Sonus Faber Tower Speaker Comparison and Design Overview

The Italian love of sculpted forms has long beenobvious. Much like fine Italian sportscars, Sonus Faber has been sculpting fine audio speakers in this tradition forseveral decades. Shod in fine lacquers,wood veneers, leather, glass, and aluminum, Sonus Faber speakers are sculpturalworks of art. Save a single speakerline, the entry level Toy collection, nothing Sonus Faber manufactures is evenremotely based on a boxed cabinet design and even the aforementioned Toy linehas sculpted panels and curved edges.

And make no mistake, they are expensive like Italiansports cars, in terms of relative order of magnitude. This expense is likely a combination of theelaborate construction described for the speakers, their espoused handmanufacturing techniques with attendant low production volume, the extremelevel of diminishing returns corresponding to the acoustic problems beingsolved, and the simple fact that by selling them at a high price that a certainwell-heeled segment of the market correlates with quality and that nothinglesser will do.

While I have little doubt that Sonus Faber puts in considerableeffort to make exquisite sounding speakers, I find the engineer in me questioningthe technical explanations about the engineering of these speakers as describedin their marketing materials. Readingthe product literature is an exercise of wading through a hyperbole oftechnical sounding buzzwords that are clearly meant to inundate the reader andoverwhelm them into submission with its own self-aggrandizedimpressiveness. Just take the followingexample:

This element was developed thanks to the work carried out on "The Sonusfaber", just through observation this is apparent: the chassis in fact, amaster element of the speaker, is similarly made up of special CNC machinedavional and gun metal from solid and through long processes to exploit thejoint behavior that, when coupled, suppresses mutual resonances and make thestructure completely acoustically amorphous.

From real time air dried non pressed diaphragms to progressivethickness triple curvature cabinet walls damped spread resonance spectrumsystem, the literature almost reads as if it was created with an audioversion of SCIgen.

In addition to this are numerous unrealistic statementsabout performance absolutes of the cabinets and electronics such as eddy current free, non-resonant electronics and zerovibration transmission, absolutespurious vibration rejecting, completelyacoustically amorphous cabinet components to eliminate all vibrationsand spurious noises that damage the integrity of the sound are atheoretical ideal but practical hyperbole. Such talk is exaggeration as these phenomenacannot be eliminated completely in violation of the laws of physics and are preciselythe point where diminishing returns comes into play in audio reproduction. This is not to say that Sonus Faber has notgone to extreme lengths to minimize these effects; they cannot be eliminated,but they can be made increasingly negligible, which is a more realisticstatement.

Perhaps it is just the English translation, which isprovided next to all of the original text in Italian, was done by someone withoutan engineering or technical background. I will give Sonus Faber the benefit of the doubt, for now, but theirclaims would carry much more weight if they actually provided research or whitepapers, but there was nothing I could find to review.

Across their product lines, many of Sonus Faber's speakersuse certain common design philosophies for elements of their cabinets and drivers.

As the primary design consideration apparent from theirliterature, to say that Sonus Faber takes controlling cabinet vibration veryseriously would be an understatement. SonusFaber cabinet designs typically use multiple strategies to generate damping toreduce vibration through complex construction including unusual physical shapes,variable thickness cabinet walls with constrained layer damping, internal stiffeningribs, variable internal and external materials, metal spines connecting dampingplates at the top and bottom, elastomer and foam damping pads, base isolation,and tuned mass dampers. In theirliterature, there is much said by Sonus Faber about eliminating microvibrations through all of this damping. But damping is simply not panacea for allvibration and really only reduces resonant vibrations. Too much damping can, in fact, increase the amplitudesof vibrations that occur between resonant peaks as well as increase the time ittakes to damp out a resonance, a phenomena know as overdamping.

Handcrafted cabinets are standard for Sonus Faber and theyare often based on the lyre, lute, and other musical instrument shapes that providenonparallel sidewalls and are constructed from cross-grained multilayeredplywood materials that are arranged to provide constrained layer damping. The cabinets are then filled with variedmaterials, which range from open celled thermoplastic foams to fibrous materialakin to felt, to provide acoustic damping of driver backpressure within thecabinets, the choice of which are said to be optimized by application andlocation within the cabinets. The outerfinish of their cabinets is often made of horizontally oriented strips of woodveneer with various sections in leather to produce a unique appearance for eachspeaker.

