The importance of the dust cap depends on how high in frequency you intend to use the driver. At very high frequencies, the dustcap is the major source of sound radiation, but at low frequencies its shape, etc, is irrelavent. Its importance varies in between. In a full range driver its shape, mounting, construction are all important above the rim resonance, but in a woofer thats not used past the rim resonance its not important at all.
If you want to pick it apart the big differences lie in the angle of contact, the length of contact, and the distance of the initial contact relative to the VC. In the case of a conventionally applied cap the contact angle is closer to perpendicular and so it is quite strong to resist radial modes appearing there, and high frequency displacement occurs in a more piston fashion for the entirety of the dome. (at whatever response the cone has at that radius) In the inverted case the best high frequency coupling to the cap occurs at the initial contact point with the cone relative to the VC as you move away from it and beyond that the response of the cap surface is affected more by the response of the cone, since it is in direct contact with it. In the inverted case for the same materials the HF radiation may begin deeper into the cone at higher frequencies, giving that the chance to affect the sound however it may.
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Fostex has perhaps one of the larger selections of full range drivers. Looking at the assortment of drivers shown at the Madisound link below, I see some DC's that look almost flat (top two drivers), and some that are quite spherically bulbus (FE E series). These look like they had some thought put into the shape with regard to high freq. performance. Foxtex calls it their 'new design center cap', but say nothing more about it. However, others don't look like that (those at the bottom of the page).
Fostex Full Range Speakers from Madisound
Otoh, one can think of the "dustcap" area as a % of the total radiating area.
I'd listen to what Dr. Geddes says on this topic, fwiw.
There's no obsession, skeptic43, but your post seems to dismiss the topic entirely WRT actual performance of a speaker.
I'd suggest that you might take some inexpensive surplus driver, find some blown drivers, lop off different size and material dustcaps, install some freeware FFT computer based measurement software, make a simple test baffle (look up IEC baffles), make a $1 electret test mic and have at it - install different dustcaps and measure! Try some different "treatments" too...
Don't forget to listen as well... you'll soon see how important or unimportant it is or isn't. Academic discussions of this sort of thing are not terribly illuminating.
_-_-bear
EDIT: read what Gedlee said again then reference that to "Fostex Full Range"?
I'd listen to what Dr. Geddes says on this topic, fwiw.
There's no obsession, skeptic43, but your post seems to dismiss the topic entirely WRT actual performance of a speaker.
I'd suggest that you might take some inexpensive surplus driver, find some blown drivers, lop off different size and material dustcaps, install some freeware FFT computer based measurement software, make a simple test baffle (look up IEC baffles), make a $1 electret test mic and have at it - install different dustcaps and measure! Try some different "treatments" too...
Don't forget to listen as well... you'll soon see how important or unimportant it is or isn't. Academic discussions of this sort of thing are not terribly illuminating.
_-_-bear
EDIT: read what Gedlee said again then reference that to "Fostex Full Range"?
Then we can have the discussion on when a dustcap is a separare entity and when it is a part of the cone too...
I would say that what you are talking about is the dustcap as a part of the cone (In your example i would say that a secondary wizzard also is a part of the cone and its designated work) and not treat it as a separate element within the speaker that does a different kind of work, like the magnet or the voicecoil.
I have most of the equipment you suggest I acquire. However, I'm the doubter of those who say the DC's make a significant difference. It's up to them to prove it as I requested of one poster earlier. Let them run the test you suggest and prove it to all of us.
BTW, not dismissing their effect entirely. Just assuming (I know, my bad) the % contribution is very low. Just look at the broad range of DC's on Fostex's full range line of speakers Dr. Geddes says where high frequencies and DC design become an important consideration. Fostex engineers are the experts in driver design. Not me or Dr. Geddes.
Having been to Foster and worked with their engineers, they are better than the norm (certainly better than the Chinese), but hardly the best that I have run across. And I don't think that you are in any position to comment on my expertise at driver design.
