the ^*BeholdeR*^ Posted January 25, 2005 Share Posted January 25, 2005 few questions!! 1. what's the function of a dust cap in a speaker? does it have any effect on the speaker performance? 2. over time, i have seen many dust caps 'crumpling'....they get flattened out! does it mean the speaker's damaged?? 3. why are the latest speakers fitted with 'inverted' dust caps? are they better?? plz help me know this! thnx!! Quote Link to comment Share on other sites More sharing options...
johnyholiday Posted January 25, 2005 Share Posted January 25, 2005 keeps the dust out, an vents the voice coil for cooling, an dust cap that is solid is vented, on the back like a k-33 woofer Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted January 25, 2005 Share Posted January 25, 2005 Think about it? The clue is in the name! Get it! Dust-Cap! It prevents dust and junk from getting into the voice coil and voice coil gap. Some are solid and others are permeable to aid in cooling the coil under when being run hard. If it gets pushed it if will not affect performance unless it is pushed in so hard that it touches the internal magnet pole piece. 1 Quote Link to comment Share on other sites More sharing options...
johnyholiday Posted January 25, 2005 Share Posted January 25, 2005 if its poked-in get a striaght pen, or a dental pik, or sewing needle ,or the jaws of life, an pull it back out Quote Link to comment Share on other sites More sharing options...
ironwoods Posted January 25, 2005 Share Posted January 25, 2005 ---------------- On 1/25/2005 9:06:59 AM Frzninvt wrote: Think about it? The clue is in the name! Get it! Dust-Cap! It prevents dust and junk from getting into the voice coil and voice coil gap.---------------- OK smart guy, what does a Foghat do? Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted January 25, 2005 Share Posted January 25, 2005 Play loud rock n roll music! Preferably live. Quote Link to comment Share on other sites More sharing options...
analogman Posted January 25, 2005 Share Posted January 25, 2005 ---------------- On 1/25/2005 9:06:59 AM Frzninvt wrote: Think about it? The clue is in the name! Get it! Dust-Cap! It prevents dust and junk from getting into the voice coil and voice coil gap. Some are solid and others are permeable to aid in cooling the coil under when being run hard. If it gets pushed it if will not affect performance unless it is pushed in so hard that it touches the internal magnet pole piece. ---------------- only partially true and unsound advice from the above post as well as others... The design of the center cap on MOST modern drivers is an essential part of the engineer's intent, primarily with regard to dispersion but also frequency response. eBay sellers and others that tell you that the driver with the pushed in cap "still works and sounds perfectly" are ignorant or just plain dishonest. If you would like to try and restore a damaged cap to it's original shape, I suggest using a funnel and a household vacuum FIRST, before punching holes in it. A hand held vacuum pump is also a good choice as it is easier to control, or if nothing else, your lungs. Be patient and use common sense. MEK can also be used to facilitate the cap's removal, allowing you to reshape or replace it but requires a bit more skill and effort. Punching a hole in the cap should be a last resort only if you are unwilling to attempt the other alternatives. If so, you'd probably be better off leaving it as it is. My comments have even more meaning if the driver(s) in question are rare or valuable. Respectfully, Analogman Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 25, 2005 Share Posted January 25, 2005 Some blathering on dust caps... Dust caps exist because of the way the speaker is manufactured, that is, being a cone shape suspended on a frame with a centrally located voice coil behind it. It has been stated that the best shape of a driver would be circular and flat, rather than an inverted conical shape, but again, the manufacturing requirement is the most-used reason behind the shape. Due to the differing shape of the cone, different portions of the cone move forward or backwards at different times mostly due to the consideration of cone mass, for instance the outermost edge of the cone is the first element to move followed by the rest of the cone as it is more distant from the whole. The direction of the movement is modified by the particular location of the "testing" point on the cone, so the differing shapes of the dust cap have an effect on the frequency response. Disregarding the "wrinkling" or non-planar behavior that occurs when moving a large diameter relatively high-mass cone from the "point" or center portion nearest the voice coil, it can be imagined that the cone itself does not flex for the purposes of this discussion as that is a subject for other discussions. As the cone needs to effect a seal against the baffle to be most effective in moving the maximum volume of air, the dust cap provides that service. Some dust caps are indeed vented to provide an air flow over the voice coil assembly, particularily large high-wattage PA drivers. The center portion of the cone (typically formed by the dust cap) is also where the higher frequencies are produced as a matter of physics. This point is where some manufacturers employ a "whizzer" cone to act as a smaller cone surface to enhance the production of higher frequencies than the larger cone is cabable of. The shape of the dust cap, whether inverted or not, only effects the particular higher frequencies that the driver in question is capable of producing. Rounded semi-circular dust caps are used for this reason. For instance, a passive driver, or a subwoofer driver would not be concerned (for the most part) with trying to reproduce any higher frequencies, so it may or may not be manufactured with an inverted dust cap. As far as a particular driver having a dented dust cap, it is not particularily noticable if the driver is intended to be limited to low frequency work. The distortions of the waveform are already present in virtually all cone drivers due to the shape of the cone anyway, and a dent will have relatively little effect on the overall performance of the driver. However, I am specifically talking about woofers, where the concerns for higher frequency response is not a major consideration. In the case of a domed tweeter, the considerations would find a dent unacceptable, of course. DM Quote Link to comment Share on other sites More sharing options...
