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QUESTION: JBL Speaker Rattle
EADGBE wrote: I recently found a very clean pair of JBL L19 speakers. These speakers look new. Before buying them, I examined the speaker surrounds thoroughly. All of them appear to be in perfect condition. I took them home and hooked them up. They sound very good, but I am hearing a slight rattle coming from one of the woofers. The rattle is not very loud at all, and in fact is almost inaudible most of the time. But you can definitely hear it if you are listening to certain things like a bass-heavy radio announcer's voice or a soft piano solo. The woofers on the JBL L19's have a bowl-shaped piece of paper glued to the center of the cone. I have verified that the glue is solid all the way around; I have even run a very fine bead of glue left over from a speaker surround kit all the way around the bowl, but the rattle persists. I can make the rattle go away if I gently put my finger on certain places in the center of the woofer cone. I can make the rattle worse if I put my finger on the surround, near the top of the speaker. One more thing: I can hear a slight rubbing noise if I gently push the woofer's cone back and forth on the top half of the speaker. I do NOT hear this rubbing noise if I push the cone anywhere on the bottom half, and I do NOT hear the rubbing noise if I push both the top and bottom halves at the same time (in other words, if I push the cone in a "balanced" way). I have verified that NOTHING is touching the back of the speaker; no wires, no insulation or anything else. I am suspecting that maybe the spider is out of round or off-center, or maybe the voice coil is off-center. What can I do to further diagnose, and then fix, this annoying problem? More than likely, the speaker was overdriven and the voice coil hit the pole piece and warped the coil. Recone or replacement is the only solution then. There is a chance that the spider has come unglued. CHeck under the cone in the basket area to confirm the spider is firmly connected to the cone and the speaker basket. I have not seen this in a JBL, but i have seen it before (not very often though) Speakers of the 10/15 year old vintage often suffer from dry rot of the cone surround. Check closely for any MICRO fracture of where the surround connects to the basket or the cone itself. THis is the first stage of self destruction. bob |
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