Speakers, rooms, and speaker sound.(SKEPTIMANIA)(Product/service evaluation)

While I any pretty much retired from the audio-journalism business, I do intend to occasionally submit copy dealing with whatever happens to be on my mind at the moment. As it is, right now there are two topics on my mind relating to audio: one personal and one related to what 1 recently read in this magazine. Consequently, I might as well get busy.

First Topic. OK, my latest do-it-yourself project regarding speaker building is complete. Previously my main A/V system had a home-built center speaker that consisted of four Roy Allison designed AV-1 minispeakers assembled into a stand-mounted, triangular shaped configuration resembling the top half (top two feet) of either of my Allison IC-20 main-channel speakers. There were two front panels, each angled 45 degrees to the side from straight ahead, with a vertical MTTM driver array on each of them. The tweeters were Allison designs, but the 4.5-inch cone midrange drivers were built in the Far East for incorporation by Allison into the AV-1 units. The crossovers were basic second-order designs (high and low pass filtering) that Allison has traditionally used in many of his systems.

The four 4.5-inch cones notwithstanding, this system was unable to go deep enough into the bass range to be operated full bandwidth, even as a center-channel speaker. However, rather than configure the center circuitry of my receiver to route its bass to my main system's Velodyne F1800II "main" subwoofer, I gave the channel its own dedicated subwoofer: basically a modified (by me) SVS 16-42 unit, powered and crossover controlled by a Hsu Research amp. The resulting center-channel performance was pretty good, but the system had several weaknesses.

First, although the Allison tweeter is a great one, with a wide-angled radiation pattern in the top octave second to none, it is at its happiest if crossed over above 3.5 kHz. In the two-way Allison models, including the AV-1, the crossover point of the Ferrofluid cooled version of the tweeter is nearly an octave lower, at 2 kHz, and down that low the tweeter has the potential to have a bit more distortion with high-powered inputs than some might like. Although using four of the things in the array certainly helps out, I still prefer a higher crossover point, if only for power-handling advantages in the 2 kHz to 4 kHz range where a typically more solidly built midrange driver would be working in three-way Allison systems.

Second, the off-the-shelf midrange driver used in the AV-1itself is problematic. The unit is OK, but if I fed single-frequency test tones into it at moderately high levels I could hear harmonic artifacts that were not showing up if I fed identical signals into my IC-20 systems. Its inherent smoothness was not all that great, either, and the genuine, "dedicated crossover" controlled Allison midrange drivers in the IC-20 units were superior to the AV-1 midrange units both in terms of distortion and smoothness. Also, with a subwoofer crossover point of 90 Hz, I felt that the four AV-1 midrange drivers were at times having to do more high-output work in the middle-bass range from 90 to, say, 150 Hz than they were comfortable with.

The replacement system uses drivers and crossovers that I pulled from a pair of no longer needed three-way Allison AL-125 systems some time back. This system, a floor-standing design, has a single forward-facing panel, with a vertically oriented MTTM driver array, eliminating any horizontal interference effects that would have existed with the previous system. The tweeters and raids are standard Allison units (identical to those in the IC-20), with the tweeter/ mid crossover point set at 4 kHz, eliminating both the low-crossover point problem and the test-tone distortion problem. The woofers are two 6.5-inchers, crossed to the midranges at 450 Hz, that are located on the sides of the enclosure near the bottom, reducing the potential mid-bass extension to 90 Hz problem.

This "super-center" system uses two fully second-order AL-125 crossover networks that I modified to work with each three-driver array. Each tweeter, midrange and woofer combination is on a separate circuit (separate crossover), meaning that the speaker system, as with the system it replaced, has to be biamped. There are dual five-way binding posts on the backside of the speaker to allow this, and I do the biamping with the two 130-watt main-channel amps in my Yamaha RX-Z1 receiver that are fed by the dual center-out hookups The crossover modification mainly involved configuring the bass output of the two crossovers to handle just one woofer ...