I posted this in a thread about repairing surrounds, but it's several years old, so I am posting here.
I am replacing the surrounds on some Scanspeak Revelator 7" mid/woofers & have a few questions. I plan to use the DC voltage or 50Hz sinewave method to help center the VC. The question is about the gluing process. These surrounds fit tightly into the rim of the frame with very, if any, wiggle room for final alignment. If I am very careful when gluing the cone would this lack of rim adjustability be a concern? On one hand I can see that this situation may benefit the accuracy of my initial gluing of the cone & on the other hand.... well it may make it more difficult. Any thoughts are appreciated.
Also: when using a regulated power supply what voltage should I set it to & should I worry about limiting the current? Power handling specs state: 100h RMS noise test = 60W & Long term Max Power = 70W
Also #2: Is the DC voltage as effective at aligning the VC or is it just a convenience for lifting the cone into position? Guess & could use both to offset the cone while still having it travel in the gap. My main concern tho, is the amount of DC to apply for the time it takes to complete the job.
Thanks,
Kev
I am replacing the surrounds on some Scanspeak Revelator 7" mid/woofers & have a few questions. I plan to use the DC voltage or 50Hz sinewave method to help center the VC. The question is about the gluing process. These surrounds fit tightly into the rim of the frame with very, if any, wiggle room for final alignment. If I am very careful when gluing the cone would this lack of rim adjustability be a concern? On one hand I can see that this situation may benefit the accuracy of my initial gluing of the cone & on the other hand.... well it may make it more difficult. Any thoughts are appreciated.
Also: when using a regulated power supply what voltage should I set it to & should I worry about limiting the current? Power handling specs state: 100h RMS noise test = 60W & Long term Max Power = 70W
Also #2: Is the DC voltage as effective at aligning the VC or is it just a convenience for lifting the cone into position? Guess & could use both to offset the cone while still having it travel in the gap. My main concern tho, is the amount of DC to apply for the time it takes to complete the job.
Thanks,
Kev
Normally, the dustcap is removed and shims are inserted around the central pole for alignment.
If you make small holes around the outside of the dustcap, and insert wires around the pole, you could seal them up afterwards. This is how the Dynaudios are centered without having the cap removed.
That's my best guess without removing the cap or just guessing at glue position.
Wolf
If you make small holes around the outside of the dustcap, and insert wires around the pole, you could seal them up afterwards. This is how the Dynaudios are centered without having the cap removed.
That's my best guess without removing the cap or just guessing at glue position.
Wolf
Except for extremely rare vintage, tight gapped drivers, I never bother to use shims, spacers or current to align the voice coil. If you haven't removed the spider there should be no difficulty in aligning the coil. The spider actually sets the centering and the surround sets the parallelism. In fact if, as you say, the surround is a tight fit then it should be self aligning.
I use an acrylic glue from Speakerbits with a little slip as it sets, which takes about 15 minutes. I test the alignment by pressing on the rim of the cone and make sure that there is no rubbing all of the way around. I've done hundreds of speakers from 4" to 12", with both rubber and foam surrounds, and never had a single problem.
I use an acrylic glue from Speakerbits with a little slip as it sets, which takes about 15 minutes. I test the alignment by pressing on the rim of the cone and make sure that there is no rubbing all of the way around. I've done hundreds of speakers from 4" to 12", with both rubber and foam surrounds, and never had a single problem.
Curious cat & non-protective Sonus Faber "grills".
I prefer NOT to remove the dust caps or put holes in the cones.
The 50Hz sinewave &/or DC voltage applied are frequently used methods to help center the VC, but I am open to more non-invasive tricks. The voice coil & former are visible & accessible from behind the spider & I could insert shims there if that will work. The shims would be on the outer gap instead of the inside & the shims would have to bend out at 90 deg. at the top.
Kev
Thanks for your response.
I like the idea of lowering the cone relative to the surround in order to make a gap to put on adhesive & then slowly raising the cone to contact the surround by adjusting the DC from neg. to pos. Works perfectly in my head. Once the surround is secure to the cone, The reverse could be applied to the edge gluing. Raise the cone/surround above the frame, put on glue & them drop the voltage & the surround. That worked great in my mind too.
Kev
I suspect your imagination is making the task more difficult than it needs to be. I strongly advise against glueing the surround to the cone when it is not in the rest position, or in two seperate stages. Doing the first will distort the surround dimensionally and potentially reduce the linearity of the driver once set. Doing the second risks not aligning the surround optimally, and not being able to correct the set without destroying the surround and starting again. The surround needs to be set and glued in place, not when displaced, both parts glued at the same time so that it forms and shapes properly whilst the glue dries. You should see what I mean when you trial fit the surrounds without glue.
