Diesis Audio Caput Mundi loudspeakers | listening test



Notwithstanding the cold, Spoleto and the beautiful Umbria region welcome us warmly. A unique landscape for culture and traditions, cookery included. We taste some specialties as guests of Giuseppe Gabbarini, responsible for Caput Mundi's dream and owner of Diesis Audio's brand.


I have spoken of "dream", so you will be asking: which one? The dream of Gabbarini - sales manager -, of Maurizio Spera - designer -, and of the architect and designer Ino Piazza: a visionary project and a concrete product as well. So make yourselves comfortable because the technical description will be very demanding.



Caput Mundi gathers two philosophies that I personally appreciate and pursue, those ones related to the horn and dipole loudspeakers.


Besides, they try answering to a long-standing issue: to offer an easy or, at least, affordable load also to amps with a restrained power and moderate current supply. If you have read in these few lines the answer "tube amps”, you are perfectly right....


Personally, I prefer light membranes and tube amps, but this is only my opinion that comes from long listening tests, heated comparisons and rigorous critical sessions.

I mean, it is easier to make a decent solid state amplification rather than an equivalent tube amp. Costs, complexity of the making, randomness of the results on the frequency extremes are just some of the factors that affect the final choice, which has to be practical too. Otherwise, from the introduction of the transistors on, the story would have been different. Therefore, every day, many of us - also despite ourselves - "stand" our best solid state amplifications, regretting the lack of money or open-minded partners which prevent us from the sparkling, also acoustic, of the tubes.


Giuseppe and Maurizio, like many others worldwide, have asked themselves the following question: at this point of the technological evolution of materials and designs, is it possible to create a loudspeaker that allows the tube amplifications, rather than demanding solid state matches?


Moreover, is it possible to do it without being forced to use the horn-loading also on the bass range?

In other words, joining the best of the past, the speed and the efficiency of the oldest speakers with the dimensions of a pneumatic suspension speaker or bass-reflex of the late '60s and early '70s, when they became “domestic".


Well, I will tell you right away: I am interested in such endeavours. Realizations like my Mantra Sound Daiko, the Arte Acustica Janas, the Leonardo Speakers or the Caput Mundis, open the musical listening to a sensation of realism, sound gratification and overall quality that is unavoidably inferior in the multiple drivers with low efficiency and complex crossovers, although apparently neutral and correct. Furthermore, these products are Italian and these days the "made in Italy" has to be strongly recognized and supported. For ReMusic is a matter of honour.


Anyway, in order to get loudspeakers suitable for tube amplifications the requirements are essentially three:

  • high efficiency, from about 95 dB up
  • regular impedance. A purely resistive load would be ideal
  • not low impedance since the tube amps have a typical low damping factor, which would make the speakers driving the amp, and not the contrary as it should be.

"Excuse me, Castelli, but you are describing the horns, the loudspeaker technology born with-and-for the tube amps, while here I can see two horns for the mid and the trebles, but also two woofers for the bass that are not horns for sure...". Yes, you are right. If you just notice the Cessaro Beethoven that I listened to and mentioned during the last Munich High End, you will immediately realize why the bass horns are not suitable for all kind of speakers. The dimensions of such transducers are demanding and sometimes unacceptable. You remember well Colonel Klipsch’ solution, the folded horn of the Klipschorn, whose dimensions require a huge room. But there is no limit to the audiophile integralism. To get the most correct answer, the horn ought to be straight. I remember the system of a Japanese audiophile who, decades ago, made built bass horns of four square meters each, in reinforced concrete and directly in his studio placed at one of the highest floors of a skyscraper. I will provide you in the next day with a scan of the review that I keep jealously...


Now, it seems clear that the implementation of the Caput Mundi transducers is not traditional. In fact, to obtain the adequate design features, it has been thought of the box, with a dipole bass section. And the dipole seems paradoxically very far from the technical logic. For sure, the appointed driver does not endure the colorations of the cabinet, is not compressed as happens with the pneumatic suspension, does not collapse in terms of emission efficiency at the tuning frequency of the possible reflex, responds promptly and without any colour to the solicitations of the amp... But, in the room, its frontal emission overlies the posterior, with consequent cancellations and reinforcements to specific and predictable frequencies. This last characteristic varies according to the dimensions of the front baffle, to the dimensions of the panel and beyond certain dimensions, easily to obtain, afflicts exclusively...the low range! Just the opposite of what you would like to get in this case! Besides, the baffle of the Caput Mundis is NOT big at all! On the contrary, it is slender and graceful because larger than the woofers. Thus, where has the big and quick bass range come out?

You already know the answer, although not explicitly. The secret of its extension, in the Caput Mundi system, does not lie in the dipole woofer, but in having... two woofers!

To maintain within acceptable limits the aesthetic impact of the speaker, the front panel could not be too large. So, to solve the drastic reduction of efficiency in the low range, Gabbarini & Co. have inserted a second woofer in parallel, which starts operating around the frequency where the first woofer sees its supply reduced. This Frequency Doppler - Fd has a value inversely proportional to the area of the front baffle surface and, in the Caput Mundis, it deploys at about 120 Hz. Below this frequency, the second woofer intervenes by filling the dip left by the first one. This happens at the expense of the impedance of the speaker, which in the low range reaches 4 ohms: a value widely within range also of monotriode amps, whether correctly made.



