MB Quart 390 Speaker System Review

The West German company MB Quart may be a new name to American audiophiles, but it has been in business for more than twenty years (formerly under the name Peerless MB) making microphones, headphones, and speaker drivers. The company’s drivers are still used by many well-known speaker manufacturers in Europe and North America, and its own line of MB Quart systems are among the best-selling speakers in Germany. Unlike most other loudspeaker companies, which purchase many of their drivers and other components from outside sources, MB Quart fabricates “in house” more than 80 percent of the parts going into its speakers.

All MB Quart speakers use infinite-baffle (sealed-enclosure) woofers and 1-inch titanium-dome tweeters. Titanium is extremely rigid and light, making it an ideal material for a tweeter dome. The woofers have butyl-rubber suspensions and ceramic magnets, and the cones are aged and processed so that they too are low in mass and highly rigid. The crossover networks use close-tolerance air-core inductors and high-quality capacitors. The cabinets are made of 7/8-inch-thick, multilayer, compressed-wood panels, with solid-wood corners and edges. The front panels are flocked with a special material whose fibers are electrostatically aligned at right angles to the panel’s surface in order to minimize diffraction effects that could affect the speaker’s radiation pattern.

The MB Quart 390 is a three-way bookshelf system that measures about 20-1/2 inches high, 12-1/4 inches wide, and 11-3/4 inches deep and weighs 28 pounds. It features a 10-inch woofer, which crosses over at 400 Hz, with an 18-dB-per-octave slope, to a 4-inch midrange driver. The soft-dome midrange is constructed much like the woofer, with a compliant butyl-rubber suspension, and it is acoustically isolated from the woofer. The 12-dB-per-octave crossover to the ferrofluid-cooled tweeter is at 1,800 Hz.

The woofer is located at the bottom of the speaker panel. The two higher-frequency drivers are vertically aligned above it, slightly to the left of the center line. All the drivers are mounted flush with the panel, and the removable black cloth grille is retained by plastic snaps. The binding-post terminals, recessed into the rear of the cabinet, accept bare wires or single banana plugs, but their Vs-inch spacing prevents the use of standard dual banana plugs (which have 3/4-inch centers). There are no external balance adjustments.

According to the manufacturer, the Model 390 can handle up to 130 watts of continuous sine-wave input, and a minimum amplifier rating of 35 watts per channel is recommended. The system’s rated frequency response is 40 to 32,000 Hz (no tolerance specified). Its nominal impedance is 4 ohms, and the rated sensitivity is 87 dB sound-pressure level (SPL) at 1 meter with an input of 1 watt.

The standard cabinet finish for the MB Quart 390 is matte gray, white, or black lacquer. Special-order finishes include pine, mahogany, rosewood, and cherry veneers, high-gloss white or black lacquer, and a high-gloss walnut. The speakers carry a five-year limited warranty. Price: $849 a pair with a standard finish.

Lab Tests

Although the MB Quart 390 can be installed on a shelf, we found it more convenient to place the speakers on 16-1/2-inch stands, which put the tweeters about 35 inches from the floor, close to a seated listener’s ear level. The speakers were about 7 feet apart and 2 feet in front of a wall.

The room-response curve was notable for its smoothness and general freedom from major peaks and dips caused by boundary reflections. There was a plateau from 70 to 500 Hz and a moderate dip and rise in the 500- to 1,400-Hz range; the curve was extraordinarily smooth from 1,500 to 20,000 Hz, varying only ±2 dB. The output level in the upper part of the frequency range was about 5 dB lower than the average level in the bass/ midrange plateau.

The close-miked woofer response peaked at 90 to 100 Hz, falling off at 12 dB per octave at lower frequencies and at about 5 dB per octave from 100 to 350 Hz, where the midrange crossover took effect and the slope became much steeper. The best splice of the woofer response to the room response resulted in a composite frequency response that was very similar to the room curve but with a better-defined bass range below 60 or 70 Hz. The output at 40 Hz, the lower limit of the speaker’s specified frequency response, was about 10 dB below the average midrange level.

The speaker’s quasi-anechoic frequency response, measured with our fft analyzer, confirmed the general characteristics of the other measurements and also established that the titanium-dome tweeter had an extraordinarily flat and extended high-frequency response. The output variation on-axis from 14,000 to 27,000 Hz (our upper measurement limit) was only ±1.5 dB, and the system response from 180 to 27,000 Hz was flat within ±3 dB. The horizontal dispersion was very good; a significant difference between the frequency response on-axis and at 45 degrees off-axis became apparent only above 10,000 Hz. The system’s excellent phase response was demonstrated by its overall group-delay variations of 0.2 millisecond from 3,500 to 22,000 Hz and 0.6 millisecond from 350 to 3,500 Hz.

The system’s sensitivity measured 88 dB spl at 1 meter with a 2.83-volt input of pink noise. Although the impedance averaged 6 to 9 ohms over most of the range from 400 to 20,000 Hz, its minimum was only 2.9 ohms at 125 Hz, and the maximum was 10 ohms at 60 Hz (the system’s resonance frequency). The bass distortion with a drive level of 3.5 volts, corresponding to a 90-dB spl, was just under 1 percent from 100 to 80 Hz, rising to 3.5 percent at 60 Hz and 6.6 percent at 50 Hz. Pulse power-handling tests showed that from 100 Hz upward, the Model 390 could absorb anything we could put into it. The amplifier clipped before the acoustic-output waveform from the speaker was visibly or audibly distorted. The power level at clipping ranged from 1,100 watts at 10,000 Hz to 1,455 watts at 100 Hz. The fact that even such a huge input did not drive the woofer to the limits of its suspension travel testifies to the high quality of its design and construction.

Comments

Following our usual practice, we listened to the MB Quart 390 speakers for some time before making any measurements. From the start, it was evident that these were truly excellent speakers, with a smooth, seamless overall frequency balance and a believable sound stage. The sound had a distinct forwardness and a clean, crisp top end that was always a pleasure to listen to. It was clear that the strong highs we heard did not result from a response peak, since there was no accentuation of background hiss and not a hint of shrillness.

The speaker’s bass was deceptively strong at first. There was certainly no lack of subjective bass output, and the overall balance of the sound was always superb regardless of the program content. But comparisons with other speakers having a deep and powerful bass response made it apparent that reproducing the lowest bass registers is not the strong point of the MB Quart 390. It did a creditable job down to 50 Hz or so, but the distortion rose rapidly at lower frequencies as its output fell off at 12 dB per octave. To a considerable degree, the subjective sensation of a satisfying deep-bass response can be explained by the fact that the distortion was almost purely third harmonic, which is not only relatively inoffensive at low frequencies but can also give a feeling of more true bass than is really present in the music.

Overall, we found the MB Quart 390 to be a better than average speaker in its size and price range. Although we did not see any of the special cabinet finishes (our test units were in standard matte black), they should make these speakers suitable for use in a wide variety of rooms. MB Quart has made an auspicious entry into the U.S. market.

Read all

MB Quart reviews

Read all