Since this is the kind of thing I hope other people will attempt (good speakers don't deserve to be left by the curb), I figured I'd write up a bit about the process. The new surrounds came from Springfield Speaker Repair, and they seem to be of very high quality. The included glue is perfect for the job as well. I highly recommend them.
Before starting, please keep in mind that if you want the refoamed tweeters to look factory fresh, you are in for a very long and involved process. Even without removing all the glue that wound up in visible places, expect to spend at least a solid eight hours on refoaming them, with a couple of hours spaced out over a couple of days for the actual gluing process.
Since I'll be rebuilding the the crossovers as well as refoaming the tweeters, I completely stripped the speakers. This goes pretty much as you would expect, and isn't particularly difficult as Pioneer chose to use threaded inserts. Even if you are only planning on rebuilding the crossovers, you will be stuck removing all of the drivers to get yourself some working space inside the cabinet.
First, remove the screws around the rims of the drivers. Take note that there are two different lengths of screws holding the drivers in, one length for the woofer, a separate length for everything else.
 |
Now take a look at the tweeters. The foam surrounds are probably the most dry-rotted foam you have ever seen in your life. Take a moment to contemplate what was going on at Pioneer that caused them to use this rubbish foam for the tweeters, but to use wonderful cloth surrounds on the midrange drivers and the woofer (if anyone knows the real answer, please post it in the comments).
Assemble some equipment to remove the rotted surrounds. I used Q-tips, dental picks, and rubbing alcohol. You will also probably want some paper towels on hand. Depending on how well the surrounds separate from the cone, you may also want a fairly coarse emery board.
Pull the trim rings (the cardboard rings on the outside of the surround) off the surround (if they don't just fall off). Now, begin removing the surround by holding the driver such that foam remnants do not fall down into the voice coil, knocking off as much of the rotted foam as you can using whatever tool feels best to you.
Next, set the tweeter down, and wet a Q-tip with rubbing alcohol. Apply the alcohol liberally around the outside (non-cone side) of the remaining surround. Begin rubbing off the wetted foam with either a Q-tip or a paper towel (or both, I actually found cutting the cotton end off a Q-tip and using the shaft as a scraper works pretty well). You have a decision to make here. You will notice the paint of the frame starts to rub away during this process. I chose to ignore this and keep rubbing to make sure all remaining surround and glue are removed. I did this to get the best possible surface to glue the new surround to. If you aren't comfortable doing this much (invisible once refoamed) damage to your tweeters, stop before you get uncomfortable and suffer the consequences.
Now the hard, tedious part. Removing the leftover surround and glue from the cone itself. This is a relatively easy process on speakers where the surround is glued to the front of the cone, but an extremely time consuming process in this case, where the surround is glued to the back of the cone.
Wet another Q-tip with rubbing alcohol, and start saturating the cone. The wetter you get the cone, the easier it is to remove any leftover foam and glue. However, the wetter you get the cone, the easier it is to damage the cone (rips, creases, bends, etc.) in the process. Be generous, but be careful. You can always make the cone wetter. If the cone has gotten too fragile to work with, let it dry completely (~24 hours) before going back to work.
Once the cone is at the desired wetness, start scraping under the edge of the cone with your dental pick, being very careful to not damage the cone. Assuming the cone is wet enough, it should be pretty easy to hook the tip of your pick on some leftover foam and pick it off. Once most of the foam is gone, switch to a more scraping type of motion to remove the leftover glue (now is your chance unleash your inner dental hygienist). All the while, you should be holding the tweeter at such an (awkward) angle to prevent as much crap from falling down into the voice coil as possible.
You will have to do many laps of the tweeter to get most everything removed, rewetting the cone many times. Be very careful, work very deliberately, and very slowly. The cone is very fragile during this process, and tears can develop without you even noticing they've happened (see extra credit below). If there is some stubborn foam you just can't get off, let the cone dry completely (again, 24 hours), and then very carefully use the emery board to sand off the leftover foam and glue.
Once you are satisfied with the gluing surface on both the frame and the back of the cone, take a paper towel made slightly damp with rubbing alcohol, wipe everything down to get everything reasonably clean and free of foam dust.
You can also clean up the trim rings with a paper towel moistened with rubbing alcohol.
Before gluing, everything must be completely dry. I recommend waiting at least 24 hours for all the rubbing alcohol to evaporate before continuing.
