KEF R&D

R Series with MAT

CONTENTS

2

Introduc�on2

Philosophy

3

R Series with MAT

412th Genera�on Uni-Q with MAT for R Series

4High Frequency Driver (Tweeter)

5

Metamaterial Absorp�on Technology

5

Coupling MAT to the tweeter dome

6

HF Motor System

6

Tweeter Gap Damper

7

Tangerine Waveguide and Shadow Flare

7

Tweeter THD performance

8

Midrange Driver8

Ultra-low distor�on midrange motor system

10

Flexible Decoupling Chassis

11

Midrange suspension

12

Midrange Cone Neck Decoupler

12

Midrange THD performance13

Low Frequency Drivers

13

System and Enclosure

13

Constrained Layer Damping

15

Damping of standing wave resonances17

Bass-reflex ports

17

Crossover

19

System THD performance

19

Summary20

References

22

Model Informa�on, Specifica�ons and Measurements

₁

Introduc�on
R Series was first introduced in 2011 as a highperformance speaker range that benefits from thetechnology developed for the Reference Series but in amore affordable package.
R Series, thus, takes on the main acous�c principles ofthe modern Reference Series:•••

A slim rec�linear cabinet heavily braced with internal
constrained layer damping

A Uni-Q driver array dedicated to midrange andhigh frequency surrounded by a Shadow Flare to
reduce baffle edge diffrac�on

A D’Appolito symmetrical array configura�on of lowfrequency drivers around the Uni-Q [1] for a smoothand symmetrical ver�cal direc�vity in thefloorstanding models and horizontal direc�vity inthe centre channel models

improvement featured in the new R Series. Every
speaker in the range thus carries the moniker ‘Meta’ in
its name.

compressions; it must have a neutral �mbral character,without resonance or imbalance; it should have a good
temporal resolu�on such that it does not “smear” thelisteners will be able to “hear through” the room in which
they are located and perceive the acous�c spacecaptured in the recorded sound.

sonic event. Each of these fidelity requirements provide‘Meta,’ nonetheless, reflects much more than theapplica�on of MAT. It implies a full research anddevelopment project has been undertaken to redesign
all cri�cal components in the speaker systems to achievea considerable leap forward in performance. This is now
what has come to be expected from any KEF speakerwith ‘Meta’ in its name and R Series is no excep�on.

clear targets for the loudspeaker designer.
However, this ideal audio system has two further
implica�ons that are more difficult to handle. Firstly, thespa�al informa�on of the original event should be
captured and replayed. Secondly, the listeners shouldhear only the acous�c space of the original event andPhilosophy

not the acous�c space in which they are located.

“Of all art, music is the most indefinable and the mostexpressive, the most insubstan�al and the most immediate,
the most transitory and the most imperishable. Transformed
to a dance of electrons along a wire, its ghost lives on. WhenKEF returns music to its righ�ul habitua�on, your ears andmind, they aim to do so in the most natural way they can...
without drama, without exaggera�on, without ar�fice.”

Technically,neitherstereonor

conven�onal

mul�channel playback are sufficient to recreate theIn summary, loudspeakers must be designed to have asmooth and balanced response both in terms offrequency and space. The sound from loudspeakers
should emanate from the drivers themselves and notfrom other components, such as resona�ng panels or
openings. The drivers should operate in a wellcontrolled manner throughout and beyond their band.
Loudspeakers should have low distor�on andcompression and a good temporal response.

R Series with MAT

exact sound field of an event. However, our percep�on
is not exact: our auditory system builds a scene in our
mind based on cues in the signals reaching our ears.
Cues such as the rela�ve arrival �me and level of thesound at each of our ears. Stereo playback provides asimple means by which the ar�st or recordist may

Raymond Cooke OBE, KEF Foundercommunicate these cues to the listener. The listenerbuilds a picture of the sonic event in their mind and•Rear-firing bass-reflex ports with op�mised
posi�ons to minimise the leakage of the enclosure’s
internal standing waves and flexible port walls todamp the ports’ inherent acous�c resonances

These principles provide a solid founda�on for an
acous�cal system that can deliver music reproduc�onwith extremely low coloura�on and a smooth off-axis
response in all direc�ons, allowing it to work well in awide variety of rooms.
In its second itera�on in 2018, R Series further becamea vessel of innova�ve technology development,
introducing the first 12�� genera�on Uni-Q featuring theTweeter Gap Damper.

