always preferable to have the dust cap attached directly to the VC as to reduce or make its mass not add to the cone (although relatively less but as said every milligram counts) ! also by attaching it directly to the cone,the interaction or the resonance in the cavity of the cone (from the beginning of the cone to the dustcap covered area) is greatly reduced !! Also the possible fixing issues (due to glues and other such factors mentioned above) of dustcap with the cone is thus eliminated !
I hope with above I've been able to illustrate some basic needs for type specific dustcap usage !
Hope the OP and others find this info useful !
Regards.
Well I've been watching this thread from the beginning but didn't comment for various reasons !
Anyways although you folks have talked bout the dust caps in a generic manner not much has been said bout it in actual tech wise.
Yes the basic duty of the dust cap is to avoid dust but its not merely for that alone !
When we see various dust caps in use we only think of it as mentioned earlier !
But here are some other facts of it !
1) A dust cap type can depend on the type of the cone for more then one reason
A) Type of cone,as in the material of the cone ( many types of cones are made of certain polymers where sticking the dust cap is not easy and special glues are to used which in itself will add certain quality to the sound and also to weight of the cone)
B) Again different types of cones have different "Cone Break-Ups" to reduce the effects of it one may choose a particular type of Dust cap,say a big dimple one as opposed to a small and almost flat one for particular cone depending its Break-Up region/point !
C) As said above the cone material has certain weight (called Mass) which relates to sound quality,so when a driver is developed with a heaver cone then to reduce the further weight a small light weight cap is used (also the glue used although little will as said above adds its weight ) so when the cone itself is weighed in milligrams or grams each drop of glue and each gram of dustcap adds to the overall mass !
2) Dust caps as mentioned by Electroaudio depends on the driver as the he said bout dustcap being equal or more of the wave length being reproduced by the driver, So if its woofer its of different type as opposed to a Midbass, Am famous example is that of B&W where in all their woofers you see that the dust caps are almost as big as the cone itself !!
3) Material choice of the dustcaps sometimes depend on the Voice Coil and motor design,if a VC is made of normal material instead of high temperature one,in those designs to keep it cool one may use a cloth or fabric dust cap to allow the Air circulation but block the dust from entering !
4) Size of the dust cap again as said above depends on the type of driver !
5) there are 1000 more such tiny little details which dictates the type of dustcap,which will take a toll on this forum server if I or we start to point one by one !! but one last point I'll add is, as said in the beginning of the thread its always preferable to have the dust cap attached directly to the VC as to reduce or make its mass not add to the cone (although relatively less but as said every milligram counts) ! also by attaching it directly to the cone,the interaction or the resonance in the cavity of the cone (from the beginning of the cone to the dustcap covered area) is greatly reduced !! Also the possible fixing issues (due to glues and other such factors mentioned above) of dustcap with the cone is thus eliminated !
I hope with above I've been able to illustrate some basic needs for type specific dustcap usage !
Hope the OP and others find this info useful !
Regards.
Concave cone profiles generally keep HF extension on-axis to a minimum, and if done correctly can align on-axis to the off-axis responses. For wide directivity designs in the Home/small room applications,This can make crossover design simpler and is very useful mating drivers like these to a wide dispersion dome tweeter esp getting away with lower order electrical/ low parts count ( uses the natural HF rolloff). Some dynaudio 170 mm cone profiles are a great example.
IMO The final goal for seamless hi-fi sound is to blend dispersion characteristics between divers within the range of the crossover< fullstop
Now if using CD horns for the top end, the cone profile would need be of a different shape. ie having greater HF extension to use "beaming" to mate to a narrower directivity designs. Pole pieces and domed centers allow this. Whizzers are another technique giving even more HF extension but the directivity is less controlled. The frequency point to cross should be selected where the off-axis response of the cone driver matches the Horn.
IMO The final goal for seamless hi-fi sound is to blend dispersion characteristics between divers within the range of the crossover< fullstop
Now if using CD horns for the top end, the cone profile would need be of a different shape. ie having greater HF extension to use "beaming" to mate to a narrower directivity designs. Pole pieces and domed centers allow this. Whizzers are another technique giving even more HF extension but the directivity is less controlled. The frequency point to cross should be selected where the off-axis response of the cone driver matches the Horn.
Dust cap has a BIG reflection on sound. I have not played with the 15W you have shown, but when listening to the 18W the dust cap affects any freq. over 800Hz even if much shorter than the wavelenght. A better solution is a one piece cone - the dust cap to be a part of the cone, not stuck on it or to stick it to the vc, not to the cone. Dome cap has an effect on the higher freq. spectrum and also on the off-axis response but suffers from glue weight and undercap compression.
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Again, how much of an effect? 1%, 5%....
Audiophiles have been living peacefully with domed dust caps for 1/2 a century. It may be a nice topic for discussion here or a Phd thesis, but IMO, don't think it's significant in the big picture of home loudspeaker performance.
I don't know. You tell me. It's you who said a dome dust cap has an effect on high freq. Help me understand your claim with some quantitative supporting information that makes some sense in the overall scheme of things.
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