Showing up under several different clusters of terminologyused by Sonus Fabers in their literature are terms like Dampshell, Dampshelves, and Exo-SqueletonClamp that typically consists of the top and bottom cabinet end platesconnected with a central spine, which is said to reduce cabinet resonance. Some of these features are said to functionas vibration collectors, a sketchy concept because vibration cannot be herdedaway from one place to another. Sound iscreated by a phenomena known as wave propagation, with waves radiating continuously through amedium from the source outward as long as the sound is being emitted. So inducing vibrations that occur over there to not occur overthere but rather over here, at somechosen preferable location, does not make the original area cease to vibrate, both areas nowvibrate.

On the higher end speakers, these clamps and spine are madeof nickel plated avional, an aluminum alloyed with copper, magnesium, andsilicon known for being high strength and low weight, but with poor corrosionresistance, hence the nickel plating, that is frequently used in aerospaceapplications. Avional has a high tensilestrength that is comparable to structural steels, but like all aluminum alloys,has a modulus of elasticity, i.e. material stiffness, of about one third that ofsteel. Note that strength affects onlythe load bearing capacity of a material, but has little influence on dynamicresponse, only the stiffness does, so use of a high strength material isirrelevant.

The higher end speakers also incorporate an isolationsupport system to decouple the speakers from the floor that Sonus Faber alternatelycalls a Low Vibration System and a Zero Vibration System. Both make use of elastomer dampers andculminate in what Sonus Faber calls the Bowspring,the version used for the flagship Aida loudspeaker. Isolation systems are generally difficult to implement without short circuiting through contact between stiff elementsacross the gap while still trying to provide adequate support of weight. The devil is, as always, in the details.

As an example, there is an image shown on Sonus Faber's web site ofone such system at the base of an Amati Futura. There is an upper and lower plate separated byan elastomer pad, but the carpet spike supports passing though the plates appearto be in hard contact with both plates. Based on what is shown, the elastomer pad may still provide some damping, but without additionalelastomer pads between the spike and each of the plates and holes in each plate that are large enough to maintain a gap with the threaded rod passing through, vibration can route around the elastomer pad that is present.

Sonus Faber's cabinet acoustics are typically based on an aperiodicdesign, which they refer to as StealthReflex Para-Aperiodic. An aperiodicport design is basically a leaky sealed cabinet which uses ports filled withfoam that allows better bass response from a smaller cabinet compared to asealed design but without the impedance peaks typical of a ported design. In other words, the behavior is somewherebetween a sealed and a ported design.

Sonus Faber speakers also use similar concepts for thedriver designs across many of their models. A number of their speakers use ring radiator tweeters, a variation on adome tweeter with a central stationary peak that acts as a phase plug while thesurrounding ring around the peak is driven to emit sound. In some speaker models, Sounus Faber uses a variationon the ring radiator that they refer to as a Damped Apex Dome. This is a dome hybrid where the peak of thedome at the center is restrained from moving by a fixed phase plug lookingframe spanning over the dome mounted to the driver flange, forcing a ring likebehavior in the driver. Tweeters andmidrange drivers are frequently isolated in acoustically tuned chambers bySonus Faber in a number of their products. Sonus Faber's midrange and woofer drivers are often based on diaphragmsmade from the aforementioned real timeair dried non pressed blend of cellulose pulp, kapok, kenaf and other naturalfibers with viscous surface treatment that also frequently make use of a devicethat Sonus Faber calls a coaxial anti-compressorat the center of the drivers rather than a dust cap or phase plug that they claimwill remove cavity resonance and distortion. A dynamic driver alternates between compression and tension as it ispushed and pulled by the motor to create sound and air, as a gas, can onlytransmit sound as variable compressive pressure in the air relative to theoverall positive compressive pressure of the atmosphere. So, based on a direct reading of the wordsused, it is not clear exactly what compression this anti-compressor is against or how eliminating it is beneficial.

a) Damped Apex Dome tweeter.

b) Ring radiator tweeter.

Then there is this business of a Tuned Mass Damper (TMD)used by Sonus Faber in some of their higher end speakers. Tuned mass dampers come in a number of forms,with the type used in formula one cars based on a one dimensional cylindricalmass spring system while those used in skyscrapers are often a two dimensionalpendulum type. These systems are notdampers by a rigorous engineering definition of the word, rather, they work bysupporting a mass with springs that are soft enough to decouple it from therest of the system such that when it does move, it is out of phase with thevibration to be suppressed. This createsa reactionary inertial force that opposes the primary inertial force of theobject to be damped, not byconverting motion to thermal energy as suggested by Sonus Faber on a numberof occasions in their literature.

a) Imageof Sonus Faber's Tuned Mass Damper from a speaker under construction.

b) Diagramof the single axis Tuned Mass Damper developed by Renault for racing.