Loudspeakers are the final stage in the soundreproduc�on chain. It is down to the loudspeaker togenerate the sound that the listener will hear. Whileother pieces of audio equipment have clearly definedroles, and it is easier to outline how they would ideally
perform, the ideal loudspeaker is more difficult to define.
It is simpler to first consider what the complete audio
system is trying to achieve. The ideal audio systemshould be able to recreate a live sonic event so that it isindis�nguishable from the original. The listeners shouldbe transported to the environment of the live event.
They should be convinced that they are si�ng in theactual concert hall in which the live event occurred. They
should experience the acous�cs of the space, perceive
the loca�ons of the instruments, interact with the space,and hear the change in the sound as they turn theirheads towards the soloist.

emo�onally connects with the experience of listening tothe original.
Loudspeakers must be designed to maximise thecommunica�on of these spa�al cues. To do this, aloudspeaker must have a response that does not change
rapidly with direc�on. An irregular direc�vity can resultin the loudspeaker communica�ng spa�al cues thatconflict with those in the recording.
Controlling the loudspeakers’ direc�vity is also key to
avoiding loss of midrange and treble fidelity, which canhappen when loudspeakers are placed in a real listening
environment. One of the features of our auditory
percep�on is that we are well used to hearing sounds
that include reflec�ons off close surfaces. Our auditory'Meta’R Series with MAT is the sixth model range to belaunched by KEF since 2020 (LS50 Collec�on, Blade and
The Reference with MAT, LS60 Wireless andCi250RRM-THX) to incorporate MAT (Metamaterial
Absorp�on Technology).
KEF’s MAT is employed as an acous�c absorber behind
the tweeter diaphragm and is the main technology

system can iden�fy the direct sound and separate out

Many recordings are available that never existed as live
events. For example, a rock band captured in a studio ormusic with synthesised instruments. Nevertheless, thesame objec�ve applies for these situa�ons: the sonic
event that we wish to hear is the one that was envisagedby the musicians and producers. For this to be achieved,
there are implica�ons for the fidelity of the replay
system: it must not colour the sound with theintroduc�on of distor�on or dynamic range

reflec�ons to the extent that we do not perceive theearly reflec�ons as separate events. The listener willa�ribute any �mbral imbalance in the reflec�ons to theoriginal source. This means that loudspeakers must have

Figure 1. 12th Genera�on Uni-Q with MAT for R Series

The development of the new R Series with MAT beganwith the design of a new Uni-Q, which belongs to thefamily of KEF’s 12�� genera�on Uni-Q driver arrays. This
Uni-Q directly benefits from the research carried out
during the development of the high-performance Uni-Q
for the Blade and Reference Meta.

a frequency response that is good in all direc�ons, notsimply in the direct path to the listener. Loudspeakers
must have a smooth and balanced frequency response
on-axis and in other direc�ons. If this is achieved, the2Integra�ng this new Uni-Q into the speakers prompted
the redesign of key system components, including new
crossover filters that benefit from new and extended3measurement and simula�on tools developed for LS50
Meta, Blade Meta, and Reference Meta.

sound produced by the dome in a way that no othermanufacturer does.

by the acous�c metamaterial absorber, where it isabsorbed almost completely.

Furthermore, many of KEF’s technologies present in R
Series with MAT have been carried over from R Series
2018 [2]:•Tweeter Gap Damper•

Tangerine Waveguide and Tangerine WaveguideS�ffening Ribs•

S�ffened Tweeter Dome•

Uni-Q Shadow Flare•

Midrange Cone Neck Decoupler•

Low frequency drive units with hybrid aluminium
diaphragm and low-distor�on motor•

Flexible Wall ports•

Cabinet bracing with Constrained Layer Damping

The result is a range of seven speaker models that
reproduce music in a cleaner, more natural, and more
realis�c way, and which be�er interact with typicallistening rooms to recreate a more holographic stereo
image from a recording.
The range consists of three floorstanding models (R11
Meta, R7 Meta, R5 Meta), one standmount model (R3Meta), two LCR models (R6 Meta, R2 Meta) and one
Dolby Atmos® cer�fied model (R8 Meta). Addi�onally,
the new S3 stand is now offered for the R3 Metastandmount speaker.

12th Genera�on Uni-Q with
MAT for R Series
In this itera�on, the Uni-Q driver array incorporates a
new tweeter and tweeter motor with MAT, a completely
new midrange motor with a low-distor�on, split top
plate design, KEF’s unique Flexible Decoupling Chassis
and a smaller higher-excursion suspension for the
midrange driver (Figure 2). More informa�on on thefundamental concepts underpinning the Uni-Q
arrangement can be found in the 2014 Reference White
Paper [1].

