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rbnjr
02-27-2016, 08:07 AM
Sort of a technical question here, the purpose of serializing a product to show exact numbers from the assembly line and to match equipment together per engineering requirements.
but as i found out, JBL has not followed those rules or someone swapped ID plates during the assembly process. i found that the serial number on the crossover boxes did not match the serial numbers found on the plates at the front of the boxes where the L pads mount. seems like they should be the same to me, but did JBL want to give the L pad assy a separate serial number? If that was the case then it should be on the board the L pads are mounted to..no such luck. As a side note does anyone know the difference between the L300 and the L300A?

If anyone could provide any insight as to why there are 2 different serial numbers im listening.

thank you. 70048

script56
02-27-2016, 10:03 AM
They're not supposed to match. The crossovers have their own serial numbers and the L300 cabinets have their own. They are the numbers on other label in pic. Your serials look correct. Each component in L300 is not going to all have same serial. The pots don't have serial numbers. The A version is later version. I think difference is ferrite woofer 136H not earlier A

mech986
03-01-2016, 03:28 AM
Script is correct. AFAIK, JBL did not "match" components to each other, nor to the individual unit. I suspect that JBL felt that their production quality and QC was good enough to ensure that, properly built and tested individually, the whole would also work just as well and "match" in sound and performance.

You will find that rarely will even an original owner get serial numbers within 10 numbers close, more like within 100. Each cabinet, crossover unit, woofer, midrange driver, mid horn, acoustic lens, and tweeter has an individual serial number, primarily for accounting sake and warranty. The actual diaphragms will have a handwritten part number on them.

If you look closely under the fiberglass inside the cabinet, you might find a build sheet if you're lucky from the cabinet shop.

Also, as JBL built lots and lots of speakers, they sent out "lots" of speakers to dealers by orders, so what was available was sent out fairly randomly, so even if you bought from a dealer, the dealer probably grabbed whatever they had, and didn't choose closely either, even though serial numbers were on the original boxes.

Just what was done in those days. It wasn't easy to do full unit by unit testing consistently, nor was there and easy way to document and record that before computers. In fact, KEF was the first to computer grade their drivers, and then component parts, even crossover components, then computer test the resulting complete speakers, and match them within 0.5 to 0.2 db. Same with the BBC LS3/5a monitors, and similar.