Hello...
Wasn't sure where to post this, since it would seem to apply regardless...
But in my case it will be a 3-way system, and for a (non standard) WOOFER re-cone.
Hoping experienced/knowledgeable re-coner types will chime in!
So... Dust-Caps....
Solid, Vented, Mesh, Heavy/light, Large/small... Plastic (poly) Paper etc...
(and anything else I haven't thought of)
What are their "properties" in terms of what characteristics do they impart?
What other factors are to be considered in choosing which type??
TIA!
Greg
Wasn't sure where to post this, since it would seem to apply regardless...
But in my case it will be a 3-way system, and for a (non standard) WOOFER re-cone.
Hoping experienced/knowledgeable re-coner types will chime in!
So... Dust-Caps....
Solid, Vented, Mesh, Heavy/light, Large/small... Plastic (poly) Paper etc...
(and anything else I haven't thought of)
What are their "properties" in terms of what characteristics do they impart?
What other factors are to be considered in choosing which type??
TIA!
Greg
Good question! Since there is all sorts of different types there can not be a single type that is best, but for woofer use i would stay away from solid phase plugs and mesh since there can be leakage between voice coil gap and phase plug and also throu the dust cap mesh.
I also think that dust caps should not be too soft or too stiff, maybe something in between that can soak up some cone surface vibration can be of good use
I also think that dust caps should not be too soft or too stiff, maybe something in between that can soak up some cone surface vibration can be of good use
ACK! The notification of reply to this thread somehow went into the spam folder, so I didn't think there was one and kinda gave up on it.
Notifications from diyaudio have never gone to spam before! (at least not that I know of) I've gotten many of them over the years..
So, sorry I haven't posted since!
Celef... thanks for the thoughtful reply!
I've since done some research, and I'll post my findings below:
It seems that Dust-Caps can add to or subtract from the overall sound of a driver.
(beyond just providing protection for the voice-coil/gap)
Usually chosen for certain properties, often for the purpose of "voicing" that driver.
The higher frequencies are produced by the center of the cone (in the area of the voice coil).
The higher, the closer to center.
Hence, the composition of the dust cap mainly affects the highs..
The most "live" dustcap material is metal... or metalized..
Aluminum most commonly.
It can actually "amplify" the highs generated by the innermost portion of the cone..
It tends to extend the range... and so, is often used in guitar speakers..
Tends to get a bit "tizzy" sounding, and isn't every guitar player's choice... and almost never used in Hi-Fi applications.
Next is pressed paper...
It has the same effect, but to a *much much* lesser degree, and over a narrower (lower) range.
It also tends to add a bit of transient "slap"..
Poly/plastic:
Same, but much less still, since it's better damped.. though it tends to add a bit of "plastic coloration".. that some find more objectionable than others.
Also a bit heavier than paper... which may or may not be desirable.
(heavy = lower Fs but slower to accelerate/decelerate)
Treated cloth/fabric:
(or untreated)
The most neutral of all..
Adds very little of it's own.. if anything.
It also doesn't radiate much sound..
"It's just there"... protecting..
Often these are also porous, in varying degrees... Helpful in cases where there is no vented pole-piece or VC former... usually the case in vintage drivers..
(some vintage paper caps have a screened hole in the center for venting.. like Altec for example)
Felt:
Very well damped..
Speaker engineers even consider it a "coloration"... A subtractive rather than additive one.
It's used to tame very ringy cones... mostly back in the old days, where the norm was very little excursion and tight suspension.
Size matters:
Beyond just covering the coil aperture, and leaving aside aesthetics...
Particular sizes are often chosen to attach to the cone at a particular point.. where there is an undesirable resonant peak, and the like.
The dust cap is, or can be.. a radiating surface.
One that contributes to the sound (and/or amplitude).... particularly in the highs and/or transient behavior, and can be used to good effect.
Conversely, one that doesn't... or even subtracts (something undesirable) from the overall sound, can also be used to good effect.
Convex is usually used, so that a woofer can go up higher into the range..
Concave can be used without a problem, provided there's no clearence issues and enough air space (or venting) behind it.
Concave only makes sense in the case of a sub-woofer or true woofer, where it's not desirable to radiate sound in higher ranges.
In the case of a cone midrange driver, a shallow domed-cap is added to the voice coil (rather than the cone) to enhance the highs without the drawbacks of a phase plug.
This is not intended to be a definitive treatise on the subject.... but rather to share what information I've been able to determine..
