Spica TC-50 loudspeaker J. Gordon Holt
Like Audio magazine's Richard Heyser, Spica Speakers' John Bau is heavily into instrumentation for loudspeaker evaluation and design. His fully equipped, computerized lab allows him to assess just about every measurable aspect of loudspeaker performance, and to design towards perfection in all of them. Having toured Spica's manufacturing facility here in Santa Fe, I can vouch for the care and attention to detail that go into their loudspeakers. (The crossover in the TC-50 includes notch filters to take out two small peaks above the woofer's crossover point).
Bau designs largely on the basis of Time-Delay Spectrometry, and this is reflected in the incredible imaging and soundstaging capabilities of his little TC-50 speakers. However, their limited low-frequency range and their rather cold overall sound has earned mixed reactions from listeners (particularly me). The Servo-Subwoofer was introduced to extend the TC-50's low frequency response and to enable higher SPLs, without degrading the imaging specificity that has been Spica's trademark. I looked to the subwoofer to cure the problems referred to above.
The subwoofer is a complete bass module including a built-in power amplifier. The supplied passive crossover connects between the preamp outputs and main amplifier inputs, and requires a long shielded cable to run signal from the crossover to the bass unit(s). The woofers are servo-controlled, which is to say a sensing circuit detects any deviation of the cone from its desired motion, and adds a correcting signal when needed.
Each woofer module has two inputs, so the right and left-channel bass signals may be combined in the woofer amplifier if you're only using one bass unit.
This system comes with one of the most detailed instruction sheets I've seen for a speaker system, rivalled only by Infinity's set-up instructions for the IRS and RS-1B! Set-up involves taking accurate measurements from the room's side walls and listening location to the speakers, and aiming the speakers precisely and symmetrically at the center of the listening area. The effort is justified, because, like all speakers with the capability of superb imaging, a half inch or a single degree of asymmetry in placement can degrade the imaging.
Preliminary woofer balance is adjusted with an oscillator and AC voltmeter; you measure the voltage relationships between the satellite-speaker inputs and those at the woofer at two test points on the front panel. Clever. (But how many audiophiles own an AC voltmeter? Most will have to borrow one from their dealer, if he's willing to loan it out.) Because he lives nearby, I was able to call on John Bau to set the speakers up for me (with a pair of subwoofers), and to ascertain that they were performing properly.
Simply speaking, I was not swept off my feet.
The system was unbearably bright and, I felt, bass-shy, but John assured me the sound would improve when the speakers "broke in" a little. So I left them on over a weekend with FM interstation hiss going through them, and gave them a re-listen the following Monday. Yes, the high end had improved, insofar as it was now at least bearable.
The TC-50's imaging and soundstage presentation is practically legendary. There is no system I know of that is better in these regards (see AHC's report on the TC-50 in Vol.7 No.2), and my relisten reaffirmed my earlier impressions. As mentioned above, I had never cared much for the TC-50's rather cold, stark sound, and I am sorry to report that the subwoofers don't do much for that coldness.
I found this system to be relentlessly analytical and uninvitingly antiseptic, as though the entire audio range were slightly tilted upwards toward the top, with a sparseness at the low end that was hard to believe from a system sporting two subwoofers!