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I have four old CTS 12" speakers, with ferrite magnets from my Ampeg V4. They all had a nasty voice coil rub, even though the cones looked to be in great shape. I replaced the speakers with new ones in the V4, but wanted to try my hand at reconing the old speakers just for the heck of it. This is the procedure I used, but others with experience might do things differently, and I'm open to suggestions.
1. Cut through the old cone with an exacto knife near the surround.
2. Peel the spider glue joint away from the frame base so the spider is free.
3. Clip the tinsel wire between the cone and the terminals.
4. Pull the cone straight out with the voice coil and spider attached to it.
5. Put a piece of duct tape over the front plate of the magnet structure to keep debris out of the voice coil gap.
6. Use a utility knife to cut away the paper laminate gasket and a putty knife to scrape away most of the paper and glue remaining near the joint where the surround attached to the frame. Use acetone to soften and remove all remaining glue.
7. Use acetone to remove glue residue from where the spider was attached to base.
8. Clean voice coil gap with vacuum cleaner. Push a piece of masking tape down in the gap to remove any debris. If you have compressed air - use it.
9. Make a shim to center the new voice coil radially in the gap. I used a 3x5" note card trimmed to size.
10. Mark a line on the note card to set the height of the voice coil axially in the gap. I tried to center the voice coil windings in the magnet structure - I don't know if this is correct. The new voice coil was a little taller than the original VC.
11. Dry fit the spider on the OD of the voice coil, set the height with the line on the shim. Draw a magic marker line on the base of the frame using the OD edge of the spider as a guide.
12. Remove spider and voice coil as a unit. Put a bead of flue just inside the line drawn on the base. The glue is brown "elephant snot", not sure of the composition. Put spider, shim and VC back down on frame to glue the spider in place. Make sure voice coil wires are lined up with terminals on frame.
13. Glue spider to voice coil with a bead of thick cyanoacrylate glue. I used a shot of accelerator to speed up the set.
14. Wait a few hours for the elephant snot glue to cure so the spider is attached to the base.
15. Dry fit the cone to the frame and voice coil. I had to trim the cone to open it up so it would fit over the OD of the voice coil. I used an exacto blade and sand paper on a dowel to trim to size. Clean the debris from the cone with vacuum and duct tape.
16. Lay a bead of elephant snot glue around top of frame for the surround.
17. Fit cone to frame and voice coil - press down on surround to glue it to frame.
18. Lay a bead of cyanoacrylate glue on the joint of the cone to voice coil. The cone and spider are butted together at this joint. Give it a shot of accelerator.
19. Drill two small holes through the cone for the tinsel wires. Solder the tinsel wires to the VC wire leads. Glue tinsel wire and VC lead wire to cone surface. I used flexible cyanoacrylate, but next time I'll try to get some rubber cement.
20. Attach a piece of masking tape to the center of the dustcap to use as a handle. Apply a bead of CA glue to the edge of the dustcap and place it in the center of the cone. Add another bead of CA at the joint and hit it with some accelerator.
21. Put a bead of Elmer's white glue on the paper laminate gasket and set in place on the speaker frame. Use another speaker on top to weight down the gasket until the glue sets.
22. Solder the tinsel wires to the terminals on the frame. Leave some slack in the wires so that the cone is free to move.
23. Let the glues cure for a day.
24. Measure ohms at the terminals to verify you didn't screw up. I measured 5.8 ohms for a nominal 8 ohm VC.
I drove down to Weber to pick up the speaker reconing supplies. They were nice enough to give me some of the CA and "elephant snot" glue. I used two different styles of cones. One was very light paper (around 12 grams) and the other was a good bit heavier and stiffer (around 18 grams). I also experimented with two different types of dust caps - one was the DCQ 1.8" diameter flat top paper dome, and the other was a DCP3 paper dome 3" diameter. I didn't use any speaker dope. The speakers work, but I can't say that I'm thrilled with the tone at high volume. The breakup distortion sound is a little harsh. I was surprised by how much the dustcap effects the tone. The large dustcap and heavy cone is my best sounding speaker at high volume.
Some remaining questions. Where should the voice coil be fit axially for smooth breakup tone? I centered it in the magnet structure, but maybe it should be fitted so the top edge of the voice coil lines up with the top edge of the magnet structure? Would they smooth out the breakup? Would that clip one half of the wave form? Would that be a bad thing? The cones I used had an ID of 1.31" and required trimming to fit over the OD of the voice coil. Perhaps I bought the wrong cones and should have used cones with a 1.55" ID. I assumed that the cones aren't designed to sit on top of the voice coil with an edge of the cone sticking out in the center of the voice coil.
