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Infinity Kappa 600 Loudspeakers Review

by December 07, 2006
Infinity Kappa 600

Infinity Kappa 600

  • Product Name: Kappa 600
  • Manufacturer: Infinity
  • Performance Rating: StarStarStarStar
  • Value Rating: StarStarStarStar
  • Review Date: December 07, 2006 12:10
  • MSRP: $ 2400/pr

Frequency Response (+/-3db): 30Hz – 27kHz
Sensitivity (2.83V @ 1m): 90 db
Nominal Impedance: 6 ohms
Tweeter: 1” Dome
Midrange: 6 ½” Cone
Woofer: 10” Cone
Crossover Frequencies: 100Hz, 3000Hz
Crossover Slope: 24db/octave
Recommended Power: 35 – 200 watts/channel
Dimensions (HxWxD):  37.38” x 8.69” x 16.75”
Weight (each): 71.5 lbs
Enclosure Type: Rear Ported


  • Detailed, natural sound that will reveal your best recordings.
  • Crisp transient response.
  • Stylish, well constructed cabinets.


  • Unforgiving of some recordings.
  • Tweeter/midrange grille is flimsy.


Infinity Kappa 600 Overview

It seems that nearly every recent review I've seen for an Infinity product laments the passing of the perceived glory days of Infinity under its founders: gone are the Infinity Reference Standards (IRS), their many reincarnations, and their offspring. Acknowledgement of what the current masters have accomplished is given almost begrudgingly. Under the guidance of the likes of Harmon International Industries Incorporated and Dr. Floyd Toole, who espouses a philosophy of simple design and good engineering, Infinity is perceived to have moved into the mainstream.

We should not forget what audio is about: the music. If esoteric design and unusual construction serve the music, then it is good. If less esoteric design and more mundane construction serve the music, this is also good, perhaps better. Good engineering is about satisfying design goals with the resources available; economics are inherent. A professor I once had said that to cross a chasm, you could fill it rather than build a bridge, but that is not good engineering; it is not cost effective. Diminishing returns is an economic truth that has a powerful influence over the quest for perfection in design. If a product can be engineered with ninety percent of the performance at fifty percent of the cost, that is good engineering; simple designs to solve complex problems are the most elegant and complexity for its own sake is unnecessary.

We should also not forget that even in those glory days, Infinity's designs always ran the full gamut from esoteric to mainstream with the IRS at one end and products like the SM series at the other. This is much like today with the Prelude MTS at one end of the spectrum and the Primus series at the other end.

The reincarnation of the Kappa series under Harman's version of the Infinity line has held to the spirit of the original series. At a list price of $2400 per pair, they are in the upper middle class of the Infinity lineup: they are of good build quality, elegant in appearance, and benefit directly from advanced technologies Infinity incorporates into its higher end designs. While some of the driver geometries may not be as unusual as in days gone by, the only real question is "What can this design do for the music?"

Infinity Kappa 600 Design and Construction

The Kappa 600's were engineered and manufactured by Infinity in Denmark, originally for the European market. They were available in the United States for a time, and are still available in Europe. Product information for the Kappa series is available on Infinity's international web site .

The Kappa 600's are floor-standing speakers with a narrow, tapered enclosure just over three feet tall. The cabinets are finished with furniture grade Danish veneers in maple, cherry, or the review pair's black ash and weigh 71.5 pounds each. The grilles and baffles for all the variants are a contrasting gray/silver. The front baffle is sloped back at 5 degrees to provide phase coherency between the midrange and tweeter and has rounded corners to minimize diffraction effects. The speakers have gold plated dual binding posts with large gauge wire jumpers allowing for bi-wiring/bi-amplification. The crossovers use air core inductors in a low loss design for increased power handling and reduced degradation of sound quality. Threaded carpet spikes are provided to stabilize the speaker on carpeted floors.

The cabinets are formed of ¾" to 1" MDF with wood veneer. The inside of the cabinets are completely covered with foam to provide internal damping. Horizontal bracing couples the sidewalls together at several points for additional rigidity. All the internal wiring is done with 16 gauge, braided copper wire with soldered connections.

The speaker is a three-way design with a driver compliment that consists of a 1" dome tweeter, a 6 ½" cone midrange, and a 10" side firing cone woofer in a rear ported design. This woofer placement allows for the narrow front baffle to improve imaging in a dedicated left/right speaker configuration. Crossover frequencies are at 100 and 3000 Hz, effectively making the system behave similar to a two-way system with a passive subwoofer. All the drivers use Infinity's Ceramic Metal Matrix Diaphragms (CMMD) for the cones.

CMMD is a composite material for which Harman International Industries Incorporated holds two patents: 6,327,372 and 6,404,897 . One is related to the composite material and the other related to the manufacturing process for the material. The composite material consists of an aluminum core with alumina anodized to the outer surfaces in a 20/60/20% arrangement.

