Jamo CBR 120 Speaker System Review

The CBR 120, part of a line of “Digital Monitor” speakers manufactured in Denmark by Jamo, is distinguished by an unusual physical shape and style. The CBR stands for Center Bass Reflex, an appropriate description of Jamo’s unusual woofer design. The woofer is in effect mounted at the end of a rigid tube of the same diameter as the woofer’s basket rim. The other end of the tube is open to the inside of the speaker cabinet. A second tube, extending inward from the molded-plastic speakerboard, surrounds the inner tube. The woofer and its attached tube are suspended from the speakerboard on four rubber mounts designed to minimize vibration transmitted to the cabinet from the woofer. The space between the two tubes forms the ducted port of the bass-reflex enclosure, with the woofer being concentric with the port. Jamo engineers feel that this design improves the performance and sound of the speaker.

The CBR 120 has an 8-inch woofer, crossing over at 820 Hz to a 4-inch midrange cone driver. The second crossover, at 4,900 Hz, is to a 1-inch dome tweeter. The three drivers are vertically aligned on the speakerboard, which slopes backward at an angle of 4 to 5 degrees. A level control on the front of the speaker, accessible when the grille is removed, can reduce the tweeter’s output by as much as 13 dB. The tweeter is also protected against excessive drive levels by an internal circuit that lights a red LED below it when an overload occurs.

The CBR 120’s specifications include an 8-ohm impedance, a sensitivity of 91.2 dB (measured at 1 meter with a 1-watt input), and a recommended maximum amplifier power rating of 120 watts (180 watts of music program). The enclosure measures 27-1/2 inches high, 13-3/4 inches wide, and 11-3/4 inches deep at the base, and it is available in walnut, “anthracite” (black), or white finishes. Each speaker weighs 37-1/2 pounds. Price: $400 each.

Lab Tests

The averaged room response of the Jamo CBR 120 speakers was quite uniform from 1,500 to 20,000 Hz, but there was a dip in the 350-to 1,000-Hz range and an increased output in the upper bass, from 100 to 200 Hz. The close-miked woofer response reached its maximum between 150 and 180 Hz, with the output falling off at higher and lower frequencies. The acoustic crossover between the woofer and its port was at 50 Hz. The combined output of the woofer and port fell rapidly below 60 or 70 Hz.

Because the woofer’s response curve and the system’s room-response curve overlapped for several octaves, we had no difficulty splicing them to form a composite frequency-response curve. The composite curve’s most obvious features were the midbass rise and the lower-midrange response dip immediately above it. The overall response was ± 6 dB from 63 to 20.000 Hz, but the variation from 1.000 to 20,000 Hz was only ±2.5 dB. The minimum impedance of the CBR 120 was 6 ohms at 170 and 2,300 Hz, with three maximum readings between 23 and 32 ohms at 31, 83, and 700 Hz. The speaker’s typical impedance was close to the rated 8 ohms.

The horizontal dispersion of the speaker was good, with no more than 3 dB separating the on-axis and the 30 degrees off-axis response up to 10,000 Hz (although the difference increased rapidly above that frequency). The system’s sensitivity was 88.5 dB, somewhat less than the rated value but fairly typical of systems of its size.

When we drove the speaker with a constant 3.37 volts (equivalent to a 90-dB sound-pressure level in the midrange), the output distortion was less than 1 percent from 100 to 65 Hz, rising to 5.8 percent at 50 Hz and 9 percent at 35 Hz. High-power pulse tests showed that the CBR 120 could easily cope with any input level it is likely to receive. At 100 Hz, the woofer reached its linear limits at 105 watts (into 12 ohms). At 1,000 Hz, the midrange cone could take 850 watts into its 18-ohm impedance, and at 10,000 Hz the dome tweeter absorbed 1,560 watts (into 7 ohms) without excessive distortion or damage.

Comments

For our listening tests we placed the Jamo CBR 120’s about 2 feet from the rear wall and several feet from any side wall. Our initial impression was of a rather prominent bass combined with a crisp and sometimes “edgy” top end. The measured response was fairly consistent with what we had heard from the speakers. After the tests, we experimented with the tweeter level control and found that a — 7-dB setting removed the irritating treble quality and made the speakers much more listenable. There was little we could do about the prominent bass, which fortunately was not unpleasant or even particularly obvious except on male voices, to which it imparted the chestiness that is common to so many loudspeakers.

These speakers give an impression of delivering a deeper bass than they actually do, probably because of the shape of the woofer’s response curve. The upper middles and highs are genuine, however, and sound fine. In our room, the tweeter level control was the key to making the system live up to its promises. (Some early production models of the CBR 120 were front heavy, but Jamo has rectified the problem by supplying special stands that stabilize the speakers.)

The Jamo CBR 120 is an attractively styled, compact speaker system with the ability to handle large power peaks (and to protect itself against tweeter burnout). Like any speaker, its sound is quite dependent on its acoustic surroundings, but judicious use of its tweeter level control, as well as some experimentation with placement, should pay rich rewards in enjoyable listening.

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