I once make a tool with a small roller bearing to smooth out the outer edge of the surround on the speaker frame. Rotating the driver running the roller around whilst the glue is in the slip phase of drying makes sure the the surround is set circularly and not elliptically. It takes a good eye to see that everything is symmetrical. This tool sped up the process so I could do a couple of drivers in a few minutes, but when I can't find it I just use a burnishing tool.
I once make a tool with a small roller bearing to smooth out the outer edge of the surround on the speaker frame. Rotating the driver running the roller around whilst the glue is in the slip phase of drying makes sure the the surround is set circularly and not elliptically. It takes a good eye to see that everything is symmetrical. This tool sped up the process so I could do a couple of drivers in a few minutes, but when I can't find it I just use a burnishing tool.
OK, fair enough. I may try without any input signal. I like the idea of gluing the cone & frame at the same time. I wonder about a technique to press on the surround to get a tight fit to the cone. Do you put a finger behind the cone to support it, or is it necessary? I will be sure to use an adhesive that has some working time. These surrounds are made of SBR, is that sometimes referred to as Butyl rubber or is that something else?
Kev
Kev
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I usually pinch the surround to the cone with fingers, and use a burnishing tool or spatula where the frame gets in the way.
Does the surround go on the front or rear of the cone? If it is the front I would run a bead of glue around both the outer section of the cone and around the frame, then drop the surround on top. If the surround is glued underneath the cone, then place the surround in position, then run a bead of glue on the inner section by gently inserting the glue nozzle through the gap, and press the surround onto the underside of the cone. Once it has set a little, lift the outer section of the surround and run a bead of glue around the frame, then press the surround down onto the frame.
I use a squeeze bottle with a ~3mm nozzle for the glue with about a 1mm orifice. I use the nozzle to spread an /\/\ shaped bead of glue as I am running the nozzle around. Be careful to not have any breaks in the bead, and also be careful not to put too much glue on which will need to be cleaned off once the parts are pressed together.
Once the glued surfaces are mated, work around the cone making sure the surround is centered, even, and that the cone moves freely when pressed gently on the edge of the cone all the way around. I actually just press at four diagonally opposite points. If the coice coil rubs at any point, then the surround needs to be moved towards the center at that point; I slide it a little with a finger if necessary.
If the surround is even all of the way around, then it should just be fine without adjustment, because it is the spider's job to center the voice-coil, and the surround just makes sure the former is parallel to the pole, which it will be if it is even.
Once the glue has set, make sure the surround is well bonded all round on both edges. Add glue if necessary, because if the surround can lift anywhere it will buzz like a kazoo.
Does the surround go on the front or rear of the cone? If it is the front I would run a bead of glue around both the outer section of the cone and around the frame, then drop the surround on top. If the surround is glued underneath the cone, then place the surround in position, then run a bead of glue on the inner section by gently inserting the glue nozzle through the gap, and press the surround onto the underside of the cone. Once it has set a little, lift the outer section of the surround and run a bead of glue around the frame, then press the surround down onto the frame.
I use a squeeze bottle with a ~3mm nozzle for the glue with about a 1mm orifice. I use the nozzle to spread an /\/\ shaped bead of glue as I am running the nozzle around. Be careful to not have any breaks in the bead, and also be careful not to put too much glue on which will need to be cleaned off once the parts are pressed together.
Once the glued surfaces are mated, work around the cone making sure the surround is centered, even, and that the cone moves freely when pressed gently on the edge of the cone all the way around. I actually just press at four diagonally opposite points. If the coice coil rubs at any point, then the surround needs to be moved towards the center at that point; I slide it a little with a finger if necessary.
If the surround is even all of the way around, then it should just be fine without adjustment, because it is the spider's job to center the voice-coil, and the surround just makes sure the former is parallel to the pole, which it will be if it is even.
Once the glue has set, make sure the surround is well bonded all round on both edges. Add glue if necessary, because if the surround can lift anywhere it will buzz like a kazoo.
Me also , a few rotations to make doubly sure it's firmly adhered. I use the side of the first two links of my left forefinger underneath, and the first three finger tips of my right pressing down from the top, move along a bit and repeat.
Then leave it over night and lift the suround (sometimes even pack the cone up with handtowel at various points between frame and cone) as you apply adhesive to the underside of the new surround, use a sawn off cotton bud to quickly spread it evenly.
Remove the handtowel (if used) then use the 3 fingertips again to secure to the frame, leave another 24hours and fit driver to cabinet - job done.
That's my method anyway, done loads with no trouble.
Thanks, now to decide whether or not to glue the cone & frame at the same time or in 2 steps???
Kev
During the final stages of stage one as the glue is starting to go off , you can check/confirm (more or less) that you got the surround centrally on the cone.
When I'm doing stage one, I often move the surround around a tiny bit as I'm using my fingers to ensure it is placing evenly round the cone edge.
I think I've only ever had to order a 2nd surround and start again in dozens of jobs.