SUBWOOFER SETUP STEPS
Sound & Vision|April - May 2020
SUBWOOFERS ARE LIKE the magic beans of audio, expanding a playback system’s dynamic range in a way that dramatically enhances the listening experience. There’s an attitude among some audiophiles that subwoofers represent, if not the spawn of the devil (there are numerous or More Subs for such spawns in audio lore), a bad compromise at minimum. But the truth is that adding a modest but well-designed subwoofer to speakers, even compact bookshelf models, can result in better performance than what you’d get from full-range towers that cost considerably more.
Thomas J. Norton

Full-range speakers present a room-friendly option, particularly for dedicated two-channel systems, and can sound very good (decades of audiophile experience isn’t necessarily wrong). But where you position the speakers for best performance—in particular, to optimize imaging and soundstage depth—will almost never be in the location where they’ll provide the most accurate bass. The main reason for this is room modes, which are resonances determined by a room’s dimensions that can dramatically affect bass and do it in different ways depending on where the speakers—and the listeners—are positioned. Sound below the typical subwoofer crossover frequency of 60-100Hz is nondirectional, however, so using a subwoofer (or two) positioned separately from the main speakers to reproduce that portion of the audio spectrum will allow you to correct for room modes using the steps I’ll describe below.

Crossover

Considerations

It may be tempting to drive big tower speakers full range even when also using a subwoofer, but that combination rarely works out well. In most situations, the subwoofer should only be engaged below a certain crossover frequency, and you should also limit the response of the main speakers below that same frequency. This low-frequency roll-off (performed by a so-called high-pass filter) lowers distortion in the main speakers by sparing them the need to produce bass that a subwoofer is better-equipped to handle. It also keeps the main speakers (which as noted above typically aren’t located in the best place to produce uniform bass) from interfering with a carefully positioned subwoofer where their responses overlap in the transition region.

While virtually all A/V receivers and preamp-processors have high- and lowpass filtering capability, most two-channel preamps and integrated amps don’t. But some stereo-only components do provide that capability (the Parasound NewClassic 200 integrated amplifier reviewed on page 50 of this issue, for instance), so if you plan on adding an optimized subwoofer setup to a two-channel system, you’ll first need to do some product research.

An effective subwoofer implementation can include either one or two subs. More than two can offer further advantages, but the law of diminishing returns sets in quickly. For the record, none of these recommendations are new—some of the best work on the subject was done in the mid-aughts at Harman Industries, and extensive discussions on the topic, along with exhaustive discussions on the setup of loudspeakers in general, can be found in Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms, Third Edition (Floyd E. Toole, Routledge, 2018).

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