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Just tried to refoam a set of Allison Five 8-inch woofers and came up non-working. I used the shim method, but noticed that there was very littly clearance for the shims, and that it seemed to not have equal clearance all the way around, but it's so minimal, it's hard to tell. I don't know if this is because the voice coil is deteriorated shapewise or if the speakers were just made that way. The first woofer came out rubbing badly, so I tried very diligently to get the second one dead center. It plays very nicely, but buzzes once the volume gets above medium at all.Is this a common problem with these speakers? I noticed that there's a pair of these on eBay now that says "needs a re-cone."
How special are these drivers? If I put a nice pair of vifa 92 db 8-inch woofers in there, will I be screwing things up obscenely? Who'd notice?
Follow Ups:
If the voice coil is not perfectly round, it may very well have overheated at some point and had its shape distorted. You'll have to pull the cone out to see. Is that area of the cone (wire wrapped) discolored or funny smelling? If so, you need a new cone.
If you have the woofers mounted in a box while hearing the buzz, try rotating them 180 degrees. If the buzz goes away, you have an offcenter voicecoil and the very small amount of sag in the spider will bring it back right into the gap, maybe. If the buzz stays, you have a sagging spider and there's no way to fix that except with a recone.Putting unfamiliar drivers into the box will be a coin toss.
More like throwing dice. Ken knows that any enclosure should be designed with the specific woofer in mind. And crossover circuts should be designed with all drivers in mind. IOW, exchange a tweeter & you would need to re-design the crossover circut, but exchange a woofer & not only the crossover, but the enclosure needs a re-design. Fewer than 100 copies of Vance Dickason's Loudspeaker Design Cookbook, 6th edition, are on sale for only $11 @ madisound.com because the 7th edition is now in print ($35) = an inexpensive education into the complexity of loudspeaker design.
I've had two different Boston Acoustic woofers that buzz despite several attempts and I've successfully refoamed mayebe 50 or 60 woofers. Sometimes the VC delaminates and I think sometimes the spider may be slightly off or sagging.As far as replacing the Allison woofers you need to try and match characteristics. IF it is acoustic suspension and there is no low pass filter(coil) to the woofer that is the hardest. I was able to use EPI woofers to fix one set of the aforementioned BA's because they were both AS in similar size boxes, about the same efficiency, and both had approximately the same natural roll-off frequency. If there is a low passs filter in becomes a little easier to use a replacement. Talk to the tech support at either Madisound or PE and they probably can help find the least of evil match.
If the shims fit that tight you cant really tell if the cone is being pulled sideways or not as you glue.I think the binder clip method could have worked better.
1. glue inner edge of surround to cone
2 let dry
3. Place paper binder clips temporarily around frame to clamp surround to frame, working from opposite sides.
4. keep checking the centering of the cone by pressing the cone center up and down as you add clips
5. Adjust clips and positioning of surround to frame as necessary if cone starts to bind. The cone needs to move through its full range of motion without any scaping resistance.
5a I think you could actually test play the driver with clips in place to see if there are any rattles or binding problems, and have the option of making adjustments to the foam position if there are problems.
6. Remove clips one at a time and glue underneath, always working from opposite sides, again checking for free cone travel as you go along.
Some drivers are just very difficult to foam. I am told that professionals only are successful in about 7 of 9 cases when refoaming the 4 inch Bose drivers.
You could always send them off to a place such as www.simplyspeakers.com for a professional refoam. It will cost about $60
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