Looks can be deceiving. The 121 "Compact" may be the smallest member of our Radialstrahler family, but a single listen will convince you that the 121’s small footprint produces essentially the same wall-to-wall, “you-are-there” sonic thrills and musical magic found in each of mbl’s Radialstrahler designs.
“Radialstrahl” means to “emit sound in a circular signal.” And unlike conventional forward-firing box loudspeakers, the 121’s tweeter and midrange drivers act not as conventional point source radiators, but instead as pulsating 360-degree omnidirectional spheres. The 121’s bass enclosure houses a specially designed 5.5” woofer that, while seamlessly blending with the Radialstrahler drivers, creates, big, bold bass notes of impressive depth from such a small system. The critical tweeter and midrange drivers of the mbl 121 share technology with our legendary mbl 101 loudspeakers.
An important design goal in the mbl 121 was to provide all of the beauty, magic, and sheer realism, while keeping the cabinet footprint compact and elegant. To achieve this goal, the mbl 121 utilizes several unique low-frequency implementations:
Passive Bass Crossover Network
The mbl 121 uses a passive low-frequency crossover in order to provide:
a: Increased bass output
Typically, a compact cabinet results in reduced bass output. The passive matched crossover in the mbl 121 essentially doubles the effectiveness of the cabinet volume, which increases the overall low-frequency output. This crossover design allows the impedance reserve of the woofers to work in a push-push series connection.
b: Suppression of subsonic information
Below the tuning frequency of a vented box design, the excursion of the bass driver could take extreme dimensions, which easily could destroy it mechanically and distort its output. The mbl 121 uses a passive subsonic filter to eliminate any possibility of the lowest frequencies interfering with the driver operation, thus reducing unwanted (un-musical) distortions.
Psycho-Acoustically Aligned Energy ResponseThe mbl 121 applies Psycho-acoustic principles to the woofers with counter compensation. This is achieved by:
a: Increasing the bass group delay time
By increasing the slew rate in the bass range of the mbl 121, the group delay time is increased, resulting in extended bass impulses. This allows low-frequency information to be perceived more fully and clearly.
b: Incline of the energy curve
We calculated the gradient of the acoustic energy in the mbl 121 so that it declines with 3 dB over 2 decades towards the higher frequencies. The result is an acoustic increase, which makes the relatively-compact enclosure sound acoustically larger.
121's Bass/ Lower-Midrange Drivers:
Bass/ lower-midrange drivers in the mbl 121 are aligned in a push-push configuration, resulting in mutual power compensation; therefore, the cabinet is not stimulated mechanically to resonate.
Bass/ lower-midrange drivers in the mbl 121 utilize high temperature-tolerant aluminum voice coil carriers and aluminum membranes, which yield high load capacity, since the heat of the voice coil is led away to the membrane via the voice coil carrier.
Bass/ lower-midrange drivers in the mbl 121 utilize aluminum membranes with flanged edges which provide an absolutely deformation-free membrane surface resulting in zero-loss transmission of the mechanical movement of acoustic sound pressure.