Ikigai – a compact TL loudspeaker designed using SpicyTL

This fascinating project began in Jan 2018 when Andrea Rubino, a customer in Italy, bought a pair of Eikonas for use in a loudspeaker he was developing. 

Usually, we’re happy to be involved in customer projects and expect a few questions along the way. In this case, however, it all went quiet for 18 months. The reason for the silence became apparent when Andrea got in touch again. He wasn’t just developing a loudspeaker, he was developing sophisticated transmission line modelling software as part of the process. He was kind enough to give us an advanced look at his work and it was extremely interesting. 

There are a number of software tools out there for modelling transmission lines; some more successful than others. One of the best known is Martin King’s MathCad model which has been used by others to design the MLTL enclosures we have on our website.

Andrea’s SpicyTL software is a simulation model based on electrical circuit theory and it includes very precise modelling for the materials used in the line, based on the target response and parameters of the drivers used. The full process is the subject of an in-depth article in the January 2021 edition of Italian magazine AudioReview (following on from his software design articles in the same magazine in 2019). SpicyTL uses a modular approach which allows fine-tuning throughout the design process, for example, changing line taper and comparing the TL with a reference sealed enclosure.

Andrea used the Jordan Eikona as the starting point for a design process which aimed at an f3 of 55 Hz and an enclosure of no more than 15 litres. He explains his choice:

“A few years ago, intrigued by the many positive reviews, I decided to build a pair of monitors using the renowned Jordan JX92S full-range drivers. I was enchanted.

Ted Jordan, a British engineer and designer who passed away in 2016, was a pioneer in the research and development of metal diaphragm cones. The sound of his loudspeakers is often compared to that of electrostatic panels, which, moreover, Ted Jordan designed for Goodmans Industries at the beginning of his long career. This similarity is probably due to the dispersion pattern of the cone, which consists of a special aluminium alloy foil called Contraflex, similar to that of an electrostatic panel. What struck me most about these speakers was their ability to reconstruct the soundstage, so much so that I named the speakers Hologram Jazz Monitor. This aspect, without demonising crossover filters, is probably due to the total absence of disturbance in the dispersion lobe at the crossover frequency, which obviously does not exist in single-driver systems. The fact of the matter is that the JX92S, even if not perfect, had a listening magic that I had trouble finding in other speakers I had listened to. Perhaps these sensations were enhanced by the total lack of reactive components between amplifier output and driver, or perhaps it was just another unfathomable aspect of this beautiful world where subjective perception of sound arises in a border zone between suggestion and reality. Anyway, when the Jordan company (EJ Jordan Design to be precise) developed its latest generation of single-driver loudspeakers, I decided to build two new monitors, but this time with acoustic transmission line loading (the HJMs were bass-reflex).”

The final Ikigai enclosure is stand-mounted and constructed with successive layers of MDF, the translam process which has been used successfully elsewhere with the Eikonas.

Andrea’s AudioReview article describes the process in great detail and he has allowed us to quote his listening impressions from the article:

“Clearly, a single driver cannot operate in full-range mode in the literal sense, but it is equally clear that there are infinite aspects of music reproduction that go far beyond the maximum bandwidth that can be reproduced. In short, the Eikona 2 cannot do everything, but what it does do, and it does a lot, it does superbly. Among the many things I liked, the richness of detail, the ability to focus and the depth of the scene deserve special mention.

The control over low frequencies typical of the transmission line is truly remarkable. The volume knob rises to unexpected levels and it is surprising how a single driver can give back a timbre so credible and detailed even in the most demanding passages.

A last note on an aspect that I consider fundamental: after many hours of listening, sometimes at very sustained levels, the sensation of fatigue is totally absent.”

Perhaps one aspect which is most remarkable about the project is how, using an entirely different modelling approach, the Ikigai is similar to our own Eikona MiniLine. It demonstrates how modern software is converging on the true physics of the loudspeaker transmission line, leaving behind the trial-and-error approach of older designs.

A preview of Andrea’s magazine article is available here and vector files for the Eikona Ikigai enclosure are available on his website.

We would also recommend the articles section as essential reading to learn more about SpicyTL and transmission line design.