I "reserve the right" to add to or amend this as needed...
Notifications from diyaudio have never gone to spam before! (at least not that I know of) I've gotten many of them over the years..
So, sorry I haven't posted since!
Celef... thanks for the thoughtful reply!
I've since done some research, and I'll post my findings below:
It seems that Dust-Caps can add to or subtract from the overall sound of a driver.
(beyond just providing protection for the voice-coil/gap)
Usually chosen for certain properties, often for the purpose of "voicing" that driver.
The higher frequencies are produced by the center of the cone (in the area of the voice coil).
The higher, the closer to center.
Hence, the composition of the dust cap mainly affects the highs..
The most "live" dustcap material is metal... or metalized..
Aluminum most commonly.
It can actually "amplify" the highs generated by the innermost portion of the cone..
It tends to extend the range... and so, is often used in guitar speakers..
Tends to get a bit "tizzy" sounding, and isn't every guitar player's choice... and almost never used in Hi-Fi applications.
Next is pressed paper...
It has the same effect, but to a *much much* lesser degree, and over a narrower (lower) range.
It also tends to add a bit of transient "slap"..
Poly/plastic:
Same, but much less still, since it's better damped.. though it tends to add a bit of "plastic coloration".. that some find more objectionable than others.
Also a bit heavier than paper... which may or may not be desirable.
(heavy = lower Fs but slower to accelerate/decelerate)
Treated cloth/fabric:
(or untreated)
The most neutral of all..
Adds very little of it's own.. if anything.
It also doesn't radiate much sound..
"It's just there"... protecting..
Often these are also porous, in varying degrees... Helpful in cases where there is no vented pole-piece or VC former... usually the case in vintage drivers..
(some vintage paper caps have a screened hole in the center for venting.. like Altec for example)
Felt:
Very well damped..
Speaker engineers even consider it a "coloration"... A subtractive rather than additive one.
It's used to tame very ringy cones... mostly back in the old days, where the norm was very little excursion and tight suspension.
Size matters:
Beyond just covering the coil aperture, and leaving aside aesthetics...
Particular sizes are often chosen to attach to the cone at a particular point.. where there is an undesirable resonant peak, and the like.
The dust cap is, or can be.. a radiating surface.
One that contributes to the sound (and/or amplitude).... particularly in the highs and/or transient behavior, and can be used to good effect.
Conversely, one that doesn't... or even subtracts (something undesirable) from the overall sound, can also be used to good effect.
Convex is usually used, so that a woofer can go up higher into the range..
Concave can be used without a problem, provided there's no clearence issues and enough air space (or venting) behind it.
Concave only makes sense in the case of a sub-woofer or true woofer, where it's not desirable to radiate sound in higher ranges.
In the case of a cone midrange driver, a shallow domed-cap is added to the voice coil (rather than the cone) to enhance the highs without the drawbacks of a phase plug.
This is not intended to be a definitive treatise on the subject.... but rather to share what information I've been able to determine..
I "reserve the right"
to add to or amend this as needed...
But lowered output, slight possibility of noise through the voice coil gap, as with mesh caps; an absorbent plug on top of the pole piece out of something that won't degrade like reticulated foam or (maybe) melamine foam should minimize the noise that is generated behind an opaque dust cap. I don't dismiss phase plugs but they don't contribute much at the lowest frequencies. Mid/wide range different story.
What Max H says. I like to add an epoxy/vermiculite ring right at the vc-cone juntion as a gusset without adding too much mass.
What Max H says. I like to add an epoxy/vermiculite ring right at the vc-cone juntion as a gusset without adding too much mass.
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Seas and Dayton audio are among most familiar brands that don't use dust caps in their top series woofers. If there's to be any noise from air leakage in the voice coil gap, it'll be when woofer is driven quite hard but by then, that noise will be much quieter than the sound coming out of woofer. When volume level is lower, then it will not make a sound - so it equalizes itself in quite a good manner.
If there is a fear of cone deformation in that area then that wasn't well engineered loudspeaker in the first place. Dust cap role should be as the name says it - protection from dust. When you try to tailor frequency response with it then there's something wrong.
If there is a fear of cone deformation in that area then that wasn't well engineered loudspeaker in the first place. Dust cap role should be as the name says it - protection from dust. When you try to tailor frequency response with it then there's something wrong.