High Frequency Driver(Tweeter)
The tweeter in the new Uni-Q contains a unique
technology package that deals with the front and rear

Between the tweeter and midrange voice coil an annular
gap is formed to allow the free movement of the la�er.
This gap creates an undesirable resonator. The Tweeter
Gap Damper resides inside a tuned cavity behind thetweeter and is coupled to this gap to reduce theresonance by providing absorp�on.

Metamaterial Absorp�onTechnology
Metamaterial Absorp�on Technology (MAT) is the namegiven to a metamaterial absorber disc that is acous�callycoupled to the rear of the tweeter dome. Its func�on is
to absorb the rear sound waves radiated by the tweeter
dome which would otherwise be a source of distor�onwhen reflected back into the dome.

Figure 2. Cutaway of the 12th Genera�on Uni-Q with MAT for R Series

Figure 3 shows a simplified sec�on view of the tweeter’s
acous�cal system. The front of the s�ffened aluminium
dome radiates into a small compression chamber loadedby the Tangerine Waveguide, a sophis�cated waveguideand phase-plug geometry that works together with thespherical profile of the dome to help it radiate more likea true pulsa�ng sphere at high frequencies, where
pistonic domes become considerably direc�onal [3]. This
waveguide smoothly flares out onto the enclosure baffle
using the midrange cone as a part of its profile. An outer
trim, the Shadow Flare, con�nues this waveguide andterminates it smoothly, while recessing the Uni-Q fromthe front baffle, effec�vely ‘shadowing’ the baffle edges
from the tweeter output and virtually smoothing theedges of the cabinet. This carefully op�mised geometry
ensures the front sound waves from the dome
propagate evenly into the listening room with a wide andsmooth direc�vity.

Figure 4. Metamaterial Absorp�on Technology

This disc comprises 30 channels of differing lengths,
formed into tubes, sharing an opening at the centre of
the disc (Figure 4). The tubes act as quarter-wavelength
resonators or absorbers, each tuned to a different
frequency with a high Q, which effec�vely absorb anarrow frequency band and its harmonics (Figure 5). The
absorp�on of these channels is tuned to overlap infrequency, leading to almost complete absorp�on acrossthe spectrum above 620Hz - well below the lower
threshold of the tweeter’s working bandwidth (Figure 6).
At 11mm deep, its performance is comparable to a welldesigned tapered tube absorber measuring 50cm long.
This allows its inclusion into loudspeakers of any size,
without taking up significant space in the cabinet [4][5].

Figure 5. Pressure response at closed end of each absorp�on channel

Coupling MAT to the tweeter dome
Of equal importance to the applica�on of MAT is how
the back wave is directed into the absorber. Thisrequires a large waveguide opening through the middleof the midrange motor stretching from the back of thetweeter dome to the rear of the midrange motor, where
the absorber disc is situated.
The conical waveguide’s length, angle and opening
diameters on both ends are specific to this new Uni-Q
since the acous�c impedance of the waveguide mustmatch that of the opening of the tweeter absorber toavoid a reflec�on of the wave back into the tweeter
dome.

Figure 3. Simplified view of the tweeter’s acous�cal system

The rear surface of the dome radiates sound directly intoa wide conical waveguide that is acous�cally terminated4

Figure 6. Absorp�on at the entrance of the conical duct, immediately behind thedome

5Tangerine Waveguide and Shadow
FlareThis waveguide is a tapered duct with a conical profile,which reduces in diameter towards the absorber’s
opening. A detailed explana�on and the mathema�csbehind MAT and its coupling to the tweeter dome can befound in the original Audio Engineering Society scien�fic
paper [4].
Figure 7 shows a diagram describing the geometricrela�onship between the spherical dome tweeter, theconical waveguide, the aperture angle to themetamaterial absorber and the absorber’s length related
to one quarter of the wavelength of its cut-on
frequency. The principle being that a spherical wave
travelling along a conical horn will avoid reflec�on at thehorn-absorber interface if the interface radius is equal toa quarter of a wavelength of the metamaterial cut-on
frequency.