Based on images found in their product documentation, the deviceindicated to be a TMD by Sonus Faber, aside from some apparent missing parts,like the decoupling spring suspension, looks to be a couple of loose stacked plates witha central bolt to hold them in place laterally. Sonus Faber claims they are used to erase micro-vibrations, but thesemasses look a bit too large to be excited into significant motion by vibrationat acoustic amplitudes and even then, they would only suppress vibration along asingle axis. Assuming the damper shownis oriented vertically in a cabinet that is set on its side for construction,it could only dampen vertical vibrations.

The efficacy of the particulars of how some of the methodsdescribed by Sonus Faber actually work may be suspect, but most of thesespeakers are pretty massive, which by itself will typically make them moreinsensitive to a given amount of energy attempting to drive the cabinets intovibration by virtue of inertia. Thecomplex geometry will also serve to limit the extent of cabinet area that canbe excited at any given resonant frequency, thereby limiting the overallamplitude of vibration that can occur. Coupledwith the complex and varied construction materials and methods, any vibrationtraveling through the cabinet will likely have to traverse many boundaries thatwill cause reflection and/or refraction of the waves, scattering them to fight andcancel each other out. Much of what Sonus Faber is attempting with these speakers is ambitious, so perhaps it is a lack of specific engineering expertise that seems common across much of the audio world. Perhaps a consultant versed in the mechanics of structural dynamics would be in order to put these system concepts to more effective use.

The entry level Toy product line features a single towermodel, pragmatically named the Toy Tower. The three way ported design uses a 1 inch ring radiator tweeter, a 4.33inch coated cellulose midrange, and a 7.1 inch hard Nomex cone woofer. The rectangular cabinet features roundedcorners and is available in gloss white or black, barred or classic blackleather, or stained wood in a medium brown. The side panels of the cabinet onthe Toy are said to be decoupled form the rest of the cabinet to controlresonances and standing waves. With arespectable 89 dB sensitivity and an 8 ohm nominal impedance, the Toy Towershould also be relatively easy to drive.

Two tower models grace the Venere line, the Venere 2.5 andthe 3.0. Geared towards home theater andease of placement, the front ported cabinets feature a curved lyre shapederived from the flagship Aida loudspeaker, a sloped baffle, and a peaked top. The Venere line is available in severalfinish options: gloss black or white along with a lacquered stained wood finishin a medium brown and feature an anodized aluminum bezel and tempered glass atthe top and bottom panels. The smaller Venere2.5 uses a 1.15 inch coated fabric dome tweeter along with a 7.1 inch Curv cone mid-woofer and a 7.1 inch Curv cone woofer on a tapered crossover. The Curvcones are made from what Sonus Faber refers to as a thermo-mouldered polypropylene fabric and are mounted in a free compression basket. The Venere 3.0 adds a 5.9 inch free compression basket Curv midrange aswell as a coaxial anti-compressorthat is said to remove resonances and distortions. From the limited description provided, it isnot entirely clear if the freecompression basket and the coaxialanti-compressor would oppose and cancel each other or not.

Next up, is the Olympica series that features two towermodels, the Olympica II and III. TheOlympica series are based on an Enhanced Lyreshaped progressive thickness triple curved wall cabinets, available in walnutor graphite stained wood, with solid walnut top and bottom plates used as avertical clamp that like the baffle are clad in leather. Cabinet tuning is based on what Sonus Fabercalls paralaminar stealth flow ventingto minimize port noise. This system consistsof a perforated metal plate along the rear edge, facing either to the left orright in paired speakers, that allow for inward or outward placement of theports to best match room characteristics. The smaller tower, the three way Olympica II, uses three drivers. High frequencies are produced by a 1.15 inch DampedApex Dome moving coil ring radiator tweeter. A 5.9 inch midrange cone driver composed of Sonus Faber's favorite blendof cellulose and other natural fibers with a viscous surface treatment. This driver uses an eddy current free voice coil and features the coaxialanti-compressor. Bass output comes froma 9 inch sandwich construction cone composed of a rigid syntactic foam core withtreated cellulose pulp surface skins. This woofer is said to be based on the driver design used in theflagship Aida speakers. The larger threeway Olympica III adds an additional woofer to the driver compliment found inthe II.

