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Multi-Way Conventional loudspeakers with crossovers

Tannoy Jupiter J40 Coil Scrape
Tannoy Jupiter J40 Coil Scrape
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Old 12th February 2019, 10:07 AM   #1
microkid2 is offline microkid2
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Smile Tannoy Jupiter J40 Coil Scrape

Hi - I have a pair of Tannoy Jupiter J40s circa 1985 that have developed coil scrape in one woofer. With the woofers removed if I gentle push it in by pressing on the (plastic) dust cover it seems ok. But if I put my finger top or bottom of it there is some scrapping. Moving fingers to left or right of it it is not so bad. If I place my fingers under the cone and bring it forwards i can feel scrape at the towards the top of the travel. If I apply pressure to the left side of the cone the scrape pretty much disappears. Doing these same tests on the other woofer produces no scrape at all.

Is this likely to be fixable? Obviously i can not get a recone kit anymore and finding one secondhand (for the jupiter) which doesnt have same issue is nigh on impossible so my options are limited it seems.

Any suggestions gratefully received.
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Old 12th February 2019, 01:13 PM   #2
charlie2 is offline charlie2  England
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Common issue, take out the driver and rotate 180 degrees spin it round so the top is at the bottom and try it, usually sagging spider if it still persists after a week of trying will probably need a new driver

Hope this helps

Ps unless it has been overdriven and abused
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Old 12th February 2019, 01:15 PM   #3
microkid2 is offline microkid2
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Yeah I dont think rotating will help this - i think ideally it needs a recone or a rebuild but I cant find a kit - perhaps I could get away with just replacing the spider and rubber surround
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Old 12th February 2019, 01:26 PM   #4
chris661 is offline chris661  United Kingdom
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Rotating and leaving it for a few months might help - these things creep over time.

You might be able to speed it up with heat to soften things up a bit.

Chris
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Old 12th February 2019, 03:23 PM   #5
microkid2 is offline microkid2
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I have had it rotated for about 1 month - no difference - I should say it only scrapes when working hard (probably towards either end of it's travel) it doesn't scrape all of the time. If I press gently directly in the middle of the dust cap no scrape. This makes me think that perhaps the spider is unable to keep the coil centered under load? I don't think the rubber surround is likley to be the issue. I'm tempted to take it apart and replace the spider (which also means the surround). Whilst its apart I can then check the voice coil which if deformed makes thinsg a whole lot harder! Anybody done this before? I have refoamed my Kef 104/2 but never replaced a spider? What would be the best solvent to seperate the rubber surround from the polyolefin (plastic) cone?
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Old 13th February 2019, 09:14 AM   #6
microkid2 is offline microkid2
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I decided I had nothing to lose by trying a few tricks before attempting a recon. I used a hair drier (as suggest above) to heat up the spider. I noticed when it was 'hot' that the scrape had pretty much gone, but returned as it cooled. I repeated the process whilst applying gentle pressure in the direction that seemed to reduce the scrape (upwards) after two or three repeats of this the scrape has all but gone. If I push the cone in 12'0' clock position at its very edge I get some gentle scrape (perhaps to be expected as I am pushing off centre) but pushing anywhere else (even the 3,6, or 9 o clock positions at the edge) no scrape. Pushing up and down from the centre (voice coil) produces no scrape. So I think this unit may live for another day now. I will of course rotate 180 degrees when back in the cabinet.

One question that occurs to me is, can the spider lose its effectiveness to return the cone to its 'null' position and if so how will this affect the sound? If seems ok to me both units about the same, but I have nothing to compare with.
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Old 13th February 2019, 10:31 AM   #7
chris661 is offline chris661  United Kingdom
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Spiders do eventually sag, but that's more of a problem for down-firing subwoofers with heavy cones.

For anything over 10 years old with a fairly large cone, I'd just rotate the drivers by 180 degrees every year or so.

Chris
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