The Tangerine Waveguide, midrange cone, and Shadow
Flare together form a smooth axi-symmetric waveguidethat is designed to propagate spherical sound waves
from the tweeter into the listening room in a controlled
way [6].
However, due to its pistonic mo�on, the spherical
tweeter dome does not produce an even, normal surface
velocity across its en�re surface. To overcome this, theTangerine Waveguide works as a phase plug that createsa small, low-compression chamber in front of the dome,
allowing it to radiate through nine computer-op�misedradial channels. It transforms the axial air par�cle mo�onnear the diaphragm into a close approxima�on of a true
pulsa�ng sphere at the end of its fins (Figure 10). The
result is a wide and close to constant direc�vity pa�ern
for the tweeter at high frequencies (Figure 11).
Furthermore, the compression chamber has thesecondary effect of boos�ng the tweeter sensi�vity
from around 7kHz upwards (Figure 12).

Figure 8. Comparison of tweeter motor geometries for R Series (2018) (red, bo�om)
and R Series with MAT (black, top)

Tweeter Gap Damper
The Tweeter Gap Damper has been redesigned to fit
between the midrange and tweeter motors (Figure 3)
following the same approach as the Blade and Reference
Meta Uni-Q.
Figure 7. Geometric principle behind the coupling of the tweeter spherical dome tothe metamaterial absorberThis arrangement further allows for an easieraccommoda�on of the absorber into the driver package
and reduces the size of the MAT disc itself. In addi�on,the increase of acous�c volume behind the tweeter due
to the presence of the waveguide reduces non-linear
distor�on associated to the spring effect of compressing
the air in this cavity.

Figure 12. Effect of the Tangerine Waveguide compression chamber on thetweeter’s axial response

The Shadow Flare further controls the direc�vity of thetweeter and recedes the Uni-Q into the enclosure by
5mm, enough to create an acous�c shadow at the baffle
edges closest to the driver. The result is a substan�alreduc�on in frequency response ripple of both midrange
and tweeter (Figure 13).

The gap that forms between the tweeter waveguide andthe midrange cone extends down to the midrange motor
and acts like an organ-pipe resonator that is excited by
the output of the tweeter, affec�ng its response. The
Tweeter Gap Damper expands this annular gap into an
acous�c cavity that works as a tuned Helmholtz
resonator and then adds acous�c damping to control its
resonance. This way the resonance is dissipated and its
effect on the tweeter response is reduced (Figure 9).
Figure 10. Tangerine Waveguide geometry

HF Motor System
The tweeter motor vent hole, forming a part of theconical waveguide that couples the tweeter dome to themetamaterial absorber, has been maximised to allow therear sound wave to travel as freely as possible. Thisrequired the design of a new motor with a Neodymium
magnet and a steel geometry op�mised to offer a highforce factor to maintain the tweeter sensi�vity and highsteel magne�c satura�on to reduce distor�on due tomagne�c hysteresis.

Figure 13. Comparison of Uni-Q driver HF response with and without Shadow
Flare

Tweeter THD Performance

Figure 8 shows a comparison of the new geometry withthe previous design where the increased rear vent area
is clear.
Figure 9. Improvement in tweeter frequency response due to the Tweeter Gap
DamperFigure 11. Tweeter Power Direc�vity Index (without crossover) as measured on
R11 Meta

6

Figure 14 shows a comparison of THD (%) between the2018 R Series tweeter and the R Series with MAT
tweeter. For this measurement, the same second-orderhigh-pass crossover with a cut-off frequency of 2 kHz
has been used to protect the tweeters from damage andto keep their output constant around 90dB at 1m up to
20kHz. Both tweeters have been measured in an R11
enclosure.

7

The motor force factor BL is the product of the flux
density B of the magne�c field crossing the voice coilgap, and the voice coil length L immersed in thatmagne�c field. BL is a func�on of the voice coil’s
displacement. Typically, as the voice coil moves awayfrom the gap, BL decreases as the length of coil present
in the gap is reduced. This modulates the force applied
to the voice coil and thus distorts the signal being
reproduced. This is one of the main sources of harmonic
distor�on in drivers.

voice coil will more closely follow the applied signal as
the voice coil moves from its res�ng posi�on.

behaviour is highly hystere�c, and the generated
distor�on has a par�cularly unpleasant characteris�c.
This is not the only issue, however. Inductance itself
varies with the posi�on of the voice coil - where thevoice coil is constantly being pulled towards where
inductance is highest. This is known as ‘reluctance force’and is highly non-linear as it is propor�onal to the squareof the current flowing through the voice coil.
To address these issues, the motor geometry has been
op�mised to increase satura�on of the steelwork to
reduce its magne�c permeability, thus decreasing its
suscep�bility to be magne�sed by the voice coil’s AC
magne�c field.

