Test Report: Thiel Audio SCS4T Tower Speakers

You already own a speaker that’s better in some ways than any ever reviewed in Sound+Vision — and you’ve owned it since you were born. What is it? 

It’s your mouth. No, it doesn’t play as low as a subwoofer (unless your name is Michael Clarke Duncan) and it doesn’t go as high as a tweeter (unless your name is Young Geddy Lee). But all frequencies emerge from your mouth perfectly in phase, a feat that even $100,000 speakers cannot equal. So next time one of your buddies starts bragging about his speakers, you can shut him up by telling him, “Sound+Vision said mine’s better.”

It’s probably impossible for any speaker to equal the phase coherence of your mouth, but the late speaker designer Jim Thiel probably came as close as anyone ever did. Thiel devoted his career to the design of phase-coherent speakers, which reproduce all frequencies of sound in phase within plus or minus a few degrees.

Designing a phase-coherent speaker without relying on digital audio processing isn’t easy. It requires that the acoustical centers of the drivers be at the same distance from the listener’s ear. In practice, that means pushing the tweeter back so that its dome is roughly even with the woofer’s dust cap. Phase coherence also requires the use of a first-order (6 dB per octave) crossover. Because a first-order crossover doesn’t filter sound as drastically as higher-order crossovers do, the drivers need to have an operating range at least two octaves past the crossover. That means that the tweeter in a phase-coherent speaker with a crossover point of 2.5 kHz should be able to handle frequencies as low as 625 Hz. If it doesn’t, you’ll get distortion at best and a blown tweeter at worst.

To my ears, phase-coherent speakers produce an especially enveloping stereo soundstage. Listen to a good orchestral recording through them, and you’ll get a more convincing sense of the ambience of the recording space. Listen to a pop recording, and the reverb effects tend to sound more intense and compelling.

There can be downsides to phase-coherent designs, though. Because of the shallow crossovers, they often exhibit high distortion. They also tend to have lousy vertical dispersion — i.e., if you raise your head a few inches, you’ll hear a difference. Many speaker designers, in my opinion, ignore these problems, but Thiel essentially eliminated them through his use of ultra-robust tweeters and coaxial midrange/tweeter drivers.

The SCS4T is the latest in a line of phase-coherent, coaxial two-way speakers that dates back to the early 1990s. It’s almost the same as Thiel’s SCS4 compact speaker (reviewed in S+V in August 2008 and available here). The difference is that the body of the speaker has been extended into a tower; the crossover has also been tweaked slightly to compensate for the sonic difference caused by the larger front baffle. Acoustically, though, that extra space goes to waste because it’s sealed off to make the internal volume match the SCS4’s. I guess Thiel’s engineers wanted the sound of the SCS4T to match the SCS4 as closely as possible.

At $3,690 per pair, the SCS4T isn’t cheap. But it’s built to a much higher standard than your average speaker. The handsome, elegant cabinet is made from thick medium-density fiberboard, covered in hand-selected real wood veneer, and finished in your choice of natural cherry, dark cherry, or black ash. A cast-aluminum baffle provides a sturdy mounting surface for the 6.5-inch woofer and the 1-inch tweeter housed in the woofer’s center. Aluminum outriggers with huge metal spikes keep the tower upright. The massive speaker-cable binding posts look like they came off an arc welder — well, a really high-end arc welder.

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