Members moody Posted November 8, 2006 Members Share Posted November 8, 2006 Refering back to this thread: http://acapella.harmony-central.com/forums/showthread.php?s=&threadid=1405800 I have been playing around with this speaker more, it has continued to stick between each period of use, and it has considerably more of a scratching with movement than I first realised. I didn't have much option with it as I couldn't sell it in this condition, didn't trust it to use and don't think it is worthwhile reconing. Having mentally rendered it in every way useless I decided to use it as a learning exercise. I took it out of the cabinet and had a look. The rear hole that goes from the voice coil to the rear of the magnet was full of some sort of foam material - presumably to keep dust out - however it was old enough that the foam was rotting and falling apart - hence little bits falling into the voice coil gap. I cleared out all the foam I could and then used a light vacume on the back of the hole to get any loose bits out. I then cut out the dust cap from the front. voice coil seemed fine but little bits of foam were stuck to it and melted on to it. I went to the supermarket, got some turps and cotten tips and started cleaning. I also coated the Hole that had been full of foam with a layer of PVA glue so that no more little bits of foam would fall into the voice coil. Now my problem - it seems to be fixed?? Voice coils as clean as i can get it to the furthest extremes that I can move it - it moves easily, doesn't stick and seems to work fine when running music through it. Is it fixed?? or have I missed something that could cause problems? What do I do now. Where do I get a replacement dust cap and how do I attatch it? What do I stick in the hole down the back to stop dust getting in? (some of my other speakers just have a metal grill there). Thanks as always. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 8, 2006 Members Share Posted November 8, 2006 Try cleaning the inside of the gap (between the center pole piece and the inside of the bobbin) with a piece of paper soaked in a solvent. I use lacquer thinner as that won't damage any modern bobbin material like Kapton. (paper is a different story because of the adhesives) Run the paper strips all around to dissolve and pickl up remaining bits of gunk down in the gap. Any speaker repair shop can sell you a dust cap, it takes a bit of effort to put it on and have it look good depending on the style (flanged or cut) but maybe the shop will put it on for you for not much money? Link to comment Share on other sites More sharing options...
Members where02190 Posted November 8, 2006 Members Share Posted November 8, 2006 If you sealed the rear port, the speaker will probably opverheat at high volume and burn the coil out, thus rendering the speaker useless. I recommend removing whatever you filled the hole with and replace the foam that was desintigrating with new foam. AFA the dustcap, use the old one if the cut is clean and close to the cone and use a flexable rubber cement to hold it in place. It has very little affect on tonality, it's function is to keep dust out of the gap. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 8, 2006 Members Share Posted November 8, 2006 Keeping the back vent open with either foam or screen is important because of it's effect on TS tuning parameters. The dust cap does have significant effect on tone and as importantly, the dome has a structural effect on keeping the cone neck concentric on speakers with lighter weight cones. The structural enhancement on a light weight cone is in part because it reduces physical distortions in the paper which reduces breakup and additional unintentional harmonics. Link to comment Share on other sites More sharing options...
Members where02190 Posted November 8, 2006 Members Share Posted November 8, 2006 Originally posted by agedhorse Keeping the back vent open with either foam or screen is important because of it's effect on TS tuning parameters. True, as well as heat ventilation, it's primary purpose. Originally posted by agedhorse The dust cap does have significant effect on tone and as importantly, the dome has a structural effect on keeping the cone neck concentric on speakers with lighter weight cones. The cone is connected to the coil, which keeps it concentric, the dust cap is completely unnecessary for the function of the speaker, it only provides a cover for the gap to keep abrasive things like dust and dirt out. Originally posted by agedhorse The structural enhancement on a light weight cone is in part because it reduces physical distortions in the paper which reduces breakup and additional unintentional harmonics. More mass makes a more rigid cone, thus decreasing physical distortion. Greater mass, more force to distort. That's why materials such as kevlar and aluminum are being used for speakers today over paper more and more. Link to comment Share on other sites More sharing options...
