JBL J216 Bookshelf speakers
The Model J216 is the smallest and least expensive speaker system to bear the JBL name. It is a two-way system based on a newly designed 6-inch woofer that operates in a vented enclosure only 14-3/4 inches high, 10 inches wide, and 9-1/4 inches deep. There is a crossover to a 1-inch soft-dome tweeter at 4,000 Hz. The system has a nominal impedance of 8 ohms and a rated sensitivity of 87 dB sound-pressure level at 1 meter when driven by 2.83 volts (equivalent to 1 watt in an 8-ohm load). It is rated for operation with amplifiers capable of delivering 10 to 60 watts per channel. Each speaker weighs 17-1/2 pounds.
JBL's aim in designing the J216 was to produce a small, unobstrusive speaker, suitable for today's smaller living spaces, that would sell for no more than $100 and deliver a balanced and musical acoustic output suitable for all types of program material. To keep low-frequency distortion within acceptable limits despite a small woofer-cone diameter, the J216 uses a "symmetrical field" magnet structure, a JBL development introduced several years ago on some of the company's more expensive speakers. The electrolytic capacitors in the crossover network are bypassed with smaller capacitors to compensate for the asymmetrical charge-discharge characteristic of large capacitors. This is said to improve midrange and high-frequency performance. To keep the cost low, the J216 production line was heavily automated, including totally computerized quality-control checks.
The wooden cabinet of the J216 is finished in oak-grained vinyl on the sides and in black vinyl veneer on the top and rear, and there is a removable black grille. The two drivers are vertically aligned, with the woofer port in the lower right corner of the speaker board. The two binding-post terminals are recessed in the rear to permit flush-mounting the speakers against a wall.
The JBL J216, with a suggested retail price of $99 per unit, is packed and sold in pairs.
Laboratory Measurements
The averaged room response from a pair of J216 speakers in a typical wall-mounted installation was within ± 4 dB from 250 to 20,000 Hz. The major departure from flatness was in the upper midrange, with a minimum output at 2,000 Hz and a broad maximum at 4,000 to 6,000 Hz, representing a total change of 8 dB. The close-miked woofer output, after combination with a separate measurement at the port, had a maximum at 150 Hz, falling off slightly down to 50 Hz and dropping at a 6-dB-per-octave rate from 200 to more than 2,000 Hz.
Because of their different shapes and slopes, splicing the two response curves was difficult without resorting to listening judgment and the results of quasi-anechoic response measurements made with the IQS FFT spectrum analyzer. The latter showed the same overall response contours as our other measurements, but they indicated approximately equal maximum output levels at low and high frequencies. Using this as a guide, we obtained an overall response curve of +6, -4 dB from 38 to 20,000 Hz relative to the 1,000-Hz level. The high-frequency dispersion of the dome tweeter was excellent, with negligible directivity below 15,000 Hz and only about 15 dB difference between the axial and 30-degree-off-axis outputs at 20,000 to 23,000 Hz.
This is, to say the least, highly creditable performance for a $99 speaker with a 6-inch woofer! JBL does not publish frequency-response data for their speakers, but they supplied us with response curves made on the test samples using one-third-octave spectrum analysis. Although their measurement method differed from ours, the features of both sets of response curves were essentially similar.
While its frequency response extends to a surprisingly low frequency, the 6-inch woofer of the J216 cannot be driven too enthusiastically without generating distortion. Following our new procedure of measuring the distortion of a speaker using a constant drive level equivalent to one that would produce a 90-dB sound level in the midrange at a 1 meter distance from the speaker, we applied 4 volts to the speaker and measured harmonic distortion from 100 Hz down to the point where it was clearly excessive. The distortion started with about 1.8 per cent at 100 Hz and rose rapidly to 5.5 per cent at 70 Hz and 10 per cent at 56 Hz. These distortion readings must be interpreted in the context of the acoustic output level of the speaker, at least 90 dB over much of the measurement range.
The impedance of the J216 was a minimum of 6 ohms at 60 and 200 Hz, but it fell to only 3 ohms at 6,000 Hz. Paralleling these speakers with another pair should be done with caution and with due consideration for the limitations of the amplifier being used. The J216 had a sensitivity of 87 dB at 1 meter with a 2.83-volt input, exactly as rated.
Comment
The sound quality of the JBL J216 belies its size and driver complement. It is not in the least "thin" or lacking in bass (or any other part of the frequency range, for that matter). The balance that JBL engineers sought has certainly been achieved in this speaker. As a matter of fact, we felt at times that the bass was slightly heavier than we would have wished (with the speakers against a wall and at ear level). Measurements showed why this was so, since the bass output reaches a maximum at about 150 Hz, giving an illusion of more bass than is actually present an octave or two lower.
When we drove a pair of J216's with amplifiers in the 100- to 200-watt class (not recommended, but we exercised restraint), the available volume was more than sufficient for our taste, and the sound never became distorted or even strained at any reasonable volume. The quality was determined for the most part by the program source, which is as it should be. It was little short of amazing to hear the sounds these tiny speakers produced from digital Compact Disc programs. The J216 speakers are not a substitute for larger speakers, but they do a fine job of music reproduction. Of course, they will not crack the plaster in your walls, but neither will they shatter your budget.
