I'm going to show you how to refoam the surround on a JL Audio W7 series subwoofer. The subwoofer we're repairing is the 10W7-3. Refoaming a W7 is a little different than refoaming a standard speaker because the surround is so much larger and the outer edge does not get glued down. The factory surround is also sandwiched between the top and bottom cone layers rather than being attached on the top or bottom of a single cone layer. Here you can see that in this cutaway drawing of the JL series woofer. We will not be able to recreate this factory sandwich method but will instead glue the surround to the top cone directly. I have already refoamed one of these subwoofers which you can see here. It was fairly easy to do and turned out pretty good as you can see. Aside from the actual attachment point of the surround to the cone the new foam is also a lighter color than the original. I picked up these surrounds on eBay for about $60 a pair.
Let's begin by removing the factory clamp ring from the subwoofer. JL Audio recommends placing a flat blade screwdriver between the top edge of the clamp and the foam surround at the split point of the ring. They caution not to insert the screwdriver so far down that it gets wedged between the surround and the O-ring. Just insert the tip of the screwdriver and twist the handle gently to pop the clamp ring off. Once you have one side released you can push the ring around the circumference of the subwoofer and it should release. Once it is fully released you can lift it away from the subwoofer.
Now we can remove the O-ring which is what keeps the outer edge of the foam surround attached to the subwoofer frame. JL Audio recommends removing the ring using your fingertips but I find that the O-ring is usually too tight to do this easily. I choose to carefully wedge a flat tip screwdriver between the O-ring and the surround and twist it as was done to separate the clamp ring from the subwoofer. You want to be careful when do this as you could slip and damage the surround. But if you're changing the surrounds as we are doing here it really isn't an issue. Work your way around the ring until you can slip it off by hand.
If you are removing the subwoofer from an enclosure you will need to pull the surround back to expose the mounting screws for removal. Do not lift the surround up or fold it against itself to gain access. Just pull the outer edge towards the center of the cone enough to expose the mounting screw for removal. Repeat this process for all mounting screws.
Now we're ready to remove the old surround. On a standard speaker we would just tear away the old foam and then clean up the two mounting edges on the cone and speaker basket. The foam on a W7 is much thicker than a normal surround so we cannot just tear it off. We will need to use a razor blade to cut off the old surround. Look again at how the surround is sandwiched between the cone layers. We will be making a cut straight down along the edge of the top cone layer. This will cut through part of the thin bottom edge of the inner cone while leaving a small bit of original foam sandwiched between the two layers. This will not be seen once we install the new surround.
To make the cut I'll be using a small razor knife with a new blade to ensure it is sharp. I'm choosing to start by making a single cut from the outer edge of the surround to the inner edge of the cone. This will allow me to pull the old surround away as I make the inner cut. Now the inner cut is made by keeping the edge of the knife parallel to the inner edge of the cone. Make short, saw-like strokes with the blade to cut through the original surround and the thin bottom layer of the cone. Use the top surface of the outer cone as a guide for the knife but be careful not to cut into the top cone layer. Remember that you only want to cut through the foam and into the thin outer ring of the bottom cone layer. We want to keep the original foam that is sandwiched between the layers intact.
Now we should have the bulk of the foam removed. You can make a second pass to clean up any stray bits but don't fuss with it too much. Keep in mind this edge will soon be covered by the new foam surround. Before putting on the new surround we need to clean up the cone. If the cone is just generally dirty you can wipe it off with a damp rag. If there is anything stuck to the cone like an adhesive or stubborn grime you can use a cleaner like Goo Gone to remove it. After the cone is cleaned up take some rubbing alcohol and clean up the edge of the cone. Let the alcohol dry completely before proceeding.
After the cone is dry add a bead of the glue along the entire edge of the cone. You want a fairly decent amount but not an excessive amount. There should be a small dome to the glue bead rather than a flat top. Now place the new foam surround on the woofer basket. As you can see it will not yet touch the cone edge. Bring the cone up to the surround by pressing up on the cone from the bottom side with your fingers. I found this to work better than trying to bring the surround down to the cone. Look to make sure the surround is still centered on the cone as you press it.
Work the attached edge with your fingers or a plastic tool as the glue sets. Don't worry about any glue that squishes out of the edge as this can be cleaned up before the glue fully dries. It will take several minutes for the glue to set so keep an eye on the edge and keep working it with your fingers. You should be able to tell when the glue is setting by the way the foam reacts as you press it. At first it will move as you press it but as the glue sets it will begin to move very little if at all. After the glue has set you can put it aside and wait for the glue to fully dry. It should be cured within an hour but I always wait a full day before handling the subwoofer again. If you notice any excess glue has squished out you can clean it up with a toothpick and your fingers. Just put the toothpick into the glue and move it around to scrape out the glue. The glue should want to ball up which makes it easier to remove. If the glue doesn't ball up let it sit for awhile longer. Usually 30-60 minutes is about right.
Once the glued has fully cured you can mount the subwoofer into the enclosure and finalize the installation with the O-ring and clamp ring. First slip the O-ring over the foam surround and begin pushing it over the surround. It will be very tight so don't push one side down fully or the other sides won't seat. Instead, work your way from one side and to the opposite side much like you would tighten the lug nuts on a car's wheel. When the ring is almost all of the way down it will be very tight on the new foam. To push it down the last little bit I found it necessary to use a small flat tool and a ball peen hammer. I'm using the side of the razor knife and carefully tapping it with the ball peen hammer. Do this along the entire perimeter of the O-ring.
Finally you can add the clamp ring. Again I found it necessary to use the ball peen hammer to gently tap the clamp ring into place. A small rubber mallet would have been even better but my clamp ring was already a little rough looking. Start at the joint edge and then move along the perimeter of the clamp ring. Be sure to hold the part of the clamp ring you previously tapped in place or it will lift off. If there is a gap in the clamp ring joint inspect the space between the clamp ring and the surround and see if any sections have pulled away. That's all there is too it. In some ways it's easier and other ways more difficult than a standard speaker refoam but still something anyone should be able to accomplish with a little patience and care.
You should also check out Advanced Enclosure Design and Fabrication. It covers designing enclosures using free computer software, maximizing the output of a subwoofer system, building the box like a pro and testing the output using inexpensive equipment. Click here.