TacT Audio RCS 2.2X Preamp

Getting the bass right with the TacT corner-woofer system

Digital room correction can seem almost like a miracle. The improvements are so spectacular that it may seem like all problems have been solved. But the final result still depends on what you start with—room correction is powerful, but not all-powerful. It is logical to expect the best end result when the uncorrected system has been set up to be as good as possible. But the system I want to tell you about here is different, because it doesn’t work at all without digital signal processing. It’s the next step in DSP control of the room/speaker interaction, and one more step into the future of audio.

Like many really good ideas, this one is simple. Decades ago, describing what is now known as the “Allison effect,” Roy Allison pointed out that it is difficult to generate bass from speakers that are out in the room. The room boundaries load the speaker in a way that varies erratically with frequency, causing big peaks and dips in response and timing errors, too. Corners are where woofers belong. (Corners are where the Allison Model 3 goes, too; see my review in Issue 150). But if you try to put the midrange and treble in a corner, early reflections will cause coloration and imaging problems.

Of course, there were and are “satellite/ subwoofer” systems that allow you to place the woofer in one spot and the midrange/tweeter in another, but they never sound coherent unless the crossover to the subwoofer is way down low. And even when it is as low as needed some of the bass still has to come from the satellites (out in the room), so much of the effect of the corner placement of woofers is lost.

What occurred to TacT was that: (1) the lack of coherence of the satellite/subwoofer system had to do with the physical separation of the woofer and satellites causing separation in timing; and (2) in the world of digital signal processing it is easy to introduce time shifts that line things up temporally. In other words, you could fix the coherence problem by time-delaying the satellites until the (sub)woofer signal from the corner had moved out to where the satellites were physically located.

Using this idea, the $3990 TacT 2.2X (X for crossover) lets you do a crossover-plus-time-delay at, say, 200Hz from a corner-placed woofer to a main speaker out in the room (where midrange and treble response are smoother and imaging better). The crossover can be configured in various ways; I used the “default” tenth-order high pass and low pass (in DSP, steeper slopes can be used without problems that would be common in analog crossover design). The RCS 2.2X also does the overall “room correction” to bring the in-room response to whatever “target curve” you choose, but it is the corner woofer arrangement that I am going to talk about here. (The TacT Room Correction System has been reviewed before in TAS by AHC in Issue 150 and by me in Issue 126.)

The theory of this appealed to me right off, and I knew from my experience with the corner-placed Allison Model 3 how good corner bass could be. But I was still taken by surprise when I first heard this system in my own room. Anyone who has worked with DSP already knows what bass sounds like when it is truly flat and phase-linear. The TacT Room Correction System already makes the bass of my Harbeth M40s exceptionally smooth and precisesounding. 1 But the RCS 2.2X cornerwoofer system pushes things further in the right direction—quite a bit further.

The first thing I played was the second movement of Dag Wiren’s Serenade for String Orchestra [Paula]. This charming music has prominently-plucked lower strings (cello and doublebass) that are strong and very precise, so it makes a great bass demo. My jaw dropped when I heard this on the TacT RCS 2.2X system (using the woofers of the Allison Model 3s for the corner woofers and the Harbeths M40s for “satellites,” even though they are almost full-range to begin with). Not only was the bass pizzicato line more defined than ever, but the whole sense of the recording venue was enhanced. And the sense of sound coming from speakers was greatly diminished.

We are always talking about speakers “disappearing,” and indeed many do in terms of side-to-side imaging (see my Audio Physic Padua RR review, Issue 156). But front-to-back imaging is a different story—so much of a different story that many audiophiles have come to believe that the front of the soundstage is intrinsically associated with the front plane of the speakers. But it should not be. With the TacT corner-woofer system, the speakers “floated” much better from front to back, and the soundstage positioned itself front-to-back according to the recording, as it should have, not automatically receding from the front plane of the speakers. Piano music is another realm in which the corner-woofer system excelled. Piano bass varies with time in a complex way, and it is really hard to get it right. But with the TacT cornerwoofer system the big Yamaha concert grand on the “Liebeslied” transcription from Freddy Kempf Plays Rachmaninov [Bis] really sounded like a concert grand piano, with all the low-frequency precision and weight that entails.