Alumina is a ceramic material also known chemically as aluminum oxide (Al2O3). It is the primary component of bauxite, aluminum ore, used to produce alumninum and is found naturally occurring in clay soils and other minerals. Metallic aluminum is highly reactive with oxygen such that any exposed aluminum surface will naturally form a thin layer of alumina that prevents further corrosion. Anodizing can be used to thicken and modify the mechanical properties of this naturally occurring layer as Infinity has done.

Alumina is a widely used engineering ceramic that has strong interatomic ionic bonds that give rise to a number of advantageous mechanical properties. In addition to having a very high stiffness, alumnia is hard and wear resistant, has good electrical and thermal insulating properties, has a melting point of 2000 deg C, and resists chemical reactions including acid and alkaline attack. It is used in a wide range of applications including: abrasives, cutting tools, high voltage insulators, furnace liners, ballistic armor, and high temperature laboratory equipment among other uses.

Infinity literature on CMMD provides a comparison between alumina and a number of other materials commonly used to construct speaker cones. Materials such as polypropylene, Kevlar, paper, and titanium are compared with the aluminum and alumina components of CMMD. Material properties such as Young's Modulus (E) that represents the linear elastic stiffness of a material, mass density (Dm), and the speed of sound in the material are provided. Young's Modulus can be calculated by taking a piece of material, of a known cross sectional area, usually rectangular, and measuring how its length changes (strain) as an applied load increases on the cross section (stress). The data can be plotted and the slope of the initial portion of the data, before any significant kinks or bends in the curve, is Young's Modulus: stress/strain. The speed of sound in a material is an indirect measure of the material stiffness and natural vibrational frequency of the material as wave propagation velocity increases with stiffness.

Of particular interest is to calculate the ratio of stiffness to a unit mass (density) (E/Dm):

1.5x10^9Gpa / 0.9g/cm^3 = 1.67x10^9
Kevlar Fabric: 3.1x10^9Gpa / 0.9g/cm^3 = 3.44x10^9
Paper: 4.0x10^9Gpa / 0.7g/cm^3 = 5.71 x10^9
Titanium: 110x10^9Gpa / 4.5g/cm^3 = 24.4 x10^9
Aluminum: 70x10^9Gpa / 2.7g/cm^3 = 25.9 x10^9
Alumina: 340x10^9Gpa / 3.8g/cm^3 = 89.5 x10^9

As illustrated by the calculations above, alumina offers a substantial advantage in stiffness for a given mass of material. Based on a linear ratio of Infinity's material thickness percentages for the components of CMMD, the combined material still retains a ratio of 56.7x10 ^9 , more than double metallic titanium and ten times greater than paper. Now consider that a material's stiffness (k) to resist deformation to an applied axial load is ka = AE/L ((area*Young's Modulus)/length) and to an applied bending load is kb = 4EI/L (where the moment of inertia I = (width*(thickness^3))/(length^4) for a rectangular cross section), is it becomes clear that for a given geometry that it will take a substantially greater mass of these other materials to achieve the same stiffness as a CMMD cone. While the mechanics of a cone loaded at its apex are a little more complicated than for a rectangular, end loaded section, these fundamentals serve to illustrate the importance of the properties Infinity discusses.

A composite material such as CMMD attempts to combine advantageous mechanical behavior for each material while minimizing the disadvantages. Aluminum has a high stiffness to mass ratio, is ductile, but has little internal damping; like all diaphragms made of a metal it will tend to ring at resonance as an underdamped mechanical system. Alumina has an even greater stiffness to mass ratio, has higher internal damping, but is brittle, with poor tensile capacity to resist the kind of cyclic loading that speaker diaphragms undergo. Combined, Infinity contends that the material is light, stiff, has improved internal damping, and is a durable material for cone construction.

The mechanical advantages have several important effects on performance. Low inertial mass allows the drivers to respond quickly to the ever-changing audio signal for improved transient response. High stiffness has a twofold effect: to minimize distortion under load, as illustrated above, and to push the natural frequencies for internal vibration modes higher. Natural circular frequency is calculated by w = (k/m)^½ (the square root of stiffness/mass) and the frequency in hertz (Hz) is f = w/2pi (the natural circular frequency/2*pi). Optimum behavior is rigid body motion of the diaphragm without any natural vibrational frequencies occurring over the audible frequency range of the driver. Any natural frequencies within the cones operational range would, under cyclic load, cause resonance and produce audible distortion of the signal. Improved internal damping will attenuate any vibrational modes within the diaphragm more quickly. Couple that with the butyl surrounds on the cones, which will damp the rigid body vibrations of the diaphragm and you should have a driver able to more faithfully reproduce a variable frequency signal. The test of the success in implementing these design goals is in the listening.

