TREBLE CLEF AUDIO

Treble Clef Audio is an interesting new Danish startup making innovative and exciting loudspeakers. Not Boring’s Eric van Spelde flew out to Copenhagen to chat with the head of the company, Ole Siig, about the concept and inspiration for the project.

Hello Ole and thank you so much for inviting us to the launch of the Treble Clef Audio TCA-M active speaker here in Copenhagen. It is said often that the most critical and defining part of music reproduction in the home is the interaction between the loudspeaker(s) and the room they are placed in. Treble Clef Audio have gone into directions and technologies that have hardly if at all been explored by other audio manufacturers to control and tailor the dispersion pattern of the speakers, especially in the bass registers.

NB. Can you explain how you have come to adopting the basic principles embodied in the TCA-M loudspeaker, and why you decided to pursue them to realise the product we have in front of us today?

OS: To properly answer this question, I think a bit of background history on my research and a look at some of the principles of hearing and room acoustics is needed.

In my experience, conventional box-type loudspeakers are associated with a more or less pronounced boomy and unresolved bass perception, unlike the instruments they are meant to reproduce, had they been played by musicians in the same room. This indicates to me, that although the room has a pronounced effect on sound, not least in the bass region, there are some fundamental differences between sound generated by instruments versus sound emitted by most current loudspeakers.

We can define bass as being below the room’s transition frequency, where more reflected than direct sound is heard. The room being the same, then what constitutes the difference between a loudspeaker source versus the original sound from instruments?

The essence of the answer is that no instruments, perhaps except for the Cajón, are shaped as a box seeking to contain half the generated sound energy inside it. With a conventional loudspeaker, one half of the sound pressure is contained inside the box. The other half of the energy, generated as the woofer diaphragm moves both in and out in opposite phase, is dispersed fully omni-directionally into the room reflecting off the walls, floor and ceiling often more than once exciting room modes with only a few Hertz between each. Conversely with acoustic instruments half the sound energy is not trapped inside an enclosure, instead, both in and out of phase sound waves flows around, in and out of the instrument’s body, forming complex dispersion patterns that do not universally excite room modes and causing standing waves in the pronounced manner loudspeakers tends to do.

Additionally, a conventional closed or vented loudspeaker enclosure must be large for deep bass and the woofer(s) must move a lot of air. Consequently, enclosure surface areas are large, much larger than the woofer diaphragm, and despite damping and stiffening efforts the enclosure will inevitably be playing along with sound that isn’t part of the music signal sent to the loudspeaker. A lack of time coherence, especially from vented designs is an issue that further distorts what we hear.

Aesthetically, a larger space such as a concert hall has a subjective living property added to the rather dry sound of say a pizzicato cello or bass. The concert hall effect is highly involving and instead of perceiving the music as static and in front of the listener, only the immediate attack of the note is in front. The subsequent body of the note seems to be all around the listener, drawing him or her into the performance. In short – the sound is beautiful. With conventional loudspeakers, reproduced sound in a room lacks this living quality.

Often low frequencies are not perceived as external and with location, but inside the head. This is because vented and closed box designs, which are fully omni-directional at low frequencies, tends to interact with and pressurise the room to a steady state and thus lack any pressure gradient; the inter aural time delay is zero, and remains zero when the head is rotated. The subconscious brain not knowing how to localise these initial sounds, will perceive them as internal. Music reproduced from loudspeakers with this property is so common that we have come to accept it as inevitable, but it is far from authentic, and not as involving as say a live trio might be in the same room.

The quest for me then became; how to design a fundamentally different bass loudspeaker system with a low frequency sound dispersion, that preserves the required interaural time difference pressure gradients in the listening room, just like they do when acoustic instruments are played. These and other details were for me an exciting research project covering room- and psychoacoustics. Then with this understanding, trying to figure out what the implications would be for the physics of loudspeaker design.

As it turns out, in early 2000 Axel Ridtahler invented a Folded Dipole (dubbed Ripol) bass ystem with the kind of sound dispersion pattern my research suggested. However, this original design had several drawbacks that needed to be addressed in terms of both enhancing the sound dispersion pattern, extending especially the upper usable frequency range and using as small as possible special woofers with a large linear excursion and suitable characteristics for the bass system I had in mind.

Completely eliminating sound from vibrating parts needed a force and internal sound energy cancelling construction, thereby completely avoiding any enclosure sound coloration.

Coloration of sound from a resonating enclosure is a pronounced issue with conventional box design that high-end loudspeaker designers are battling with. The original Ripol design that I built, despite its relatively compact square box like enclosure, is no exception in terms of vibration and a box sound of its own. The reduced sidewall reflections and somewhat asymmetric sound dispersion pattern limits the standing waves in the room and, despite the enclosure sound coloration, certainly sounded much nicer than my own large conventional box speakers, or any I had heard. The box sound vibrations were quite evident and confirmed by accelerometer measurements. The useful upper frequency range was also limited to about 100Hz by a very pronounced resonance peak at about 150Hz, an inherentproperty of a folded dipole.

