Jensen System 400 Speaker System Review

The Jensen System 400 is a three-way speaker system consisting of a 10-inch acoustic-suspension woofer, a 3-1/2-inch high-compliance midrange cone driver, and a 1-inch soft-dome tweeter. The midrange and high-frequency speakers are acoustically isolated from the woofer within the enclosure. The crossover frequencies are 1,500 and 4,200 Hz, and the nominal system impedance is 8 ohms.

The System 400 has an acoustically transparent “minimum-diffraction grille” designed to minimize the interference effects often caused by the edges of a framed grille or by the speaker’s baffle board. The grille is made of an open-weave brown cloth stretched on a molded frame that is largely open around its edges as well as in front of the speakers. A level-control knob (behind the grille) provides a continuously variable combined middle- and high-frequency adjustment calibrated from 0 to — 10 dB with a fully “off” setting. The spring-loaded connectors (which accept the stripped ends of the wire leads) are recessed into the rear of the cabinet, which is finished in walnut-grain vinyl veneer.

Laboratory Measurements

The room response of the Jensen System 400 speakers with their level controls set to 0 (maximum highs) was relatively uniform from about 500 to 5,000 Hz, showing only the minor peaks and dips that are normal in a live-room measurement of this type. Above 5.000 Hz, the average output dropped about 5 dB and then fell off at about 10 dB per octave between 10,000 and 20,000 Hz. The response curves from the left and right speakers (on axis and about 30 degrees off axis, respectively) diverged only moderately above 7,000 Hz, showing the typical horizontal dispersion pattern of a 1-inch dome tweeter.

The bass response was measured with the microphone close to the woofer cone. The woofer output was very uniform from 100 to 1.000 Hz, with only about ± 1 dB of variation over that important part of the audio band. The low-frequency output reached its maximum at 60 Hz, where it was about 5 dB greater than the upper portion of the woofer’s operating range, and it fell at 12 dB per octave below 60 Hz.

When the two sets of curves were spliced, the composite frequency response was within ±3 dB from 80 to 6,000 Hz. Including the effects of the bass rise and the lower plateau of the tweeter’s output above 5,000 Hz, the overall frequency response was ± 5 dB from 40 to 18,000 Hz.

We also measured the quasi-anechoic on-axis response of the System 400 using our IQS (INDAC) FFT computer program. It differed from the room-response measurement significantly. At a 1-meter distance, the output variation was no more than ±2 dB from 300 to 11,000 Hz (on axis), rising to a plateau of about 5 dB in the 12,000- to 17,000-Hz range. We obtained our flattest overall response in this test by setting the mid/high level control to —8 dB, resulting in a ±3-dB variation from 180 to 18,000 Hz. (Note that those limits are those of the measurement system, not necessarily those of the speaker.) The apparent anomaly of a peaked high-frequency characteristic in the IQS FFT anechoic measurement and a depressed output in the same frequency range in the averaged room-response measurement is not actually inconsistent with the speaker’s performance. The tweeter’s dispersion, although reasonable for its size, nevertheless restricts its total acoustic-power output in the 2π solid angle facing the speaker. Listened to and measured on axis, the speaker actually does have an accentuated output in the upper octave, but its total power output into the room falls with increasing frequency since at off-axis angles the tweeter output is down compared to its axial output.

The woofer distortion with a 1-watt signal input was extremely low, varying between 0.1 per cent at 100 Hz and 0.4 per cent at 60 Hz. Even at 40 Hz, the speaker’s effective lower frequency limit, the distortion was a mere 1.6 per cent. A power increase to 10 watts had only a moderate effect on the distortion, which remained between 0.25 and 1 per cent from 100 to 60 Hz and reached a maximum of 10 per cent at 30 Hz.

The system sensitivity was 89 dB, as rated. The impedance minimum was 6.5 ohms at 20 Hz and from 100 to 150 Hz; it was between 7 and 20 ohms over the rest of the audio range.

Comment

The Jensen System 400, as might be expected from its measured performance, was a very smooth, uncolored-sounding speaker. Normally, on musical material without significant bass, it gave no indication of its excellent bass potential, but when the program called for it, the bottom-end performance was equal to the task.

In our listening room (the same one used for the measurements) the frequency balance of the speaker seemed best with its mid/high control turned down about 6 dB, although the optimum position would no doubt be different in other rooms. With the control set for maximum high-frequency output, there was a slight but audible crispness to the sound.

As we have noted on several occasions, the $200 class of loudspeakers is an extremely competitive one in which is to be found the highest ratio of sound performance per dollar. The Jensen System 400 falls squarely in this category. Frankly, we would have difficulty choosing between this speaker and several other fine similarly priced units we have tested in the past. The System 400’s performance is truly excellent in each part of the audio range as well as when taken as a whole. This speaker is, above all, balanced, which means that it is likely to give satisfying performance in a wide variety of listening environments.

It is worth mentioning that the high sensitivity (efficiency) of the System 400 and the fact that its impedance never falls low enough to present problems to any amplifier contribute in no small measure to making it suitable for any home music system. It does not need a lot of power to play loud, yet it will handle just about anything one might supply to it without distress or damage. Although we usually prefer that the level balancing of a multi-way speaker system be done in its design and not left to the possibly inept hand of the user, the action of the mid/high control on this speaker is both beneficial and highly unlikely to degrade its sound in any way. All in all, the experience of testing and living with the System 400 convinced us that it is a fine product, well designed and executed, honestly rated, and reasonably priced.

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