A long introduction for an interesting realization before answering the question: how has been obtained the adherence to the design idea? I will answer item by item, also gaining data and info from the exhaustive company’s website.


Let us start by saying that Caput Mundi is an entirely handmade speaker, one meter and thirty cm high and with ninety-seven kg of weight.


To obviate to the poor efficiency and to the reduced power handling of the low range, which is typical of the dipole load, the designers have used two 12" high efficiency Beima woofers with differentiated filtering.

In the back, the shape of the cabinet consents to the minimum loss in efficiency and the light front horn load on the woofers improves the efficiency of the acoustic emission in the mid-low and mid range, contributing in a significant measure to the outcome, which is of great sound realism.

The cabinet has been made using the Clad 58, a conglomerate formulated by Diesis Audio and composed of mineral powder and resins. Poured in liquid form into a single mould, once solid it assures more rigidity and damping than the wooden cabinets whose vibrations make disperse a lot of the sound level that a dipole can give back.

In order to get more solidity in matching the woofers (the vibrant elements) with the structure where they are inserted (cabinet), they have been blocked inside a notch (with the interposition of a PVC gauge) with a 20 tenths thick stainless plate. The plate is fixed through nine M8 bolts screwed into nine sockets inserted in the Clad 58. The plate, damped by a leatherette layer, pushes on the entire surface of the loudspeaker flange and assures a good continuity of contact between the parts.


The use of the German BMS coaxial compression driver has made possible, with one horn only, a coherent and linear emission from about 600 to 25.000 Hz.

The shape of the horn and its radius of curvature consent the obtainment of a great dispersion also out of axis - confirmed during the listening tests - and a regular response of the drivers. Amazingly realized in Corian – a solid surface material created by DuPont, whose primary use is as a countertop/benchtop surface, see also here – this material has been chosen because compact and solid. Realized in such material, the horn is only six millimetres thick. The Corian can also be perfectly smoothed and become capable of an extremely quick and precise emission since it is not altered by refractions. This is a very important thing when the frequencies that have to be emitted are so short as happens in the mid and high range.


Beima and BMS are industrial drivers although custom made. Such feature make them reliable and adherent to superior design qualities.

Clad 58, Corian, anodized aluminium, stainless steel, PVC, MDF and solid wood... every part of the Caput Mundis has been realized with the most suitable material for its specific function, independently from the cost. The air-wired crossover, for example, has been mounted on different boards and the masses have been completed separated, to take fully advance of bi-wiring and bi-amping. The boards are in 10 mm PVC and obtained using numerically controlled machines so to use the connection cables as wiring cables. This operation has been made to avoid any contact resistances that are typical of the traditional fibreglass boards and to get a better transport of the signal.  


Besides the Audin Cap and Mundorf Silver Gold capacitors and the Mundorf OFC Copper Foil coils, the other components are of high quality and there is no electrolytic capacitor that is bipolarized or in parallel to the signal.


N.B. For the most demanding audiophiles there are also some carbon resistors that give separate level controls for the mid-high range and that can be inserted in the clamps on the crossover board in order to adapt the loudspeaker to the characteristics of the room and/or to the user's tastes.



Let us start with the focusing that can be obtained with horn mid-high or high range: it is keen but unavoidable, once tested. Caput Mundi, from this point of view, creates dependence...

Great sound. They perform great, they perform loud. A feature appreciated by the visitors of the recent and first PrimaverAudio held in Rome, where they were performing in a hall, overcoming all the difficulties.

Temporal coherence. With the not very high dispersion of the horns, realized to concentrate the efficiency - not the width of the emission - and the virtual unlimited efficiency of the dipole, which is concentrated on the low range, you get an uncommon mix: a speaker where rise time and tone colour can be obtained also with different reproducing techniques: not easy at all.

Power handling. They do not need a strong driving, but if the amp is powerful and undistorted it can get to great sounding, well beyond the physical appearance of the speakers themselves.

Room fitting. Target reached, I would say. Aesthetically intriguing, slender, light, with a naked touch that make them courageous, nonconformist and somehow "wild":



They fit large rooms. The listening test has been made with the speakers unavoidably placed on the long side of the room. The dipole feels the effect of the distance from the back wall. If you consider one meter and a half or two meters from the back wall, at least a couple of meter between them, if not more, and something less from the side walls, the dimensions of the room are important. An absolute "con"? No, not necessarily. The reproduction of music is a question of physics, where "the dimensions count" and, to get good results, you have to go along with these speakers.

The image forms itself at a certain distance from the vertical of emission, they are not monitor or nearfield, though: but I would like to run some tests if I have the opportunity...



Although the Caput Mundis have a theoretical reduction on the low frequencies, they practically compensate it with velocity and intelligibility. These qualities make forgive and maybe completely forget this supposed weakness. Take into account that, being a dipole, they must-and-can deploy the placement in room... And here, you can play!