MEOW! lol
the drivers i'm using have a AL cone and a 'soft' plastic dust-cap, and it really is VERY soft. I have no doubt it affects FR to a degree. Although whether it is good or bad, i guess the designer of the drivers, only, would know. I'm sure these caps are experimented with during design, and not simply just plonked on.
Personally i think i would prefer a cone with integral dust-cap, a la the MARK audio drivers, as it would seem to me that a cone without a hole at the centre would be more rigid for the weight, and i guess, logically, it would follow that it would then operate in a more piston like manner, and HF roll off earlier as a result. UNLESS the VC design and cone weight are tailored to a wider band reproduction goal. In this way i DO believe that MOST dust-caps, less so on paper drivers, are experimented with to tame the FR of the driver, or provide useful HF extension, as the dome helps dispersion and reducing 'beaming' to my knowledge.
the drivers i'm using have a AL cone and a 'soft' plastic dust-cap, and it really is VERY soft. I have no doubt it affects FR to a degree. Although whether it is good or bad, i guess the designer of the drivers, only, would know. I'm sure these caps are experimented with during design, and not simply just plonked on.
Personally i think i would prefer a cone with integral dust-cap, a la the MARK audio drivers, as it would seem to me that a cone without a hole at the centre would be more rigid for the weight, and i guess, logically, it would follow that it would then operate in a more piston like manner, and HF roll off earlier as a result. UNLESS the VC design and cone weight are tailored to a wider band reproduction goal. In this way i DO believe that MOST dust-caps, less so on paper drivers, are experimented with to tame the FR of the driver, or provide useful HF extension, as the dome helps dispersion and reducing 'beaming' to my knowledge.
If you look at the Fostex full range drivers you will see that whatever the dust cap looks like it is attached to the voice coil, and in the case of drivers larger than five inches nominal it is a whizzer decoupled by a portion of the center spider as in the Voight patent drivers.
If you go back to the 70's there was a speaker system called Advent that featured a woofer with a heavy fibre dome attached to the cone.
The idea of this was to give a clearly defined low pass response to the driver allowing a simpler crossover system.
rcw.
If you go back to the 70's there was a speaker system called Advent that featured a woofer with a heavy fibre dome attached to the cone.
The idea of this was to give a clearly defined low pass response to the driver allowing a simpler crossover system.
rcw.
Get a cheap vintage fullrange driver and experiment with it. You will see that every single change in the centre of the cone - adding or removing a cap, adding a piece of cotton and etc., will result in different high-midrange/treble reproduction. And the change is big enough to consider it.
I do not care much about how the Fr will change for as long as I like the sound. The Veravox 5s has a lot of dips and peaks in its freq. response and yet it sounds pretty good and not fatiguing for a ferrite driver ( especially if you remove the aluminum dust cap
). This is why I prefer to listen first and then to look at measurements, not the opposite.
skeptic, why do I or anyone else need to "prove" anything to you?
...read the literature, get an advanced degree in EE/acoustics, work in the industry and then you too can be an expert?
Otoh, just do what has been suggested (do some tests on ur own) and draw your own conclusions?
Of course you give the impression that you think the Bose Waveradio is just fine as they claim to be "equal" to large systems in all regards, and this is about right?
So, can we sum up your position as being that dustcaps make so little sonic difference that they can be disregarded and if present chosen entirely for cosmetic/aesthetic reasons?
_-_-bear
_-_-bear
...read the literature, get an advanced degree in EE/acoustics, work in the industry and then you too can be an expert?
Otoh, just do what has been suggested (do some tests on ur own) and draw your own conclusions?
Of course you give the impression that you think the Bose Waveradio is just fine as they claim to be "equal" to large systems in all regards, and this is about right?
So, can we sum up your position as being that dustcaps make so little sonic difference that they can be disregarded and if present chosen entirely for cosmetic/aesthetic reasons?
_-_-bear
_-_-bear
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