Bose Model 601 Series II Speaker System Review

The Bose Model 601 Series II, like the other Bose speakers, is designed for “direct/reflecting” operation in which a large part of its total acoustic output is reflected from one or more room boundaries before reaching the listeners (part of the speaker’s output is directed forward to the listening area in the conventional manner). Externally, the Model 601 Series II resembles a conventional floor-standing speaker. Its front and top are covered by an attractive dark-brown textured grille cloth. The top section is surrounded on the top and three sides by the grille and louvered plastic panels and is open to the rear. The top grille is hinged at the front and when lifted reveals an 8-inch woofer, tilted about 30 degrees forward of- the vertical, and four unbaffled 3-inch cone tweeters angled to the sides and rear. Pulling off the front grille, which is integral with the top grille and is retained by sturdy plastic pins, reveals a second 8-inch forward-facing woofer on the front of the speaker cabinet.

The two woofers operate together up to 2.5 kHz. The four tweeters overlap the woofer range, operating down to 1.5 kHz. The two rear-facing tweeters are angled slightly upward, radiating across the front of the top woofer and outward toward the wall behind the speaker at a horizontal angle of about 30 degrees. The front tweeters are angled outward at almost 45 degrees and are nearly horizontal. The woofers are in separate internal sub-enclosures, which are ported individually into the main volume of the cabinet and from there to the outside through a single opening on the top.

The overlap in frequency coverage between the tweeters and the woofers, allowing them to operate together over nearly an octave, is said to minimize phase-shift effects and audible coloration of the sound. Also, since several drivers are operating together in each part of the frequency range, their individual response irregularities tend to average out and give a smoother overall frequency response. There are no user-adjustable level or balance controls. In the rear of the enclosure are binding-post speaker terminals and a third (covered) terminal reserved for use with future (unannounced) Bose electronic components.

The Bose Model 601 Series II is nominally an 8-ohm system, suitable for use with amplifiers rated from 20 to more than 150 watts output. The tweeters are protected from burn-out by a small thermal device whose resistance increases during periods of high input level, limiting the power delivered to the tweeters without silencing or even audibly affecting the sound of the speaker system. When used with amplifiers rated at more than 100 watts per channel, Bose suggests connecting a 2-ampere fuse in series with the line to each speaker. The Bose Model 601 Series II is covered in walnut-grain vinyl veneer. It is 29-1/2 inches high, 14 inches wide, and 13 inches deep, and it weighs about 40 pounds. The suggested list price is $445 per speaker (they are sold only in pairs).

Laboratory Measurements

The unconventional radiation pattern of the Bose Model 601 Series II makes it difficult to measure its performance in a conventional anechoic environment (or to describe its performance in terms of the quasi-anechoic measurements provided by our FFT signal-analysis system). This is because the angled or rear-facing drivers do not all contribute directly to the speaker’s sound-pressure output along any arbitrary axis. In fact, in an anechoic measurement the rear radiation is totally absorbed and never reaches the measurement microphone.

On the other hand, the averaged room response, a normal part of our measurement procedure, takes into account the total output of the speaker as modified by absorption by the room boundaries and furnishings. Since this corresponds closely to the usual operating mode of the Model 601 Series II, one would expect it to give a realistic picture of its true performance qualities.

Our initial reaction to hearing the Bose Model 601 Series II in our familiar surroundings was that it had a superbly balanced octave-to-octave response, with an effortless smoothness that ranked with some of the finest speakers we have used. The bass was very powerful, yet without boom or any undue emphasis in the upper bass or lower midrange, where so many dynamic speakers suffer from coloration. The highs were silky and free from brightness or harshness. The midrange smoothly connected the two ends of the spectrum.

It was not too surprising to find that our measurement microphone “heard” essentially the same characteristics as our ears. Even without averaging the measurements from the left and right speakers (which are identified by Bose for those specific positions, although they appear to be identical and symmetrical), the room response was exceptionally smooth, and the multiple tweeter array provided essentially perfect horizontal dispersion.

The averaged room response was impressively smooth and uniform down to about 200 Hz, although room effects became evident below that frequency. The two speakers were about 10 inches from the front wall and 10 feet apart, with the measurement microphone placed some 12 feet in front of them. The close-miked bass response was identical for both woofers. When the curve for one woofer (increased by 3 dB to account for the contribution of the other) was combined with the port response (corrected for the relative areas of the cones and the port), the total bass response was every bit as exceptional as it sounded. The output varied only ±2 dB from 27 to 900 Hz. Combining this curve with the middle- and high-frequency room curve resulted in a composite frequency response of ±3.5 dB from 20 to 16,000 Hz. A small peak at 13,000 Hz was the highest point we found in the combined curve.

While our composite frequency response curve cannot be compared directly with any manufacturer’s response figures (and Bose does not publish frequency-response data for their speakers), it does, in our experience, correlate well with the sound of a speaker, especially in our fairly typical listening environment. In this case, the measurements coincided exactly with the way the speakers sounded to us.

The FFT response curve, as anticipated, was slightly ragged (though much less so than we would have expected from the multi-driver configuration of the speakers). Even so, its ±6-dB variation over the 180-to 15,000-Hz measurement range would be considered quite creditable for most good conventional speakers in this type of quasi-anechoic measurement.

The sensitivity of the Model 601 Series II is also not easy to measure or specify accurately because of its spatial characteristics. Measured at a 1-meter distance at the level of the forward-facing woofer, the sound-pressure level (SPL) was 85 dB for a 2.83-volt input of random noise in an octave bandwidth. At a more realistic “listening” position—the height of the tweeters—the SPL was a good 89 dB. The minimum system impedance was about 7 ohms at 35 Hz and 8 ohms between 130 and 300 Hz.

The bass distortion with 1 watt input was less than 1 per cent from 100 to 50 Hz, rising gradually to about 6 per cent at 20 Hz. At 10 watts input the distortion was substantially higher, between 2 and 4 per cent from 100 to 45 Hz and 12.5 per cent at 20 Hz. At the lower frequencies a high power input produced audible air noise from the system’s port.

Comment

Although individual preferences vary widely with respect to the dispersion patterns of speakers (and we have found good and not-so-good examples of both forward-radiating directional speakers and wide-dispersion “omnidirectional” speakers), we prefer to judge a speaker by its sound, not its operating principles. The Bose Model 601 Series II is, in our judgment, an unequivocally fine-sounding, thoroughly natural and smooth speaker. It does not appear to require critical or aesthetically awkward room placement or to impose any other undesirable constraints on its use. Not only is it priced well below the Bose leader, the Model 901 Series IV, but it requires no external equalizer and is certainly more conventional looking.

The sound we heard from the Model 601 Series II, on a broad variety of program material, was the kind we simply enjoy listening to. This extended “listenability” is a property of almost any really good audio component, and especially of a speaker. The 601’s spatial effect was one of its most striking and enjoyable features. The panorama of sound across the front wall of the room, behind the speakers, extended well beyond the speakers themselves, in a way audibly similar to that provided by electronic signal processing with ordinary speakers.

Those who may have found either the spatial properties or the physical appearance of the Bose 901 speakers to be too unconventional for their tastes should audition the Model 601 Series II. It is clearly a close relative of the 901 series, with considerable refinement in ease of installation and use, and (we suspect) a greater adaptability to different listening environments. It is one of the better speakers we have used, even at or well above its moderately high price.

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