Over the years I have seen several articles on how the human ear perceives lower frequencies similar to this one:  

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earcrv.html

This quote is interesting:

"One of the implications of this aspect of human hearing is that you will perceive a progressive loss of bass frequencies as a given sound becomes softer and softer. For example if you are listening to a recording of an orchestra and you turn the volume down, you will find that the bass instruments are less and less prominent. This is the purpose of the so-called "loudness contours" on audio amplifiers; they allow you to boost the bass frequencies when you are listening at low sound levels to give you a more realistic balance of the high and low frequencies in the music."

If you go to the link and look at their graphs the frequencies between 50 and 150 Hz really take a hit (compared to higher frequencies) as volume is reduced. The Mid Bass Module reinforces that frequency range making listening at low to moderate volumes very satisfying.

4krow,

I appreciate your input and agree with your statement regarding traditional subwoofers:

"But, as I stated, matched with the right speakers was important so that the two could be as seamless as possible. Driver distortion is unbelievably high in the lower regions of frequency, making less of a note and more of a thud as a rule."

Since the Mid Bass Module is not a Subwoofer it does not seem to present the same challenges integrating with the mains. And the light weight 12" driver really pumps out the notes and not the thud.

"Still, we have all visited those who have systems that they are so proud of because it can rattle windows....hmmmm to each his own I guess."

LOL !!  Yea, we have all met that guy at one time or another.

My fasination with the HSU Mid Bass Module really centers around what it adds to the listening experience at low to medium volumes. This is where I listen 90% of the time and there are certainly no windows rattling.

Man, That's what I love about these issues. The different ideas that have been tried, some successfully. I never quit experimenting with sound. It still is important to me to be able to return to the original if I don't like what I hear.
Bass is so special because of our rooms and taste. And sometimes I wish I had several systems to listen to in order to get what I want at that moment.

Looking at the spec on my m/l`s they go down to 40Hz. Not sure what the double bass is capable of but not ever having tried subs I`m sure
I can hear well enough a long way down to the point where the air shift takes over and you get that `felt` pulse, even to the point where you think your ears may not take to kindly to low sonics.
Given that my Decware amp gear is renowned for bass reproduction this means that they pass on the large wattage shift of some bass extensions by using very generous component specs so they dont get `swamped`.
The band sound balance is a touchy subject if you`ve ever played live. Volume controls easily creep up if not kept an eye on by a third party aka recording engineers in studios or if a big band the control desk, PA, in live play.
Ideally your finished recorded sound should be `just so`.
Listening to G.Deads live double I cant help but ask the bass player to back off as it is very raw and transmits a lot of energy. Not comfortable but for `Dead heads` which I`m not. There are many similar recordings where bass `energy` is felt more than others.
Live, the whole band will be very loud and in my experience the bass is not usually prominent, but is more the texture or floor that the rest of the band live in.
Bad experiences, one or two : Humble Pie in S. Marriots home town Assenbly Hall. OMG the bass was dangerous. Windows were very loud, you could feel the blood draining as your chest was being thumped. It was total nausea and you really thought eardrums were at risk. Took some time to acclimatise.

marky,

Good Observation:

"Live, the whole band will be very loud and in my experience the bass is not usually prominent, but is more the texture or floor that the rest of the band live in."

Some of that depends on the band, music style, the acoustics of the live venue or recording if listening at home. I listen to a lot of Live Blues in local clubs and they tend to have the balance such that you can hear the individual bass notes as you watch the bass player pluck the strings.

I have been to more than a few live shows where the bass is more of a soup, not much bass note definition. On recordings some times the bass sounds more like a broth (thin and no defined notes).

The Mid Bass Module I've been using seems to have the ability to lift the individual bass notes out of the soup. Especially at low to moderate volumes where I do 90% of my listening.

For the last 4 days I have really been hooked on the Red Hot Chili Peppers. I've had these CD's for years but they were never my favorites. Now that I can hear all the individual bass guitar notes I have to say their bass player "Flea" really lays down a nice groove on all their songs.

Great thread and great info. One of things I noticed with the Anedio D2 Dac was how much more satisfying the music was at low volume levels. Same output volts as the other dac. More more weight and body. Recently I changed my source feeding the Anedio with a Bryston BPD-1 music player. Even more improvement. I now listen at lower volume levels and still feel the same weight and body. Both these units offer extremely low distortion levels and noise floor. Is that what accounts for what I am hearing?