I have 1 damaged bass/mid driver in my sonus faber cremoa auditor loudspeakers. I measured across the voice coil and there was no resistance so i set out to remove the cone from the unit. There is a break in the loop right at the bottom of the coil and wondered if anyoe had any tips on repairing this? How would i join the 2 together and coat the wire and also fix it back in place.
You *might* try to repair it if you have high manual exterity and good sight.
You will never be able to rejoin them end to end, so next best is to partially unwind the last turn on the outer layer, cut end so it still overlaps the end of the other half by 5 or 6 mm, carefully scratch ends, put them flat side by side against the VC former and solder them.
You do NOT want to create more thickness, gap is incredibly tight, that´s why I insist on "side by side against the former".
If space is too tight, unwind two turns, that will not affect sound at all, it´s a long coil anyway.
If solder makes a blob, file it down with a fine tooth die maker file or a nail sanding one.
IF you succeed, apply some epoxy with a toothpick and swipe most of it away with a fingertip, leaving only something between wire and former..
Let it dry and reassemble speaker.
You will never be able to rejoin them end to end, so next best is to partially unwind the last turn on the outer layer, cut end so it still overlaps the end of the other half by 5 or 6 mm, carefully scratch ends, put them flat side by side against the VC former and solder them.
You do NOT want to create more thickness, gap is incredibly tight, that´s why I insist on "side by side against the former".
If space is too tight, unwind two turns, that will not affect sound at all, it´s a long coil anyway.
If solder makes a blob, file it down with a fine tooth die maker file or a nail sanding one.
IF you succeed, apply some epoxy with a toothpick and swipe most of it away with a fingertip, leaving only something between wire and former..
Let it dry and reassemble speaker.
The reconing is probably very hard, you need to reposition it exactly. It is much easier if you dissolve the glue between coil and membrane with acetone (coil up, you don't want to remove the glue of the coil on the former) and the dustcap too. That's a requirement to assemble it correctly. You'll need spacers too (you can create them yourself from foil, paper etc.).
The repair of the coil is not of much use though if the membrane is damaged and/or you can't get the surround (or a similar one).
The repair of the coil is not of much use though if the membrane is damaged and/or you can't get the surround (or a similar one).
Not sure which generation but SF generally use scanspeak drivers. Should be a part number on the side. Might be a SF custom version so you can't get a replacement but might be a start finding if anyone can fix it. Braver than me dissecting a £300 woofer!
Thanks for all you replies. It is well out of warranty so would have no chance with sonus faber. There are no scanspeak markings on the unit but i know which scanspeak unit it is. Thing is from what i have read and been told by loudspeaker retailers is that they had them modified by scanspeak and there is no longer any replacements. I might as well atempt repair now. After joining the 2 wires what coating coukd i use to insulate as per the original enamel? Also how could i adhere it back to the rest of the voice coil?
To glue it down it's best to use very thin fluid epoxy. Other 2K glues would work theoretically but most make the repaired area too thick. To isolate it, you can use a lot of different temperature stable paint types but as the 2nd reason for epoxy, it isolates well too, so I would just put on a (very thin) layer.
For a quick repair or experimental use cyanoacrylate ('super-glue') is interesting since it is very little effort, very fast result, an extremely thin layer is possible, it's extremely cheap and available everywhere. It is also easily removable with acetone (the voice coil lacquer probably too, though, chose a resistant paint). For permanent use it is unfortunately not suitable because it's not long-term temperature stable.
For a quick repair or experimental use cyanoacrylate ('super-glue') is interesting since it is very little effort, very fast result, an extremely thin layer is possible, it's extremely cheap and available everywhere. It is also easily removable with acetone (the voice coil lacquer probably too, though, chose a resistant paint). For permanent use it is unfortunately not suitable because it's not long-term temperature stable.
It looks like it failed at the layer transition, where the wire jumps up from the lower layer to the upper.
That is actually where the physical structure is the weakest and the thermal transfer is lowest.
Advice given is good. Just make sure the transition is not where the solder joint is. Have the solder joint on the lower layer so the epoxy can hold well to the former. And make sure from the joint up to the second layer it is well bonded so that it cannot be pulled from the structure. Remember, all of the wire is being forced by the current within the flux field, so it must be held well.
Get epoxy that has the highest glass transition temperature. If the wire exceeds that temp, the epoxy will go plastic and let go.
Go for it, have fun. After all, you can't break what's already broken, no?
John
That is actually where the physical structure is the weakest and the thermal transfer is lowest.
Advice given is good. Just make sure the transition is not where the solder joint is. Have the solder joint on the lower layer so the epoxy can hold well to the former. And make sure from the joint up to the second layer it is well bonded so that it cannot be pulled from the structure. Remember, all of the wire is being forced by the current within the flux field, so it must be held well.
Get epoxy that has the highest glass transition temperature. If the wire exceeds that temp, the epoxy will go plastic and let go.
Go for it, have fun. After all, you can't break what's already broken, no?
John
Normal epoxy is stable up to 150° and you will not be able to get to that temperature because of the power needed for that before you reach the mechanical limit of the driver. It is true that the ends of the voicecoil become hottest but you can see at the coil it never reached any critical temperature. At 150° you would see at least scorching marks on the coil, higher temperature would cause mechanical failure such as malformed former, brittle, burnt edge of the spider if not fire.