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Hi, not wanting to disagree, but, depending on what the "music" content is, the air leakage from around a phase plug, where there is an air gap back into the enclosure, can be audible, especially when the said speaker is in a vented enclosure, it behaves like another vent and because of its small size it "chuffs", the only manufacturer that i know of that has fixed that problem is Kef, where they have a small internal rubber surround inside the gap, http://au.kef.com/explore-kef/kef-innovation/sst and also max h is correct in what he says.
Of course you can disagree.
Have you ever heard effect that you are talking about and in what woofers ? Just to be clear, i wrote woofers not midwoofers.
The effect is more pronounced in closed cabinets not vented because pressure you are talking about will be released through bass reflex and there wouldn't be enough of it to make chuffing effect passing the voice coil.
I am listening my Seas L15 two way and Kef R300 and none of them exibits any effect you are talking about. Seas L15 two way i drive quite hard because of their low sensitivity and there is nothing remotely similar to chuffing effect you mention. R300 doesn't have that Kefs solution implemented. None of new series does as far as i know and i've dismantled q100 and r300 concentrics. Maybe Kef Egg does, i wouldn't know about that. So naturally i'm interested what loudspeakers do make a sound through gap between voice coil and magnet pole piece that you've listened ?
Your link says this, which is in line with my experience:
"For normal sized enclosures the internal acoustic pressure is not sufficient to cause any turbulence - it only noticeable when the enclosure is very small and the required maximum output level is high."
I never said Max was wrong. I said that if that is the case, it's a lousy woofer to begin with.
Have you ever heard effect that you are talking about and in what woofers ? Just to be clear, i wrote woofers not midwoofers.
The effect is more pronounced in closed cabinets not vented because pressure you are talking about will be released through bass reflex and there wouldn't be enough of it to make chuffing effect passing the voice coil.
I am listening my Seas L15 two way and Kef R300 and none of them exibits any effect you are talking about. Seas L15 two way i drive quite hard because of their low sensitivity and there is nothing remotely similar to chuffing effect you mention. R300 doesn't have that Kefs solution implemented. None of new series does as far as i know and i've dismantled q100 and r300 concentrics. Maybe Kef Egg does, i wouldn't know about that. So naturally i'm interested what loudspeakers do make a sound through gap between voice coil and magnet pole piece that you've listened ?
Your link says this, which is in line with my experience:
"For normal sized enclosures the internal acoustic pressure is not sufficient to cause any turbulence - it only noticeable when the enclosure is very small and the required maximum output level is high."
I never said Max was wrong. I said that if that is the case, it's a lousy woofer to begin with.
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one that comes to mind is the Dayton RS100, in a small vented box the air from the gap chufffs, it doesnt (as much) in a sealed box (air leakage in vented boxes are more audible than in sealed boxes, try it), a recent released Dayton coax driver had to be pulled off the market due to voice coil gap "noises" so it could be rectified, admittedly these small drivers are not classified as woofers but that depends on application,
i suggest you run a sine wave through your speakers and have a listen (or measure) to the air coming out of the gap
PS i have observed/heard the effect on many speakers that have the "gap" on the speakers that i have worked on in the past (you sometimes see an impedance "blip" corresponding to the gap resonance on built loudspeakers specification graphs)
cheers, Arthur.
i suggest you run a sine wave through your speakers and have a listen (or measure) to the air coming out of the gap
PS i have observed/heard the effect on many speakers that have the "gap" on the speakers that i have worked on in the past (you sometimes see an impedance "blip" corresponding to the gap resonance on built loudspeakers specification graphs)
cheers, Arthur.
Bass reflex enclosures have high internal pressure at the tuning frequency and low pressure above and below the impedance peaks.
Those of us with limited budgets sometimes resort to attempts at remedying the faults of our crap speakers. I would love to buy the good stuff but the medical/house maintenance/etc costs use up the scant mad money. Waahhh...
Those of us with limited budgets sometimes resort to attempts at remedying the faults of our crap speakers. I would love to buy the good stuff but the medical/house maintenance/etc costs use up the scant mad money. Waahhh...
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As for me...
And what's best for me....
Probably an audio 12-step program...
Alternatively.. a lobotomy, many would say.......
Ask the old lady... a frying pan to the head would do..
Meanwhile.... I'm reading all the replies, cogitating, and taking it all in.
So, for an OB application and a 15" woofer which will operate only below 100hz and probably mainly below 75-80hz....
This woofer does NOT have a vented pole piece nor VC former....