Infinity Kappa 600 Setup and Listening Tests

Listening tests were conducted with the speakers placed about 12" clear of the back wall with a slight toe in and the listening position was approximately at a ratio of 1.25:1 to the speaker separation. The dedicated left/right configuration was placed as suggested by Infinity with the side-firing woofer aimed inwards. I also listened with the tweeter/midrange grilles both on and off; I quickly concluded the sound clarity was definitely improved upon their removal. These tweeter/midrange grilles were constructed from a light plastic frame that, unlike the woofer grilles constructed of MDF, seemed rather flimsy.

Overall Impressions

My first impression of these speakers was twofold: sounds and details that are often relegated to the background or ignored altogether made themselves obvious, almost jumping out of the speakers into my listening room; however they tended to be a little on the bright side. The former suggests high resolution and good imaging while the latter I will temper with further observations.

After some initial break in, I noticed that the sound filled out, somewhat mitigating my initial impression of brightness. Early listening was reevaluated with the same recordings to confirm this opinion. Once broken in, perception of brightness became more a function of the recording rather than the speaker and that the speakers simply reproduced the sound as recorded. Bright recordings remained bright while warm, rich recordings were allowed to come to fruition.

The sound, in general, was clear and very detailed with excellent transient response. Slight variations in instrumental timbre were audible; a good example of this would be percussion with slight shadings between similar drums or in how or where a particular drum is struck was apparent. Nuances in a performer's playing such as articulation and decay, the textures of each note, were revealed. Complex musical passages could be resolved into component instruments. Individual instruments sounded distinct with a sense of space around each performer. Each individual sound still fit into the whole but was not absorbed into a more homogeneous mass of sound as is common with many speakers. This impression is further exemplified as the speakers performed with varied musical styles. Even at moderately loud listening levels the speakers did not strain, but sounded as if they were being held back, like they were ready to run but being told to walk. Dynamic transitions were handled well by the Kappa's; delicate and authoritative were sonically interchangeable.

Stereo imaging was very good, the soundstage was wide, instruments had distinct locations, and a sense of space was present. After the initial break-in, the illusion of real instruments solidified in space and the Kappa's would seem disappear from the room. The only shortcoming was that the soundstage did not quite seem as deep as I am used to. Every loudspeaker has some variation in how the stereo image of specific instruments is localized, the Kappa's abilities in this regard served to enrich many familiar albums.

I subjected these speakers to a wide range of musical types. All of it was reproduced with a natural sound quality and without the perceived preference to some musical genres that occurs with certain loudspeaker designs. The reproduction, to my ears, always sounded natural and unbiased. I will say that music with a lot of transient demands was particularly engaging. Sounds with a more staccato articulation, such as plucked strings, percussion, and taut electronics came to life.

David Sylvian - Secrets of the Beehive

This is a layered, ambient album full of contrasting instrumentation. The Kappa 600's portrayed Sylvian's voice as clearly centered and forward with vocals and acoustic instruments, such as strings, solo flute and trumpet, and guitars, having substance and a very natural sound. The instruments also had clear separation with articulation and decay of notes distinct. Layers of detail in the arrangements and various exotic percussions came out of the speakers and occupied space in the room. Bill Frisell's playing on "Dobro #1" was rendered as sharp and articulate and on "Krishna Blue", the tabla, layers of supporting percussion, bansuri, guitars, and dobro were again in the room, presented with a large sound stage. Segments of string arrangements throughout the album were richly presented with warmth in the viola and cello and substance in the double bass.

Tori Amos - The Beekeeper

Moving forward with my inadvertent bee theme, the primary vocals were focused and centered with layers of overdubs resolved almost as if there were background singers. The speakers located the piano clearly below and slightly to the right of Tori's voice where it is when she performs and was rendered with a full and natural sound. The sound was warm with details of accompanying and background instruments clearly audible on the Kappa's. Bass guitar and drums were deep and meaty and the midrange was also full. Dynamics transitioned easily between delicate and forceful. The title track is an electronic piece; these sounds were rendered crisply and opened into the listening room.

Yes - Union

This recording has a somewhat thin sound but was selected because it has always given me the impression of sonic envelopment. When a pair of speakers image well, the guitars, synthesizers, drums, percussion, and myriad overdubs of Jon Anderson's voice all seem to swirl around the listener; almost with a headphone-like effect. The sound appears in front, above, behind, and beyond the speakers to the left and right. This effect, portrayed on the Kappa's, was engrossing and among the better presentations that I have heard. The details and separation of the instruments was definitely better than I am accustomed to. There is also a segment on the track "Dangerous", while not my favorite part, which cuts into a dance beat with deep bass that will put on display how well bass reproduction is controlled by a loudspeaker. The reproduction of this section was deep, without an over accentuation of the upper bass frequencies that commonly occurs in many lesser speakers.

