Beyond Frequency | How the TCA-M Preserves Musical Reality — Part III

From Reproduction to Illusion

A piano radiates sound from a distributed acoustic structure comprising multiple strings, a large soundboard and a resonant enclosure. Each element contributes frequency-dependent radiation patterns, phase relationships and temporal behaviour that vary across space. Scaling up to a trio and a full symphony orchestra spread across space only complicates the sound field created.

From a physical standpoint, such a sound field cannot be reproduced by a compact loudspeaker and its diaphragms acting as a single radiator. Fortunately, sound reproduction does not aim to recreate the original spatial field itself.

During recording, the complex acoustic event is reduced to a time-varying pressure signal that encodes the essential temporal, spectral and amplitude relationships perceived by human hearing. Successful playback depends on preserving those relationships.

When a loudspeaker launches air motion with accurate timing across frequencies, minimal stored energy and controlled interaction with the room, our auditory system reconstructs the event as external, coherent and spatially plausible. The perceptual realism arises not from geometric similarity between source and reproducer, but from fidelity to the temporal and spectral cues that the brain uses to infer size, distance and physical presence.

Attack versus body of sound

In live performance, only the initial attack of a note is sharply localised. The subsequent body of the sound arrives moments later through reflections, surrounding the listener and creating a sense of immersion. This balance between immediacy and envelopment is central to how music feels alive. When reproduced sound lacks this behaviour, the presentation can feel static or constrained, even when tonal balance is correct.

Creating a believable musical illusion is not a trivial act of reproduction. It requires persuading human hearing to accept a reconstructed acoustic event as real, coherent and emotionally meaningful. That task begins with respect for the musician’s intent, the timing, dynamics and expressive microstructure shaped through years or a lifetime of practice. It also demands a deep understanding of psychoacoustics, of how the brain binds sound across time, frequency and space to form a convincing auditory scene.

Only when those human realities are taken seriously can engineering become more than optimisation of specifications. Loudspeaker design must translate insight into perception from physical behaviour, controlling timing, dispersion, stored energy and interaction with the room in ways that align with how we naturally hear.

Reflections as contributors, not enemies

Rather than attempting to suppress reflections entirely, a loudspeaker can be designed to control how energy is launched into the room. When off-axis radiation remains spectrally consistent with the direct sound, reflections reinforce spatial realism rather than undermine it. In such conditions, the room becomes part of the listening experience, supporting a stable soundstage across multiple listening positions rather than restricting realism to a narrow sweet spot.

When this translation is successful, playback stops calling attention to itself. The room recedes, the loudspeaker disappears, and what remains is the illusion of presence, not as a technical trick, but as a faithful reconstruction of musical intention made believable by the way our hearing works.

This is the challenge the TCA-M was created to address

Owning the Full Transfer Function

The TCA-M Active Loudspeaker and the patented Sound by Design® Acoustic Platform is not bound by the limitations inherent in passive loudspeaker systems. The TCA-M is conceived as a fully active, DSP-controlled system that owns the entire Transfer Function from input to integrated acoustic output. This approach makes it possible to:

• Fully time-align all drive units
• Implement Linear Phase and constant Group Delay
• Maintain this behaviour across the full audible band
• Demonstrate these qualities clearly through an exceptionally clean Step Response

The chart below shows the TCA-M Step Response of the full Transfer Function from the Analog Balanced Input signal to the Acoustic integrated output. All frequencies from below 20 Hz to over 20 KHz aligns in time within 0.1 milliseconds demonstrating practically complete time coherence.

The TCA-M Active Loudspeaker Architecture

At the core of this architecture is a DSP platform that operates with a short lookahead buffer of a few milliseconds. This buffer allows the system to apply precise mathematical processing to the incoming signal, calculating in advance how it must be divided, delayed and shaped for each drive unit. When the acoustic outputs of the bass, midrange and high-frequency systems recombine in space, the result is simultaneous coherence in frequency, amplitude and time.

In the TCA-M, every element from the analogue and digital input stages, through the DSP platform, power amplifiers and short internal cabling, to each individual drive unit mounted in its respective enclosure is treated as part of one continuous electro-acoustic system. Nothing is assumed and nothing is left uncontrolled.

Each of the TCA-M’s three active ways is measured under anechoic conditions, from the system inputs through the electronics and power amplifiers to the acoustic output of the drivers operating in their respective housings, with no DSP correction applied. This establishes the complete native frequency and phase behaviour of each signal path.

