Revisiting the topic of ReQuests woofer replacement

[Spike]

Given that my ReQuests are approaching 25 years old, I am contemplating to "refresh" the ReQuests by:

1. replacing with new panels.
2. recapping the PSU and crossover boards.
3. replacing the woofers.

The woofers with the closest specs to the original ones are Eminence Lab 12C, but these are 89db efficiency compared to 91.6db for the original woofers. I am currently (passively) bi-amping so it is not an issue (yet). But I am thinking that while messing around with the crossover, I might as well modify it to accomodate for the 3db difference, just in case I want to simplify to 1 monobloc for each channel. For the gurus (JonFo?) knowledgeable with the ReQuest schematics, how do I modify the crossover to balance the panels with the new Eminence Lab 12C woofers.
Here's the link to Eminence Lab 12C woofers: Eminence Lab 12C Info
Here are the T/S parameters for both woofers:

Thiele & Small Parms	Stock ML Woofer	Eminence LAB 12C
RE OHMS	3.14	3.11
LE MH	0.65	1.09
QM	10.01	11.70
QE	0.36	0.34
QT	0.35	0.33
XMAX MM	7.90	13.00
BL TM	10.13	13.36
EFF%	0.91
FS HZ	25.78	23.00
MMS GMS	72.70	136.00
CMS mm/M	1.18	0.36
VAS LTRS	198.81	128.31
SD SCM	519.45	506.70
EBP	71.60	67.00
SPL db	91.60	88.90

 

[Rehan Azim Hashmi]

Good to know that something that has given you so much satisfaction over the years you value and have opted to refresh rather than scrap and buy recent models. Hope you are able to fully refresh. Hope these great loudspeakers provide you a minimum of another twenty years of great service.

 

[Spike]

Good to know that something that has given you so much satisfaction over the years you value and have opted to refresh rather than scrap and buy recent models.

Being an...enginerd, I adhere to the "keep it simple" and "do it once, do it right" principles when I put together my system. I just went through re-capping my amps & preamps and now, the ReQuests are next on the list.
For me, the biggest difference between the newer models vs the ReQuests is the internal class-D amp for the bass. I prefer the passive model so I can use my Levinson 331 class-A amp on the woofers. I have not heard the latest models ESL models, but the Summit-X did not impress me with its powered woofers, especially with the deep, male (baritone) vocals. The panels on the Summit-X are lightning fast, providing more details, but the vocals left me unimpressed. There is something right (tone/presence?) with the Levinson driving the woofers that makes voice magical. Perhaps it has to do with the right combination of low 180Hz crossover point, AND class-A amp for the bass. I wanted to like the passive ESL9, but the 2 8" woofers just don't do it for me w/o subwoofers (another class-D amp). I am sure the Materpiece series are great, but I don't have tens of thousands laying around for speaker upgrades.

 

[Rehan Azim Hashmi]

The 9’s may not have great classic understated acoustic suspension bass of Quest loudspeakers. They have a low frequency cut off point at 34 hz. But the quantity of bass is greater than Quest loudspeaker.

The 9’s are very well balanced with nothing lacking in highs, mids and low frequencies. In my system in which I use 2 amplifiers they sound great.

If I am not mistaken the 9’s will sound great when used with your amplification gear. However, a properly refreshed Quest will sound amazing for is a classic. Both options may give you amazing sonics.

 

[JonFo]

For the gurus (JonFo?) knowledgeable with the ReQuest schematics, how do I modify the crossover to balance the panels with the new Eminence Lab 12C woofers.

Well, my usual answer is 'ditch the passive and go active' so you have full control. You already bi-amp, so that part of the equation is solved.
Since you are technical, setting up a DriveRack Venu360 should be easy enough. You would need a REW measurement setup to measure and tweak.

But to directly respond, you just increase the gain to the woofer amp, or conversely, pad the input to the panel amp by however many dB you need to rebalance. Probably padding the line-level input to the panel amp is the easier to do.
There is even a review of another ML owner using attenuators for exactly this purpose: Robot Check

 

[Spike]

JonFo,
I am aware of the full active route where I can adjust the gain at the active crossover. Perhaps I did not word my question clearly... If I want (in the future) to simplify my system to using an integrated amp, I will need the ReQuests to be balanced between the panels and (new) Eminence woofers. Currently, I can just hook up the integrated amp to the ReQuests and be done. But in the case of a refreshed ReQuests with the new Eminence woofers being 3db less efficient than the stock woofers, I will need to modify the crossover to make up for the 3db loss. How would I modify the crossover to accommodate for the 3db difference between the stock and Eminence?

With regards to the Harrison Labs attenuators, I've been using 3db attenuators at the input of my Levinson to balance the gain with my SixPacs.

 

[JonFo]

How would I modify the crossover to accommodate for the 3db difference between the stock and Eminence?

Got it. But sorry, I'm not much help there, I'm not an EE, which is why I went active, much easier for me. Maybe one of our regulars who do know what values to recommend can help.