@zx10 The route you have taken is a growing trend and one methodology for using a Speaker that is worthwhile making the time for, to have it known about in a location where there is a broader audience.
A Speaker Model that has been used for this type of refurbishment with the end result being similar to your own, being a modern Xover Design built with Modern Components when Interfaced to a Olden Speaker Design brings exceptional results.
Myself I endorse this type of activity for two reasons, but my first reason is not exactly audio related, it more aligned to being active by doing less to encourage less CO2 release.
I am a Advocate of and Adopter of, being proactive in what is referred to in todays world as the Circular Economy.
My second reason is that designs from a particular era have been invested in quite healthily for the Parts that are able to be seen by the Purchaser, but under the hood, where concealment is the advantageous condition created, costings awarded to produce the Parts that are concealed have been scrimped on as a BOM and the concealment has been very very deliberate.
Why not at another time when Warranty Issues are over and other ideas are surfacing as a result of being inquisitive, spend a little time to Ponder how it might be if one was to couple to Quality Speaker Drive Units used from a past era of production, the most modern electrical parts and design concept for the Xover Interface.
Additionally, why let cost be the constraint, if $400 - $1500 is the costing for BOM of selected Parts and is inclusive of the cost of assembly of the electronics, then as a comparison to other options, this one is looing to be well within the boundaries of VFM.
What happens when the outcome of following through on such a methodology to experience something new from a Speaker, produces a Speaker that really does make a discernible change for the better, when using recollection if Olden Speaker Design to New Design for assessing the end sound. With better as the outcome, then what is the issue there are plenty of positives and wins with adopting this method.
A comparative Updated Speaker Design from certain Brands or a Build produced in recent times can easily be costing 400% - 2000% Increase in cost to own the Speaker as a current New Purchase. The Purchase comes with the unavoidable added condition, where after approx' 18 months - 30 months there will be seen a depreciation of Value of the Purchase by 30% - 50%.
In relation to the Speaker Model JBL L-100T, this model is replaceable currently with a Modern Design being the L100 Classic MkII. The Classic Mk II is going to cost the best part of $4K as a New Purchase and approx' 40% less as Used Item Purchase ($2.6K)
The Owned 100T Speakers, were most likely purchased in 1986 @ approx' $1K. $1K over the the 40 Years owned are actually costing $25 per year or $00.50c per week, which is great VFM, and in relation to the method used to make changes to the Speakers by zx10, there are other bonuses.
Bonus No1, Great VFM has been attained from the original purchase, especially with the outcome the Speaker are remaining wanted to be kept in daily use - Bonus No 2, The Owner of the Speaker, knows every day of the Upgraded Donor Speakers usage History - Bonus No 3, The Most Recent Xover Upgrade, is one that is producing a Bespoke Design for this Speaker and as a design it is highly likely the end design will be a challenge for the latest 100 Model to show where it is the better producer of an end sound.
As an investigator of Build Costs for Speakers, as having a commission built Speaker is an interest of mine. I am familiar (not expert) on costs of a small range of Drivers. From the 80's / 90's Drivers built to a High Spec' can easily be costed in todays monies at $2K to $4K if a set of 6 x equivalent drivers are being selected for a BOM.
I have seen on a few Build Topics for Speakers, where the guidance is for a Particular Model of Speaker, where a Modern Tweeter to be used in place of a Original Tweeter that is Shot, or being suggested as an Upgrade Tweeter for a Olden Design Speaker where the Pair of Tweeters being suggested are to cost as a New Part, the best part of $1K.
If an individual is in the fortunate position to have the set up in the listening space, where the Speakers are Coupled to the Room, where the energies produced from the Sound are managed to the point the energies are not interfering negatively with the Produced Sound. In conjunction with the management of Produced Sound, if the system can produce a Signal that is of the quality when it arrives at the Speaker Xover it is unadulterated.
It makes absolute sense that a improved electronics selected for the Xover, can add further attraction for the end sound that is being produced as the result of the changes made.
As stated in an earlier Post:
"Coupling a Speaker to a room is the way forward to create a confidence the speaker interacts at its best when transmitting sound through the physical structure of the room, including the floor, walls, ceiling and locally placed items.
The Speaker / Room Interaction can have a profound effect that is a negative impact on the quality of the sound being transferred. Creating effects like room modes (standing waves), Reflected Sound, Causing Local Placed Materials to produce sound. Each when being generated will be negatively affecting the overall acoustic characteristics of the room.
Xovers design does not do anything to alleviate the above influences on produced sound."
"The $27,900 disappointment? Wilson Audio Watt Puppy 8 issues..."