The work to fully characterise the detailed behaviour of each end-to-end input signal to anechoic acoustic output of the 3-way system was accomplished with the help of Prof. Dr. Ing. habil. Wolfgang Klippel and team at Klippel GmbH in Dresden Germany.

These measured acoustic responses form the basis for calculating the Finite Impulse Response (FIR) crossover filters. The resulting FIR implementation compensates both magnitude and phase, integrating the three ways into a single Time Coherent acoustic system with near-ideal frequency response and Linear Phase behaviour across the entire operating range.

In this sense, the TCA-M represents a system-level realisation of psychoacoustic insight. It addresses not only Time Coherence within the loudspeaker itself, but also the perceived integration of direct and reflected sound. This depends on the physical geometry and dispersion characteristics of each system and on their complete integration when reproducing music in a real listening room.

All these behaviours are fully characterised using the Klippel Near Field Scanner, which over many hours generates a comprehensive database comprising thousands of individual measurements forming a sphere all around the speaker system under test.

Klippel’s analysis software then reconstructs, visualises and quantitatively describes the loudspeaker’s acoustic behaviour, including at the lowest bass frequencies, with an accuracy that exceeds even that of the largest and most costly anechoic chambers.

Without the compromises imposed by passive crossovers, conventional bass designs, or externally selected amplification and interconnections, the TCA-M is able to preserve the temporal and spatial relationships that allow the brain to recognise sound as coherent, expressive and real. A passive loudspeaker system with external dependencies simply cannot own the Transfer Function in the way the TCA-M Active Loudspeaker does.

Bass as a spatial cue

Low-frequency reproduction is often discussed in terms of depth and power, yet its spatial behaviour is equally critical. Bass transients generate evolving pressure gradients that allow the auditory system to locate sound sources during the chaotic initial moments of an event.

When these gradients are preserved, bass is experienced as external and physically present. When they are not, bass collapses into a non-directional pressure field that lacks realism, regardless of extension or output level.

Bass, Space and the Physics of Believability

As a fully integrated, DSP-controlled active system, the TCA-M maintains Time Coherence with a precision that is unattainable in conventional passive designs. Its folded-dipole air-velocity bass system stores virtually no energy and avoids the delayed port output and enclosure-related resonances that are intrinsic to boxed loudspeaker architectures, even when carefully controlled.

Force-cancelling operation, internal absorption of sound-pressure energy, and a structurally rigid, acoustically optimised geometry together enable a folded-dipole bass system that extends cleanly below 20 Hz, delivering bass that is both exceptionally deep and precisely time-resolved.

Unlike conventional dipole implementations that trade efficiency and output for openness, the TCA-M’s patented folded-dipole architecture combines specially developed drive units, powerful amplification and tightly controlled DSP to deliver the full physical force of very low frequencies. This includes the fundamental energy of a double-stop 16 Hz organ pipe and the ability to move large volumes of air without compression or time smear, at realistic sound pressure levels.

Equally important, the TCA-M is not omnidirectional in the bass. Whereas a conventional box loudspeaker radiates low frequencies in all directions and excites room modes, these modes act as another form of stored energy that lingers and masks detail. By contrast, the TCA-M’s asymmetric, opposite-phase bass dispersion minimises energy exchange between room boundaries.

Room modes can produce decay times on the order of hundreds of milliseconds, as documented by Fazenda. In his doctoral research at the University of Huddersfield, he notes that “the limen is reached at values larger than 100 ms” and that “a decay rate of one second or less at 32 Hz would be unnoticed."

The Patented Folde Dipole Asymmetric Dispersion Pattern significantly reduces room modes and standing waves.

With dramatically reduced room-mode excitation, bass decays cleanly rather than booming or smearing. This preserves the Pressure Gradients and low-frequency envelope cues that our hearing relies on to interpret how real acoustic instruments behave in a room.

As a result, the temporal signature of music remains intact. The microtiming between hi-hat and kick, the coordination of a pianist’s hands, the articulation of vocal consonants, the interplay of string instruments and the natural decay of a piano soundboard are all preserved coherently and truthfully.

Musicians, recording professionals and experienced listeners notice this immediately. What they hear are timing relationships and resonant characteristics as they were performed and recorded, not as they have been filtered, delayed or overlaid by the loudspeaker.

When timing errors are removed and stored energy is eliminated at both the loudspeaker and room-excitation level, the brain receives the acoustic event in its natural temporal form.

