ttrhp Posted October 23, 2006 Share Posted October 23, 2006 Klipsch Fans, I just found out that the passive woofer on my forte(both of them) doesnt have the dust cap in the center of the woofer.is it replaceable? if so,where can I purchase one?...the speakers seem sound fine to my ear.what is the purpose for this cap anyway?..thanks tom Quote Link to comment Share on other sites More sharing options...
Guest " " Posted October 23, 2006 Share Posted October 23, 2006 dust cap is normally to keep dirt and debris from getting trapped inbetween the voice coil and the motor magnet assembly. Since there is no voice coil on a passive radiator You should probally call klipsch and ask then if the passives on the forte are supposed to have them. Quote Link to comment Share on other sites More sharing options...
TheEAR Posted October 23, 2006 Share Posted October 23, 2006 Nice dustcaps BTW. On a serious note,passive woofers are called PR's passive radiators.They work by being motivated by the pressure created by the active woofer piston movement.With no dustcap,a PR is no longer working as it should be.Air(pressure)escaping by the center. Yes a dustcap's role is to prevent debris from gathering in the VC/pole piece.This debris in the worst case would cause friction leading to the VC failure(burning).Only applies to an active woofer. Quote Link to comment Share on other sites More sharing options...
SilverSport Posted October 23, 2006 Share Posted October 23, 2006 Since my Quartets have them, I am sure your Forte' should as well... Bill Quote Link to comment Share on other sites More sharing options...
Moderators dtel Posted October 24, 2006 Moderators Share Posted October 24, 2006 My Forte's and Forte ll's both have them. With no magnet there can you see into the cabinet or do they have a voice coil ? Just asking because they are made like a speaker not like a normal PR . Never seen the back side of one of these. Quote Link to comment Share on other sites More sharing options...
ttrhp Posted October 24, 2006 Author Share Posted October 24, 2006 dtel, it appear to me that the dustcaps on the forte's PR are for cosmetic purpose only.inside the caps,there is a round piece of metal about a size of a quarter in the center,and there are no connection between the caps and the center.thank you everyone for your help. tom Quote Link to comment Share on other sites More sharing options...
mas Posted October 24, 2006 Share Posted October 24, 2006 Aside serving to protect and seal, the dust cap is also often used as a heat sink. As the others have mentioned, assuming that it does not significantly change the mass of the PR cone assembly (and it should not), and the PR is still sealed (meaning no vent now appears in the PR) you should be fine. Quote Link to comment Share on other sites More sharing options...
djk Posted October 24, 2006 Share Posted October 24, 2006 "the dust cap is also often used as a heat sink." Only driver I know of built like that is the old Peavey Black Widow. The voice coil former/dust cap is like an aluminum beer can, one piece. Very few drivers are built this way. Now if you had said that a properly sealed dust cap is part of the heat pump in a driver like the VGC series JBL drivers, I might have bought it. Quote Link to comment Share on other sites More sharing options...
mas Posted October 26, 2006 Share Posted October 26, 2006 Talk to Dave Gunness. How's that for name dropping? [] (I mention this as he gave an excellent presentation regarding thermal limits in dynamic transducer design at the 2nd Loudspeaker Design Seminar in Atlanta in 1991...) In addition to the dust cap in a driver creating a small high-Q resonant cavity between itself and the polepiece of the magnet (an issue for the engineers to deal with), it also helps to dissapate heat. Magnet pole piece venting allows air trapped behind the dustcap to be forced past the coil and out the channel to convectively cool the coil. The ambiant temperature of the voice coil, the vented pole piece and surrounding region reaches a relatively uniform temperature, and while the vented pole piece assembly is used to 'pump air' providing moderate cooling into what quickly becomes a warmed internal volume of the cabinet, the aluminum dust cap also acts as an effective sink to the exterior region characterized by a much lower temperature and a greater thermal differential. The aluminum cap draws heat away from the assembly as the ambient heat is dissapated directly to the lower temperatures of the external environment via conduction. Thus it indeed acts as a sink for the thermal environment of the complete speaker motor assembly. Every little bit helps, as the thermal limits are the single biggest largest limiting factor in transducer performance and indeed in their survival. After all, the power ratings of dynamic transducers are indicative of when the transducer goes into a destructive mode due to thermal failure of the various components and component assemblies.. Also, models such as the Eminence Kilomax® Pro 18A 1250W woofer has an aluminum heatsink specifically designed to act as a sink to transfer heat from the motor structure and to provide periphery core ventilation. http://www.usspeaker.com/KilomaxPro-18-1.htm http://www.proaudioreview.com/may00/EminenceWeb.shtml The aluminum dust cap has been used as a fundamental part of the total system cooling mechanism, directly via conduction and indirectly by convection, acting as both a component of the pole piece vent convective 'pump' as well as a conductive interface sink dissapating heat directly - especially many JBL and Altec Lansing designs and becoming a standard feature in most latter designs by many other manufacturers. Quote Link to comment Share on other sites More sharing options...
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