WARNING : Don’t read this if you are squeamish about doing operations on large powerful audio speakers. Don’t think that this A-Z will apply to any or all speakers or any or all circumstances. The sequence here did apply to one speaker of mine, but I am sure that all speakers are individual, just like people.
The patient in this case is a large sealed 100W speaker cabinet. Weighing in at around 25 kilograms, it had a brilliant sound, but for now is reduced to just a persistent cough, no matter how much encouragement given.
a. Take the speaker cabinet, it is probably heavy so get a mate to help bring it down to the shed. Put it on blocks on the table. Reassure the poor tweeter lying there beside the woofer it will be just ok, no need to worry.
b. Turn the speaker patient over, and gently unscrew all the rusty screws holding the back on. The screws are long, and the wood is tight, for putting up with 20 years of weather and globe trotting.
c. Carefully prize the back off with a small chisel. Careful how you do that, since it might chip, and mar the paintwork. OK did you get it off. Lets assume you did. Open up the back, and remove it, keep all the screws, you probably might not be able to buy replacements. Put the screws and the back over to the side.
d. Look inside to see if the wires are ok, and if the crossover may be burnt out. No.. everything ok. Then the problem may be with the speaker cone, or the cone winding.
e. Gently push down on the speaker cone, the large paper thing inside the speaker frame. Watch out for your watch in case you may have it magnetised on the large magnet on the back of the speaker.
f. Shut the door, turn down the radio, make it all quiet inside the shed. OK… now do it again. carefully push down on the cone, and listen. What do you hear ? If you hear nothing, then it is probably ok. If it sound a bit raspy then you will have a problem with the speaker cone. The voice coil could be out of line.
g. Disconnect the woofer driver, and then unscrew each of the 8 or so screws holding the rim of the driver to the front baffle. Once again keep all those screws, don’t lose them, might be hard to find replacements.
h. Ok check disconnected. Check screws are somewhere safe – not likely to get lost.
i. Pick up the speaker, take it out of the enclosure, take it over to the bench. Wind out the vise, and then put it in magnet first. So that the cone of the driver is facing up toward the roof. You looking down on it. You should be able to see the centre of the cone, and all around the edges of the cone, where it is glued down onto the rim under a baffle ring.
j. You will note that since the driver is rubbing, it is rubbing its voice coil on the inside ring slot of the magnet. This is due to distortion in the cone, and the voice coil part of the lower cone, stuck inside the magnet has become out of line.
k. Take a stanley knife, or a scalpel, borrow one from your husband or wife if you need a sharp one. Then carefully cut the cone out by running the scalpel around the widest part of the cone, where the cone sharply angles from around 30 to 40 degrees to the point where it becomes horizontal and all wavy out to the rim.
l. You should now have the cone cut free of the rim, and looking like an ice-cream cone, or the cone of a funnel, and standing just near where you cut it. If the speaker is not distorted, like in a new one, the cone will be almost unmoving and sitting just like where you cut it, with almost no gap where you cut it. However if the cone is distorted, the gap will adjust to allow the cone to relax into the right alignment of the voice coil, since there is nothing holding the cone to the rim. Walk around the cone, shining a torch from underneath, and you will see lots of light coming through where the gap increases, and no light where there is no gap.
m. When you push the cone back down onto the rim, you will see the cuts separate a little as the cone lies flatter.
n. You will go to the chemist/drugstore and you will ask the nice shop assistant for help finding special medical paper tape, used to bandage up wounds on real people. You get some, a small roll of it, you only will need about a foot or so of tape most probably.
o. You will go to the supermarket and get some shockproof superglue.
p. You will come home and you will go down to the shed, turn on the light, and then move back over to the poor woofer, lying there in the vise, awaiting your expertise to work on its poor recently distorted cone. You will then get the paper medical tape, and undo the packaging, and then find the end, and then cut off a bit, and apply it to the underside of the cone, being careful to push the cone back down on the rim, apply the paper to the slit and then once again to all the cuts you have made.
q. You will then get the superglue, careful not to get in fingers, it sticks shocking to skin, particularly when you get it on fingers and then use fingers to think with. You end up permanently stuck in thought mode with your finger on your temple.
r. You will apply the superglue carefully along the slits and then immediately apply more medical tape over the top of them. The superglue should basically start seeping through the tape and the tape lie flat on the slits cut radially into the speaker cone, and now the cone should be lying gently against the rim, and everything looking round on good again.
s. Wait a bit….that was tough… now to get breath back and think over the next step while the superglue sets.
t. When the glue is set, take a breath, you will now have to get the superglue and go carefully right round the outside rim of the cone and glue it back onto the rim you originally cut through. Put strips of medical tape on top just to help hold the glue together and give it something to bind to as well as the cut edges of the cone and the rim.
u. Wait a bit longer….. come back after lunch.
v. Check your success by carefully pushing down on the centre of the speaker cone. You should now hear nothing since the cone will now be lined up with the voice coil magnet and also the rim.
w. It will look pretty ugly, so get some paint and go paint the whole speaker cone carefully, it will add a bit to the weight of the cone, but it will seal it against the weather and will seal over the medical tape patches and it will look ok to people who really like to see their speaker cones made up and looking good.
x. Wait till it dries, then put it carefully back into the enclosure, screw it down, reconnect the wires.. making sure they are all around the right way. Put the back of the speaker cabinet back on, screwing it in place carefully.
y. Turn the patient over on its back, now reassure the tweeter that things are ok, then get the speaker wires from the amp and connect it up, switch on power. Get a decent CD with a lot of good dynamic music on it. Attach and gradually turn up the volume.
z. If you are feeling good again and the sound is clear across the range, and loud and no coughing sneezing or other ridiculous non-speaker sounds are being made, then you are done. Back in business.