Members moody Posted November 8, 2006 Author Members Share Posted November 8, 2006 Lots of information !! Thanks all - and of course that leaves me with another heap of questions. Originally posted by agedhorse Try cleaning the inside of the gap (between the center pole piece and the inside of the bobbin) with a piece of paper soaked in a solvent. I use lacquer thinner as that won't damage any modern bobbin material like Kapton. (paper is a different story because of the adhesives) Run the paper strips all around to dissolve and pickl up remaining bits of gunk down in the gap. Ok, didn't think of that. The bobbin itself is clean (and appears to be aluminium - crome material whatever it is). Is mineral turpentine (which I've been using) a valid alternative or should i be looking for thinner. Originally posted by agedhorse Any speaker repair shop can sell you a dust cap, it takes a bit of effort to put it on and have it look good depending on the style (flanged or cut) but maybe the shop will put it on for you for not much money? I'll look for a 'local' repair shop - I think I know where one is but I'm not sure i'm not sure if I can be there during opening hours. Depending on what the cost is I'll try to get them to put it on. Originally posted by where02190 If you sealed the rear port, the speaker will probably opverheat at high volume and burn the coil out, thus rendering the speaker useless. I recommend removing whatever you filled the hole with and replace the foam that was desintigrating with new foam. I do realise that the hole has to pass air, I'm after what material I should put in it (something that won't disintigrate like the current foam). Would a layer of some sort of material (wool or cotton?) be a usable alternative. Originally posted by where02190 AFA the dustcap, use the old one if the cut is clean and close to the cone and use a flexable rubber cement to hold it in place. It has very little affect on tonality, it's function is to keep dust out of the gap. The dustcap unfortunately isn't as clean a cut as I would like - though I could glue it back into place as it is. I was thinking of finding a 'slightly' oversized one so as to go over the remaining rim of the old one and still look neat. Link to comment Share on other sites More sharing options...
Members moody Posted November 8, 2006 Author Members Share Posted November 8, 2006 Originally posted by agedhorse Keeping the back vent open with either foam or screen is important because of it's effect on TS tuning parameters.The dust cap does have significant effect on tone and as importantly, the dome has a structural effect on keeping the cone neck concentric on speakers with lighter weight cones.The structural enhancement on a light weight cone is in part because it reduces physical distortions in the paper which reduces breakup and additional unintentional harmonics. I think I can safely say that it isn't a light weight cone. The cardboard is quite thick and it's not a small speaker in general (one of the larger magnets of the 15" speakers I own). That was probably a big help in being repairable. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 8, 2006 Members Share Posted November 8, 2006 Originally posted by where02190 True, as well as heat ventilation, it's primary purpose.Cooling is only one purpose but it's mostly to reduce air pressure that builds up under high excursion conditions and affects the linearity by changing the TS parameters. The other way to address this is by using a compressed felt or linen dust cap which is also done. Think about a high powered co-axial driver that has no central vent. The cone is connected to the coil, which keeps it concentric, the dust cap is completely unnecessary for the function of the speaker, it only provides a cover for the gap to keep abrasive things like dust and dirt out.The dust cap reduces the mechanical deformation by providing a concentric structural ring support to the cone. This very definately affects the sound of the speaker, especially when operated in extended range mode. More mass makes a more rigid cone, thus decreasing physical distortion. Greater mass, more force to distort. That's why materials such as kevlar and aluminum are being used for speakers today over paper more and more. More mas MAY make a more rigid cone but it may not as well, depending on the designer's needs. You will not see Kevlar or Aluminum in guitar speakers, and softer and smaller dustcaps for example because the deformation of the cone's added harmonics, while being undesireable for most PA applications, may be highly desireable for a guitar amp manufacturer. Link to comment Share on other sites More sharing options...
Members moody Posted November 9, 2006 Author Members Share Posted November 9, 2006 ok, I finished cleaning out the voice coil gap as best I could - thickish paper soaked in spirits around the edges. I then hooked up the speaker to an amp and ran music through it quite loudly with a lot of bass (ran through a graphic eq) - it seems to work very well and the bass came through great (for not being in a cabinet). A couple of times when it was at its very loudest I got a very loud pop and I've no idea what could have caused it - it didn't stop the music playing. I Went to a speaker shop just to price a dust cap and got completely lost. How do I tell my current dust cap material and whether it's doped or not etc. I'm completely lost. When I cut out the old dust cap I left the edges attatched to the cone - (the lip). Do I have to cut these away before I put a new dust cap on or can i put a slightly larger dust cap over the top? What glue do I use? I still don't know what sort of material I should put in the back of the speaker - foam or some kind? A grill of some kind? When it's put back together, the two speakers are going in a couple of cabinets on ebay - but I think that I'll have a reasonably clear conscience that there isn't anything wrong with them. Link to comment Share on other sites More sharing options...
Members where02190 Posted November 9, 2006 Members Share Posted November 9, 2006 Originally posted by agedhorse You will not see Kevlar or Aluminum in guitar speakers, Guess you never heard of Hartke, eh? Good soft foam will last for years, and will allow air to freely pass while filtering out dust and debris. I Went to a speaker shop just to price a dust cap and got completely lost. How do I tell my current dust cap material and whether it's doped or not etc. I'm completely lost. Don't worry about the material, bring the old cone and get one of the same size. As previously stated, it has very little affect on the tone of the speaker, and the speaker will function perfectly without it, but the speaker will fail prematurely because of debris in the coil and gap. When I cut out the old dust cap I left the edges attatched to the cone - (the lip). Do I have to cut these away before I put a new dust cap on or can i put a slightly larger dust cap over the top? No, unless you left an extrordinary amount of the old cap there, it'll be fine. What glue do I use? Any semiflexable rubber cement will do fine. You want something that does NOT dry to a rigid form, but something that has some give to it, otherwise it will evetually either break loose and vibrate or rip the cone. Link to comment Share on other sites More sharing options...
