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JBL's advice for the D-series drivers (except the D-145) was to tune the box to 40 Hz, but I never saw any evidence that Fender ever heeded it.
![jbl serial number registry jbl serial number registry](https://www.picclickimg.com/00/s/MTQ0MFg4MTA=/z/t9cAAOSw-ldZa2Nc/$/Vintage-JBL-L100-speakers-matching-serial-numbers-_1.jpg)
And after THAT, their respective work may have been known and understood at JBL, but that doesn't necessarily mean that it had been disseminated to or understood at Fender - witness the ill-fated mid-70's era 'pyramid' 4-12's cab that seems to have no basis in any sort of acoustic theory whatsoever. Thiele's basic paper had been published in Australia by then, but was relatively unknown until it was republished in the AES Journal in 1971, and Small's articles expanding on Thiele's work weren't published until after that. Click to expand.Not to be too pedantic, but I'm not certain this is accurate that cab was designed (such as it was) in about 1967.
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