MBL 111B loudspeaker
By John Atkinson   •   August, 2002 It was almost five years ago that I first spent some serious auditioning time with an omnidirectional two-piece speaker from German manufacturer MBL: the four-way MBL 111. When I reviewed the 111 in the April 1998 Stereophile, I had been extremely impressed with the speaker's stereo imaging, which was superbly stable and well-defined, with images that floated completely free of the speaker positions. The tonal balance was also excellent, with a rich midrange, superbly clean highs, and extended lows. "This Radialstrahler is one of the best tweeters I have experienced," I wrote. In fact, the 111 was let down only by bass frequencies that tended to lag behind the music slightly.

All in all, the original 111 was a favorite speaker of mine, so when MBL of America's Peter Alexander contacted me about reviewing its successor, I needed little persuading.

Doing it differently
The very strange-looking MBL 111B features upper-frequency drive-units resembling an array of orange segments. Each Radialstrahler uses a magnet/voice-coil "motor," but this is arranged vertically rather than horizontally. The voice-coil is fastened to the ends of a number of vertical petallike elements, these arranged in a circle around a central sphere. Each "petal" is fixed to a cap at its other end. As the coil moves up and down in response to the electrical signal, the petals are forced to bend in and out, producing sound in a manner analogous to the ideal "pulsating sphere." Because of the circular array of petals, there is no preferred axis, implying an omnidirectional radiation pattern.

To complement the omnidirectional radiation pattern in the high frequencies, the original 111 used a single midrange driver firing upward into a conical diffuser. This has been replaced in the 111B by a pair of 5" units placed on the sides of the cabinet. (All that can be seen on the front, where you'd expect to see a drive-unit, is a brass styling disc.) While this placement may seem perverse, the small radiating diameter of these units and the low frequency at which they hand over to the upper-midrange Radialstrahler mean that they still radiate a full complement of midrange frequencies to the front of the speaker.

As in the 1997 version, low frequencies are handled by a separate woofer enclosure housing a 12" metal-cone unit made by MBL. This energizes an internal cavity that in turn radiates sound from two 2"-diameter flared ports at the unit's base. Because the wavelengths of sound below are enormous compared with the size of the radiating ports—greater than 10' vs 2"—the 111's low-frequency driver is inherently omnidirectional.

Electrical connection is via two pairs of binding posts. As I've come to expect from MBL, the 111B's fit and finish are superb (the review samples had a gloss-black finish). The 111 had featured an array of four rods that continued the pyramidal styling upward to meet at a gold-plated metal diffuser. The 111B replaces the rods with a substantial perforated metal hood or grille that clips into place over the bending-wave driver. Sturdy spikes are supplied to couple the speaker to the floor.

The upper-frequency enclosure is also available as a center-speaker version, the MBL 111RC, for $5800 each. The passive bandpass woofer enclosure can be replaced by a less expensive active woofer.

Sound
MBL's designer, Jürgen Reis, had warned me that the 111B sounded its best with the spikes fitted and without the grille. But to get a baseline on the speaker's performance, I did my preliminary auditioning with the grilles in place and the speakers' broad feet resting directly on the carpet. The listening axis recommended by MBL's informative handbook is a quite high 43" from the floor. However, I didn't notice much change in tonal balance as long as my ears were somewhere around the height of the higher-frequency omnidirectional drive-units.

Setup was a little problematic: the exact balance between the low treble and the top two octaves was very dependent on both the room acoustics and the distance between the omni drivers and the room boundaries. In a sparsely furnished room with lively acoustics, it's possible that the 111Bs might sound tilted-up. After some experimentation, I ended up with a high-frequency balance that sounded neutral, if rather laidback, but the sound got distinctly brighter when I moved to the speakers' sides—which emphasizes the need for the sidewalls in the vicinity of the speakers to be fairly well-damped.