Monolith III one note bass fix

It`s done a friend helped me measure the resonant peak, which was about + 4-5db at 80hz. The LCR network to get this flat is 18mh in series with 900uf in series with 5.6ohm across the bass speaker, in the Monolith`s case it`s easy to fit outside as the xover is outside the box. Just put it across the bass terminals on the back of the speaker. (btw this mod is NOT for MonolithIII`s with active IIIx xovers, only Monolith III`s using the IIIp passive xovers)
These values for the LCR are for my speakers which are 100% stuffed this may vary from the standard which is only 30% stuffed.
Anyhow the bass is now tight smooth and dynamic, much different to the standard one note bass the the Monoliths had.

One day i`ll do the standard measurements, but i like the detailed tight sound of an overdamped, low Q bass, it suits my not so large listening room.

I`ve done the measurment for the standard factory amount of stuffing and it`s the same, so use the same LCR components.

Cheers george

Some people have decided to go another way as well, (ACI SV12) with mixed reactions ( some finding a soft upper bass).
They have been replacing the Martin Logan driver with the ACI SV12.
I have gone into this the ACI driver, is a good sub woofer driver, however the upper bass 100hz to 200hz is not controled very well because of the heavier mass (weight) of the cone, i put this to the ACI head tech and showed him the specs on the original driver and he aggreed the the original would be better in the upper bass, and with the lcr network across, it`s almost as good in the lower bass. (I can send the spec sheet to anyone who wants it, ca`nt post it because of the limit of size, it`s 1meg) I got this from Jim Power at ML. Thanks Jim!
Cheers George

Spec Sheet for the original 12 in Monolith III driver

Here is a spec sheet on the original Monolith III 12in driver, thanks to Jim Power for the spec sheet, as you can see the MMS and MMD figures are 30grams below the ACV 12`s cone mass figures. Which makes it a far faster and better driver for the 100hz to 200hz region.

Thanks again to Jim from ML for the specs

Cheers George

Sorry it still sounds better with the sv12

Remember the crossover of the MLIII is 120-125hz so it doesn't really matter if the sv12 is slower in the 100-200 hz range. I have listened to the ML III stock (good), with the notch filter (much better, Ill give you that), and with the sv12 and notch filter (best). It's not even close and I'm using a tube amp to drive the ML III's.

Yeah Ted, the crossover is at 125 but it's only a 12db per octave slope, so we have quite a lot of usable output at 200hz still.
I had all intensions of getting the ACI Sv12's, then i read a couple of users remarks about the soft upperbass, which led me to have disscussions with the design tech for ACI and he was the one who said that after looking at the specs of the original driver, that he also had doubts about the performace capabilities of the SV12 against the original Eminence drivers in the 100hz to200hz region because of the 30gram extra mass the SV12 has to push. But that extra mass does give the SV12 a lower F/S 18hz (resonant fequency) than the Eminence 30hz, that's why the SV12 is considered a great subwoofer driver. good for 100hz down.

Cheers George