Still trying to reason out what type dustcap.
Some have also suggested it should be part of the "radiating area".. but since it's a 15, maybe the cone is enough? High sensitivity (for low power) is important too though...
Of the selection of caps I have on hand.... 2 of the same material jump out at me...
One about the size of the VC and another much larger, just under 6" in diameter...
It's some fabric.... semi porous.... very light, and very little resonant... less than any other I've on hand.
Have plastic (poly I guess) hard paper, the above mentioned... and another in some plasticized fabric (that doesn't breathe)...
All but the last in large and small versions.
I'm thinking that the fabric/semi porous one would be a good choice..
In OB box caused pressure isn't an issue...
Pressure, both positive and negative as a result of excursion IS...
With no venting, I'm thinking a semi porous cap is the best choice..
Breathes, but in a controlled manner, might add some damping of the movement/venting..
Seems like a good idea in an OB where excursion happens a LOT...
Grateful for any further thoughts/suggestions!
Greg
And what's best for me....
Probably an audio 12-step program...
Alternatively.. a lobotomy, many would say.......
Ask the old lady... a frying pan to the head would do..
Meanwhile.... I'm reading all the replies, cogitating, and taking it all in.
So, for an OB application and a 15" woofer which will operate only below 100hz and probably mainly below 75-80hz....
This woofer does NOT have a vented pole piece nor VC former....
Still trying to reason out what type dustcap.
Some have also suggested it should be part of the "radiating area".. but since it's a 15, maybe the cone is enough? High sensitivity (for low power) is important too though...
Of the selection of caps I have on hand.... 2 of the same material jump out at me...
One about the size of the VC and another much larger, just under 6" in diameter...
It's some fabric.... semi porous.... very light, and very little resonant... less than any other I've on hand.
Have plastic (poly I guess) hard paper, the above mentioned... and another in some plasticized fabric (that doesn't breathe)...
All but the last in large and small versions.
I'm thinking that the fabric/semi porous one would be a good choice..
In OB box caused pressure isn't an issue...
Pressure, both positive and negative as a result of excursion IS...
With no venting, I'm thinking a semi porous cap is the best choice..
Breathes, but in a controlled manner, might add some damping of the movement/venting..
Seems like a good idea in an OB where excursion happens a LOT...
Grateful for any further thoughts/suggestions!
Greg
Hi Wikkid, the porous dustcap on the 15" OB woofers shouldn't be a problem, i have just finished modding/rebuilding some old 18" goodmans 18P bass guitar speakers (with no magnet pole piece vents) for OB use, and i used some old tannoy porous HPD dustcaps on them, because solid dustcaps make too much noise for OB use, re the kef R300, there wont be any chuffing noise because the mid driver with the air gap isn't doing any woofing (it is a mid driver) and as to the the seas L15 driver, i dont have any experience with that model and its loading, but a few years ago i had to repair the crossovers on a pair of Australian made boutique speakers with an MTM arrangement of seas drivers, and i did my regular sine wave test after repair and I noticed a bit of a noise (good speakers get a more of a work out when i test them) and i noticed some chuffing, so i did a bit more testing, and yes they chuffed at a certain frequency and power input level, you couldn't hear the noise with most music, but "hyperballad" by Bjork at high level shows it up, cheers, Arthur
) and i noticed some chuffing, so i did a bit more testing, and yes they chuffed at a certain frequency and power input level, you couldn't hear the noise with most music, but "hyperballad" by Bjork at high level shows it up, cheers, Arthur
yes, ears, and volume control, and in my workshop, the only reason i mentioned the audio observation I have encountered is because i have encountered it, nothing more, just the way it is, i haven't needed to use my measuring gear because it wasn't necessary as part of the repair, it was purely an observation during testing (it is sort of interesting to see some of the good name drivers have issues that you might not expect them to have)
air leakage around the voice coil gap can/will also cause problems when the driver is used in bandpass enclosures, which is one of the reasons kef use the external "doughnut " surround on the outside of the cone (where they use the force cancelling rod which is attached to the pole piece) to keep air leakage losses to a minimum.
cheers, Arthur.
air leakage around the voice coil gap can/will also cause problems when the driver is used in bandpass enclosures, which is one of the reasons kef use the external "doughnut " surround on the outside of the cone (where they use the force cancelling rod which is attached to the pole piece) to keep air leakage losses to a minimum.
cheers, Arthur.