The following article appeared in The Audio Critic
Issue No. 16 Spring through Fall 1991;
written by Peter Aczel, Editor & Publisher.

"This is a beautifully engineered, electronically flawless piece of equipment of limited usefulness. Crossing a separately amplified subwoofer over to the main speaker would be one of its more obvious applications; more about that in a moment. Here's what the lOB can do - and anything it can do, it really does perfectly.

In each channel, it can select 12 crossover frequencies, more or less evenly spaced between 70Hz and 4.5kHz, and activate Butterworth lowpass and highpass filters that have the selected frequency as their passband edge. The attenuation slopes of the lowpass and highpass filters are separately adjustable to 6, 12, or 18dB per octave (1st, 2nd, or 3rd order), and the highpass filter level as referenced to the fixed lowpass filter level can be set in 1 dB steps from -5dB to +5dB. And that's not all, as they say in those special offers on TV. By manipulating connections on the back panel, you can turn the lOB into a mono crossover of even greater versatility- would you believe a variable-slope threeway or a 4th-order Linkwitz-Riley two-way?--but then of course you'll need two units for a stereo system. There are also professional versions with balanced inputs and outputs, special Linkwitz-Riley modules, you name it- hog heaven for the biamp/triamp crowd.

My measurements revealed absolutely no flaws, errors, or glitches in this complex system; the filter contours that I checked at random among the available permutations and combinations were all dead-on; distortion and noise were pretty nearly unmeasurable on my test bench at all audio frequencies regardless of the filter settings; in other words, the signal paths of the device appear to be perfect. (All right, there is one potential-but easily remediable-problem. Inside the unit, a 10-ohm resistor between chassis ground and signal ground appeared to be the cause of a slight but audible hum in the biamped system of one of my associates. Shorting the ground side of any one of the output jacks to the chassis killed the hum.)

David Rich, whose various EE degrees also stand for El Exigente, had only good things to say about the circuit design, which is implemented with discrete op amps. He praised the elegant simplicity of various engineering solutions in the 10 B and called designer Chris Russell "a ridiculously good engineer," by which I think he meant that Chris goes to almost ridiculous lengths to refine his circuits and minimize distortion, without allowing the cost-effectiveness of his designs to go down the drain. That's what good engineering is all about.

As for the limitations of the 1OB, they have nothing to do with engineering but stem from the basic problems of crossing over real world drivers, which are very different from the idealized amplifier loads assumed by a "perfect" electronic crossover. Realworld drivers are, in effect, lowpass and highpass filters; only a dedicated crossover, whether passive or active, can process those filter characteristics in such a way that the interacting electrical/acoustical poles and zeros will yield the combined, measurable lowpass and highpass responses required in a particular design. In other words, a truly good crossover for a specific speaker system can't be separately bought off the shelf. The exception to that rule would be a subwoofer crossed over well below its upper roll-off frequency to a more or less full-range main speaker system. That way there are no preexistent poles imposed on the electronic crossover in the vicinity of the crossover frequency. Bryston has also come to the realization that this is the best possible use of the l0B and has recently added a new model, the "10B-sub," to the line, with all 12 crossover points at lower frequencies (40, 50, 60, 70, 80, 90, 100, 200, 250, 300, 400, and 500 Hz). I think that makes a lot of sense.

As a subwoofer crossover, the 10B is unquestionably state-of-the-art and very reasonably priced for such a complex piece of equipment. I see no point in evaluating it subjectively, since the perceived sound quality will depend entirely on the speakers used and on the specific settings of the controls; the electronic signal path as such is obviously transparent. If your biamped subwoofer setup requires, let us say, 18 dB per octave Butterworth filters crossed over at 100Hz for best results, you can be certain that no better solution exists than the Bryston 10B. And if you then decide that 70Hz would be a better choice, the changeover will be totally painless. But don't imagine that you're a crossover designer for 2-way and 3-way speaker systems just because you own a 10B. There's a little more to it than that.

We invite you to experience the Bryston SST² Series amplifiers

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