Although there are many reasons to like loudspeakers built around purely analog components—whether they’re all-passive or analog-based active designs—one benefit that owners of those loudspeakers can never enjoy is getting a digital upgrade that can improve the speakers’ sound and maybe even add new features. With digital active speakers, such benefits are possible.

Passive vs. active

Before I describe what such an upgrade can deliver, I’ll first explain the difference between passive and active loudspeakers—and differentiate between the two types of active speakers that exist in hi-fi today.

Nearly every loudspeaker includes some type of enclosure and one or more drivers. If the speaker has multiple drivers that cover different parts of the audioband (this is the case with most loudspeakers), there is almost always a crossover that divides the signal into different frequency bands. These separated signals are then routed to the different drivers.

A passive loudspeaker is still the most common type of loudspeaker available. In a passive loudspeaker, the crossover, which is almost always located inside the enclosure, consists of passive analog components (i.e., inductors, capacitors, resistors), and this crossover comes after the amplifier in the signal chain. The amplifier driving a passive speaker is almost always an external component.

Active speakers come in two forms. An analog active speaker has a line-level crossover built from analog components preceding the amplification stage, which means, in a multi-driver speaker (e.g., a two- or three-way design), there need to be amplifiers that come after the crossover to boost the separated signals for each frequency band. Analog-based active speakers have been around for decades and are common in the pro-studio world, but less so in home hi-fi.

Newer forms of active speakers work similarly but use DSP (digital signal processing) for crossover manipulation, meaning that frequency separation is performed in the digital domain. Once the signal is divided digitally, the resulting signals are converted to analog and routed to dedicated amplifiers for the different frequency bands. A DSP section can potentially perform other tasks, such as equalization for room correction. Incoming signals to the DSP section must be digital. DSP-based active speakers typically have digital and analog inputs, with an analog-to-digital (A/D) converter situated after the analog input to create the necessary digital signal.

The TCA‑M and the bass puzzle

Treble Clef Audio’s TCA‑M, which is a wildly ambitious, unique-looking, cost-no-object digital active loudspeaker, has both digital and analog inputs. I’ve been using a pair of TCA‑Ms in my living room since the beginning of the year, and have very little to complain about. However, I did notice one quirk with the low frequencies, which are reproduced by a patented dual-woofer configuration, when I played “Orphan Girl” from Emmylou Harris’s Wrecking Ball. In an earlier article, I wrote:

The puzzle lies in the bass—specifically, the deep, resonant hand-drum sound from U2’s Larry Mullen Jr., which anchors the track. As I mentioned earlier, the TCA‑Ms delivered deeper bass than any other speakers I’ve had in this room, and in doing so they revealed ultra-low frequencies I hadn’t heard in this song before, just as they’d done with other songs. But unlike other speakers I’ve used in this room—such as the Arendal 1528 Tower 8s, set up in nearly identical positions—the TCA‑Ms didn’t provide the same upper-bass punch; this is something I didn’t notice with the other tracks. This difference wasn’t subtle. Through the TCA‑Ms, the track sometimes felt like a darker, weightier, alternate version of itself.

DSP perfectionism

After he read my article, Treble Clef Audio’s founder and designer, Ole Siig, wrote to me saying that he thought what I was hearing was the time-coherent nature of the loudspeaker—meaning all the drivers, including those that handle the bass range, start and stop essentially in unison. This is made possible through DSP and is something almost all loudspeakers based on passive analog components cannot achieve.

Since then, I’ve learned that Siig is a perfectionist who never stops tinkering, so my experience must’ve inspired him to experiment. The result came to me on October 31, when he informed me by email that I could update the DSP code in the TCA‑Ms I have on loan by installing a file he’d attached. A few days later, he followed up with more details, including:

I am quite pleased with this DSP update.

Keeping the step response perfect across all target curves is something I have long wanted as a native part of the FIR crossover, and it’s now possible.

With the Peak Limiters, we now effectively emulate the way a conventional bass speaker naturally rolls off at lower frequencies. It turns out this behaviour is essential for certain types of electronic music that include waveforms you really don’t want to hear—and conventionally don’t—even in the studio during composition and mixing.

Regarding the Emmylou Harris “Orphan Girl” track, you may find the experimental TCA‑M Midbass Lift target curve a good match for your room and preferences. It’s identical to the standard TCA‑M target curve, but with a gentle lift in the mid-bass. Once you have the app installed, you can of course tweak it in any direction—the step response will remain intact when EQ adjustments are made via the TCA app.

