HSU Mid-Bass Module
First time post here at AVS. I've have twin Mid-Bass modules and twin USL-15 subs for some time now. Since this is my first AVS post I'm not allowed to post links. If you Google (MBM Adding Weight & Body) you will find my thread over at the Decware forum for a lengthy discussion.
An important area I cover later in the thread is potential ground loop hum on the MBM-12's. HSU elected to use a 2 conductor power cord Hot & Neutral (No Earth Ground). In some cases this produces a low level 60hz hum (ground loop) causing a boomy effect if you turn the MBM volume up past about about 10 O'clock. In my case it was a simple fix as described and I now run the MBM volume at about 1 O'clock with very smooth & solid mid-bass. So if your MBM gets boomy as you turn it up anywhere near 12 O'clock then you will want to check this portion of the thread out.
IMO run the MBM full range 150hz. Even though this overlaps your mains it integrates seamlessly. The MBM due to it's specific design will reproduce the 50-150hz range with more punch and clarity than your mains are capable of. In my thread I reference a link to an interactive chart that provides a graphic display of how music material resides in the 50-150 range. I listen at much lower volume levels now because the music is so much fuller and with improved clarity.
I use twin MBM's running full range located along the front wall near my mains to avoid localization. This works great on music & HT. I've experimented with a single MBM located anywhere between the mains and get about 90% of the performance compared to using two MBM's. So you don't need two MBM's to get a big performance upgrade.