Next we have the Elipsa Red, a three way ported model withan elliptical shaped cabinet made of sandwiched layers of solid maple orientedfor resonance control. Here, unlike mostof Sonus Faber's cabinet designs, the curved wide face is oriented for mountingthe drivers. The Elipsa makes use of a1.3 inch ring radiator tweeter driver mounted in a wood internal acousticchamber with an anti-resonator and an acousticambient. A 5.9 inch black wood fibercone driver provides the midrange with a SymmetricDrive Motor System that is mounted in a vented internal chamber. The woofer is a 10.25 inch cone made of aluminum/magnesiumwith the coaxial anti-compressor at its center. The Elipsa Red is available in either lacquered red violin or graphitestained wood finish with the baffle clad in black leather.

The Homage Collection, which are named after Italianviolin makers, features two tower models, the Amati Futura and the Stradivari,with the former a narrow tower while the latter is a wide faced elliptical designsimilar to the Elipsa Red.

The first Homage tower is the 3.5 way Amati that SonusFaber describes as a lute shaped progressive curvature cabinet constructed of multilayeredcross grained Okoumè plywood, weighing in at 122 pounds each. The Amati cabinet design incorporates constrainedmode damping, an avional Exo-Squeletonformed from a spine and the cabinet end plates, and a tuned mass damper. The cabinet acoustics are based on SonusFaber's Stealth Reflex Para-AperiodicPort system and the sub chambers formed between the internal stiffeningribs are filled with a variety of acoustic damping materials ranging from opencelled thermoplastic foams to fibrous material akin to felt, that are said tobe optimized by application and location within the cabinets. The tower is mounted on an elastomerisolation base that Sonus Faber refers to as a Low Vibration Transmission system to decouple the speaker from thefloor. The driver compliment of the Amati consists of a 1.15 inch dome witha vibration optimized mechanical interface, a 7 inch real time air dried and non pressed cellulose fiber cone with anacoustic chamber and an eddy current freevoice coil, and dual 8.67 inch elastomer foam damped aluminum/magnesium alloycones with the coaxial anti-compressors. The woofers use a tapered crossover and also feature a 1.5 inch longthrow motor with a voice coil designed to control eddy currents. Finish options for the Amati include red,walnut and graphite stained wood covered in seven layers of hand polished lacquerwith a black leather baffle and the nickel coated avional caps and exposedspine at the rear.

Homage number two is the three way ported Stradivari, awide face elliptical cabinet like the Elipsa that is constructed using multilayerwood with constrained-mode damping and weigh in at nearly 128 pounds each. Sonus Faber describes the elliptical shape asthe form of two facing lutes and that the wide face cabinet approach is used tosimulate infinite baffle behavior into a 2π space. Furthering the musical instrument analogy, thewide faces of the cabinet are also joined internally as the plates of a violin arejoined. The tweeter used for the Elipsa isa 1.3 inch ring radiator that is mounted to the cabinet in a dual toroidalwaveguide with an anti-resonator. Internally,the tweeter is housed in a wood acoustic labyrinth chamber with an integrated acoustic ambient. The midrange driver consists of a 5.9 inchcone said to be optimally vented for resonancefree response according to Sonus Faber. The driver uses an eddy currentfree voice coil and is mounted in a vented internal chamber. Bass output onthe Stradivari is produced by a pair of 10.25 inch aluminum/magnesium alloycones with the coaxial anti-compressor. Thewoofer motors are an eddy current freevoice coil design that allows for 2 inches of movement. The Stradivari cabinet is available in eitherred, walnut, or graphite lacquer stained wood with black leather front baffleand rear and gloss black side panels.

