Foam rot, cheap repair and what's the result/effect ? -

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Latest post 11-02-2008 5:12 PM by ipaul. 3 replies.

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07-22-2007 5:21 PM

ipaul
Joined on 04-22-2007
Posts 378

Foam rot, cheap repair and what's the result/effect ?

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In a way this is linked to the thread below (about foam rot) but more about the solution.

This weekend i got a couple of CX50's with (known) foam rot.

Now i don't mind: it's a good way to get them cheap: i'll replace the woofers by new, original B&O's from a dealer (wonder how much they are these days as 'Denmark' seems to double/triple prices for parts in recent times...) and with new units they'll be as good as new.

However, as you may have seen on the web, several people offer new surrounds (to glue on yourself or companies do it, some even change them to rubber so it'll never rot again).

Now so far i haven't been keen to do so: my guess is if it's not exactly the same material and positioned (centered) the same way the specs of the driver will not be the same.

Where i'm getting at is that here and there people will do this 'cheap fix' and these (B&O) speakers will be 'on the market', but may not meet the specs anymore !!

Has anyone experience with this or are there any known measurement results ?

My guess is so far: nobody knows/tested so i'm happy buying 'rotten' CXs, at least i'll know how they're being repaired....:) but maybe my guess is totally wrong....????

07-22-2007 5:48 PM In reply to

Dillen
Joined on 02-14-2007
Copenhagen / Denmark
Posts 5,008

Re: Foam rot, cheap repair and what's the result/effect ?

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I've done countless refoam jobs, also on the CX range, a couple of pairs in currently.

A certain amount of skill and practice is needed to get it right
and, considering the repair cost, I wouldn't recommend anyone
to have a go themselves. The risk of ruining something or getting
it out of alignment could do permanent damage to the woofer and
it could end up a total waste of money and time instead of a cheap solution.
If you don't carefully shim up the coil and, in some extreme cases,
also the spider, you won't get a good solution.

Done correctly, the woofers are practically returned
to a "like new" status, also with the right frequency range etc.
The coil and impedance aren't changed so no worries at all regarding
the electric specs.
The woofers will need a certain amount of "playing-in" again to
losen up and sound right - not unlike when they were actually new.
Obviously, I cannot tell you what other people use but the surrounds I use for the repairs are extremely close to the originals - when they were new that is.

Martin

11-02-2008 8:09 AM In reply to

Good Hifi
Joined on 11-01-2008
Netherlands
Posts 18

Re: Foam rot, cheap repair and what's the result/effect ?

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Please note these 'new' replacement drivers are also 12 or more years old. They have been stocked on the shelves, so the foam rot didn't go that fast, but even in stock the foam rots! It's best to replace the rotten rings with new rings that have been pressed in recent times so they will last longer. It's also possible to replace these rings with rubber ones - results are very good if you you use the right (very rhin, low weight) rings. If you replace your units with the ones by B&O you may suffer foam rot again in a few years.

Good Hifi

11-02-2008 5:12 PM In reply to

ipaul
Joined on 04-22-2007
Posts 378

Re: Foam rot, cheap repair and what's the result/effect ?

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Did B&O tell you this or is it an assumption rather than a fact ??

Because to me it sounds very unlikely B&O (or any manufacturer) stocking up spares in advance for years, not knowing how much demand there is for it.

I've ordered many drivers also for (MX) tv's in the recent past and never had even the slightest impression it was 'old stuff', more logical would be that if they run out of stock they just have them made again from their supplier (say 500 poeces or so) as happened a few years ago with the battery lid for the 'chocolate bar' remote: it was out of stock but apparently still so much demand they had them made again.

If a manufacturer has to stock up spares for all their products for their lifespan they'd be broke and need enormous warehouses :)

(imagine the pile of picture tubes for Avants.......).

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