JBL L46 Speaker System Review

The JBL L46 is a compact, two-way bookshelf speaker system whose newly designed components are said to provide performance typical of quality three-way systems. The L46 has an 8-inch woofer in a ported enclosure crossing over at 3 kHz to a 1-inch dome tweeter. The system impedance is 8 ohms, and it is designed for operation with amplifiers delivering between 10 and 100 watts per channel. The enclosure of the L46 is veneered in oiled walnut and has a dark-brown grille cloth retained by plastic snaps.

The woofer of the L46 employs JBL’s Symmetrical Field Geometry (SFG) magnetic structure. First used on higher-price JBL speakers, the SFG creates a symmetrical magnetic field in and around the voice-coil gap, greatly reducing second-harmonic distortion during normal operation. The woofer cone is of paper laminated with a plastic damping material, and it is supported by a rugged die-cast frame.

The tweeter’s dome diaphragm is formed of a phenolic material and coated with aluminum by vapor deposition. In the crossover network, the large capacitors are all shunted by smaller capacitors, a technique said to improve the waveform accuracy of the speaker system. Since the driver sensitivities have been closely matched, the manufacturer chose not to provide a user-adjustable tweeter control.

The enclosure of the L46, relatively compact even for a bookshelf speaker, has been designed for the deepest possible bass response consistent with the design constraints. It is constructed of 3/4-inch-thick wood, it is heavily braced internally, and it is damped with fiberglass. Unlike most inexpensive systems, the L46 cabinet has a fine, hand-rubbed wood finish.

Laboratory Measurements

The mid-and high-frequency room-response measurement of the JBL L46 speakers, when spliced to the close-miked bass response, yielded a composite response curve that varied only ±4 dB from 25 to 19,000 Hz. Through most of the audible range, from 100 to 6,000 Hz, it was within ±2.5 dB. The high-frequency response from the left and right speakers (measured, respectively, on axis and about 30 degrees off axis) diverged above about 5,000 Hz, indicating the directivity of the high-frequency output from the 1-inch tweeter. Our measured result is not atypical for a dome radiator of this size.

The woofer response was measured with the microphone close to the cone and again at the opening of the port. Combining the two curves, with a correction for the relative areas of the cone and port, produced a surprisingly extended response curve. Above 70 Hz it sloped slightly downward (by about 4 dB at 500 to 1,000 Hz) but was almost totally free of minor irregularities. The effective acoustic crossover to the port radiation was at about 52 Hz; response below that frequency fell at a rate of 6 dB per octave, so the output at 20 Hz was only about 4 dB less than at the midrange level.

The woofer cone’s output distortion at a 1-watt drive level was about 1 per cent from 100 Hz down to 50 or 60 Hz, increasing slowly at lower frequencies. Since at those frequencies the cone contributed only a small part of the total bass output of the speaker, we used the distortion readings at the port for frequencies below about 60 Hz, making a smooth transition between the two as we plotted the curve of distortion vs. frequency. The port distortion was considerably higher than the values we read at the cone, so the composite bass distortion reached 10 per cent at 40 Hz. When the drive was increased to 10 watts, the shape of the curve was similar, with readings in the range of 2 per cent down to 70 Hz and climbing to 10 per cent at 60 Hz and 15 per cent at 50 Hz.

The system impedance was at least 6 ohms over the full audio range except between 3 and 4 kHz, where it fell to 4 ohms. The speaker’s sound output at 1 meter with an input of 2.83 volts (1-watt nominal) of pink noise in an octave band centered at 1,000 Hz was 89.5 dB, typical of small ported systems and 1.5 dB higher than the speaker’s rating.

Using our FFT computer-analysis program, we measured the anechoic frequency response of the L46 at a number of angles to its forward axis at a distance of 1 meter. The measurement covered a range of 180 to about 15,000 Hz (the limits of the analyzer range). On the speaker axis the output was flat within about ± 3 dB over the full range, which is an excellent frequency response. At 45 degrees off axis the response was still very smooth, but at frequencies above 5 kHz or so the output was down about 6 dB from the axial response level. At a 60-degree angle the frequency-response curve was more irregular, dropping to a broad minimum between 9 and 10 kHz and rising to a maximum at 14 to 15 kHz (where it was actually greater than the axial response at that frequency).

Comment

The measurement data implied that the JBL L46 was a very good loudspeaker, and that is what it proved to be in our listening tests. Its sound was notably smooth and unboomy, with a more natural-sounding lower midrange and upper bass than we hear from most speakers in our listening room. The extreme high end was slightly prominent, and the low-bass output belied the small size of the speaker’s woofer. It could be almost palpable, yet without a trace of over-emphasis. To our ears, the measured bass response was validated by the actual listening situation (which, for some reason, does not always happen).

As we listened to the L46 speakers for some time, both by themselves and in comparison with some others, we found ourselves enjoying their sound without thinking of them as loudspeakers. As we have said before, the true mark of a good speaker (or of any other component, for that matter) is that it can be ignored as a piece of hardware and appreciated simply for the sound it produces. The L46, despite its small size and price, is a full-size speaker in its sound. It is so smooth and balanced sounding that we cannot imagine its being less than pleasing in virtually any environment. JBL can justifiably be proud of the L46, and audiophiles who have wished to own JBL speakers but found them too expensive can now indulge themselves without financial strain.

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