Members NMR Posted November 9, 2006 Members Share Posted November 9, 2006 Originally posted by where02190 Guess you never heard of Hartke, eh? i thought they only used aluminium for their bass cabs? Thus they are designed to produce lower frequencies. Thus the extra mass helps? i may be wrong but i haven't seen a guitar cab from hartke with aluminium drivers. NMR Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 9, 2006 Members Share Posted November 9, 2006 AFAIK, Hartke's aluminum cone speakers are only available in their bass products and the reason (IMO since I'm not a Hartke guy) is because their coloration is part of their design goals. Aluminum is NOT a very viable choice for guitar speakers for exactly the reasons I stated before, and nobody that I know of makes aluminum coned guitar speakers for commercially viable products. Aluminum cones do not break up very nicely for guitar. Bring the old speaker and piece of the dust cap in and the shop will be able to match it easily. Yes, there is a VERY big difference in the material and it's affect on tone depending on the application. For some applications, such as unvented pole pieces with large Xmax operation, a breathable dust cap such as compressed felt or linen is mandatory otherwise the backpressure behind the dust cap can tear the dust cap to cone bond. There have been a few manufacturer recalls because of this. I use a rubberized latex glue for this purpose generally, but it does NOT need to be flexible if that's what the manufacturer's design parameters were. If it did, both Peavy and JBL would be screwing the pooch right now as both use an epoxy material for this bond. (Where... look at one first before arguing this point). Link to comment Share on other sites More sharing options...
Members where02190 Posted November 9, 2006 Members Share Posted November 9, 2006 Hartke makes both guitar and bass enclosures, and you can get either with aluminum cones. Aluminum cone speakers have a much higher frequency response than paper. Rigid glue on the dust cap will prematurely tear away from the cone, causing a rattle in the speaker (the cap against the speaker) or tearing the cone. The former is easily fixed, the latter would require a reconing. Link to comment Share on other sites More sharing options...
Members moody Posted November 9, 2006 Author Members Share Posted November 9, 2006 Thanks people!! Good seeing two different philosophies of dustcapology. I'll try to take in in over the weekend. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 9, 2006 Members Share Posted November 9, 2006 Originally posted by where02190 Hartke makes both guitar and bass enclosures, and you can get either with aluminum cones. All of their current speaker products appear to be Celestion loaded, paper cone. I do not know of any aluminum cone guitar speakers used in their products. They have also added paper cones to some of their bass products. Aluminum cone speakers have a much higher frequency response than paper. Not always true. Generally aluminum cones have a very ragged but somewhat extended frequency response with heavy coloration, contributing to the Hartke sound. There are some VERY popluar drivers used for bass guitar that have paper cones and VERY extended but still smooth frequency response. The first one that comes to mind is the JBL D-130 and 120, a 15" and 12" driver that extends to over 6kHz, then there's the K-110 that extends to 8k. The 2135 is a great example of what can be done with a lightweight paper cone, which was designed with a -10dB down point of 12kHZ!!! Rigid glue on the dust cap will prematurely tear away from the cone, causing a rattle in the speaker (the cap against the speaker) or tearing the cone. The former is easily fixed, the latter would require a reconing. Then you better give JBL a call to inform them thatthey have been doing it wrong all these years. Link to comment Share on other sites More sharing options...
Members where02190 Posted November 10, 2006 Members Share Posted November 10, 2006 The rigidity of denser material such as aluminum allows for faster transient response, resulting in better accuracy of reproduction and higher frequency response over slower materials such as paper. That's why compresion drivers aren't made of paper. Stick a pencil into the surround glue on your JBL's and see how it flexes into the glue. It's not a solid, it is flexable. Hartke will gladly load their cabs with anything you want, including their own speakers, which are aluminum cones. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 11, 2006 Members Share Posted November 11, 2006 The dustcap clue that he is talking about is very hard epoxy. The surround is a completely different discussion that we haven't had yet. Ever looked into a piezo driver??? the diaphram material is very lightweight paper:eek: Hartke makes both aluminum and paper. Their GUITAR cabinets come loaded with paper cones. For the right amount of money, I'm sure they will load the cabinet with bull{censored} too:rolleyes: Link to comment Share on other sites More sharing options...
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