The target curves that Siig refers to pertain to various frequency-response curves preprogrammed into the speaker as presets. These presets adapt the speaker to rooms of various sizes and reflective properties. As I wrote in the September article, I’d initially tried the TCA‑M Small preset, which is intended for small rooms, and TCA‑M Large, for large rooms, but settled on TCA‑M, which basically splits the difference between the two and can be considered the default curve. More ambitious listeners can program their own curves, but I haven’t gotten there yet.

As Siig implied in his note, TCA‑M Midbass Lift is the newest preset curve. He emphasized that the software update will improve time-domain behavior for all target curves, including existing curves.

Updating before a Bruce Cockburn night

While I was intrigued by the update, I couldn’t implement it immediately—I had pressing matters to attend to that week. But I had some free time on Saturday, November 8, which coincided with a presentation a friend and I were to attend that night at the Canadian Museum of History in Gatineau, Quebec, Canada. Bruce Cockburn was scheduled to talk about his career in music, which spans more than 55 years (he’s now 80), during which time he’s released around three dozen albums (studio, live, and compilation).

I’ve been a Bruce Cockburn fan for as long as I’ve been an audiophile—since 1980. I credit this to Andrew Marshall, publisher of a now-defunct Canadian print magazine called Audio Ideas Guide. In a 1980 issue I wish I still had lying around, there was a review of Humans, Cockburn’s newest album at the time. As I recall, the review was written by Marshall, but I can’t be sure. Nevertheless, it praised the album wholeheartedly and said something to the effect that if the label issued an audiophile pressing of Humans, it might be a masterpiece.

I rushed out and bought Humans, and quickly realized it didn’t need an audiophile pressing; the music on that standard vinyl release spoke to me, and I still consider it a masterpiece. It remains one of my favorite albums of all time. From then on, I followed Cockburn’s career and purchased most of his albums.

I carried a CD copy of Humans (Deluxe Edition), which was released in 2002, to the talk that night—and at the end I had Cockburn sign it. That CD is far better-sounding than any previous CD version of Humans I’ve heard; and although it’s an apples-to-oranges comparison, I think it sounds far better than my vinyl version. That LP has mysteriously gone missing, but I’m hoping it will turn up in some pile of music I’ve forgotten about.

A Bruce Cockburn primer

The friend who was to accompany me to the presentation didn’t know Cockburn’s music at all. In fact, when we first decided to get tickets, he couldn’t name a single song. But when I mentioned “If I Had a Rocket Launcher,” from Cockburn’s 1984 album Stealing Fire, he responded, “Oh yeah, that’s a great song.” Then I mentioned “Wondering Where the Lions Are,” from Dancing in the Dragon’s Jaws, released in 1979, a year before the original release of Humans. He knew that one too, but after that he was stuck. I told him that Cockburn had recorded many great songs, and I invited him to come to my place a few hours before the talk so I could introduce him to Cockburn’s music and help him make better sense of it all.

Where Bruce Cockburn first wrote lyrics for “If I Had a Rocket Launcher”

Installing the update

I was a little apprehensive about updating the speakers before my friend arrived for fear of something going wrong, rendering the speakers inoperative. But Siig was confident everything would go smoothly and was available by email all day to help with any problems.

He’d already emailed me a software package from a company called Four Audio that performs the update, a license key for the software, and a single update file with a “ddd” extension intended for each speaker’s DSP section. I first had to install the Four Audio application on a computer connected to the same network as the speakers. That meant I also had to connect the speakers to my network, which I hadn’t done to that point. I’d been using a Simaudio Moon 791 streaming preamplifier connected to the TCA‑Ms’ analog inputs, so no network connection was required for the speakers.

To connect the speakers to my network, I used a 100-foot ethernet cable I keep around for this kind of chore. I first connected the cable to an RJ45 port on the base of the right speaker and to my router. I opened the Four Audio software and installed the license key, but I saw nothing in the area of the screen that displays the speakers on the network. I disconnected the ethernet cable and powered the speaker off and on several times, but still nothing. I switched to the left speaker and experienced the same issue.

I emailed Siig, who immediately wrote back and asked me if I’d plugged the cable into the correct RJ45 port. There are two ports on the back of each TCA‑M and the cable had to be in the one marked Config. I felt a bit stupid, because I hadn’t looked closely; I’d felt around the back of each speaker base with my fingers, found an RJ45 port, and plugged the cable in without looking—and I’d picked the wrong port for each speaker.

Once correctly connected, each speaker showed up in the Four Audio control panel. If I disconnected the cable from one speaker and moved it to the other, neither speaker would disappear from the listing—the software remembers discovered speakers, and simply shows whether a speaker is on the network or not. I was able to update each speaker’s DSP code one at a time by pressing the configuration icon and uploading the configuration file that Siig had sent. Each update took only a few seconds.

