What, me worry?
How to refoam speakers.
I received a couple of inquiries after posting about this to another thread, so I thought I'd post it here, along with additional details.
For those who don't know, refoaming is replacing the foam "ring" around woofers, that sometimes deteriorate over time and occassionally get damaged by mechanical action (kids, screwdrivers, etc).
Refoaming isn't hard, although it is possible (though not nec. required!) to screw up one or two drivers (mostly temporarily) while learning.
The thing that goes wrong with refoam jobs is coil rub. It would be hard to describe this if you aren't familiar with it, I suggest you actually tear an old, worthless woofer apart to see it. There is a hollow coil of fine wire under your dustcap that fits into a "groove" in your speakers' magnet. When the electrical current is given by your amplifier, it turns it into an electromagnet, which causes your woofer cone to move, creating sound. If your woofer is not aligned properly, this voicecoil will rub against the side of the "groove", causing a "grating" sound, which not only sounds bad but could very well cause serious damage. If you have a woofer that needs refoamed handy, move the cone up and down gently and feel for this to happen. THAT is coil rub.
This should not discourage you from attempting a refoam, I'm just trying to describe the potential problem so your chances are greater for a successful refoam the first time.
There are basically two methods. The easiest, most foolproof, and of course most expensive way is to go to this company:
They will sell you a kit (about $30.00), based on the dimensions you give them on a form (available at their site), which includes shims that fit into the "groove", virtually guarenteeing a proper alignment. This method requires that you cut the old dustcap, and replace it when you're done. They include the dustcap, rings, shims and glue and offer a video walking you through the process.
The only difference between the method outlined below and the newfoam method is cutting the dustcap and using the shims. You will not have to do the alignment steps using shims.
If you're more adventurous, the method below is not only much cheaper (10" rings are $1.50/ea at MAT Electronics, and to me seem exactly like the newfoam ones), but also do not require you to cut the dustcap. MAT Electronics has a $25 minimum order, so for roughly the same price as one pair from newfoam you get a bunch of rings, or other stuff they have.
1) Clean off the old foam. You might have to use a knife or scaper to remove the gasket first. Place the gasket off to the side, you'll need it later. On the cone, you can usually rub it off with your fingers. On the basket you can use a small scraper and even solvent, it's metal. Don't worry about perfection, just make sure the loose stuff is off. [Note: The better you clean the old foam off, the closer to original the finished product will look. It won't effect the sound. I personally aim for the finished product to look at least 85%. If you destroy the gasket during removal they have generic gaskets at MAT.]
[If you are using shims cut the dustcap off now and install the shims.]
2) Check the new rings for fit, then glue the new ring to the cone. I use Elmers glue. I apply a bead of glue to the cone, place the ring on, then remove it and let the glue "set up" for 15-20 minutes. It is generally better to use too much glue than not enough - it dries clear. After waiting for the set up (the glue will get tacky to the touch), place the ring back on and center it. Let this dry till the glue is clear, at least 2 hours. While it's drying keep an eye on it, make sure it's stuck down firmly.
[Note: I personally will lift the unglued basket side of the ring after the cone side has dried and apply another bead of glue there (the edge of the cone and the ring underneath the roll). I do not believe this is absolutely neccessary, that's just me ]
3) After the glue on the cone is COMPLETELY DRY (totally clear), apply glue to the basket side. This is important, and usually the thing that gets messed up: push the cone down gently, moving it up and down. Make sure it doesn't "rub". Then, again, wait for the glue to dry. It will take longer than the cone side 'cause you can't let the glue set up. Keep an eye on it. Every time you touch it MAKE SURE there's no rub!!
[If you are using shims skip everything related to "rub" or centering the cone, the shims keep it centered.]
There is another way to center the cone. If you have a test tone disc handy (I have Strykes' basszone, but there are many, and there are tones downloadable off the web here: http://www.snapbug.ws/sinewaves/ ), hook the woofer up to an old receiver and give it a LOW LEVEL 10hz tone (SIN010 at snapbug) after gluing the basket side. [Note: 10hz will screw up your woofer very easily if overdriven. Start at zero on the volume, go up slowly, use common sense!!] The woofer should move up and down a little. Feel and listen for rub. I actually move the woofer each way till it rubs, then attempt to center it. After centering it, turn off the test tone. MAKE SURE it's centered before letting it dry. Since you can't let the glue set up when doing the basket side, I usually go back after 15-20 minutes or so and check the alignment again, as well as making sure it's still glued down securely. If you have to press the foam down during the drying process CHECK FOR ALIGNMENT AGAIN. Every time you touch the woofer, check the alignment!!
After the glue dries clear, poof!! You've got a refoamed speaker. Hook it up and see if it rubs! [Note: if you're using the shim method remove the shims before trying the speaker.]
If it does: you'll have to refoam again . Sometimes it's not an option, but it's worth trying. After over 15 pairs I haven't had a problem yet. Once I refoamed a 10" woofer out of a pair of Boston Acoustics' A-100 that had a slight rub when finished - arrgh! I tried "spinning" it 180 degrees and remounted it - it worked (and still works) great!!
If it doesn't: Congratulations, you're an experienced refoamer ! Glue the gasket back on, let it dry!! Be careful not to glue the gasket to the actual roll of the surround. At this stage I also add an additional small bead of glue where the ring meets the cone. [Note: If you're using shims you glue the new dustcap on here.]
Start playing! As you play it it will sound better, there is a break in period for new foam. I run the speakers with the 10 hz test tone at a level high enough to move the cone, again being VERY CAREFUL not to overdrive them, for ten hours using an old receiver before popping them back in the cabinet.
That's it, it's that easy ! And even if it gets screwed up, the consolation is: it didn't work before, either.
I am posting a thread in the Speaker room for comments & suggestions regarding this post. Please, if I'm missing something, or you have something to add, post it there or PM me, and I'll edit this post!!
uncooked pointed out that there are some unusual drivers out there, that he probably has to glue to the basket first. He also says the gap in his driver is very small, that rubbing is much more likely. If in doubt come to your own conclusions. If a standard ring doesn't fit your application Newfoam may have a better fit, and with the small gap shimming may be the best bet. Trimming the ring may be in order, as well.
pelly3s adds this:
ok i do this for a living, first step is if you have all the stuff you need then you attacted to the cone first and then center it on the basket. a good tip so you don't have to cut off the dust over and shim it is to apply a small amount of DC voltage such as 9 volts or so to the speaker to raise the cone or lower it making centering much easier and just listen to it and if it sound like something is buzzing really loud its not centered. alway go to the cone first though, and make sure not to use too much glue when glueing to the basket or the surround may make a ticking sound. what makes it hard to center is when the maginet gap between the mag and the center pole is tight.
Thanks guys, keep'em coming!
Last edited by piece-it pete; 07-01-2004 at 06:50 AM.
I fear explanations explanatory of things explained.
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