Stiff surrounds on 60s Coral woofers

[oldman55]

I am replacing some vintage 60s Coral 12" woofers with crimped paper surrounds. However, the surrounds only allow the cone to move in and out about 1/8" in either direction unless a lot of pressure in put on them.
Is it possible that the cardboard cone/surround has stiffened with age or were they originally like that. Sure doesnt have much displacement.
I was thinking of putting a liquid butyl coating on the surrounds to make them more pliable but dont know if that was the intent of the design. These are ported speakers.

 

[teal'c]

No experience with those, but my 60's JBL LE-10 woofers don't move much either. I don't think there was a lot of thumping going on back then.

 

[macgolf]

The 10" drivers on my 2 pairs of Corals don't move much. They play through 8,000 hz so not a lot of base. My 1st set I had success with petroleum jelly and playing them for a few weeks. The second set, I picked up last spring, I used baby oil and followed up with the petroleum jelly prior to putting them into service.

 

[oldman55]

Any idea if these were stiff from the factory or stiffened over time? As they are just pressed paper pulp, you would think that they would be stable over time.
But on the other hand, why would they cut a port in the speaker face especially when the mids are in their own cans unless there was significant air movement (which there is not with these stiff surrounds).

 

[bazz_77]

Those kind of surrounds are usually very stiff by nature. I don't think there's nothing wrong with them.

 

[macgolf]

Any idea if these were stiff from the factory or stiffened over time? As they are just pressed paper pulp, you would think that they would be stable over time.
But on the other hand, why would they cut a port in the speaker face especially when the mids are in their own cans unless there was significant air movement (which there is not with these stiff surrounds).
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My BX-300's were supposed to be 102db 1w/1m yet even after a few hundred hours of playing they were no more sensitive than my 90db Marantz speakers. I treated one with petroleum jelly and forgot until a few weeks later when a channel imbalance developed. Promptly treated the other to right things. That was 2 years ago. This past spring I got the ported floor version(BX-1001). The surrounds were extremely stiff compared to my treated pair so they got the treatment.
Not sure of the composition of the surrounds but both of my pairs have small sealed mids so there should be some reason for sealing the back. They are still fairly stiff ,so I expect that may have been part of the design.

Nice pics, what model are these?

 

[oldman55]

Those kind of surrounds are usually very stiff by nature. I don't think there's nothing wrong with them.

Kanazawa KS 54H. I have a pair of recapped KS 55H and they sound fantastic. I didnt pull the woofers on them to see the surrounds but from the back they appeared to have a butyl coating and they had more movement.

I put these woofers in and they sound terrible, no bass to speak of.

I think I am going to replace the woofers but being 16 ohm, choices are limited. How much modification would be required to the xover if I replaced them with 8 ohm? Or can I just add a resistor to one or both leads of an 8 ohm woofer?

55H prior to recap: