I just wanted to take a minute to share my experiences I have had with your JBL 125A Aftermarket Kit.
I am using 8 JBL 125A woofers in a project I am building as I have long loved the sound of these wonderful vintage drivers. After messing around with the inconsistencies of re-foaming old 125A drivers I have come to the conclusion that re-coning these old drivers is the best way to go if you want a properly
aligned and functioning 125A. Re-foaming these old drivers can work out well sometimes if the cone, spider and voice coil are in great shape but from what I have found in my experiences is that in most cases the spiders are deformed and miss-shaped so even the best re-foam job can be troublesome with poorly aligned voice coils being the result in these old drivers. especially under high excursion cone positions. Plus, the old spiders just seem to loose their compliance and overall control of the voice coil with age resulting in a “floppy” suspension rendering the driver subject to alignment errors.
In worst cases I have actually seen the paper voice coil formers distorted and bubbled from not heat but moisture because in some cases these drivers are nearly 40 years old and have been stored in basements or non-climate controlled lockers. Imagine how worn out and fragile a 40 year old newspaper would be after 40 years of being tossed around!
So all this leads me to where I am at now, re-coning 40 year old JBL 125A drivers. The first and probably the best option is an original JBL re-cone job that is guaranteed to be exactly like the original but at a very pricey figure. Well, like I mentioned before I am using eight of these drivers in my speaker
project so that option is pricey times eight. Ouch! So that brought me to a second option which is the aftermarket JBL 125A/127A unassembled kit. The kits were very carefully packed and shipped in a box that gives generous space for all the parts so everything arrived at my door in perfect condition.
After examining and comparing the parts to the original parts from an old 125A I found the parts to be a very good to near perfect match. First off, the new voice coils provided in the kit are wound in the same manner as the original voice coils and measured very close to the same DC resistance as the original coils but are wound on what appears to be a Kapton former instead of the original paper former. Some people may be judgmental to this change but I know from experience that a Kapton former will keep its shape better over time and handle rough conditions better than paper. Next I compared the cones and outer suspension, I must say here that the cones are in my opinion exactly identical, period. They seem to have the exact same shape, thickness, fit, density, weight, and outer foam suspension as the original JBLs. In my opinion JBL could be using these cones and nobody would know the difference. Then I compared the spiders, the new spider is just slightly smaller in outer diameter than the original JBL spider and it has one less “hump” although it was a perfect fit to the voice coil and allows proper alignment and does not limit cone travel. The new spider does seem to have a slightly lower compliance than the original one but keep in mind I was comparing it to a spider that was 40 years old and loose as a goose. Finally the kit is supplied with two dust caps, one for the inverted 125A driver application and the other for the convex 127A . These dust caps are also as close to the originals as one could ask for. The outer gaskets are somewhat different though in style to the originals so I very carefully removed my old gaskets and used them instead of the new gaskets and that made the driver practically indistinguishable from the original driver.
And finally, the sound? First I compared the finished driver with the new aftermarket kit to an original 125A with like new, near perfect suspension. I was powering the drivers with a Hafler 500 I use on my test bench so available power was not a limiting issue. In the first test I wanted to compare excursion capability with respect to distortion so I set my tone generator to 15 hz and took the drivers for a slow but hard drive. Clearly, the driver with the aftermarket kit could be driven much harder and could produce far more travel with absolutely no distortion or suspension noise as compared to the original JBL cone and suspension. The original driver would start making pumping noises when slightly over-driven but in comparison with the same signal applied the aftermarket driver remained silent and in complete control. This most likely is the result of the looseness associated with the older more compliant spider I mentioned earlier however the outer foam suspension was in like new condition so I doubt that had any effect.
When the drivers were compared in listening tests they sounded pretty much the same overall, however the original drivers did sound “boomy” and a bit resonant in the extreme low end response as compared to the aftermarket kit drivers. This could be the cause of a number of different reasons, one could be the fact that the old suspension in the original driver was “loose” and that of course would increase its compliance as compared to the new suspension that was not even broken in yet. It could also be related to the fact that the original JBL spider was slightly larger than the aftermarket one and that could as well cause a change in overall compliance.
My final words on all this is that the aftermarket kits are well worth the money and for my purposes a great deal! I must add that the kits are completely un-assembled, so if you have never had any experience with speaker re-coning or have an unsteady hand this process may not be for you. The kit comes supplied with detailed instructions but are somewhat generic for a number of drivers and styles of kits but will give you step by step instructions and the answers most would need to perform the job of re-conning a speaker.