Bose 10.2 Speaker System Review

The Bose 10.2 “Stereo Everywhere” speaker system is a direct descendant of the company’s earlier Direct/Reflecting speakers. Unlike conventional forward-radiating speakers, whose full stereo properties are usually audible only in a restricted portion of the listening room (typically along a line midway between the two speakers), the 10.2 has specific directional and frequency-response properties designed to generate an exceptionally strong, three-dimensional stereo sound image throughout the listening area.

To achieve such a sound image, Bose uses a controlled dispersion pattern in which the signal radiated at a 45-degree angle into the room is 5 to 10 dB louder than in other directions. The 10.2 speaker has four drivers. Two 10-inch woofers are mounted 90 degrees apart on the speaker’s front and inward sides near the top of the columnar cabinet, about 33 inches from the floor. The combined radiation pattern of these drivers slants 45 degrees inward in the frequency range of 600 to 1,200 Hz. Two 3-inch cone tweeters', angled respectively 45 degrees inward and outward from the forward axis of the system, are mounted in front of the forward-facing woofer.

The tweeters operate out of phase with each other, the inward-facing unit being in phase with the woofer behind it, which tilts the speaker’s overall radiation pattern 45 degrees inward (toward the in-phase tweeter) in the frequency range of 1,200 to 2,500 Hz, where both the woofers and the tweeters contribute to the total sound output. From 2,500 to 5,000 Hz, the tweeters alone operate, and their opposite-phased cones produce a figure-eight pattern favoring the inside and outside, with a forward null. Above 5,000 Hz, the outward-facing tweeter is shut off by the crossover network, leaving the natural directivity of the inward driver to beam its energy along its own 45-degree axis.

Bose points out that none of these features is sufficient to create the desired result by itself but that their combined effect is a directive pattern from 600 to 20,000 Hz that results in Stereo Everywhere. Another benefit of the 10.2’s driver array is what Bose calls “Stereo Targeting,” a broad vertical radiation pattern that produces a stereo image independent of a listener’s height. This effect results from mounting the 10.2’s tweeters in front of the forward woofer, in contrast to the usual configuration in which the tweeter is placed above the woofer, often at some distance, thereby narrowing the beamwidth in the crossover region and changing the speaker’s sound and imaging with the height of the listener.

Although the bass region below 600 Hz is not critical to the Stereo Everywhere concept, it is important to the overall sound quality of the system. In the Bose 10.2, the two woofers are rear-loaded by a common series of three chambers. The speaker’s rear radiation path extends downward into the back half of the cabinet, which is divided by a board across its full width from top front to bottom rear. A hole in the divider couples the bass energy into a second chamber of about the same size and then out through a vertical slot (24 inches high and 3/4-inch wide) along the inboard side of the cabinet.

The Bose 10.2 is rated for a nominal impedance of 4 ohms and an amplifier power requirement of 10 to 180 watts per channel. It is 12 inches square and about 40 inches high. The top 12 inches—where the drivers are located—are covered by a black, non-removable grille cloth, and the rest of the cabinet is finished in a genuine teak veneer. Each speaker weighs 61 pounds. Price: $1,199 per pair.

Lab Tests

The averaged room response of the Bose 10.2 system was exceptionally smooth and flat from 400 to 10.000 Hz, then it sloped down slightly to about —3 or —4 dB at 15.000 Hz and dropped rapidly at higher frequencies to about —12 dB at 20,000 Hz. The close-miked woofer response decreased at about 12 dB per octave below 60 Hz, with a minor dip at 110 Hz. The maximum bass output occurred at 130 Hz, and the response fell off a total of 5 dB from the maximum level between 130 and 1,500 Hz. A pronounced irregularity in the 1,500- to 2,700-Hz range indicated that ther crossover to the tweeters was in this region.