Figure 14. Comparison of the tweeter measured THD (%) between R Series (2018)(red) and R Series with MAT (blue) as measured in an R11 enclosure at 90 dB SPL at
1m with the same second-order high-pass crossover with a cut-off frequency of
2kHz
Figure 17. Midrange motor flux density B(x)Midrange Driver
Ultra-low distor�on midrange motor
systemFigure 15. Detail of the midrange motor within the Uni-Q

This arrangement is par�cularly advantageous. Si�ng
right in the middle of the two top plate sec�ons andaligned with the voice coil’s centre along its length, theconduc�ve copper ring’s effect on lowering distor�on ismuch greater, and symmetrical with displacement.

The new midrange motor is closely based on the one
developed for Blade and Reference Meta. It has been
specifically designed to eliminate force factor
modula�on with displacement, minimise voice coilinductance magnitude and minimise inductancemodula�on with displacement. These are the primaryfactors responsible for midrange harmonic andintermodula�on distor�on.
The motor top plate is an unconven�onal design
consis�ng of two sec�ons separated by an air gap. A
short voice coil moving within forms an underhung
arrangement. Inside the gap, and slightly indented, sits acopper ring which is aligned with the centre of the voicecoil.
The motor pole also now accommodates the tweeter
rear waveguide inside it as well as the Tweeter Gap
Damper above it. Figure 15 shows a sec�on view of the
Uni-Q highligh�ng the midrange motor system and its
split top plate design.
Figure 16 shows the magne�c circuit of the Uni-Q
midrange and tweeter motors. The behaviour of themagne�c flux at the split top gap is observable.

The wide copper insert placed within the air gap createdby the split top plate works as a conduc�ve region and it
couples to the voice coil allowing the flow of induced
current through it. This produces an opposing magne�cfield to the one created by the voice coil, further
reducing the ability of the voice coil to magne�se themotor steel.

Finally, an added benefit of the copper ring being so
close to the voice coil is that it efficiently dissipates heataway from it. This reduces thermal compression of thesignal whilst improving efficiency.
Figure 18. Midrange motor force factor BL(x) normalised to 0mm displacement

As AC current flows through the voice coil, an
alterna�ng magne�c field is produced. Its strength
depends on the inductance of the voice coil, with higher
inductance producing a stronger field. This AC magne�cfield is conducted by the steel in the motor system andsuperimposed on the DC field produced by thepermanent magnet.

Figure 16. Uni-Q motor system magne�c circuit. Magne�c field lines (top) and flux
isovalues (bo�om)

The new split top plate design focuses the magne�c flux
available from the motor’s ferrite magnet away from thecentre of the voice coil towards its ends. This creates an
M-shaped magne�c flux density profile B(x) that
decreases around the voice coil’s rest posi�on (Figure
17).

Steel is highly magne�cally non-linear, and thesuperimposed AC magne�c field causes some of themagne�c domains within the steel to reorient. This
results in a shi� in the permeability of the steel, leading
to modula�on of the DC magne�c field, and a
modula�on of the motor BL. These sudden shi�s in themagne�c domains are also picked up as induced voltage
signals in the voice coil, corrup�ng the music signal. ThisThe resul�ng BL(x) is thus fla�er along the voice coil’s
excursion of +/- 2mm compared to the previous motor(Figure 18). A fla�er BL(x) means the force applied to the8

Figure 19 shows a visualisa�on of the flux density
modula�on regions present in the steelwork of the
motor near the voice coil gap at 500Hz, a representa�vefrequency in the midrange. A considerable reduc�on canbe observed when the op�mised conduc�ve region ofcopper is added to the motor.
Figure 20 shows a comparison for the previous and new
motors of the voice coil inductance across frequency forseveral voice coil posi�ons ranging along +/-2mm where
the reduc�on in inductance modula�on withdisplacement is observable.
Taking a slice of Figure 20 at 500Hz reveals thatinductance modula�on is almost eliminated across voicecoil displacement (Figure 21).