Emotional consequence

When timing errors and stored energy are removed, listeners do not describe the result primarily in technical terms. Instead, they report clearer phrasing, stronger rhythmic intent and a greater sense of emotional contrast. Music feels less fatiguing and more involving because the brain is no longer forced to reconcile conflicting temporal cues. The loudspeaker ceases to impose its own behaviour and allows musical intent to pass through intact.

Analogue and Digital Sources with the TCA-M

At Treble Clef Audio we listen extensively to vinyl, reel-to-reel tape, high-resolution streaming and downloaded files. We have also recorded at the Rudy Van Gelder Studio for the TCA Private Vault with Joe Lovano, Sam Yahel and Kresten Osgood, with Maureen Sickler recording and mixing in the analogue domain before printing to 24-bit, 96 kHz master files. Experiences like these reinforce just how much musical information exists in well-made recordings, including sessions dating back to the late 1950s and beyond, when reproduced without added time smear, stored energy or tonal manipulation.

The freedom to experience recordings in their most original and least constrained form is one of the great pleasures of the TCA-M. Rather than imposing a signature sound, the system preserves timing, dynamics and spatial relationships so that the intrinsic qualities of each source emerge clearly. Vinyl sounds like vinyl, tape sounds like tape and high-resolution digital reveals its depth and scale, all without the loudspeaker becoming the bottleneck.

In this way, the TCA-M honours both the artistic intent of musicians and the remarkable sensitivity of human hearing. It allows listeners to move effortlessly between formats while maintaining the coherence, presence and realism described throughout the Beyond the Sweet Spot series, where instruments and voices feel present in the room rather than reproduced by a system.

Discussions about analogue and digital playback often become ideological. At Treble Clef Audio, our position is practical and grounded in listening, recording experience and engineering reality. The purpose of the TCA-M is not to favour one format over another, but to remove the loudspeaker as a limiting factor so that each source can be experienced for what it truly is.

The TCA-M supports one dedicated analogue source front end and dedicated digital source front ends via Dante and AES/EBU or S/PDIF coaxial inputs, each connected directly to the active loudspeaker. Input selection and switching between analogue and digital sources is handled transparently via the control application, making it straightforward to compare different releases or formats of the same recording, whether vinyl, reel-to-reel tape or high-resolution digital files.

Understanding the intrinsic limits of the source formats themselves is essential. High-quality vinyl playback typically offers a practical dynamic range of around 60 to 70 dB, with the effective noise floor set by surface noise, rumble, tracing distortion and wear. Even under ideal conditions, dynamic range above roughly 75 dB is rarely achieved. By contrast, 24-bit digital audio has a theoretical dynamic range of 144 dB, and modern converters routinely deliver more than 120 dB of usable dynamic range, with a noise floor far below audibility. When analogue recordings are captured or mastered at 24-bit and 96 kHz, the full dynamic envelope, low-level detail and transient accuracy of the original performance are preserved without the mechanical constraints inherent to vinyl playback.

Also worth noting is that most vinyl releases since the 1990s have, in practice, been digitally mixed and mastered before the lacquer is cut, typically from 24-bit, 96 kHz master files.

Mixing and Mastering Releases

An often overlooked aspect is that vinyl and digital releases of the same recording are frequently mastered differently, not merely distributed on different carriers.

Vinyl mastering requires specific constraints to be respected, including limits on low frequency amplitude and stereo width, careful control of high frequency energy to avoid tracing distortion, and overall dynamic shaping to ensure reliable playback across turntables. These constraints often result in masters with gentler peak limiting, different equalisation choices and, in some cases, greater macro-dynamic contrast than their digital counterparts.

Digital releases, by contrast, are free from these mechanical limits and may prioritise absolute bandwidth, channel separation and noise floor, while also reflecting contemporary loudness targets or streaming platform norms.

For the listener, this means that vinyl and digital versions of the same album are not simply different formats, but often different artistic realisations of the same performance. The TCA-M makes these differences audible without exaggeration. It allows listeners to hear the consequences of mastering choices clearly, whether that manifests as the physical density and flow often associated with vinyl cuts, or the extended dynamic range, low level resolution and spatial precision of high resolution digital releases.

Rather than collapsing these differences into a house sound, our Sound by Design® acoustic platform preserves them, enabling meaningful comparison and deeper engagement with the recording process itself.

Listening to a master tape copy on the TCA-M Active Loudspeakers, such as the 1964 Oscar Peterson We Get Requests Ultra Tape from Acoustic Sounds Inc., is, in our experience, as close as it is currently possible to come to the sound captured in the studio.