I next looked at the little touchscreen on the base of each speaker and noticed that both had retained my original settings but now had two new target-curve presets: L TCA‑M Midbass Lift and R TCA‑M Midbass Lift. They’re both the same, but are for the left and right channels, respectively. Which one you choose only matters if you’re using the ethernet input on the TCA‑M, which uses the Dante networking platform for streaming media. I was using the speakers’ analog inputs, so channel allocation was determined by the output connector of the source component—in my case, the Moon 791. Still, just because I’m a stickler for getting things exactly right, even when it doesn’t matter, I picked the appropriate channel preset for each speaker.

Listening

The update went smoothly, leaving me plenty of time to experiment before my friend arrived for his Cockburn tutorial. I decided to play “Orphan Girl,” which I streamed from Qobuz in 24-bit/44.1kHz FLAC format. Since the TCA‑M Midbass Lift preset is an add-on, not a replacement, I could toggle back and forth between it and TCA‑M.

Based on its name, it should be obvious what the difference is between TCA‑M and TCA‑M Midbass Lift—more mid-bass energy from the latter. I deliberately didn’t ask Siig how much more energy is provided or what frequencies are affected (and I still don’t know for sure) because I wanted to listen first.

The difference I heard between the two presets wasn’t drastic, but it was noticeable and important. All the low-bass depth and heft of the TCA‑M preset was there with TCA‑M Midbass Lift, but there was more energy around (this is a guess) 70Hz. Not drastically more: 2dB, maybe 3dB tops. A precise measurement might show something different, but that’s how it sounded to my ears in my living room (the same space I wrote about in the September article, with the same speaker positioning).

When my friend came over and I presented my Cockburn-through-the-years tutorial, I conducted no back-and-forth comparisons of target curves. Instead, we just listened with the TCA‑M Midbass Lift preset engaged. My friend is not an audiophile and doesn’t care about the differences we audiophiles fuss over. But as I played tracks starting with Cockburn’s self-titled debut album, which was released in 1970, and ending with his latest (and, according to his talk that night, possibly his last), O Sun O Moon from 2023, my friend listened intently and picked out favorites. Meanwhile, I concentrated on how these songs were being reproduced.

The TCA‑M is a neutral transducer that can reveal all the details of a recording. From the bass up through the highs, no part of the audioband is emphasized or de-emphasized, unless you pick a preset that’s inappropriate for the size of your room and end up with too little or too much bass.

But there’s something more important to highlight about the bass, something I discussed in my previous article but is worth repeating here. I’ve read comments disputing Treble Clef Audio’s claim that the TCA‑M can provide sufficient output down to 20Hz. From what I can tell, critics base these comments on the speaker’s modest size. In fact, it does dig that deep. For example, when I played “Rumours of Glory” from Humans, the drums thundered as powerfully as a large floorstander with one or more big woofers. The hard-hitting drums in “Kit Carson,” from Nothing But a Burning Light, were reproduced with tremendous impact that gave the song power. Cockburn’s two newest albums—Crowing Ignites and O Sun O Moon—have a dynamic, full-range sound I really like, and the TCA‑Ms reproduced the bass from these albums in a way that rivals very large passive speakers.

Active advantages

This highlights another advantage of active speaker technology, particularly when implemented digitally. With DSP and proper drivers, amplifiers, and enclosures, a designer can overcome the limitations that plague purely passive designs, especially in terms of bass extension.

Then, of course, there’s the potential of online updates for the DSP section. This feature is not unique to Treble Clef Audio—Buchardt Audio, System Audio, Kii Audio, Dutch & Dutch, and other companies are delivering updates of various types, too. But awareness of this in the audiophile community is not yet widespread. In fact, I believe that the idea remains as unfamiliar to audiophiles as Cockburn’s music was to my friend until our afternoon of listening and Cockburn’s talk that evening.

After these experiences, the light went on for him about Cockburn and his music. And after you live with a pair of active speakers like the TCA‑Ms and experience not only the performance benefits of an active design, but also the improvements in sound quality and feature set that can be delivered online, it makes living with traditional passive speakers seem like a thing of the past—which it is.

Speaking of the past, if you want to play one Bruce Cockburn song to show your system off, try “Pacing the Cage,” from The Charity of Night, released in 1995. Its recording quality is as good as the music. On the Treble Clef TCA‑Ms, the new Midbass Lift preset really makes Rob Wasserman’s bass on this great track shine.

. . . Doug Schneider
das@soundstage.com