Any advice or suggestions appreciated as far as optimizing tone during speaker reconing - especially on the selection of cone material, dustcaps, and voicecoil.
1. Cut through the old cone with an exacto knife near the surround.
2. Peel the spider glue joint away from the frame base so the spider is free.
3. Clip the tinsel wire between the cone and the terminals.
4. Pull the cone straight out with the voice coil and spider attached to it.
5. Put a piece of duct tape over the front plate of the magnet structure to keep debris out of the voice coil gap.
6. Use a utility knife to cut away the paper laminate gasket and a putty knife to scrape away most of the paper and glue remaining near the joint where the surround attached to the frame. Use acetone to soften and remove all remaining glue.
7. Use acetone to remove glue residue from where the spider was attached to base.
8. Clean voice coil gap with vacuum cleaner. Push a piece of masking tape down in the gap to remove any debris. If you have compressed air - use it.
9. Make a shim to center the new voice coil radially in the gap. I used a 3x5" note card trimmed to size.
10. Mark a line on the note card to set the height of the voice coil axially in the gap. I tried to center the voice coil windings in the magnet structure - I don't know if this is correct. The new voice coil was a little taller than the original VC.
11. Dry fit the spider on the OD of the voice coil, set the height with the line on the shim. Draw a magic marker line on the base of the frame using the OD edge of the spider as a guide.
12. Remove spider and voice coil as a unit. Put a bead of flue just inside the line drawn on the base. The glue is brown "elephant snot", not sure of the composition. Put spider, shim and VC back down on frame to glue the spider in place. Make sure voice coil wires are lined up with terminals on frame.
13. Glue spider to voice coil with a bead of thick cyanoacrylate glue. I used a shot of accelerator to speed up the set.
14. Wait a few hours for the elephant snot glue to cure so the spider is attached to the base.
15. Dry fit the cone to the frame and voice coil. I had to trim the cone to open it up so it would fit over the OD of the voice coil. I used an exacto blade and sand paper on a dowel to trim to size. Clean the debris from the cone with vacuum and duct tape.
16. Lay a bead of elephant snot glue around top of frame for the surround.
17. Fit cone to frame and voice coil - press down on surround to glue it to frame.
18. Lay a bead of cyanoacrylate glue on the joint of the cone to voice coil. The cone and spider are butted together at this joint. Give it a shot of accelerator.
19. Drill two small holes through the cone for the tinsel wires. Solder the tinsel wires to the VC wire leads. Glue tinsel wire and VC lead wire to cone surface. I used flexible cyanoacrylate, but next time I'll try to get some rubber cement.
20. Attach a piece of masking tape to the center of the dustcap to use as a handle. Apply a bead of CA glue to the edge of the dustcap and place it in the center of the cone. Add another bead of CA at the joint and hit it with some accelerator.
21. Put a bead of Elmer's white glue on the paper laminate gasket and set in place on the speaker frame. Use another speaker on top to weight down the gasket until the glue sets.
22. Solder the tinsel wires to the terminals on the frame. Leave some slack in the wires so that the cone is free to move.
23. Let the glues cure for a day.
24. Measure ohms at the terminals to verify you didn't screw up. I measured 5.8 ohms for a nominal 8 ohm VC.
I drove down to Weber to pick up the speaker reconing supplies. They were nice enough to give me some of the CA and "elephant snot" glue. I used two different styles of cones. One was very light paper (around 12 grams) and the other was a good bit heavier and stiffer (around 18 grams). I also experimented with two different types of dust caps - one was the DCQ 1.8" diameter flat top paper dome, and the other was a DCP3 paper dome 3" diameter. I didn't use any speaker dope. The speakers work, but I can't say that I'm thrilled with the tone at high volume. The breakup distortion sound is a little harsh. I was surprised by how much the dustcap effects the tone. The large dustcap and heavy cone is my best sounding speaker at high volume.
Some remaining questions. Where should the voice coil be fit axially for smooth breakup tone? I centered it in the magnet structure, but maybe it should be fitted so the top edge of the voice coil lines up with the top edge of the magnet structure? Would they smooth out the breakup? Would that clip one half of the wave form? Would that be a bad thing? The cones I used had an ID of 1.31" and required trimming to fit over the OD of the voice coil. Perhaps I bought the wrong cones and should have used cones with a 1.55" ID. I assumed that the cones aren't designed to sit on top of the voice coil with an edge of the cone sticking out in the center of the voice coil.
Any advice or suggestions appreciated as far as optimizing tone during speaker reconing - especially on the selection of cone material, dustcaps, and voicecoil.
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