I started by gluing the new surround to the cone. We are only gluing either the inside seam of the surround to the cone at this point, do not do both at once. By the fourth tweeter, I'm sure you'll have a process that works for you. There is no magic here. First, get the foam surround in position around the cone. Now get enough glue on both the foam, and the cone, by whatever method works best for you. I used another Q-tip with the end cutoff. Dip and roll the cut end in the glue, and then roll it between the foam and the cone. When you are convinced you have enough glue in place, press the cone down into the surround (or use some kind of thin tool to press the surround up into the cone, or both). The glue has a kind of contact cement type behavior, so once some pressure is applied, it becomes pretty permanent. You have roughly 10 minutes of working time (though the glue will start getting annoying stringy before that), which may seem short, but the tweeter isn't that big, so you should be fine.
At this point, you have another choice to make. If you absolutely must have that OEM, factory fresh, no extra visible glue anywhere, type look, it may be easiest to wipe up any extra glue now. I did not do it this way, since I wanted to make sure the bond between the foam and the cone was as strong as possible. But if you insist on the most professional result possible, you can use either a Q-tip or paper towel slightly dampened with rubbing alcohol to wipe up excess glue. The foam will deform slightly as it soaks up rubbing alcohol, but I promise you it'll retake its proper shape once the alcohol has dried.
Once you are done gluing (and possibly cleaning up extra glue), let everything dry for 24 hours. Now is a good time to watch the video the fine folks at Springfield Speaker Repair put together about centering a voice coil using a tone generator. It's the method I used, and I was very satisfied with the results (I have never used shims on a refoam before, I've always centered the coil by hand, this seemed even easier).
After the initial glue job has finished, it's time to glue the surround to the frame. We need to be careful that we do not misalign the cone and voice coil relative the frame during this step. Failure to do so will result in coil rub (and probably another refoam job). I connected my computer to a receiver, and the receiver to the tweeter using speaker wire terminated with clip leads. Once everything was connected, I turned the receiver down as low as possible, and turned on the online tone generator I found (sine wav, 50 Hz). I then slowly turned up volume on the receiver until I could just hear the tone coming out the tweeters, I then turned the receiver down a couple of clicks.
With the signal still being routed to the tweeters, I started applying glue to the frame and surround using essentially the same method as above. Roll Q-tip shaft in glue, roll shaft between frame and surround. Repeat until I feel there is an adequate amount of glue between the frame and the surround. Once there is enough glue, press the surround down into the frame with even pressure (I used the trim ring for this). If you are not cleaning up glue as you go, feel free to also glue the trim ring to the surround at this point. Otherwise, start cleaning up any leftover glue.
Double check for coil rub. Take your (clean) fingers, and press down on the cone, just outside the dust cap. Repeat a few times. If you feel (or hear) any rubbing, try to separate the surround from the frame, and repeat the above steps. If it's too late to separate the surround from the frame without tearing, congratulations, you get to do this whole process again! Don't screw up next time...
With the signal still connected to the tweeters, flip them over so they are resting on their trim rings. At this point, disconnect the signal, and let them dry for 24 hours.
Once the speakers are dry, you are free to remove as much leftover glue as you feel is necessary for whatever aesthetic you are going for. Rubbing alcohol will help loosen the glue somewhat (but will make everything, both surround and cone, more prone to damage). Use a mix of dental pick and Q-tip to remove as much glue as you feel necessary. This process can take a long time if you are being thorough. Be careful to not poke holes in the surround, or create tears in the surround or cone.
Check one last time for coil rub by pressing down toward the center of the cone (don't press directly on the dust cap, though the ones on these drivers are amazingly stout). If you don't feel or hear any, you did it! Congratulations! You're done, see you next time for the crossover recap...
Extra credit: I ripped the cone
You talentless hack! Your speakers are bad, and you should feel bad.
Seriously though, this is extremely easy to do, especially when the cone is saturated with rubbing alcohol. I ripped one while removing leftover surround from the back of the cone, and didn't even notice until I was checking my work. That is how easy this is to do, you screw up, and you don't even get the pleasure of realizing you screwed up until after the fact.
Luckily, patching a ripped cone isn't a huge deal, especially with the driver disassembled like this. Simply cut a patch out of some material you deem suitable (I used brown paper bag, 'cause I'm classy like that). Cut that patch as accurate to the shape of the cone as possible, while generously oversizing (without going outside the bounds of the cone). With patch in hand, glue it using white glue (or the glue provided in the refoam kit). I glued it to the top of the cone, thinking that the composite of foam->glue->cone->glue->patch would be the strongest possible fix, but if you are cosmetically inclined, you can try to slip the patch into place on the backside of the cone.
Do however, make sure you patch any tear, no matter how small. They can easily propagate once the speaker is in use,.
It was great of you to share your work with us. Thank You! I re-capped my CS-88a's about the same time you were re-foaming. I chose not to re-foam mine at the time, as it is only a cosmetic thing. It makes no sonic difference to the sound that Tweeter makes. The Re-cap though...BOOM! What a great difference that made! Now, years later, I am finally thinking it's time to tackle the re-foam...
ReplyDelete