Spica Angelus loudspeaker Page 2

Based on extensive work with computer modeling, the crossover is not as simple as some, though not nearly as complicated as those found in "flat-amplitude-response-above-all" designs. Though the high-pass leg for the tweeter is basically first-order, the corresponding low-pass drive to the woofer is fourth-order Bessel. This, coupled with the time alignment of the drive-units due to the sloping front baffle, gives what John Bau feels to be the most linear amplitude and phase response through the crossover region; ie, the output of each driver sums to unity on the listening axis and the phase angle to 0 degrees. Electrical connection is via sturdy angled binding posts on the black-painted cabinet rear. The base contains bushes for carpet-piercing spikes, which are supplied.

As noted by LA in his "Final Word" column last month, the review pair of speakers was purchased through a dealer, rather than being borrowed from the manufacturer, as is our usual practice.

Test procedure
This followed, with minor changes, that established for my previous loudspeaker reviews in Stereophile. Amplification was all-Krell—KRS2/KSA-50—with speaker cables and interconnect from Monster. Source components included a Mission PCM 7000 CD player (used both direct and driving a Sony DAS-703ES outboard decoder from its digital output), an up-to-date Linn Sondek/Ittok/Troika combination (with the latest composite armboard) sitting on a Sound Organization table, an LP12/SME V/Koetsu Red player sitting on a RATA Torlyte stand, and a trusty Revox A77 to play my own master tapes.

The frequency response was measured in the room—spatially averaged across the listening window in order to minimize the effects of low-frequency standing waves—using 1/3-octave pink noise at a reference level of 90dB, 1kHz; this will also give an idea of the speaker's dispersion characteristic in the upper midrange and treble. In addition, the nearfield low-frequency response was measured with a sinewave sweep to get an idea of the true bass extension relative to the level at 100Hz. Voltage sensitivity (using the 1/3-octave pink noise band centered on 1kHz and referenced to the sensitivity of Celestion's SL600) and the change of impedance with frequency were also assessed.

Sound quality
The loudspeakers were carefully positioned for optimum performance, well away from room boundaries, and coupled to the tile-on-concrete floor beneath the rug with their screw-in spikes. As the speakers are mirror-imaged, the narrower borders to their baffles were placed to the inside, with the speakers toed-in to the listening position. As the grille follows the line of felt on the front panel, the auditioning was carried out with the grilles in situ.

The Angelus seems to beam relatively severely in the vertical plane: the most neutral response with pink noise seemed to be with the ear level with the tweeter, though there was then a slight mid-treble emphasis; desirable, I thought, to compensate for a slightly shut-in quality in the top octave, especially with naturally miked strings. Above this axis the treble became increasingly uneven; by the time the ear is normal to the angled baffle, there is a considerable excess of mid-treble energy apparent. However, as you would have to be sitting on stacked bar-stools to be on this axis, or at least standing up, this is not a problem. Below the tweeter axis, the HF rolls off, the exact head position for the right treble balance being quite critical, I found. The bass level also increases once you get below the level of the woofer. This is an unrealistically low seating position, however.

In their manual, Spica recommends a "break-in" period of up to 48 hours before any serious listening takes place. As LA used the speakers first, he set a CD player to continuously play Dave Grusin tracks through them all night—I'm glad I wasn't around! When they eventually found their way to my house, I used them for a Saturday night's worth of heavy rock, with SPLs in the high 90s—LA's glad he wasn't around! Nevertheless, over the three-week period that I used the Spicas, I kept feeling that the bass was continuing to loosen up right up to the moment of booting up the word processor. This should be borne in mind when reading my description of the character of the low frequencies. If the Angelus were a wine, it would definitely be a red Bordeaux, a wine that improves with age. (A good Bordeaux even, but then, that's running ahead.)

After what I felt to be an appropriate break-in period, I started my serious listening. My initial impressions were that the low to mid-bass was depressed in level, leading me to suspect a rather more damped alignment than the Q of 0.5 quoted in the specification. This made the speaker sound "smaller" than I had expected from its size, although the definition in the upper bass was excellent. I discussed this apparent shelving-down of the Angelus's LF response with John Bau, who immediately asked if I had any ASC Tube Traps in my listening room. I do: four pairs of the 16"-diameter cylinders in the room corners to smooth out the upper-bass room sound, as well as various rugs hanging on the walls behind the listening chair to suppress reflections. Bau explained that the Angelus was intended to be used in rooms rather more live than mine and recommended I remove the Tube-Traps. I did so: though the low frequencies then had more weight, this was at the expense of upper-bass smoothness.

In the end I compromised by putting back enough Traps to civilize the room's low end. Ultimately, though, as I said above, the mid- to upper bass kept improving during the time I used the speakers—presumably the suspension was getting more compliant—and by the time I stared to write the review, I was not having any problem with the quality of low bass.