Strange death of Scanspeak mid range drivers - diyAudio
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Old 23rd January 2012, 12:59 PM   #1
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Question Strange death of Scanspeak mid range drivers

Can anybody explain this?
I have two mid range Scan Speak 13m/8636's, the ones with kevlar cones and both have died while not being used. They are in a pair of three way active speakers I made a few years ago but have been unused for 4 years due to a house rebuild... they were in safe dry storage and protected.
Now I come to fire them up and both these are open circuit. Checked the amps and they are fine with no offset voltage (they have protection for that anyway) so they seem to have died doing nothing: boredom?

Need to look for something else, pref' same size, 130mm and not too dear, any ideas please on both counts.
Thanks
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Old 21st January 2013, 08:03 PM   #2
ctrlx is offline ctrlx  United Kingdom
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check the braids that go from the speaker tags to the back of the cone
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Old 21st January 2013, 08:11 PM   #3
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I once had some Dynaudio 2 inch mid domes burn out seemingly too easily, and after dissecting them, I found that the ferro fluid only cover part of the voice coil...
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Old 21st January 2013, 09:01 PM   #4
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So what you are saying is that if you take an ohm meter to them they have no continuity? If they were working before I would almost suspect a failed solder connection between the lead out wires and a voice coil wire. I can't see any other failure mode that is electrical in nature, a voice coil just sitting will not fail by itself. If they contain ferro fluid perhaps it would be a chemical attack but since I do not know this particular driver I can't say.

Bob,
Ferro fluid is expensive, they were just probably using the minimum amount to increase power handling or to solve a resonance problem or to stop voicecoil rubbing or buzzing. It is a cheap insurance policy that many manufacturers use. The other thing that happens is if the device is not properly vented around the voicecoil gap you will often find the ferro fluid has actually been pushed out of the gap and is down in the bottom under the top plate or back at the back plate just sitting there. People seem to think that you can just add ferro fluid to any speaker, no you can't because of no venting to keep it where you put it, the mechanical forces from the voicecoil movement will hydraulically push it out of the gap.
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Old 21st January 2013, 09:07 PM   #5
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Quote:
Originally Posted by Kindhornman View Post
So what you are saying is that if you take an ohm meter to them they have no continuity? If they were working before I would almost suspect a failed solder connection between the lead out wires and a voice coil wire. I can't see any other failure mode that is electrical in nature, a voice coil just sitting will not fail by itself. If they contain ferro fluid perhaps it would be a chemical attack but since I do not know this particular driver I can't say.
Its a 5" midbass.

I'd expect the voice coil wire to be fairly thick, too, so wouldn't expect a failure mode common in tweeters.

Was the temperate kept fairly consistent?

I'd consider alerting Scan Speak to what's happened. They might request that you send them back so they may investigate, in which case, who knows, you might get some new drivers (its probably a slim chance, but its worth a go IMHO).

Chris
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Old 21st January 2013, 10:00 PM   #6
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Chris,
The voiccecoil wire itself will be rather small whether a high frequency or mid range driver. I would suspect the connection between the braided lead-out wire and the voicecoil wire. Sometimes they are not soldered at all but are a crimped connection. This is where I would be looking myself. Your advice to contact Scan Speak is a good idea though, he may find out that there was a bad batch of drivers. Though they have a good reputation so does Apple computers and they have hidden lots of bad product by just denying the existence of the problem.
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Old 21st January 2013, 10:27 PM   #7
VaNarn is offline VaNarn  Australia
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The soldered connection of the voice coil wire to the flexible braid could have corroded under the covering adhesive,a relatively easy fix. Another possibility is that the rigid glue bonding the voice coil former to the cone has shrunk or has become subjected to extremely cold conditions and has caused the wire to split. I suggest that if the problem is not tied up with the braids then you will need to remove the cone assembly for an examination.The surround should peel away from the frame after a light smear of water or alcohol is applied to the bonding area.(use an artists brush).The corrugated disc will require the use of acetone as a solvent,used sparingly and possibly repeated several times.Hopefully after the cone assembly has been inspected the cause of the failure will be known.
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