JBL HP520 Floor standing speakers
JBL says that its HP series of loudspeakers is designed to bring many of the features of the company's professional theater and monitor speakers to home systems at affordable prices. The HP520, the larger of the two models currently available, is a floor-standing four-way system with five drivers. Its attractively finished seven-sided columnar cabinet has no parallel exterior surfaces; even the top resembles an upward-facing parabolic cone, although it is normally covered by a decorative black glass insert.
The bass frequencies are generated by what JBL calls a Double Chamber Bandpass (DCB) system, consisting of two internally mounted 8.5-inch drivers located about midway up the column. The dual woofers, which face each other on a baffle plate that divides the interior of the enclosure, are driven out of phase, effectively operating as a single piston. The two-chamber internal volume forms a tuned system that concentrates the bass energy in the range below 120 Hz while cutting off sharply above it. The woofer system radiates into the room from the top of the cabinet through a slot about 1-1/8 inches high that extends completely around the periphery. The curvature of the cabinet's conical plastic top presumably is designed to provide a smooth acoustic transition from the interior of the cabinet to the external room volume.
The other drivers are located conventionally on the upper half of the cabinet's front panel. The upper bass and lower midrange, from 120 to 1,200 Hz, is radiated by a 6.5-inch driver. Above it, in a separate sealed subenclosure, is a 5-inch midrange driver that operates up to 4,000 Hz, where there is a crossover to a 1-inch titanium-dome tweeter, placed at the top of the speaker panel. The panel itself is covered with rubber foam to minimize diffraction at the boundary between each driver and the panel, which could distort the system's radiation pattern. A removable black cloth grille covers the entire front of the cabinet, and the black glass insert for the top of the cabinet further enhances its appearance and utility.
The input connectors (insulated five-way binding posts on 3/4-inch centers) and a three-position room-compensation switch are located in a recess in the bottom of the cabinet. The switch adjusts the balance of the lower frequencies to compensate for the placement of the system near a corner, against a wall, or away from any wall. The cabinet is fitted with rubber feet, and spikes are provided for optional installation.
JBLs specifications for the HP520 include a 4-ohm nominal impedance, a frequency range of 34 to 27,000 Hz, and a maximum recommended amplifier power of 200 watts. Its rated sensitivity is 90 dB. The system weighs about 55 pounds.
The HP520's raw (unsmoothed) room response varied less than +/-3.5 dB from about 60 Hz to our upper measurement limit of 20,000 Hz. It was difficult to measure the bass response with close microphone spacing below 100 Hz or so, since it radiated around the full periphery of the cabinet, and the results could not readily be combined with room measurements in any meaningful way. The closest we could come to making our usual smoothed room-response measurement yielded a very good +/- 2-dB envelope from 110 to 10,000 Hz. A quasi-anechoic MLS response measurement, valid above approximately 300 Hz, yielded a very similar curve: +/-2 dB from 400 to 16,000 Hz, rising to +4 dB at 20,000 Hz (relative to the average output from 1,000 to 10,000 Hz).
The tweeter's horizontal directivity, measured with one-third-octave noise, was typical of 1-inch dome radiators. At 45 degrees off-axis, the output (relative to the on-axis response) fell to -3 dB around 7,000 Hz, -5 dB at 10,000 Hz, and -12 dB at 20,000 Hz. Although our room-response measurements stop at 20,000 Hz, they showed increasing output from 10,000 to 20,000 Hz, where it equaled the highest level recorded at any lower frequency.
The system's impedance was unusual in having three peaks below 100 Hz, at 28, 50, and 90 Hz. Within that range, the impedance varied between 6 and 11 ohms. Above 100 Hz, the curve was more conventional, swinging from a minimum of 3.4 ohms at 120 Hz to a maximum of 11.8 ohms at 3,000 Hz. Over most of the audio band, the impedance remained well above the rated 4 ohms.
The HP520's measured sensitivity was unusually high, with the system producing a 94.5-dB sound pressure level (SPL) at 1 meter on the tweeter axis with a 2.83-volt input. Bass distortion, with an input of 1.7 volts (corresponding to a 90-dB SPL), was about 1 percent from 50 to 120 Hz, rising at lower frequencies to 5.5 percent at 30 Hz. The upper-bass driver also produced low distortion, about 0.6 percent from 120 to 750 Hz and about 0.8 percent at the 1,200-Hz crossover to the midrange driver. The latter, whose cone excursions were small, generated less than 1 percent distortion throughout its operating frequency range and less than 0.4 percent from about 1,300 to 2,400 Hz. The group delay in the tweeter's range varied about 100 microseconds overall.
The HP520's woofers were able to absorb a single-cycle sine-wave input of about 600 watts at 100 Hz before their cones reached their mechanical limits of movement. At 1,000 and 10,000 Hz, the driving amplifier ran out of power at about 850 watts before the speaker showed any signs of distress.
For all our testing and listening, the HP520 speakers were placed about 3 to 4 feet from the walls behind and beside them, and the room-compensation switch was set appropriately at its "0 dB" (maximum bass) position. We did not install the spikes, which would have complicated moving the speakers about.
The HP520's sounded every bit as good as the measurements would imply (better, actually, because their very solid low bass was far superior to what our measurements could confirm). Despite a total absence of the upper-bass heaviness that mars the sound of so many loudspeakers, the low-frequency output remained clean and palpably strong down to the 30-Hz region.
Stereo imaging was likewise excellent, with a better-than-average illusion of depth behind the speakers as well as a seamless soundstage between them. The sound was totally integrated at all times, with never a hint it was coming from five separate drivers in each speaker cabinet.
The JBL HP520 ranks as a worthy competitor in what is today the midprice bracket for good loudspeakers. Like any good speaker, its sound is "right" from first hearing and tends to be even more satisfactory with extended listening.