9

Flexible Decoupling Chassis

dissipated by the damping pads. The result is the motor
vibra�on cannot leak into the cabinet and be re-radiatedAnother technology directly carried over from Blade andReference Meta is KEF’s Flexible Decoupling Chassis.
The new Uni-Q chassis is constructed of a composite
material. While its outer rim is directly a�ached to thefront baffle through a s�ff steel plate, the chassis legs
incorporate eight flexible spring elements connec�ng
the rigid por�on of the structure to the midrange motor.
In parallel to the flexible spring elements a set of four
damping material pads provide mechanical damping to
the springs. Figure 22 shows this arrangement together
with a diagramma�c representa�on of the mechanism
involved in the decoupling.

as sound into the listening room. Furthermore, the backof the Uni-Q, previously anchored to the rear wall of its
own enclosure through a damping pad, is no longer
connected to it in order to allow the decoupling chassis
to work as intended.

This leads to the baffle radia�ng this as sound. In
contrast, in the case of the Flexible Decoupling Chassis,
the measurement shows no trace of the motor mass
resonance leaking to the baffle, having been reduced bymore than 30dB.

Midrange suspension
The suspension centres the voice coil in the magne�c
gap and provides a high restoring force that protects thevoice coil from damage at extreme displacements.
A large suspension with more rolls allows a greater rangeof mo�on, which is essen�al for high performance low
frequency drivers. However, large suspensions sufferfrom mechanical resonance within the driver passband.
When this happens, a glitch or dip forms in the driver’s
frequency response, which is undesirable and easy toperceive as the ear is most sensi�ve in the midrange
frequency region.

Figure 19. Midrange motor flux density modula�on at 500Hz without (top) and withcopper conduc�ve region (bo�om)

Figure 23. R Series (2018) Uni-Q rigid aluminium chassis directly affixed to motor

A more detailed descrip�on of driver decoupling
approaches can be found in the Blade and Reference
Meta white paper [7].

Shi�ing the suspension’s resonance out of the midrange
opera�ng frequency band is challenging since it requiresa very low mass while s�ll allowing the driver to move its
full linear excursion.
The suspension profile (Figure 25) has been redesigned
to reduce its width to 0.69cm (0.27”), which has theeffect of decreasing its mass and increasing its resonant
frequency out of the passband while s�ll allowing alinear excursion of more than +/- 2mm.

Figure 20. Comparison of midrange voice coil inductance modula�on withdisplacement

Figure 22. R Series with MAT Uni-Q Flexible Decoupling Chassis (top) anddiagramma�c representa�on (bo�om) showing the flexible spring elements
highlighted in green and damping material highlighted in red

Figure 24. Effect of the Flexible Decoupling Chassis on baffle vibra�on

In comparison, Figure 23 shows the previous designfrom R Series (2018), where the aluminium chassis isbolted directly onto the midrange motor.

Figure 24 shows a comparison of the rigid chassis andthe flexible decoupling chassis performance through a
point velocity measurement

Figure 21. Comparison of normalised midrange voice coil inductance modula�onwith displacement at 500Hz

When the mass of the midrange motor vibrates when
excited by the reac�ve force from the moving voice coil,this vibra�on is ‘decoupled’ or disconnected from theenclosure by the flexible spring elements and quickly

10

made with

a

laser

vibrometer on a speaker baffle when the midrange driveris excited by a sine sweep. In the case of the rigid
chassis, the measurement clearly shows the motor mass
resonance, around 310Hz, has leaked onto the baffle.

Figure 25. Compara�ve view of midrange suspensions. R Series (2018) (top) and R
Series with MAT (bo�om)

Figure 26 shows a comparison of the FEA-simulated
frequency response of the 2018 R Series midrange

11

driver and the new midrange driver demonstra�ng thedisappearance of the dip at 950Hz caused by thesuspension resonance.

The following features can be highlighted:

turbulence noise and acous�c loading from the air
trapped inside the voice coil.

• The distor�on is considerably lower at the lower
midrange frequencies as a result of the new split top
plate design.

The surround is a linear-excursion inverted half-rolldesign that reduces the effect of diffrac�on for theneighbouring Uni-Q by not protruding from the speakerbaffle.

• The overall drop in THD across the driver’s wide
passband owing to the new motor design

System and Enclosure• The disappearance of the glitch around 310Hz where
the new decoupling chassis takes effect• The disappearance of the glitch around 950Hz where
the suspension resonance has been dealt with by the
new midrange suspension design
Figure 29. Comparison of measured THD (%) between R Series (2018) (red) and R
Series with MAT (blue) as measured on an R11 enclosure without crossover at 90 dB
SPL at 1m

Low Frequency Drivers
Figure 26. Midrange frequency response FEA simula�on on an infinite baffle
showing the disappearance of the ‘dip’ caused by the suspension resonance around
950Hz

The low frequency drivers in R Series (Figure 30) provide
high output and low distor�on with high power handling

Midrange Cone Neck Decoupler

as well as pistonic mo�on well beyond their crossover
frequency.

