Originally Posted by hdmi4ever
Your observation of this weakness above 50 Hz compared to the MBM would also be observed in almost any other subwoofer. The main reason for the MBM's existence is that subwoofers aren't going to be as good at 50Hz and up as a woofer specifically designed for that 50+ range. For a fair comparison, you should be comparing the Rythmik with a VTF-2 alone (i.e. without the MBM).
Another thing is punchiness. I used to have a pair of Harbeth LS3/5A. It is one of those speakers begin with a big hump at 80hz before rolling off at the lower end. The perception of the bass quality is it is punchy and exciting at first. Linn, Harbeth and Rogers's competitor in UK, however came up with a similar speaker but has no hump at the same frequency. Linn had to explain to customers that it actually sounded more natural without the hump. I agree. I later sold my Harbeth LS3/5A. Long term listening experience is the bass actually sound pronounced and forward (as if the drummer sits in front of everyone else, which we know is not true. Drummer sits in the back). Actually it is very easy to explain. A hump is a high Q value, which means a signal can ring/linger longer (this applies to those argument that we should use multiple subs over different frequency band). That for some people produces a more solid/punchy bass (similar experience when I heard a Genelec PA subwoofer in a show, PA subwoofers often use high Q roll-off to attenuate low frequency more rapidly). Introducing another subwoofer will no double introduces a source of ringing. Speaker such as MBM is not critically damped at all. Most likely it is a Butterworth alignment. And that introduces an additional ringing that is otherwise absent if we use without MBM.
Most subwoofers are not coherent at 60hz-80hz. I have a measurement on the web showing that a nonservo subwoofer cannot even maintain same output over 4 sec of time.
This plot shows the continuous output at 60hz 200WRMS
The heat-up the voice coil is pretty noticeably and the output continue to go down. The means the first drum beat sounds louder than the last drum beat in a song even if they are meant to be the same strength from the recording. And in between, because the complex heat-up and cool-down processes interleaved with the song's rhythm, each drum beat has a slightly different deviation, a micro rhythm by itself.
In frequency domain, it shows significant side band energy. Side band energy means the signal is no longer a steady 60hz signal. It has warbled or drifted around 60hz.
Also notice the extra non-harmonic distortion (actually they are sub-harmonic distortions) begins to appear. This type of warbling is worst at the frequencies where impedance value is close to voice coil DC resistance. (And MBM indeed can alleviate this type of problem as its impedance peak should be around 60hz to 80hz.)
On the other hand with servo in the same driver and test condition we have
The spectral plot is
The background is also cleaner with only harmonic distortion observed.
Warbling can be translated to deterministic jitter. We all know how a low jitter CD player improves sound. Reducing warbling has the same effect. It is like a veil has been taken off.
I have been to a few live performance and often am surprised by how those bass instruments sound less punchy, but instead more free flowing like they are effortless and have no dinosaur tails. But that is just my experience. I am not saying one is better than other. That is why we say it is the art of sound. There are multiple angles.
I am glad that the posters use the word "real" to describe the bass sound from our subs. If you already have that, you are in the right direction Monomer. My comment was more of trying to learn from your setup to see if we have covered everything.