Speaker testing: an overview.(COMPONENTS)

Twenty-five years ago, Peter Aczel's Audio Critic magazine review of the DCM Time Window introduced audio enthusiasts to the first affordable full-range speaker system that could handle dynamics and be free of performance quirks. Later on, when mini-monitor/subwoofer solutions appeared on Audio Critic's radar screen, Peter Aczel was cautious with his approach and preferred the full-range, single-speaker option for a cost effective system. Many of those full-range speakers evolved into boxy three-way designs with 8-10 inch woofers that Peter dubbed "monkey coffins." I did not follow Peter's advice and fell into the abyss of mini-monitors. At first impression, owing to their size, mini-monitors imaged better than the big boxes, and subwoofers were able to extend the bass to below 40 Hz. Unfortunately, subwoofers failed to solve the problem of bass response with the mini-monitor, except below 40 Hz, because it muddied the lower mid-range during the crossover from the satellite to the subwoofer. (I discussed this problem in issue 97.)

Moreover, the six-inch woofer struggled with bass below 200 Hz, and in the process of engineering it to do just that, performance above 1 kHz was sacrificed. At the top of a 6.5-inch woofer's crossover-controlled operating range, the woofer directionality narrows (less energy is radiated off-axis), which results in tonal balance shifts as the woofer crosses over to the tweeter. Though masked when viewed on an on-axis frequency response plot, the effect is observable in plots taken across the horizontal axis where a dip in energy of the woofer below the cross to the tweeter occurs.

With hard-material cones (metal, ceramic etc), it was important to cut the woofer off as quickly as possible so the crossover could attenuate the driver before the out-of-band resonances emerged. In many instances, as a byproduct of trying to obscure the woofer directionality while attenuating resonances, the tweeter crossed over too low in frequency. The fad (at the time) to get flat phase response only worsened the problem, because the low-order crossovers required for flat phase response kept the tweeter energized to well below 500 Hz. With both the tweeter (below its crossover point) and smallish woofer (down into the bass range) stretching too low in frequency, the mini-monitor struggled to produce dynamics.

Long-time readers will recall my review of a closed-out pair of speakers, the AR302s. I purchased them for an auxiliary system on a tight budget. For this system I wanted more bass extension than a mini-monitor without the expense of an outboard subwoofer and crossover. While the AR302s have problems with large changes in frequency response with vertical position, they are otherwise quality speakers. As I got to know them, they appeared in some ways to reproduce better than my mini-monitor-based system.

Finally, I dragged the AR302s into my main listening room and matched the levels against the expensive mini-monitors. I then discovered that the minis could not compete when it came to dynamics. In addition, the midrange also was better defined at lower listening levels, sitting on the optimal vertical height, with a real midrange producing that key spectrum and not a woofer that was being stretched outside of its optimal frequency range.

Although the AR302s had some appealing attributes, their imaging still was not to my liking, with the drivers being too easy to localize. I therefore went off in another direction and experimented with Sound Lab Quantum electrostatic hybrid speakers--similar to the Sound Lab Dynastats recently reviewed in T$S. (the Quantum model used an 8-inch woofer and had a smaller electrostatic area than the Dynastat.)

In a two-channel world, the room's wall reflections did some nice things for the overall tonality and gave the illusion of music coming from across the wall and not from a box. Dynamics were lackluster with the Sound Labs, but that did not seem to bother me at the time. They also owned your room, meaning that to have them play properly, the wall behind the speakers needed room treatments, and the speakers needed lots of distance away from the walls. Some rooms were simply not simpatico with the speakers.