Poles Apart Page 3

Testing, One Two That's where I come in. I chose the M&K Surround-250 MKII speakers ($1,499 each) for this comparison for two reasons: 1) I already have an M&K speaker system and the S-250s blended well with my front speakers. 2) Since the S-250s are designed to operate as monopoles, dipoles, or a blend of the two, they let me judge the relative merits of direct radiators and dipoles without having to switch between two sets of speakers. Each S-250 has three sets of drivers - three 1-inch tweeters and two 5 1/4-inch woofers in front, plus two 3-inch midrange drivers on each side. The comparison wasn't altogether seamless, however, since I had to rebalance the surround-channel levels every time I switched between speaker types.

For simplicity's sake, I kept the S-250s in fixed positions, placing them on my side walls, slightly behind the listening position. Because dipoles generally sound best elevated above the listener while monopoles sound best at ear level, I compromised and placed the speakers slightly above ear level. My listening position is about 6 feet from the rear wall, which is just about optimal.

For source material, I selected two movies on DVD-Video, Vertical Limit and The General's Daughter, while three DVD-Audio discs - Randy Travis Live, Fleetwood Mac's Rumours, and Vivaldi's Four Seasons - represented the music world.

At the Movies I've always found high country to be peaceful and quietly serene, but in Vertical Limit (Columbia Tristar) the slopes are very busy with lots of sound coming from all around. In Chapters 8 and 9, a storm kicks up as climbers are perched at 26,000 feet on K2 in the Himalayas - not a good thing. The surrounds carry deep-throated gusts of wind as it whips through on the left and right sides. To make matters worse, blasts of thunder trumpet in all five main channels. In Chapter 10, the intrepid explorers are caught in an avalanche. The subwoofer carries the weight of the massive onslaught, but the surrounds convey a dizzying array of rushing, ripping sounds as the climbers tumble down the slope.

In both of these scenes, the sound designer intends to immerse you in the action. While some localization is needed to reproduce the broad stereo effects, nothing is precisely placed in the sound field. Just as in a real storm or avalanche, ambient sounds seem to come from everywhere. With the dipole setting, the M&K speakers not only created an impressively realistic surround effect, but also effectively gave the sense of being in a large movie theater. With the monopole setting, on the other hand, the rear sound field was diminished. The same sounds still came out of the speakers, but the effect was not nearly as realistic as in dipole operation. The wind and thunder emanated from distinct locations, and the sound effects jumped from one speaker to another rather than sweeping continuously across the arc.

The General's Daughter (Paramount) is a good military-flavored whodunnit with some fairly subtle surround effects. The setting for Chapter 3 is the waterfront, with the sounds of whippoorwills and creaking boats, water lapping against their hulls. Sounds like these, which in reality come from all around, were most convincingly reproduced in dipole operation - as were the nondirectional sounds of gunfire and flying debris.