The midrange cone is made from an aluminium alloy toensure low mass and high rigidity. This results in pistonic
behaviour throughout the passband, which is an
essen�al requirement of a high-performance driver
design. However, due to low internal damping,aluminium midrange cones typically break up in thetweeter frequency region, resul�ng in severe peaks inthe frequency response and direc�vity aberra�ons thatremain audible despite the low-pass crossover on the
midrange.

Figure 27. Behaviour of the Cone Neck Decoupler (highlighted in green) aroundtuning frequency

To avoid these issues, a lossy interface between thevoice coil and the cone called the Cone Neck Decoupler
has been tuned to disconnect, or decouple, them justbelow the break-up frequency (Figure 27). Figure 28
shows the effect of the Cone Neck Decoupler on the
midrange axial frequency response.

Figure 30. R Series LF driver

They employ a lightweight and highly rigid moving
structure comprising an aluminium diaphragm coupled
to the voice coil through a paper cone with an angle andcoupling radius op�mised to push the first break-up
frequency as high as 2.3kHz, by which point the driver

Midrange THD Performance

Figure 31. R11 Meta system inside view

output is a�enuated more than 30dB with respect to thesystem output.

Figure 29 shows a comparison of THD (%) between the2018 R Series midrange and the R Series with MAT
midrange, level-matched at 90dB at 1m, both measured
on an R11 enclosure without a crossover.

A sizeable 50mm (2”) voice coil is employed for highpower handling. The motor employs a highly saturated
undercut pole design to reduce inductance and its
Figure 28. Aluminium cone midrange axial frequency response with and without
Cone Neck Decoupler

associated distor�on and a wide central vent to reduce

12Constrained Layer Damping
One of the main goals in high-performance loudspeakerdesign is for all sound to emanate from the drivers, andnot from any other parts of the loudspeaker. Good
enclosure design is key to achieving this goal, as it must13

remain as inert as possible without reac�ng to excita�on
from the drivers.
At low frequencies, the whole enclosure tends to movein the opposite direc�on to the low frequency drivers’
diaphragms. To ameliorate this, the enclosure is built of
thick 25mm (1”) MDF and 30mm (1.18”) on the bo�omface and front baffle and anchored to the floor via four
protruding aluminium feet fi�ed with adjustable spikes.
The LF drivers are mounted on the front baffle and are
constrained at the back with a transverse brace and a
proprietary damping material layer, effec�vely couplingthem with the mass of the enclosure.
At higher frequencies, even thick enclosure panels tend
to flex and resonate like the walls of a musical string
instrument. To reduce this effect, the inside of theenclosure is heavily braced. However, bracing mostly
provides s�ffness and some mass to the panels. This
reduces the velocity of the resona�ng panels to someextent but mainly shi�s their resonance frequencies tohigher frequencies.

Adding resistance (damping) to a resona�ng system
reduces its velocity, just like a car suspension’s shock
absorber (damper) reduces the velocity of thesuspension’s resonance a�er a bump on the road. Figure
32 shows a diagram representa�on of a simple singledegree-of-freedom (SDOF) resona�ng system and its
associated fundamental resonance velocity behaviour toillustrate the effect of damping.

top layer while a layer of viscoelas�c damping material isused only in the interface area between the panels andthe braces (Figure 34). This layout outperforms lining theen�re inside area of the panels while making a more
efficient use of the material.
Figure 35 shows a comparison of an enclosure wall
vibra�on measurement with and without bracing
incorpora�ng Constrained Layer Damping. The velocityof the panel reflects the appropriate broadband
a�enua�on of panel resonances.

posi�oned away from the pressure nodes due to theirexterior arrangement, other techniques must be used.
Acous�c damping materials, like wadding or foam,provide a tortuous path for sound to travel through, i.e.
providing resistance (damping) to the air par�cles’
velocity.
When the air inside the enclosure is resona�ng, thedamping provided by the wadding is maximised when it
is posi�oned at the resonance’s highest velocity point.
This op�misa�on is relevant to avoid stuffing theenclosure with wadding in inefficient posi�ons which
reduce the enclosure’s internal volume, thus decreasing
low-frequency output with no other benefit.