With the Treble Clef Audio® patented folded dipole principle, the upper frequency range is significantly extended based on modelling efforts supported by experiments and measurements, such that we can comfortably crossover up to about 220Hz, amply avoiding the inherent folded dipole resonance now occurring at about 370Hz. This way a smooth directive transition to a small diameter high quality midrange system became possible.

The relationships between the inner, and outer folded dipole volume and port size also emphasise the air velocity transducer properties of this kind of bass system. Air velocity is the means of creating the low frequencies pressure gradients in the room that enable us to locate bass sounds experienced from the transient attack and initially chaotic sound field of for example drums, piano, string instruments, an organ pipe and another low frequency complex sounds that we naturally and subconsciously recognise and need to hear for an authentic experience. Our white paper, available from trebleclefaudio. com, represents my notes and conclusions of this research effort as it applies to loudspeaker design considerations, a fundamentally different loudspeaker design that we achieved a granted patent for in just under 2 years. The patent of course shows that we have gone in a different and unique direction with the TCA-M and our future range of loudspeakers. This to include at-home extraordinary theatre surround sound experiences.

Aside from the challenges that conventional boxtype loudspeakers present in the bass region, further phenomenon in the midrange and treble frequencies are exacerbated by placing front firing drivers on the relatively large baffle of the typical high-end loudspeakers. It further emphasises the advantages our slender sculptural design that emerged from my research, where we avoid the typical baffle step and beaming directivity that also comes with diffraction challenges causing extra sound artefacts and so-called lobing that causes dispersion patterns of lacking sound. Instead, above the room transition frequency, the TCA-M design has a 180-degree dispersions pattern with the off-axis responses perfectly uniform with the direct sound up to about 4000Hz, then gradually and uniformly tapering off as the sound energy dissipates at higher frequencies.

The TCA-M speaker achieves a pleasurable phantom 3D psychoacoustic soundstage, the precision of which to a degree depends on the timing, related to room size, of reflections. Our loudspeakers are purposefully intended for ordinary rooms as an integral part of an interior design, sized from about 20m2 –60m2, and importantly without consideration to any need for specific acoustic room treatment intended to reduce reflections. We purposefully want to keep reflections and let them be controlled by the sound dispersion pattern suggested by my research.

According to quite recent research, the dispersion pattern of the TCA-M loudspeaker is also designed to be equivalent to human speech and song. As a result, the sound is spectrally balanced and engaging both in and even outside the listening room, where only reflected sound is heard, just like would be the case if someone were playing actual instruments in the room.

NB: Active loudspeakers are still struggling somewhat to find acceptation in the world of high end audio, as most people who form the traditional target market for a loudspeaker system in the high five figure euro/dollar range, have already put significant investment into amplification and dealers are unsurprisingly reluctant to tell them to divest from expensive hifi gear they have sold to them before. In what ways is active, DSP-controlled drive integral to the sonic results of the TCA-M speaker, and to what extent is Treble Clef Audio aiming at a market outside the high end hifi microcosmos as we know it? And how did that shape the decision to launch the TCA-M as part of a design event rather than a HiFi show?

OS: For me regarding our intentional use of state-ofthe-art DSP technology, the short answer is that the acoustic properties from my research that I wanted to accomplish are impossible with passive speakers and permutations of external component choices.

Of course, exactly that audiophile enthusiastic exploration into combinations of amplifiers, cables and so on is an exciting hobby, as it certainly has been for me, experiencing many fleeting moments of potential greatness, but with little concrete explanation as to why and an ability to consistently repeating how.

I couldn’t see it feasible to create a loudspeaker like the TCA-M with the properties we desire without taking full control of the signal path from inputs to the acoustical output from the several electro acoustic transducer systems that must integrate as if a single sound source.

We are now seeing a trend of high-end loudspeaker brands introducing an active or semi- active loudspeaker series to their range. Most of them of course still conventionally closed and vented box-type speakers with inherent properties that even active DSP control is unable to fundamentally overcome. Equalising a speaker for a more ideal response in rooms will at some level be limited by its fundamental acoustic design principles. For example, the monopole and omnidirectional nature of an enclosed either vented or sealed woofer bass system or the off-axis response above the room transition frequency that may not be uniform with direct sound, again due to fundamental design principles, can’t be universally addressed by DSP technology.

Another important factor for achieving authentic reproduction of music, is an overall phase-linear, or more encompassing fully time-coherent, acoustic integrated system response. For that purpose, a correctly designed DSP-controlled crossover is essential, not least in the bass region where time coherence down to the lowest frequencies have proven a necessary property for reproducing the true nature of bass. For the TCA-M loudspeaker, that means constant group delay from 30Hz to 24KHz and only gradually increasing to about just 13ms down to 20Hz. An accomplishment that with the TCA-M bass system design is possible only in conjunction with DSP technology. The bass clarity and resolution achieved by the TCA-Mloudspeaker, I believe few have heard or at present appreciate how much these properties matters for bass reproduction in ordinary rooms.

