This has nothing in particular to do with JBL products, but in a "meta" way, has a lot to do with them in general, or more precisely, our "duties" as "caretakers" of history, among other concerns.
The below "essay" was a reply to a message on another board, as a response to someone who was considering sending parts from a pair of the legendary Dahlquist DQ10s to Regnar, for "upgrade" (ie, lots of changes- different crossovers, different wiring, driver changes, etc), that essentially, in MY eyes, result in a speaker that is NOT a Dahlquist anymore, in any functional sense of sound balance, etc.
Here goes. Comments anyone?
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(Please don't take this the wrong way...)
... but to tell the truth, the ONLY repair I am in favor of in a DQ10, is re-foaming (replacing the foam surrounds) the woofer when needed, or replacing anything that is ACTUALLY broken, ie, NOT working as it originally did.
IME, unless the speaker has been abused and things physically damaged or burned out, there is little or nothing in a DQ10 that suddenly quits working properly. Yes, if something is actually damaged, replace/repair it... but all this talk about "upgrading" a DQ10, is IMHO, a big waste of time. Where are you going to start, and where are you going to end? Heck, pretty much ANYTHING in a DQ10 can be "upgraded", technology has given us better drivers, better crossover components, better wiring... but the thing is- IF YOU LIKE THE SOUND OF THE DQ10 NOW, THERE IS NO GUARANTEE YOU WILL LIKE THE SOUND- AT ALL- AFTER ALL THE CHANGES.
Basically, in short, EVERY mod done to the DQ10, CHANGES the sound of the speaker in some way. Usually, it's tonal balance shifts (any driver change or crossover component change is GUARANTEED to do this, in some way, shape or form), sometimes it's change in phase behaviour (crossover mods and changes to driver location/geometry are pretty much guaranteed to do this). Once you've started the "upgrade" path, it's like opening the proverbial Pandora's Box... one "upgrade" upsets the tonal balance in ONE direction, which requires ANOTHER change to try to correct that, which usually requires yet ANOTHER change to offset unintended consequences of the SECOND upgrade... ad infinitum. In a speaker as complex as the DQ10, this can turn into a real quagmire, REAL quick.
The bottom line is, in any case... if you LIKE the DQ10, LISTEN to the DQ10, as it is. If not, for the money you'll spend upgrading EVERYTHING that can be theoretically "upgraded" in a DQ10, you can EASILY build a more modern speaker, with MUCH MORE ADVANTAGEOUS driver layouts, that will KILL the DQ10 baffle/driver layout in EVERY way. The speaker was designed as it was, as a BRILLIANT solution to the rather stark limitations of drivers in its day... limitations that NO LONGER exist, to ANYWHERE NEAR the degree that they did then. We have MUCH higher bandwidth, better behaved drivers, and the capability of designing networks to maximize their performance by computer, to the point where you don't usually NEED a 5-way speaker, to get every driver in its' optimal operating range, unless you want to play 120 dB and actually NEED an 18" woofer to get that loud in the bass(and a 3-way or more to keep up with that on the mids and highs).
Simply put, if it ain't broke, don't fix it. If you want different, buy or build different, it'll be MUCH easier and more time efficient, than flogging this poor 25 year old speaker like the proverbial dead horse...
Sorry if this ruffles feathers here... but IME, this is the stone cold truth. With speakers designed by people as talented as Jon Dahlquist, it's hard to improve them, without going to pretty big measures, because of the deliberate optimization (and inherent inter-dependence of components such optimization introduces) that was so pain-stakingly done in the first place...
Not only that, but there's also the HISTORICAL aspects of this. How many people have seen the automotive equivalent of this- the value of an UN-MODIFIED classic car, vs. that of one that has has "upgrades" (ie, hacked up, non-original parts installed, etc) done to them? In a long-term historical perspective, modified products, with the exception of the cases where by rare good fortune of having a modifier SO compelling, that the mod ITSELF becomes classic), have VERY little value in keeping a record of a time and place. I personally just hate to see legitimate pieces of history, marred beyond recovery...
who's seen more Dynaco and Dahlquist equipment BUTCHERED over the years, sacrificed on the altar of "upgrade"...