I'm refoaming a pair of Ohm D2's and I found this... (See dent in first coil.) Pic of other driver included for comparison.
Should I be worried? It doesn't rub, thankfully.
How does this even happen? There's no way to move the cone that makes the dent match up to the inner magnet btw.
Stress buckle? Since it occurs at the gap just below the cone. How would you even generate that much motive force, though.
I'm wondering if it's just a manufacturing defect. The dust cap was also crooked & not well glued, which is how I came to remove it and see this. They seem to be the genuine article, though: there's an authentic looking sticker on the back stamped June 6, 1977.
I suppose they could have been reconed once and damaged then; a lot can happen in 42 years! (I should know; I work on old cars...)
On the other hand, the previous owner told me they had been running them without surrounds and they "sounded fine", seemed unaware they were missing or supposed to have them (!!!) So maybe it was damage incurred from running without the support of surrounds, but then my first two points still stand: it's the wrong shape for a magnet collision, and would take a heck of a lot of electrical force to push that hard. But I suppose without surrounds to keep them from going crooked, it could have bound up or something...
Should I be worried? It doesn't rub, thankfully.
How does this even happen? There's no way to move the cone that makes the dent match up to the inner magnet btw.
Stress buckle? Since it occurs at the gap just below the cone. How would you even generate that much motive force, though.
I'm wondering if it's just a manufacturing defect. The dust cap was also crooked & not well glued, which is how I came to remove it and see this. They seem to be the genuine article, though: there's an authentic looking sticker on the back stamped June 6, 1977.
I suppose they could have been reconed once and damaged then; a lot can happen in 42 years! (I should know; I work on old cars...)
On the other hand, the previous owner told me they had been running them without surrounds and they "sounded fine", seemed unaware they were missing or supposed to have them (!!!) So maybe it was damage incurred from running without the support of surrounds, but then my first two points still stand: it's the wrong shape for a magnet collision, and would take a heck of a lot of electrical force to push that hard. But I suppose without surrounds to keep them from going crooked, it could have bound up or something...
If I had to guess I would say the driver has bottomed out the voice coil against the magnet backplate.
The circumfrential yielding of the former below the cone attachment point is consistent with this.
The following is not a recommendation unless you have a problem with the driver, as it is radical surgery. I have done this successfully about half a dozen times - but always where the alternative was an unusable driver.
If you are confident, and a little brave, it is entirely possible to dissolve the glue holding the spider to the frame, and surround from the frame, and from there remove the cone, spider and coil as an assembly.
I speculate that if you did this you would find damage to the rear of the coil.
The best solvent is toluene which with a few minutes of painting onto the glue (several coats to keep it wet) does amazing things to the glue.
Perhaps a second question is... what is all that yellowish greasy gluey looking stuff in the magnet and on the former?
The circumfrential yielding of the former below the cone attachment point is consistent with this.
The following is not a recommendation unless you have a problem with the driver, as it is radical surgery. I have done this successfully about half a dozen times - but always where the alternative was an unusable driver.
If you are confident, and a little brave, it is entirely possible to dissolve the glue holding the spider to the frame, and surround from the frame, and from there remove the cone, spider and coil as an assembly.
I speculate that if you did this you would find damage to the rear of the coil.
The best solvent is toluene which with a few minutes of painting onto the glue (several coats to keep it wet) does amazing things to the glue.
Perhaps a second question is... what is all that yellowish greasy gluey looking stuff in the magnet and on the former?
Ah, that makes more sense. The impact from bottoming out could have done it. Likely if it was run with no surround it had less mechanical and aerodynamic resistance to hitting the end of travel.
I found out the manufacturer will rebuild these to newer spec with long life surrounds, ferrofluid fill, and a sub-bass suppression circuit. It is tempting but at $145 per driver that's a steep increase from speakers I paid $50 for at a yard sale and hoped to fix with a $25 surround kit, that I didn't even know were valuable until last week. (I was using them for a makeshift coffee table - I'm a terrible person.)
But if I get to the point of considering dissolving the glue between the cone and voice coil, I think that would be the time to send them to the manufacturer. They said they take it down to the basket, anyway, and build it back up. They also offer trade-in value on a new set of speakers, like trading in a used car on a new one!
The brown stuff on the magnet that you asked about is grease. Yes they greased it, appears to be the same kind as you'd find in a gearbox or kitchen mixer motor. Guess they did them that way in the 70s; I've read that sometimes the grease gets hard and binds up.
I found out the manufacturer will rebuild these to newer spec with long life surrounds, ferrofluid fill, and a sub-bass suppression circuit. It is tempting but at $145 per driver that's a steep increase from speakers I paid $50 for at a yard sale and hoped to fix with a $25 surround kit, that I didn't even know were valuable until last week. (I was using them for a makeshift coffee table - I'm a terrible person.)
But if I get to the point of considering dissolving the glue between the cone and voice coil, I think that would be the time to send them to the manufacturer. They said they take it down to the basket, anyway, and build it back up. They also offer trade-in value on a new set of speakers, like trading in a used car on a new one!
The brown stuff on the magnet that you asked about is grease. Yes they greased it, appears to be the same kind as you'd find in a gearbox or kitchen mixer motor. Guess they did them that way in the 70s; I've read that sometimes the grease gets hard and binds up.
- Status
- Not open for further replies.