Most probably, the loudspeaker keeps on emitting with some cancellations and level reductions at the low frequencies but, just few days ago, Angelo Recchia-Luciani, our shining technical and theorist brain, confirmed that the listening of the first octave can "last" in our ears up to distortions of 30%! So: who really realise that?


Quick metaphors and final recap

I want to add that, in Diesis Audio's listening room, front end and amplification were blazoned and above suspicion: all Nagra, with CD player, DAC, preamp and power amp.


The cables were Diesis Audio prototypes, pure silver, without sleeve and the connectors were simple tips soldered on the cables.


The listening test has given the real immediacy of the speaker, a sense of ruggedness, which we are no more accustomed to. On the contrary, speaking of the tone colour, the analyticity of the system prevails.

Caput Mundis feel at home and you feel at home with both classical music and rock. Actually, I find them more suitable with "cultured" music than with "heavy metal" and high-pressured music.

Great rise time, great focus, great contrast: everything with that sensation of body and matter that is more typical in the dynamic loudspeakers than in the dipole systems. The parameter of the dynamics is limited only by the amplification with a virtually endless power handling.


These Caput Mundi speakers perform commendably. They can "fiddle" the high efficiency and make it acceptable in a traditional environment like that of the most common audiophiles’ rooms. This outcome has not been reached or is difficult to reach with most labelled names like Acapella or Avantgarde. Another Caput Mundi's point of superiority is the ability of integrating different components without getting to annoying or imperfect "detachments" in the ranges.

And these are great results: I would have them among my reference speakers as part of a list of no more than a dozen of models and brands.




Tone colour | frequency extension, ability to faithfully reproduce the instrument and its harmonics

The absence of sound colorations - usually caused by the "sound box" - and the damping of the drivers are works that make appreciate themselves through the restitution of the detail and sound articulation. The system slightly favours more the "attacks" than the "releases", meant as sound emission and its persistence in the ambiance: that feeling of relative improvisation that often goes with the big horn systems, here it is just a hint.

Dynamics | micro (detail) and macro (absolute) extension and rise time

Obviously, one of Caput Mundi's strength points. Great ability of "surprising" and move with clear and sudden attacks, but only if the amplification can support (obviously likewise). The detail of the instruments is always intelligible, also in the fortissimo. Really involving.

Image| ambiance, transparency, scene, sound planes, virtual stage, sense of presence, resolution

Although it has been obtained with horn components, the soundstage of these loudspeakers is great also when you are "walking" in front of them. The image does not collapse, but for in extreme positions. The soundstage is always deep and never "put forwarded" like in the more classic or old horn systems.

In conclusion, all the components of this parameter (see list) go from good to excellent.

Tone | general equipment setting, if present or characteristic: e.g warm, cold, changing, amber, glossy, mat...

A characteristic that strongly depends on the amplification, but in general the speaker is blunt, fast, clean, shiny but not sharp.

Emotion | the capacity of emotional involvement, depending a lot on couplings, an absolutely anarchic and personal parameter

Great, as I like it. They are speakers for large rooms but I would have them at home also if I had just few square meters: you only live once.

Dynamics, transparency and absence of sound pressure stay together with coherence and no listening fatigue, if supported by amplifications that are up to them.

Manufacture and Packaging| Manufacture? Do I have to add something else? As the listening test was "simple" but significant, I have not considered the packaging, but the manufacturer assures exemplary delivers worldwide.

Price/quality ratio| All is relative. But consider that for the attentive and smart fine-tuning and performance of these speakers what is around them is anything but "innovation". A DIYer cannot replicate them.



Official technical specifications

3.5-way system with four drivers

Dipole woofers: two 12” paper woofers

Coaxial compression drivers: 90mm Midrange, 45mm Tweeter

Sensitivity: 94dB /2.83V/M

Impedance: 6Ohms nominal

Frequency response: 40 to 25,000Hz +/-3db, 30 to 30,000 Hz +/-8db

Power handling: 10-250watt

Crossovers: 150, 600 and 6,500Hz

MID range level control through resistors: -1,5/0/+1,5/+3dB

HIGH range level control through resistors: -1.5db/0db / +1.5db/db+3

Possibility to drive independently the lower woofer (8ohms) and the other drivers (8ohms) with separate masses

Dimensions: 512x1,370x365mm (WxHxD)

Weight 97kg

Warranty: 5 years

Notes: Caput Mundi system is recommended for environments from 20 to 50 m2. The recommended tilt angle is no more than 20 degrees towards the listening point. The front panel and the horn are replaceable in order to modify the look of the speakers.

Official current price in Italy: 24,900.00 EUR per pair, with white horns

Official Italian dealer: to Diesis Audio website

Giuseppe (Castelli) and Giuseppe (Gabbarini) amid the Caput Mundi; just to give you an idea about the dimensions of the speakers (not of the listeners)
Giuseppe (Castelli) and Giuseppe (Gabbarini) amid the Caput Mundi; just to give you an idea about the dimensions of the speakers (not of the listeners)
by Giuseppe
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