KEF 104/2 donut replacements

[Sub]

I recently bought a pair of these speakers, a matched set as have same serial number one marked A and the other B.
I found speaker A donuts on both woofers had perished, so decided to disassemble both speakers, replace the donuts, and also remove the crossovers to replace the circa 30 year old capacitors (I have bought replacement sets from Falcon Acoustics).
I discovered that the donuts on speaker B had been replaced at some time and were still intact - which begs the question, why weren’t the donuts in speaker A replaced at the same time?! I’m not going to get an answer from the guy I bought from - he was selling on behalf of his 85 year old father and has no knowledge of any work that may have been done in the past.
The replaced donuts are not made of the usual “foam” material, but are made of rubber.
I have searched extensively online, but can find no reference to replacement donuts being made of rubber. Anyone here heard or know of rubber donuts being used in the past?
Would it make a difference if the new donuts to be installed on speaker A are of a different material?
The donuts on speaker B are still in good condition, but should I replace them to ensure both sets of woofers have donuts made of the same material? My perfectionist self says yes, but would it be necessary?

[jandl100]

It would kind of niggle at me that they might sound different, so I would replace the donuts for both speakers.
Not that I am OCD or anything.

[fatmarley]

Can you not compare the speakers with some mono music? Obviously it's the low fequencies that are going to be affected, so it would be best to place both speakers next to each other and at equal distances from the walls because the distance from back and side walls will have an affect on low frequency response.

[Bigman80]

If you are doing one, you should do the other.

The surrounds should be the same material and the crossovers should age at the same time.

Whenever anyone buys KEF 104/2 you should always factor this necessity in to the price.

Get them done, sit back and know they really are a matched pair.

[Beobloke]

As above - replace the donuts in both speakers and put the proper foam replacements in.

[Sub]

Thanks all, have made up my mind to have all donuts of the same material. That will involve a 4.5 hour round trip to the nearest trusted technician with the necessary experience. At least I will have saved some cost by disassembling the speakers myself.

I would still be interested in knowing when rubber donuts were used, who made them and who sold them. Haven’t found anything online, so is a bit of a mystery I would like to clear up!

[Bigman80]

Thanks all, have made up my mind to have all donuts of the same material. That will involve a 4.5 hour round trip to the nearest trusted technician with the necessary experience. At least I will have saved some cost by disassembling the speakers myself.

I would still be interested in knowing when rubber donuts were used, who made them and who sold them. Haven’t found anything online, so is a bit of a mystery I would like to clear up!

Rubber donuts were on the later units. KEF did it and there were a few kits about that had rubber donuts. They aren't uncommon. What's odd is if one was foam and one was rubber.

You've made the absolute right choice in getting them all done and getting the same material on them all.

They are good speaker and you'll be very pleased once they are done.

[Sub]

The rubber donuts on spkr B look like they have been there a while and look very professionally done. Which had me wondering if it was a factory install. But that didn’t make sense to me, that a matched pair would have rubber donuts on one and foam on the other!

I have read all early woofers had foam surrounds as well, but mine clearly have factory installed rubber surrounds.

Life is full of mysteries.

[Bigman80]

The rubber donuts on spkr B look like they have been there a while and look very professionally done. Which had me wondering if it was a factory install. But that didn’t make sense to me, that a matched pair would have rubber donuts on one and foam on the other!

I have read all early woofers had foam surrounds as well, but mine clearly have factory installed rubber surrounds.

Life is full of mysteries.

I'd suspect a repair was done at some point but that's just speculation.

No matter now, you've done the right thing.

[Lawrence001]

Or the B200s were blown and replaced with new units with rubber doughnuts. I have to admit I've never heard of any original Kef units with rubber doughnuts. The earlier ones had rubber surrounds and foam doughnuts, the later ones all foam, in the 104/2s that is. Can't speak for 105 types, never owned any.

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