I have a sub where the voice coil is scraping.
If I put a side load on the cone, I can get full motion w/o scraping.
INSPECTION:
Surround:
Inspection revealed something pretty weird: the OD surround is massively off center by 1/8" relative to the basket - in the direction of scraping!
The surround is in excellent condition, suspiciously so given the speaker is probably 20 years old. The ID appears to be properly glued to the cone with a hard black glue and measured concentric with the dust cover.
What is further perplexing is that the thick gasket where the surround is offset the most actually touching it, has rolled inward approximately 15 degrees lifting the surround off the basket glue - almost as if the gasket shrunk. I can't see the surround glue failing and rolling that heavy gasket.
Spyder:
Inspection of the spyder indicates the glue has failed and it is now sliding along a segment of the VC tube - it has not pulled away from the tube. The segment is closer to 45* than 90* of the tube.
Offset Direction:
The surround offset shift axis appears to be aligned with the VC glue failure.
Which way is the offset: If we look at this shift axis, the glue failure is at +R where R is the VC tube radius, and the shifted surround OD axis is at -1/8 inches. The OD surround center moved away from the glue failure.
FAILURE THEORY:
Perhaps the gasket shrunk and over the next 20 years it slowly sheared the surround/basket glue and actually failed the surround glue in shear at the highest loading point causing it to lift and roll?
Now with the surround offset and placing a constant side load on cone and torque to the VC tube, the spyder glue failed at the greatest outward shear. NOTE: Why it didn't fail at the greatest inward shear is because the cone supports the spyder in thrust.
REPAIR PROPOSAL:
Glues:
Am I missing anything?
Thanks
Tom
If I put a side load on the cone, I can get full motion w/o scraping.
INSPECTION:
Surround:
Inspection revealed something pretty weird: the OD surround is massively off center by 1/8" relative to the basket - in the direction of scraping!
The surround is in excellent condition, suspiciously so given the speaker is probably 20 years old. The ID appears to be properly glued to the cone with a hard black glue and measured concentric with the dust cover.
What is further perplexing is that the thick gasket where the surround is offset the most actually touching it, has rolled inward approximately 15 degrees lifting the surround off the basket glue - almost as if the gasket shrunk. I can't see the surround glue failing and rolling that heavy gasket.
Spyder:
Inspection of the spyder indicates the glue has failed and it is now sliding along a segment of the VC tube - it has not pulled away from the tube. The segment is closer to 45* than 90* of the tube.
Offset Direction:
The surround offset shift axis appears to be aligned with the VC glue failure.
Which way is the offset: If we look at this shift axis, the glue failure is at +R where R is the VC tube radius, and the shifted surround OD axis is at -1/8 inches. The OD surround center moved away from the glue failure.
Perhaps the gasket shrunk and over the next 20 years it slowly sheared the surround/basket glue and actually failed the surround glue in shear at the highest loading point causing it to lift and roll?
Now with the surround offset and placing a constant side load on cone and torque to the VC tube, the spyder glue failed at the greatest outward shear. NOTE: Why it didn't fail at the greatest inward shear is because the cone supports the spyder in thrust.
REPAIR PROPOSAL:
- Free surround from basket by carefully slicing though the glue
- Find surround location that does not scrape
- Glue spyder
- Confirm no scraping and glue surround
Glues:
- Spyder - gel superglue - fillet between spyder and cone, try to get on tube OD too
- Surround - ???
Am I missing anything?
Thanks
Tom
Gravity could have been into play here. Don’t use superglue (maybe only for fixation), use 2k epoxy. Repairing/glueing surrounds requires some PVA glue, because there comes a time you have to replace the surround.
Thanks for the glue advice.
Still don't know if this was an OE failure or a bad refoam.
The unit (MTX PS15 Powered Subwoofer) has a reputation for frying the plate amp. I'm thinking if what I'm looking at is an OE failure, could the voice coil rub and eventually start shorting windings out on the magnet thereby overloading the amp? The amp build quality looks good to me.
NOTE: The driver is TWO ohms.
Still don't know if this was an OE failure or a bad refoam.
The unit (MTX PS15 Powered Subwoofer) has a reputation for frying the plate amp. I'm thinking if what I'm looking at is an OE failure, could the voice coil rub and eventually start shorting windings out on the magnet thereby overloading the amp? The amp build quality looks good to me.
NOTE: The driver is TWO ohms.
UPDATE:
Finally had time to dissect the surround from the frame (cutting through the glue) and when finally freeing the cone OD, pushing the dust cover up and down significantly was totally silent - NO scraping!
I'll use some JB Weld to reattach the spyder to the VC tube with the cone surround free. It looks like the glue failed on the spyder so it should be a good glue joint.
The surround is still very flexible and strong - while dissecting, I was pulling with some force (like cutting the stitching in a seam you want to open) and no part of the foam tore. I can only assume this must have been refoamed since this sub is from the mid-90's.
I expect the project to be a total and it looks like the remote for the motorized front volume knob is still available on eBay! Now who could possibly pass up something so wicked cool???
One comment on this sub (MTX PS-15) is that the surround is of conventional dimensions - approximately 5/16 radius. Not like the 1/2 inch-ish on the SVS I just bot. So it is possible the "blown amp" history of these units could be from over driving??? It is a bit of a mystery because the build quality of the amp board looks as good as anything I've seen in consumer electronics - and all the caps looked good.
Finally had time to dissect the surround from the frame (cutting through the glue) and when finally freeing the cone OD, pushing the dust cover up and down significantly was totally silent - NO scraping!
I'll use some JB Weld to reattach the spyder to the VC tube with the cone surround free. It looks like the glue failed on the spyder so it should be a good glue joint.
The surround is still very flexible and strong - while dissecting, I was pulling with some force (like cutting the stitching in a seam you want to open) and no part of the foam tore. I can only assume this must have been refoamed since this sub is from the mid-90's.
I expect the project to be a total and it looks like the remote for the motorized front volume knob is still available on eBay! Now who could possibly pass up something so wicked cool???
One comment on this sub (MTX PS-15) is that the surround is of conventional dimensions - approximately 5/16 radius. Not like the 1/2 inch-ish on the SVS I just bot. So it is possible the "blown amp" history of these units could be from over driving??? It is a bit of a mystery because the build quality of the amp board looks as good as anything I've seen in consumer electronics - and all the caps looked good.