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  DCM SurroundScape Loudspeaker

      Date posted: April 24, 1997

DCM SurroundScape

Sugg. Retail: $2198 pr (U.S.)
Size: 46″H x 16 1/4″W x 12 1/2″D
DCM SurroundScape Centre Channel
Sugg. Retail: $279 (U.S.)
Size: 7 1/2″H x 23″W x 8″D
Manufacturer: DCM Loudspeakers
670 Airport Boulevard, Ann Arbour, Michigan 48108 U.S.A.
(313) 994-8481 FAX (313) 994-0190

     DCM was a fairly well known speaker line in Canada a few years ago, but since Bryston ceased distribution of it, the brand has pretty much gone away. In the U.S., however, the company has remained active with a strong dealer base that starts with Circuit City. I’ve known DCM designer Steve Eberbach as a talented and creative engineer, and have owned two of his TimeFrame transmission-line models over the years.

     It was just two years ago that I encountered his first approach to the SurroundScape home theatre speakers, which attempt to provide full surround sound with only front speakers. It’s basically a Time Window with a twist of phase, so to speak, for the surround signal, which is fed to the outer array of drivers on each side.

     But maybe I’m getting a little ahead of myself. The original Time Window design used a forward-pointed enclosure with a pair of baffles containing identical driver complements opposed at about 80 degrees. This allowed wide dispersion and very even radiation at all frequencies into the room. Bass loading of the woofers is via a transmission line that ports at rear.

     Steve’s big idea was to take this design and, as noted, utilize the outer driver set (a 6 1/2″ woofer and dome tweeter in a coaxial array) to carry the surround information, bouncing it off side walls; some electronic phase manipulation was provided in the crossover to make the sound seem to come from behind. Now, this type of processing is no longer uncommon, starting even before Q-Sound and now found in the Spatializer and Virtual Dolby techniques being now being included in multimedia computer systems.

     So in the SurroundScape system we have the inner drivers facing in towards the listener on a quite narrow baffle not unlike Ken Kantor’s approach with NHT, while the outer ones face outward to use wall reflections to reinforce the surround effect. There are also rear-mounted tweeters for front and rear sound to add spaciousness, and the front woofer system is augmented a powered internal subwoofer, with adjustment of level and upper crossover on the rear panel. As you can see, this is a pretty sophisticated piece of design work.

     DCM call their crossover design PrestiDigital, allowing “precise time equalization” in the phase shifting that creates the surround effect. The literature sheet goes on: “Our new Shadow Driver ManagementTM System produces a spectrally-shaped, phase matrixed, ambient field that completes a seamless surround soundstage of front and rear speakers.”

     The accompanying centre channel looks pretty ordinary, shaped to fit on top of or under a monitor. But removing the grille cover reveals not a D’Appolito array, but a coaxial driver array identical to those in the SurroundScapes, with tweeter mounted on a perforated metal screen that covers the woofer/midrange driver. The tweeters in both speakers are all identical small domes with phase plugs suspended across their centres, this determined largely by feel in the case of the left and right speakers, the black cloth grilles not removable.

     The measurements of this system were somewhat more complex than usual, and took the better part of a working day to accomplish. The first chart shows, from top to bottom, the Pink Noise Sweep, with the bass controls set for flattest response (this is the squiggliest one in the bass) with smoothed similar measurements showing the highest and lowest bass crossover settings. SurroundScape Frequency Response

     The fourth curve in this group, the one that slopes off below 1000 Hz is the PNS of the rear driver array, which clearly has its bass rolled off, obviously to prevent cancellations of the front drivers’ low end response because of the electrical phase inversion employed for the surround effect. The surround channels are also a db or two lower in level in the midrange.

     Below are quasi-anechoic curves for both driver arrays taken on axis, which here means not on the axis of the baffle board, but at the listening axis. This means that each baffle was angled about 40 degrees away from the listener, the inside ones facing in, and the outside ones at the side walls with the speaker cabinet facing straight ahead.

     Thus, the central listening position is best represented in the axial curves by the 15 and 30 degree curves, which are very smooth, the latter having a midrange dip. It goes without saying that there are a lot of acoustic things happening in this system, especially with surround encoded material, and Eberbach has achieved excellent overall linearity for such a complex design. At bottom, the rear channel’s responses can be seen to match timbrally quite well.