When we spliced the close-miked woofer and room response curves, the composite response was ± 4 dB from 56 to 15,000 Hz. When we added the contribution of the port to the woofer’s output in the usual manner, the bass response seemed almost too good to be true: the ±3.5-dB variation from 23 to 1,500 Hz was not consistent with what we heard from the speakers, which, though very good in the bass, were not that good! We did find a discrepancy in our measurements—we had incorrectly weighted the relative contributions of the forward and rearward radiation from the woofer section. We would judge from our listening experience that the 10.2’s actual effective limit of useful bass response in a typical listening room would be somewhere between 56 and 23 Hz—probably about 35 Hz.

The system’s impedance reached its minimum, about 3.5 ohms, at 150 and 10,000 Hz and its maximum of 15 ohms at 60 Hz. Over much of the audio range, the impedance was from 5 to 10 ohms. We measured the sensitivity of the Bose 10.2 along its key directional axes, and although there were small differences between them, we estimated its effective output sound-pressure level (SPL) as 86 dB at 1 meter from the grille with an input of 2.83 volts. An input of 4.5 volts was required for the reference output of 90 db that we use when measuring bass distortion. At 90-dB SPL, the distortion was in the range of 1 to 2 percent from 100 down to 50 Hz and only 4.5 percent at 30 Hz.

Quasi-anechoic FFT response measurements along the inward 45-degree axis of the speaker showed moderate peaks at 7,000 and 9,000 Hz, and a smaller peak at 11,000 Hz. The peaks were not evident along other measurement axes (forward or on the outward 45-degree axis), however, and the response was within ±3 dB from 180 to 15.000 Hz when the peaks were ignored. The frequency response on the outward 45-degree axis was ragged, with a noticeably reduced output at the higher frequencies reflecting the combination of two opposite-phase drivers and the treble rolloff on the outward driver designed into the crossover network. The differences between the inward and outward axes were even more striking in the group-delay measurements, which produced an excellent overall variation of only 0.4 millisecond from 500 to 23,000 Hz along the inward 45-degree axis but a ragged ± 2-millisecond measurement from the other tweeter.

In two of our peak-power-handling measurements, the amplifier clipped before the speaker drivers distorted significantly: at 1,030 watts into 3.5 ohms at 10,000 Hz and at 355 watts into 9 ohms at 1.000 Hz. At 100 Hz, the woofer cones reached the linear limits of their excursions at 230 watts into 4 ohms.

Comments

From the outset it was obvious that the Bose 10.2 was an excellent speaker. Its octave-to-octave frequency balance was among the smoothest we have heard in some time, as evidenced by its freedom from mid-bass colorations, upper-middle forwardness, or stridency. In fact, its “all there” sound was one of its most striking characteristics.

The big question, of course, is whether “Stereo Everywhere” is a real quality of the speaker or merely a clever slogan. As we moved around the room and from side to side a few feet in front of the speakers, we noticed that the audible contributions of the left and right channels remained clearly distinguishable. An instrument heard playing through the left speaker remained at that position even when we stood in front of (or behind) the right speaker, and the same fixed localization was experienced as we moved elsewhere in the room.

There is more to stereo than left and right sound sources, however. Instruments or voices positioned between the speakers tended to shift laterally at some points when we moved from one side to another. Fortunately, such shifting was not obvious from listening positions more than a few feet in front of the speakers. In general, we found that the stereo sound stage was stable over a very large part of the room unless we made a special effort to move about while listening for spatial anomalies. For the majority of us who prefer less mobile listening, then, Bose’s “Stereo Everywhere” description seems quite valid.

If you demand a specific, unvarying stereo sound stage from loudspeakers, however, the Bose 10.2 may fall a bit short of that ideal. You do get very recognizable stereo imaging from almost everywhere, but the sound stage in one location will not always be the same as it is in another.

The approach taken by Bose in the Point Two series (besides the 10.2 there is also the smaller 8.2) is similar to those of some other speaker manufacturers in its use of shaped polar patterns to achieve image stability, but the Bose design seems to be somewhat more economical in number of drivers and overall physical complexity. The Bose 10.2 is also one of the best sounding speakers we have heard, even without considering its spatial qualities. Altogether, it appears to represent a genuinely worthwhile development.

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