So no, higher temperature tolerance won't be necessary. It is so much more important to get a resin which you can work the easiest with. For such jobs that's the critical part what decides if you can save the driver or to dump it. Epoxy comes in a vast variety of viscosity, hardening time and usage range. Remember: You will most likely have no 3rd or even 2nd chance to correct any mistake. Take the one you can work with.
I would suggest you try that first on a driver from the 'cheap spare box' everyone got laying around.
The failure mode here is not uncommon.
The 'last' turns were not glue bonded properly causing the glue to let go and allowing the last turn of the VC to freely vibrate resulting in VC wire fatigue failure.
This would have occurred at significant power level with thermal and mechanical loads causing faulty glue bond failure.
In gross overload conditions multiple windings can shift causing mechanical rattling/scraping and ultimately VC wire fatigue failure.
The Voice Coil (Part 1) will give some insight into the operating conditions encountered by the adhesives used.
I have successfully repaired failures such as photographed above.
My procedure was to remove one turn, appropriately cut overlap lengths, tin 1mm or so of each wire end and then 'sweat' the joint at the same time pushing the windings together ensuring no looseness of the turns.
The next step is to bond the final turn to the coils and former by working high temp epoxy on/around the wires and also forming a chamfered meniscus between the final turns and VC former ensuring no raised protrusions.
Refitting of the cone/VC assembly requires removal of the dust cap and fitting of shims/shim material to ensure correct alignment around the central pole piece whilst glueing spider and surround.
This driver is repairable with care and skill.
Dan.
The article is interesting, but but not that thoroughly researched. There are several mistakes or at least one-sided arguments in it.
The stated copper percentage of the CCAW (copper clad aluminium wires) are not true. It varies from company to company, it does not matter from which country it comes. To claim it's dependent on the country is -
honestly said - rather ridiculous, you can order all over the world whatever you deem appropriate and also custom dimensions and percentages.
Instead of implying a higher copper percentage introduces a weight disadvantage (-> the copper makes your VC heavier) I would have expected mentioning both advantages and disadvantages of a higher copper part (up to 100% copper wire), i.e. the wire gets thinner (smaller air-gap possible), the much lower resistance of copper or that all of these characteristics can be an advantage or the opposite, depending on the situation and that none of that is strictly on only one side of the argument.
Also, the claim copper is cheap is plain wrong. It's been much more expensive than aluminium for a long time, that was the main reason for developing CCAW. Copper clad aluminium wire is also not suitable for a lot of uses because its lack of flexibility.
Another issue is the section about the defect voice coils. The 'Photo 7' which allegedly shows an intact and a destroyed VC, got a wrong description. They both are damaged. Look at the left one and compare the winding height of its left and right side, an intact one would be identical on both sides. You can clearly see the left side is much higher and got an uneven edge (goes like a wave, esp. on the left).
There are some more minor issues and a lot missing about the former material, especally in conjunction with the adhesives and temperatures (power), the geometry like importance of layers, inward/outward wound coils and so on. I mean, that's about production, why leave such things completely out and that heavily impacts the production and is also important for a lot of the behaviour of the driver in extreme situations, like power compression, stability/deforming. I don't expect all these things to be explained but at least some of them at least to be mentioned.
*ehem* back to topic..
The defect voicecoils in the article are all from PA drivers, which have completely different power levels, which also introduce much higher temperatures than this driver will ever reach without intentional damage.
The stated copper percentage of the CCAW (copper clad aluminium wires) are not true. It varies from company to company, it does not matter from which country it comes. To claim it's dependent on the country is -
honestly said - rather ridiculous, you can order all over the world whatever you deem appropriate and also custom dimensions and percentages.
Instead of implying a higher copper percentage introduces a weight disadvantage (-> the copper makes your VC heavier) I would have expected mentioning both advantages and disadvantages of a higher copper part (up to 100% copper wire), i.e. the wire gets thinner (smaller air-gap possible), the much lower resistance of copper or that all of these characteristics can be an advantage or the opposite, depending on the situation and that none of that is strictly on only one side of the argument.
Also, the claim copper is cheap is plain wrong. It's been much more expensive than aluminium for a long time, that was the main reason for developing CCAW. Copper clad aluminium wire is also not suitable for a lot of uses because its lack of flexibility.
Another issue is the section about the defect voice coils. The 'Photo 7' which allegedly shows an intact and a destroyed VC, got a wrong description. They both are damaged. Look at the left one and compare the winding height of its left and right side, an intact one would be identical on both sides. You can clearly see the left side is much higher and got an uneven edge (goes like a wave, esp. on the left).
There are some more minor issues and a lot missing about the former material, especally in conjunction with the adhesives and temperatures (power), the geometry like importance of layers, inward/outward wound coils and so on. I mean, that's about production, why leave such things completely out and that heavily impacts the production and is also important for a lot of the behaviour of the driver in extreme situations, like power compression, stability/deforming. I don't expect all these things to be explained but at least some of them at least to be mentioned.
*ehem* back to topic..
The defect voicecoils in the article are all from PA drivers, which have completely different power levels, which also introduce much higher temperatures than this driver will ever reach without intentional damage.
Well, be honest, the only really useful part of the article for this VC repair was 'do not use thermoplastic adhesive' - and that was determined in this thread already.
Several reasons.
Al is cheaper than Cu is a primary reason.
For VC application lower mass is claimed to be a benefit.
Counter claims are susceptibility of terminations to corrosion.
Other subjective claims is that it sounds just plain bad.
Dan.
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