Tool - Lateralus

This HDCD recording remained bright, but considering the material, it is more likely the recording rather than a flaw of the speakers. This album has a substantial amount of percussion and has an articulate electric bass part that was presented with depth and conviction on these speakers. The drumming clearly moved around an elaborate kit. Subtle distinctions between drums were audible and cymbals were spaced and clear. Transients of the picked bass and harmonics were vigorously presented. Multilayered vocals were clearly centered and solid. A couple items of particular note in how the Kappa's presented this album: about 10 measures into "The Grudge", the drums drop pitch to a thunderous depth with controlled booms, and during "Lateralus", you could actually feel the compressional waves produced by the undulating deep synthesizer part that seemed to somehow whisper to the listener at the same time on these speakers.

King Crimson - The Power to Believe

The Infinity Kappa 600's were able to convey the wall of sound that is King Crimson. An album with musical content of this nature can easily force a shrill presentation from a speaker, but the Kappa's reproduction was not unduly bright. Drums and percussion sounded solid and palpable, and the bass lines played on Trey Gunn's Warr guitar were deep and articulate. There was a distinct separation between all the various guitar parts and percussion. The layers of percussion and sound effects used throughout the album jumped right out of the speakers and into the listening room. In particular, the section of "The Power to Believe II" that features metal percussion and bells wove a sonic tapestry around my ears, and many of these sounds seemed to occur beyond the known boundaries of my listening room.

Al DiMeola - Orange and Blue

The sound on this album was smooth. The custom Gibson electric that DiMeola plays was rendered as rich and warm; the articulations and decay of the notes was distinct on the Kappa's. Acoustic guitars were full and very natural sounding. Elaborate drum and percussion parts were clearly defined and layered; the myriads of cymbals were clean and open, not harsh. The sound stage was large and somewhat forward, and all the sounds presented on that stage were clear and open. Thick, varied arrangements were resolved by the Kappa's into component parts with multiple acoustic and electric guitars, keyboards, pianos, violins, and various pipes and flutes all distinct.

Mark Isham - Blue Sun

This album was also smooth with a convincing soundstage that put the listener at the front table in the bar. The wind instruments, trumpet and tenor saxophone, were natural sounding with a rich immediacy. The instruments had a clear sense of space, especially the cymbals. Percussion was also natural with subtle variations in timbre between drums evident. The music would swell and recede; delicate sounds with detailed nuances would grow to develop authority. The detailed presentation of this album by the Kappa's clearly revealed the subtle under layer of electronic sounds, electric guitar and vocal loops that would float out of nowhere and surround the acoustic instruments.

Stravinsky - Petrushka - David Zinman with the Baltimore Symphony - Telarc

The Kappa's conveyed a clear attempt by this recording to put you in a seat, mid hall; the symphony was centered below and behind the speakers. Locations of different instrumental sections were distinct and inner parts could be resolved even during complex passages. The Kappa's clearly revealed hall ambience; the sound of a live hall was readily apparent because the decay was not muddled into the rest of the sound like with many other speakers. Instruments were full and natural within that ambience. The full brass section did come across as bright in certain instances, but I believe that had more to do with variations in the arrangement rather than the speakers. Dynamics were controlled and delicate sounds were clear. During "The Shrovetide", the bass drum and timpani section was presented with a deep, accurate timbre.

Infinity Kappa 600 Conclusion

In time all things change, some for the better, some for the worse. All sorts of comparisons between the old and new will persist with proponents on both sides.

My impression of the current Kappa's is positive. Some may persist with comparisons to earlier models, and in truth, there are merits to some arguments on both sides. With excellent resolution and openness, wide sound staging, controlled dynamic response, and the ability to transport one from their listening room to a performance, I believe the current Kappa's show all the markings of a good quality loudspeaker. If simpler, more cost effective designs can serve musical fidelity without significant diminishing returns, then that is good engineering.

Infinity has changed, true, but if the goal is still fidelity, has it really changed?

Infinity Kappa 600
MSRP: $2400 pair
Infinity Systems, Incorporated

Associated Test Equipment



PS Audio 100 D

128 wpc dual mono power amplifier

PS Audio 6.0


Wadia 12

D/A converter

California Audio Labs Delta

CD transport


Speaker cable, interconnects/digital interconnect

Power Wedge 112

AC Line Conditioner/surge suppressor

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
Build QualityStarStarStarStar
Treble ExtensionStarStarStarStar
Treble SmoothnessStarStarStarStar
Midrange AccuracyStarStarStarStar
Bass ExtensionStarStarStarStar
Bass AccuracyStarStarStarStar
Dynamic RangeStarStarStarStar
About the author:
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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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