michael hurd Posted January 25, 2005 Share Posted January 25, 2005 A dustcap can also be used to increase the high frequency response of a driver, if it is aluminum and connected to the voice coil former. A phase plug is attatched rather to the central pole piece than the cone, if the design utilises it. On most of the eminence drivers, the dustcap is a felted paper material that will allow small amounts of air through it to increase the amount of cooling. On the Kilomax series of prosound woofers, they utilize an aluminum heat sink to help cool the driver under extreme wattages. I would not use MEK on a poly woofer. If they have a painted coating, it will soften, or come off. Quote Link to comment Share on other sites More sharing options...
WMcD Posted January 25, 2005 Share Posted January 25, 2005 I believe the "clown nose" type are partially to seal off the voice coil former and partially structural. The diaphragm is conical and this gives it much more stiffness than any flat piece of cardboard would have. In center it is attached to the "former" which is a tube extending behind the diaphragm. The voice coil is wound on the former and sits in a ring shaped gap in the magnet structure. So without the dust cap, there would be hole open to the back of the driver structure. We want an airtight situation and the dust cover provides that. This is one good reason why a hole in a dust cap creates an air leak and is not a good idea. It is not a good idea to pull it out with a needle unless you seal up the needle hole. The voice coil and magnet form the motor which drives the conical diaphragm by imposing a back and forth force to the center of the diaphragm. The diaphragm has the least area here in the center, just because of the geometry. So I'd think that the domed dust cap adds appreciable strenght where it is needed. I note that the flat dust covers are used on diaphragms which are coated with metal by some process. It may be that these are stronger and thus do not need the dome. Prof Leach has pointed out that a bigger dust cap gives the impression that it is covering up a former of larger diameter, even if the former is small. I have a pair of drivers with the wizzer cone. I can't say it doesn't work to extend high frequency response, but it seems more an act of desperation. Light on effect but appealing to buyers in those old days. It is better to find a midrange to take over. Jaws of Life. I liked that! Best, Gil Quote Link to comment Share on other sites More sharing options...
analogman Posted January 25, 2005 Share Posted January 25, 2005 ? What I said Analogman Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 26, 2005 Share Posted January 26, 2005 In many full range designs the D cap is designed to contribute to the high frequency response after main diaphragm breakup occurs. A multipurpose thing then.. Quote Link to comment Share on other sites More sharing options...
analogman Posted January 26, 2005 Share Posted January 26, 2005 ---------------- On 1/26/2005 7:31:49 AM KT66 wrote: In many full range designs the D cap is designed to contribute to the high frequency response after main diaphragm breakup occurs. A multipurpose thing then.. ---------------- ...as well as on "woofer" designs such as those from B&W. Thank you for an insightful post KT66 Analogman Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 27, 2005 Share Posted January 27, 2005 analogman I like subbtle humour.. a wooffer isn't exactly a full range driver - in this case the function of a dust cap is pretty clear. Quote Link to comment Share on other sites More sharing options...
johnyholiday Posted January 31, 2005 Share Posted January 31, 2005 he just pulled out his dust cap on his passive on these autographed forte's i feel used. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=5745871024&ssPageName=STRK:MEWA:IT Quote Link to comment Share on other sites More sharing options...
the ^*BeholdeR*^ Posted January 31, 2005 Author Share Posted January 31, 2005 thnx guys!!! all of u.....for all the info! the last question...why do all the latest speakers hav inverted dust caps? they sure look good...but do they make good sound??? wutsay?! Quote Link to comment Share on other sites More sharing options...
boom3 Posted February 1, 2005 Share Posted February 1, 2005 ---------------- On 1/31/2005 11:16:57 AM the ^*BeholdeR*^ wrote: thnx guys!!! all of u.....for all the info! the last question...why do all the latest speakers hav inverted dust caps? they sure look good...but do they make good sound??? wutsay?! ---------------- I have two theories: First, some believe that an inverted dust cap dome is more rigid than a non-inverted, or "proud" dome. In years past, some tweeters have been made this way. There are a number of variables that make such a blanket assumption risky. Moreover, an inverted dome will strike the pole piece sooner than a "proud" dome, and decreases the amount of air trapped between the dome and the magnet, affecting Xmax and high-frequency resonances. Secondly, every speaker manufacturer wants to make his product distinctive, so, surround color, cone color, non-functional doo-dads of all types are added to make a product stand out. Inverting the dustcap is pretty much a no-cost means of making a speaker look 'different'. In sum, I would give the inversion, or non-inversion, of a dust cap ZERO weight in considering the merits of any driver. Quote Link to comment Share on other sites More sharing options...
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