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The 'donuts' in the 103-3 boxes-how important?

 
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jagster
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Joined: 11 Feb 2014
Posts: 12

PostPosted: Tue Feb 11, 2014 7:03 pm    Post subject: The 'donuts' in the 103-3 boxes-how important? Reply with quote

No, not Dunkin Donuts or any other favorites sweets. I don't quite understand why these are in there. From what I can observe, they do not attach themselves to the 'Pole' that seems to come down the center of the box. How would one go about replacing these little foam things? I have examined the speakers and do not see any access besides through the larger speaker hole, or the vent in the bottom of the cabinet. Is there another woofer inside the box or is there a passive radiator in there? I know, lots of questions, but this is a new one on me, and I have owned more speakers than a care to admit to having.
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g8xlh
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Joined: 25 Aug 2008
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PostPosted: Mon Feb 17, 2014 10:09 pm    Post subject: Reply with quote

I believe the donuts were designed to keep debris out of the magnet and voice coil. If the donuts have disintegrated there is a good chance the surrounds have gone as well. There are two drivers either end of the rod, one is easy to get too via the bottom of the cabinet, the other is via the crossover panel which needs removing. A socket set will help, but a lot of the car types will be too short to accomodate the length of the protruding screw . I have removed mine, and a few bleeding knuckles and a course in gynacology may help

Not sure what to do with mine, as the cost of surrounds and donuts, plus having never refoamed a speaker puts me off.

So at the present time they are resting in garage waiting further thought......
Alan
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Mon Feb 17, 2014 11:37 pm    Post subject: Reply with quote

The doughnuts seal the front from the back of the cone. i.e. if they are not there you have a front to back leak, via the voice coil. It does affect the alignment and the maximum output from the system at low frequencies.

"Doughnuts" perform the same function as conventional dustcaps but have to clear the anti-vibration rod joining the two drivers; hence doughnuts instead of domes.
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jagster
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Joined: 11 Feb 2014
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PostPosted: Sat Mar 29, 2014 8:46 pm    Post subject: Donuts and the design KEF 103-3 Reference Reply with quote

I, for one, am not impressed with this design, and if the main purpose was simply to strengthen the cabinet, then I believe other methods could have been employed. The little speakers and stands are already quite heavy and it would take substantial SPL's to make them 'rattle'. My thinking is to forego the huge metal rod and find typical high-end woofers that had the same specifications. In the alternative, why not just fit them with domes and be done with it? All suggestions and comments greatly appreciated. I have little invested in the pair, and have sourced the Kube and power supply for a sum total of $225 U.S.D. I am a tinkerer and will play with these in 'stock' form and try some alternatives. Interesting enough, the on-line sellers are commanding huge prices for these old oddities.
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audiolabtower
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PostPosted: Sun Mar 30, 2014 12:12 am    Post subject: Reply with quote

The rod is an integral part of the design and is called "force cancelling" because by coupling the 2 bass drivers together in this way their chassis vibration is much reduced by action and reaction reducing the resonances passed through to the cabinet and consequent unwanted colouration. Unfortunately it was not foreseen at the time that the foam surrounds required for the low resonant frequency drivers had a reduced lifetime compared to more traditional plastics or rubbers and would rot after a couple of decades.
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