To design an all-encompassing optimal transfer function for the system, we must understand its inherent native behaviour; through input stage analog and digital electronics, via the DSP implementation, through each power amplifier and via optimally short cabling to each speaker drive as built into some form of enclosure. We make anechoic (without room reflections) measurements that fully characterise the behaviour of, in the case of the TCA-M loudspeaker, the three-speaker driver system signal chains; folded dipole bass, monopole wide dispersion midrange and tweeter systems, all of which must ultimately integrate as one coherent sound source.

Visiting Dr. Wolfgang Klippel and his wonderful team of experts, I learned a lot about the detailed behaviour of a prototype TCA-M loudspeaker by using the Klippel Near Field Scanner and deep expertise of the team in Dresden. I think this kind of approach is the future for truly high-end loudspeaker designs. It will get us to a stage where inventions within transducer units, their principles and motor system, diaphragm materials, coating etc. is optimised by simulation of the physics involved and material science being fully exploited to tailor the parts of an overall amazing loudspeaker systems. The TCA-M being a step in this direction. Inevitably, new generation audiophile enthusiasts and music lovers alike will likely focus their attention more on the music, artists and recordings smitten by more up-to-date authentic experiences brought to ordinary living rooms.

The choice of input music playback source is completely open to the user as our loudspeakers come with very high dynamic range and extremely low noise analog input, digital AES/EBU, RCA SPDIF and even a Dante® lossless Ethernet LAN input. Our loudspeakers therefore suit both a fully analog frontend preamplifier with for example vinyl and R2R tape sources. Alternatively, one of the growing choices of high-end digital pre-amplifiers that features both analog and digital inputs as well as lossless streaming, excellent optimally implemented volume control etc. can all be connected. Finally, using the Dante® input the TCA-M and future Treble Clef Audio® loudspeakers connects directly to the recording, mixing mastering studio technology over a multi-channel lossless Ethernet LAN, which is also great for a home theatre installation with hidden wiring.

As we introduce our home theatre complementary and physically smaller loudspeaker series based on our patented acoustic platform, two such speakers will exhibit our Sound by design qualities, albeit with less power than a set of our main TCA-M speakers, with a very respectable actual bass extension of about 30Hz, and at a more affordable price point. The decision to launch Treble Clef Audio® and the TCA-M loudspeaker during 3daysofdesign in Copenhagen was quite deliberate. I have often been wondering why interior design magazines rarely, if ever, feature loudspeakers in a beautifully curated home interior. I can’t imagine it’s because people who care about their homes, spending effort, time and no doubt discretionary funds to achieve a beautiful interior are not also music lovers. My dream is to change that by hopefully one day having the TCA-M loudspeaker as part of a magazine featured interior. I don’t know if that is too ambitious, but I can’t think of a better event than the 10-year anniversary of the Copenhagen 3daysofdesign week to communicate that idea. Let’s see, next year we may also be found at a HIFI show or two.

We build our loudspeakers by custom order only, with unique styling choices such as hardwood, colour and finish of certain parts. This also speaks into the creative minds of those that work in and enjoy the interior design realm, and whom attend such events.

Furthermore, the TCA-M Loudspeaker is built with the notion of ‘Form follows Function’, but none-theless, is presented as a beautiful sculptural object, as much as a functioning loudspeaker. Our customers will be investing in a piece of art for their home, as well as a sound system, making the design world as much our target audience, as the high end hifi microcosmos.

It remains to be seen who might become our customers, but first and foremost I imagine it will be critical listeners who loves the combination of music and styling in their home without need for lots of additional technical gear, cables and acoustic room treatment other than rugs, furniture and people. As Miles Davis said, “For me, music and life are all about style”.

NB: Can you tell us more about the collaborations with local craftspeople and engineers that resulted in the realization of this project? What will the production/value chain of Treble Clef Audio production look like, and how does it differ from the way high value consumer goods are normally produced and marketed?

OS: Launching Treble Clef Audio® and the TCA-M loudspeaker in Copenhagen and our exciting plans for extending our product range based on our patented acoustic platform, is the culmination of 6 years of development, industrial design considerations and the creation of a new and quite different Danish loudspeaker brand, all made possible only because of serendipitous meetings and close collaboration with a small group of independent, highly talented engineers, craftsmen and creative people. After hand building the first set of treble clef design loudspeakers and encouraged by the feedback and sound, I wanted to find out if perhaps I could obtain a design patent. Having thought more about the research and principles I had employed; I wrote an invention disclosure and sent it for review to a highly respected Intellectual Property law firm in Copenhagen. Their feedback was to opt for a full utility patent, which meant a need for precise drawings, CAD modelling and building a complete version of TCA-M including all my ideas, which wasn’t quite part of the hand-built set of speakers made in my own simple workshop and had to be captured to define the full set of patent claims.