1) Un-denting the dust caps
2) Re-foaming the woofer
3) Repairing paper cones
In order to complete these steps we need the following materials:
-sewing needle or safety pin
-speaker re-foam kit that fits the woofer in question (I got mine from SpeakerWorks.com http://www.speakerworks.com/foam_surround_sizing_s/63.htm)
-source of cotton fibers (cotton swabs, cotton balls, yarn, or whatever you have)
Step 1: Un-denting the Dust Caps
This is where the sewing needle or safety pin comes in handy. Poke the tip of the needle or pin into the dent in the cone, and position the needle sideways so as to allow one to pry/pull the dent out. Using the needle/pin to get inside the cap, one can push out smaller dents and wrinkles.
Alternatively, a vacuum cleaner hose can be carefully placed over the cone, and the vacuum may pull the dents out. This works for larger dust caps.
The dust cap won't look like new, there may still be creases in it and a small pin hole or two, but it will be in much better shape than it was.
Step 2: Re-foaming the Woofer
So fixing the surround is the next step! Remove the entire woofer from the cabinet, to so it can be worked on more easily. Pry off the paper or plastic ring around the outermost edge of the woofer, and set it aside. It is glued in place, but it is okay if this ring is damaged slightly, but if one is careful, it can remain mostly intact. Remove excess glue and debris from the metal basket of the woofer. Carefully scraping away material with a razor blade, and using rubbing alcohol or nail polish remover to clean the surface very will is important, as the new surround will be glued directly to this metal basket. Please TAKE CARE to use the razor blade, rubbing alcohol and nail polish remover CAREFULLY and SAFELY, making note of all warnings and directions for those tools. After cleaning the metal basket, clean the cone of the woofer very gently, trying to avoid using solvents and sharp cutting tools on the cone, instead rub off the old surround with your finger or a cloth. Once both the basket and cone are mostly clean, the new surround can be mounted to the woofer.
A tip to note is that if one side of the cone is clean, and the other isn't, for example if the original surround was mounted to the back of the paper cone, and the front of the cone remains clean, it may be alright to mount the surround to the clean side. In my case, the old surround was mounted to the back of the speaker cone, and I mounted the new one to the front. This will likely make no difference in how the speaker sounds in the end, but will make sure the new surround adheres to the cone correctly, which is very important.
In order to make sure the new surround is mounted correctly, the dust cap is cut off of the woofer, in a manner so that it can be attached again later. Be VERY CAREFUL not to cut too deeply into the dust cap, as you could damage the cone or wires underneath. With the dust cap removed, the motor structure of the woofer is exposed. The cone is attached to a cylinder called the voice coil, and there is a concentric piece inside that cylinder. It is crucial that the voice coil cylinder does not touch the inner concentric piece after the new surround is installed. To avoid it, one must "shim the voice coil" by sliding pieces of paper evenly into the gap between the voice coil and the concentric piece, until it is snug and the cone does not wobble side to side. This ensures a linear alignment of the voice coil when the surround is glued on.
The foam speaker surround kit came with a small bottle of glue, and an application brush. These were used to apply a thin layer of glue around the outside of the cone, so that there was a 1/4 inch wide border of glue around the cone. Apply a thin layer of the same glue to the inside lip of the new surround, and let them both sit for a few minutes, until the glue becomes tacky. Being careful to center the surround on the cone, place it on the cone so faces with glue mate with each other. Begin to press the two together evenly and uniformly around the perimeter of the cone. Make sure the surround is placed as it was designed to be on the cone, for example, the surround I used was meant to be red side up, with the half-roll round-side-up. Let the glue dry for a good while (several hours, or as according to the glue's directions).
Apply the glue to the speaker basket and outside lip of the foam surround, let it become tacky, and then press the two together uniformly around the perimeter of the woofer. PUSH LIGHTLY on the cone, and ensure that there are no scraping sounds or feelings, and that the voice coil remains properly shimmed and centered. place the paper or plastic ring back on the edge of the speaker, and place it face down (with weight... say a bowl of apples...) so that there is pressure on the newly glued outside edge of the surround. Allow it to dry for 24 hours.
Glue the dust cap back in place, using some tape to hold it while the glue dries, if necessary, and also glue the paper or plastic ring back in place. Wait 24 hours and HORAY! A repaired woofer! Re-install the woofer into the speaker cabinet.
Step 3: Repairing the Paper Cones
The glue supplied with the woofer re-foam surround kit has the valuable property of being somewhat flexible when dry, and it bonds readily to paper, making it an exemplary candidate for repairing paper cones. The idea is to use a diluted solution of this glue (about one to one), along with coffee filter paper and cotton fibers to create a kind of paper mache patch for a torn paper cone. The diluted glue soaks into the paper and actually bonds both sides of the tear back together, with the light-weight patch for added support. If the cone is torn at the edge, where it meets the paper accordion-style surround, cotton fibers can be used instead of the coffee filter patch. The cotton is used where the cone meets the surround because it is more durable over time than the paper, and also more flexible at the high-motion flexing point where the cone and surround meet.
Remove the tweeter from the loudspeaker enclosure to make it easier to work on. Pour a small amount of glue into a small tray or the bottom of a plastic cup. A blob about the size of a dime is enough to repair the small tweeter in the picture. Add the same amount of water, and mix thoroughly. Cut a piece of coffee filter large enough to cover the tear in the cone generously, and keep it hand for use in a moment. Brush the diluted glue over the tear in the cone, and align the parts of the cone so the edges of the tear are touching each other. Do the same with any other tears in the cone or where the cone joins the surround.
Take the coffee filter patch that was cut just a moment ago, and dip it in the diluted glue. Wipe off any extra glue, so the patch isn't dripping wet, but is more than moist, and place it paper mache style over tears in the cone. If the tear is bad, and needs stability, a second less wet patch can be applied, all the while being careful not to knock the parts of the cone out of alignment, so the edges of the tear remain touching. Pull off a very small pinch of cotton, so the strands and fibers stretch. Pull out those fibers and place them, several fibers at a time, along the edge where the cone meets the surround. Let the diluted glue that is there absorb the fibers and adhere to them. Try and get the fibers to adhere to both the surround and the cone. Next, let the whole thing dry in a safe place for 24 hours. Check to make sure the tears were all successfully sealed, and your done! Re-install the tweeter into the enclosure!