Many sellers of speaker surrounds (the red foam "rings" you referred to) include a full installation kit...glue, shims and/or test tone CD for centering the coil, and a set of step by step instructions. The woofers in your DX-5's are quite easy to do. Just find an online seller...the larger ones will have a search function so that you can easily find and order the correct kit.
The basic steps:
- Remove the old foam, cleaning the edges of the cones and the frame
- Glue the inner edge of the new foam to the outer edge of the cone and let dry.
- Glue the outer edge of the new foam to the frame.
- Center the cone while glue is still wet - this can be done using a low frequency test tone played thru the speaker (if you hear rubbing or buzzing, push the cone up to detach the foam from the frame and then let it come straight back down...let the cone find its own center). Tweak as needed.
I would advise you to find some speaker diagrams of so that you begin to understand their basic mechanics. Here's a good, short YouTube video that might work for you:
The idea here is to minimize the confusion you will have when you read the instructions and they talk about the coil and how it must be centered around the pole piece (the magnet). This is the most important thing to understand, as the woofer will not work correctly and can be badly damaged if the coil is rubbing on the magnet. The cone must be able to move up and down (in and out) freely...and the only way that can happen is if the voice coil (the wire-wrapped tube attached to the cone) is centered over the pole piece section of the magnet. If the foam is glued to the frame in such a way that it pulls the cone unevenly, the coil rubs as the cone moves up/down.
The explanation makes it sound more complicated than it really is. In practice, the cone will have a tendency to find its own center...so when lowering the edge of the new foam onto the frame (already prepped with glue), simply allowing the cone to "fall" into place does most of the work. The test tone just gives you a way to be sure, and the wet glue means you can still tweak the foam one way or the other to get it completely right.
There is a nearly foolproof way of getting the cone/coil centered, using thin plastic or paper shims (think strips cut from a business card) between the pole piece and the coil tube (aka the "former"). This method, however, requires that the dustcap be cut off, or nearly cut off and folded back, and then replaced (new one glued back in, or old one folded back into place and re-glued). This is the way I do it, but I've done a lot of them. I think the test tone approach is much easier for a beginner.
Good luck.