Moving on, we have the Lilium, a 3.5 way orthogonal non interactive dual enclosuretower speaker, which at 227 pounds, each, over a hundred pounds more than theStradivari, makes the jump to the truly massive. Sonus Faber describes the Lilium as a Lyrashaped and having progressive thicknesstriple curvature cabinet walls damped spread resonance spectrum system. The top and bottom of the cabinet consists oftwo double dampshelves of avional connectedby a column down the back of the cabinet. The main enclosure housing the tweeter, midrange and woofers is said tobe decoupled from the infra woofer enclosure through a variation of the Zero Vibration Transmission system, whichalso isolates it from the room as well, and is said to radiate orthogonal tothe main enclosure to avoid intermodulation. The Lilium cabinet also houses a dual frequency TMD said to futher controlmicro vibrations. The main portion ofthe Lilium cabinet is tuned with the StealthReflex System while the infra woofer chamber is tuned using a passiveradiator. The Lilium tweeter is a 1.1inch arrow point Damped Apex Dome mounted in a natural wood acoustic labyrinthrear chamber. Mid frequencies areprovided by a 7.1 inch driver comprisedof a viscous surface treated cone of realtime air dried non pressed blend of cellulose pulp, kapok, kenaf and othernatural fibers with the coaxial anti-compressor. This midrange uses an eddy current free voice coil and is mounted in an acoustic chamber. The triple forward firing 7.1 inch cone woofersuse a tapered crossover across the divers which consist of sandwichconstruction diaphragms made from a rigid syntactic foam core, itself aparticle reinforced composite material, with cellulose pulp surface skins. The woofer motor structure can accommodate1.5 inch movement and the voice coil is designed to control eddy currents. The top firing 10.25 inch cone infra woofer isfashioned from a hard paper composite sandwich with a long throw motor thatallows for 2.5 inch movement and has a rear mounted level adjustment to tune itto the system and room. The Lilium comesfinished in either red or walnut stained wood with black leather around thedrivers in the baffle and the exposed avional of the rear spine and cap plates.

Rounding off the list is the massive flagship Aidatower. Similar to the smaller Lilium,the nearly 5’-8" tall 364 pound Aida is based on a Lyra shaped cabinet with dualcurvature sides formed from layers of cross grained Okoumè plywood that, accordingto Sonus Faber, provide a constrictionlayer damped configuration that is vented using the Stealth Reflex Para-Aperiodic Port system. Also incorporated into the design of the Aidais an avional spine with connected top and bottom plates that are said tofunction as vibration dampers and again features a dual frequency TMD.

The Aida is a bipolar loudspeaker with additional high andmid frequency drivers mounted at the rear of the cabinet. The Aida uses an adjustable level 1.15 incharrow pointed Damped Apex Dome mounted in a natural wood acoustic labyrinthrear chamber. The midrange driver is a7.1 inch cone comprised of Sonus Faber's favorite blend of surface treatedcellulose and other fibers with the accompanying real time air dried non pressed processing. The midrange includes the coaxial anti-compressorand is also mounted in its own internal acoustic chamber. Sonus Faber makes further mention that themidrange has an eddy current freevoice coil and that the basket is made of machined avional/gunmetal which issaid to be thoroughly optimized toeliminate any resonance. Both thetweeter and the midrange drivers are mounted with an anti-resonator to decouple them from the cabinet. The dual 8.67 inch woofers are mounted in aninternal Stealth Reflex chamber and comprisedof sandwich construction cones made from a rigid syntactic foam core withtreated cellulose pulp surface skins and include the coaxial anti-compressor. The motor structure for the woofers is a longthrow design that can accommodate 2 inches of movement with voice coilsdesigned to control eddy currents. The downwardfiring infra woofer is housed in the main portion of the cabinet and consistsof a 12.6 inch honeycombed nanocarbon composite sandwich cone that has anadjustable level and a long throw motor capable of 3 inches of movement. At the rear of the Aida are the adjustablelevel Sound Field Shaper driversconsisting of a 1.15 inch dome tweeter and a 4.75 inch paper pulp/natural fiberblend cone driver. The finishesavailable for the Aida are lacquered white, red, walnut, or graphite stainedwood with a black leather baffle and avional rear and cap plates.

The Sonus Faber product line covers a very wide range ofprices that extends over two orders of magnitude, from what most would merelycall expensive to where the products are truly a luxury. For mortals of ordinary means, the joke of mortgagingones home to own such speakers is not really a joke, and it would be a firstmortgage, not a second.

With such prices, the affluent expect extraordinary effortand quality to be put into the design and construction of these speakers, andby appearances, Sonus Faber accommodates expectations. Diminishing returns very likely dominatesover any performance improvements at the price, but that is not why one wouldbuy such speakers. Elaborate handcraftedconstruction, draped in fine woods and leathers, imposing size and weight, andboisterously described technical features, owning Sonus Faber speakers wouldcertainly make for a centerpiece of discussion.

Despite the hyperbole of the literature describing theproducts, I am sure these gorgeous speakers likely sound equally gorgeous, justprobably not for the quasi/pseudo reasons elaborately rambled about in theSonus Faber literature. Either way,these beauties are not the kind of speakers one would metaphorically kick outof bed just for eating gibberish flavored crackers. Metaphorically.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.

Professionally, David engineers building structures. He is also a musician and audio enthusiast. David gives his perspective about loudspeakers and complex audio topics from his mechanical engineering and HAA Certified Level I training.

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