HSU Research HRSW12V Subwoofer Review

Hsu Research specializes in subwoofers—loudspeakers that operate only at very low frequencies where the output of a conventional “full-range” speaker begins to fall off. Although some speaker advertising can be misleading in this regard, the bass modules that extend the range of small satellite speakers lacking the ability to generate useful signals below 150 Hz or so are rarely true subwoofers. In most cases they are simply the system’s woofer and themselves roll off below 50 Hz or so. A subwoofer, as I understand the term, is a speaker that operates only in the low bass (certainly not over 100 Hz, and sometimes only below 50 Hz) to extend a system’s response downward by one or two octaves to the lower limit of audibility.

The new HRSW12V from Hsu Research, which sells its products factory-direct only, is a tme subwoofer no matter what your definition might be.

It doesn’t look much like a loudspeaker (an important consideration for anyone trying to avoid violence to room decor), bearing more resemblance to an end table than an audio component. It is cylindrical in shape and drum-like in its proportions, 23 inches in diameter, 22 inches high, and supported 2-1/2 inches off the floor by three sturdy (but not needle-pointed) feet. It is covered by a tightly fitting black cloth sleeve except for the top, which is a 3/4-inch-thick gray speckle-finished disc of what Hsu calls Zolatone granite (it has the look and feel of stone).

The driver, a 12-inch cone with a long-throw voice coil, was developed specifically for this application and is mounted on the bottom of the enclosure, facing downward. Its shielded magnet structure enables the speaker to be placed close to a video monitor or TV without affecting the picture. Also on the bottom is a port, 3-1/2 inches in diameter, terminating a tubular duct that extends most of the way to the top of the enclosure.

The HRSW12V is normally powered by an internal amplifier, accessible from the bottom of the speaker, but the system is also available with the amplifier external to the speaker. Hsu says the amplifier can deliver 150 watts to the speaker’s 3-ohm nominal impedance. It includes a Linkwitz-Riley crossover network (a plug-in module) with 24-dB-per-octave slopes. The standard crossover frequency is 91 Hz, but a number of other choices, from 28 to 155 Hz, are also available.

The amplifier has a phase-inversion switch to facilitate blending the subwoofer’s output with that of the main speakers, a defeatable soft-clipping circuit to reduce harmonic distortion and improve reliability, an infrasonic filter to prevent overload, an equalizer circuit to flatten the subwoofer’s response, and a bypass switch for the crossover network, intended primarily for use in Home THX systems with a crossover built into the controller. The line-level signal inputs are standard phono jacks (for left and right channels) whose input impedance of 100,000 ohms is compatible with any preamplifier or other signal source. A second set of jacks carries the high-pass output from the crossover to the regular main-amplifier section, removing the low-frequency portion of the signal from the front speakers (desirable but not essential). A pair of screw terminals is also provided to accept input to the subwoofer crossover and amplifier from the loudspeaker outputs of the system’s main amplifier.

The amplifier panel contains, in addition to the several switches and connectors, a level-control knob and line fuse. When purchased as an external component, the amplifier is housed in a gray patterned case about 9-3/4 inches wide, 7-1/4 inches high, and 5-1/2 inches deep, with external heat-dissipating fins on its front panel.

A unique feature of the Hsu powered subwoofer is its recommended placement—close to the listening position. Although a subwoofer’s location is usually undetectable by ear, subs are typically installed at the front of the room somewhere in the vicinity of the main speakers.

The HRSW12V’s crossover network places the subwoofer’s output in phase with that of the main speakers, but delayed by a full wavelength. If the subwoofer is located one wavelength closer to the listener than the main speakers, their outputs will be more nearly in phase where it counts —at your ears.

At the standard 91-Hz crossover frequency, that spatial difference amounts to about 10 to 15 feet, so that in most installations where the listeners are at that distance from the main speakers, the deep-bass output of the subwoofer and the sounds from the main speakers will reach the listener at nearly the same time. Whether this produces an audible effect is perhaps debatable, but certainly any difference should be toward more accurate sound reproduction.

There are other advantages as well. If the subwoofer is very close to the listener, its direct sound output predominates and room effects (which can be considerable at the very low frequencies) are minimized. Also, being immediately adjacent to the subwoofer results in higher levels at the listener’s ear, requiring less power for the same listening level.

Measuring the performance of a subwoofer like the HRSW12V is both easier and more difficult than for a full-range speaker. On the one hand, an anechoic environment (other than the outdoors) is almost impossible to obtain, and interaction with the room boundaries makes distant-mike measurements impractical. So the only practical procedure is to use close-miked (near-field) measurements, as we normally do with the woofers of conventional speakers.

Depending on the signal (sine wave, swept noise, or wide-band noise with a swept filter) and the exact placement of the microphone relative to the cone (and the vent, in this case), a variety of response curves can be generated. We tried all of these methods, and a general pattern emerged from the plots.

The speaker’s response was down 3 dB at 23 Hz and about 6 dB at 20 Hz. At the upper end of its range, it was typically down 3 dB at 75 Hz and 6 dB at the 90-Hz crossover frequency (as rated). Its total harmonic distortion plus noise at a 100-dB level measured at the outer diameter of the enclosure was a minimum of 0.4 percent at 55 Hz, rising to 7 percent at 20 Hz and 2.2 percent at 90 Hz. A spectrum analysis of the output at 50 Hz under the same conditions, but using a separate, unequalized amplifier, showed second and third harmonics slightly below 0.1 percent, a very low figure for a speaker in that range.

In use, the HRSW12V did a fine job. There was never an audible clue to its location next to the listener, and it provided the tactile full-body stimulation in the lowest octave that is the real justification for using a subwoofer. A final comment on that: The speaker makes a convenient seat during a listening session, but in that case the massage it delivers to the listener (sitter?) is a constant reminder of its presence!

The HRSW12V is one of the most potent subwoofers we have used. Sonically, it is all one could wish for, and the price is right.

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