     Impedance curves were also quite similar, peaking at 13 or 14 ohms in the midrange, and being lowest at higher frequencies. With a powered subwoofer, low-frequency impedance is a simple resistance of 7 ohms for the front, with a mild peak of the same value just below 100 Hz in the rear channels. SurroundScape Impedence Curve      Phase shift through crossover is well controlled in both, with a double shift seen in the rear, the trace rising with increasing frequency above 4 kHz. I’m not sure of the significance of this, but it does suggest some electrical phase shifting in the midrange to enhance the surround effect.

     The centre channel speaker matches well timbrally as far as the measurements are concerned, with the same moderate forwardness giving way to flatter response as we move around to 30 degrees; those to the left and right of the centre seat will find dialogue emphasized a little more than with most D’Appolito-configured designs, perhaps a good thing if you’re close to the left or right speaker.
SurroundScape Centre Channel Frequency Response      Most such designs, with midrange/woofers flanking the tweeter show a significant suckout in this middle frequency range off axis.

     Impedance of the centre channel is a little higher, peaking at 27 ohms in the bass, and 20 at crossover; electrical phase is quite similar to the left, right, and surround speakers.

     I’ve heard these speakers at CES shows do some quite amazing things, their ability akin to a true ventriloquist in throwing images behind the listener (though that part of ventriloquism is not actually possible). The effect is totally dependent on side walls, and when I first hooked them up in my home theatre room I was not surprised that the same thing that helps other surround systems to be effective, namely my ACCO panels absorbing first reflections, virtually destroyed the illusion of SurroundScape. Removing the panels, and some careful speaker placement allowed me to hear what had been so impressive at shows.

     These speakers like to be fairly close to side walls, and work best in a fairly narrow room; ours is a little wide at 14 feet. While trying to tune the bass, I realized why both level and crossover controls are provided; it will take time for any new owner to optimize these speakers to the room. I found a problem in mine in the mid-bass: there was hardly any, while the deepest bass was overwhelming around 30 Hz. Experimentation solved this imbalance.

     Another thing to look out for is too much delay in the rear channels; since this is done acoustically by the wall reflections, delay in the receiver or surround processor should be set to its minimum value to avoid a quite pronounced flutter echo that muddies images. This was worst with DSP modes that use a lot of digital delay. Avoid these with SurroundScape.

     Having set things up, I started watching movie clips and listening to both discrete and matrix surround program material. In the former case, the `Cows’ segment of Twister from the Pioneer DVD sampler was very effective in Dolby Digital (”I gotta go, Julie, we got cows…”), the swirling tornado all over the room.

     With music, especially classical, the soundstage was huge, extending well outside the speakers, and occasionally wrapped right around the listener. With such LDs as Hell Freezes Over the audience seemed between the listener and the Eagles, but applause tended to come from outside the speakers, not from behind.

     In other words, the surround effects are not always as predictable as with real speakers behind, but if you forget about all this you can become immersed in the home theatre experience, forgetting speakers altogether. DCM do suggest that in some circumstances rear speakers should be added (check out their excellent web site: (www.dcmspeakers.com), especially in larger rooms, but in many you can get along fine without them.

     And in smallish rooms, you can also avoid worrying about a subwoofer, the Surroundscape system capable of powerful bass down to about 25 Hz; I don’t know how Eberbach has done this with relatively small woofers, but his transmission line definitely transmits. This was also true of my TimeFrame 1000s.

     For stereo music listening, this may not be the system for the purist, with all that PrestiDigital crossing over and Shadow Driver ManagementTM (though the latter characteristic might make it the speaker for Lamont Cranston: “The Shadow knows…ha, ha, ha, ha”), but it can present a very convincing soundstage with acoustic music, especially when using a simple matrix like DynaQuad or other ambient recovery techniques that avoid digital delay or other artificial processing. In this configuration the system can become quite revealing, with oodles of spatial information that somehow gets lost in many high end minimonitors. I think these speakers are excellent reproducers of music, with good transient speed, broad, quite smooth frequency response, and very convincing imaging. Being a fan of surround music listening, I guess I’m predisposed to like the latter effect.

     Whether you do or not, the DCM Time Window Surroundscape is a fascinating and challenging speaker system that should be auditioned if you’re intrigued by the concept. This is a completely realized design that is unique, and provides a compelling listening experience for both music and home theatre.

Andrew Marshall

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