SpeakerTalk

[iso]

I bought pair of 12" JBL 123A-1 woofers from early 70´s. Both units are in reasonably good condition.

When measuring fs, it was apparent that one unit has maybe 5-10 hz lower resonance than the other unit and Q of resonance is also much higher. Cloth surround of the other unit seems to be perfect. Surround of the unit in question looks OK from back, but front side of the surround seems somehow dried and worn out from accordion highs and lows. Both spiders look quite alike.

Serial numbers of woofers are close ea other and cone numbers are correct fo 123A-1. So... it somehow seems that other unit has been reconed later with original reconekit. Only aftermarket recone kits are available now. Even if original ones should exist, it would probably be wiser to recone both units.

As there is not too much to loose, I figured that I should try to patch worn out surround. From Lancing heritage pages I found out that new water based surround dopes are not compatible with dopes used in 70`s. It came to my mind that Edelbrocks gasket glue (I suppose trade name is something like Gasgainch) can be used for dressing automotive drive belts, so it should be quite flexible.. Or does anybody have any better ideas for cloth surround refurbishing? Have I figured correctly that adding layer of dope to surround of woofer will make suspension stiffer and raise fs and make Q lower?

Best Regards

Kimmo

[ColinR]

Like shock sled silicone damping for radio controlled cars to damp lift/lower deices or dampers on tone arms, you should be able to source some cellulose dope from model plane/glider enthusiast sources, do a Google.
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