dbx Soundfield SF5000 Speaker System Review

About six years ago dbx introduced an innovative loudspeaker system, the Soundfield One, that was designed to provide a firmly fixed stereo stage over a wide range of listening and speaker positions. In contrast, conventional speakers of the time (like most of today’s speakers) either did not generate a stable stereo image or provided it only in relatively restricted areas of the room. In essence (although the specifics of the design were quite complex), dbx achieved a relatively stable sound stage by shaping each speaker’s pattern of horizontal directivity toward the center of the room. As a listener approached one speaker, its contribution to the total perceived sound decreased while the contribution from the other speaker increased thus keeping the apparent sources of the sound fixed regardless of the listening position.

The Soundfield One, which is no longer in production, did its assigned job very effectively, but it was large and very expensive (each speaker unit contained fourteen drivers and a complex crossover network). Subsequently, dbx refined the design to achieve comparable results with much simpler and more competitively priced speakers.

The latest smallest, and—at $450 a pair—least expensive Soundfield speaker is the dbx SF5000, which provides the essential qualities of the basic design in a bookshelf-size speaker (although it is not really intended for shelf placement). The SF5000 achieves its controlled radiation pattern by having two angled speaker panels, which give the speaker enclosure a triangular cross section. It is designed to be used in mirror-image pairs.

The inward-facing panel of each speaker unit, which makes an angle of about 30 degrees with the forward axis of the system, contains a 6-1/2-inch long-throw woofer in a vented enclosure, a 2-1/2-inch midrange cone with fluid cooling, and a fluid-cooled 1/2-inch wide-dispersion tweeter. The outward-facing panel, which is 45 degrees off the forward axis, has a similar 1/2-inch tweeter at its top and the woofer port just below it. The rear of the enclosure normally positioned parallel to the wall behind it, contains recessed banana jacks for the amplifier connection. Plugs are furnished with the speakers, and the jacks also accept standard dual banana plugs.

The entire exterior of the cabinet is finished in an attractive walnut-grain or black vinyl veneer. Each speaker panel is covered by a removable cloth grille retained by plastic snaps. The cabinet dimensions are 11-3/4 inches wide, 7-3/4 inches deep, and 15-1/8 inches high, and each speaker weighs 13 pounds. Although dbx states that the spatial properties of the system are relatively unaffected by speaker placement or listener location, placing the speakers 7 to 12 feet apart and 4 to 12 inches out from the rear wall is recommended.

The rated frequency response of the SF5000 is 65 to 20,000 Hz ±3 dB over a forward angle of more than 100 degrees. Its sensitivity is given as 89 dB sound-pressure level (SPL) at 1 meter with an input of 2.83 volts. The nominal impedance is rated as 6 ohms, with a minimum of 4 ohms. The recommended amplifier power is 30 to 150 watts per channel into 4 ohms. The crossover frequencies are given as 1,600 and 4,500 Hz.

Comments

The spatial characteristics of the dbx SF5000 lived up to expectations, having the same basic qualities that had impressed us years ago in the Soundfield One. When we listened to a program having distinct left/right positioning of some of its sound sources, it was possible to stand in front of one of the speakers and walk to the front of the other while the apparent source positions remained fixed. Moving about elsewhere in the room had a similar effect—no significant change in the apparent placement of identifiable sound sources. The only deviation from this characteristic (and it may have been related to a less-than-ideal room environment) was a tendency for the image position to shift slightly, and momentarily, at two points near the center of the sound stage during the lateral listener transit. Under ordinary listening conditions, the imaging was rock-stable.

The sound quality itself, apart from its spatial characteristics, was excellent for a speaker of this size and price. The bass, in particular, was solid and clean, with an impact that was surprising for such a small system. The overall sound impressed us as being smooth and slightly distant, with no evidence of the excessive “presence” effect that results from a midrange emphasis. At the same time, there was an occasional edginess to the highs that may have resulted from the large tweeter resonances, although the resonances themselves occur well above the frequency range that can normally impart an audible coloration to the sound.

The dbx SF5000 does not create the kind of broad sound stage that extends beyond the speakers in all directions. That quality is not often encountered, especially in inexpensive speakers, and the full effect of an extended sound stage is usually audible only over a limited listening area. In contrast, the sound stage from the SF5000's, although less spectacular, being limited to the area between the speakers, presented the same imaging characteristics throughout the room. The clear imaging did not need any critical placement and angling of the speakers, nor did it require listeners to remain in a limited “sweet spot” that may not be consistent with room decor or might accommodate only a couple of people.

This trade-off between sonic spaciousness and noncritical speaker listener placement may well be fundamental to loudspeaker reproduction. In any case, the dbx SF5000 is the smallest and least expensive speaker we know of that can do what it does so effectively. Altogether, it embodies a rare and happy combination of qualities!

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