Figure 33. Diagram of a constrained layer damping arrangement

The Reference white paper from 2014 provides adetailed descrip�on of the behaviour of standing waves
in enclosures and the effect of adding damping material
in different posi�ons within the enclosure [1].
Figure 36 depicts a simplified long enclosure closed atboth ends with a subop�mal asymmetric driver posi�onalong with the sound pressure and air par�cle velocity
profiles of the first longitudinal mode. The compromise
between driver posi�on and exci�ng and trea�ng thestanding wave can be visualised.
Figure 35. Enclosure wall vibra�on comparison when adding the Constrained Layer
Damping arrangement

Damping of standing wave
resonances

Figure 34. R11 Meta enclosure showing the bracing and viscoelas�c material
highlighted in orange forming the Constrained Layer Damping arrangement

Figure 32. Single-degree-of-freedom system and its velocity with and without
damping

To dissipate energy away from the resonances andreduce their amplitude, mechanical damping can beprovided by adding a layer of viscoelas�c material to thevibra�ng panel. An arrangement that is well known inacous�cs to deal with vibra�ng panels involves
employing a second layer of a s�ff material that
constrains the viscoelas�c one. This top layer causes
shearing of the viscoelas�c layer, increasing its damping
effect (Figure 33). Original research done during thedevelopment of LS50 [8] showed a similar effect can beachieved by using the cabinet braces as the constraining

14

Another type of resonance that can occur within speakerenclosures are acous�c standing waves. These acous�cresonances take place when the air inside the enclosure
resonates when excited by the driver at frequencies
whose wavelength is rela�vely small compared to theenclosure size. Due to the enclosure internal dimensions
and the posi�on of the drivers, one or several standing
waves may be excited, and they can easily colour thesound from the speaker as they escape into the room
through the driver diaphragm, ports, or by exci�ng theenclosure walls.
The most effec�ve way to mi�gate standing wave
resonances is to avoid exci�ng them in the first place.
This is achieved through posi�oning the driver at theresonances’ sound pressure nodes, i.e. where the soundpressure is zero. In cases where drivers must be

Figure 36. First standing wave mode shape in a long enclosure with closed ends

The arrangement and type of acous�c damping material
inside the midrange and low frequency cavi�es of R
Series with MAT has been re-op�mised to dampen
standing waves resul�ng in a perceivable sonicenhancement in the clarity of the upper bass andmidrange.
Figure 37 shows measurements of the R11 Meta LF
driver diaphragm velocity taken with a laser vibrometer15

Bass-reflex ports

with and without wadding inside the enclosure. The
glitches observable in the response at ~250Hz and
490Hz correspond to the first two longitudinal standing
waves and their disappearance is obvious when wadding
is added at strategic points. The further improvement
between R Series (2018) and R Series with MAT isshown as well.

Bass-reflex ports are very useful in passive
loudspeakers. At low frequency they are tuned to workin tandem with the LF drivers and the enclosure’s
acous�c volume to further extend the system’s bass
response and reduce driver displacement and thus
distor�on.
However, ports add complica�ons to a system, two of
which are air turbulence noise and leakage of enclosure
standing waves at higher frequency.
The noise from air turbulence is greatly reduced byop�mising the profile of the inner and outer port
opening flares through a Computer Fluid Dynamics(CFD) numerical simula�on (Figure 41).

Figure 38. Measured midrange cone velocity of R11 Meta showing the effect ofstanding waves and their improved damping

Figure 37. Measured LF cone velocity of R11 Meta showing the effect of standing
waves and their improved damping

Figure 38 shows a similar comparison for the midrange
driver for resonances occurring at 770Hz and 1.5kHz.
For R Series with MAT the midrange acous�c damping
has been changed from BAF wadding to high-density
Ethylene-vinyl acetate (EVA) copolymer foam to further
increase damping of the sharp resonance around
1.5kHz.

In R Series, the ports are located on the back of theenclosure so that their internal opening can be freely
posi�oned in loca�ons that minimise the leakage ofinternal acous�c resonances (Figure 42) (see Damping ofStanding Wave Resonances).

Even with a s�ff, heavy, and well damped enclosure, thehigh acous�c pressure of standing waves inside theenclosure can press against the enclosure walls like aballoon and make them vibrate, crea�ng a large radia�ng
surface for the resonance to efficiently transduce into
radiated sound.

Another challenge seldom discussed with ports are theirinherent tube-like resonances. These resonances arenaturally related to the size of the port ac�ng like a smallorgan pipe and at high frequencies, typically aroundmidrange, ports produce their own dis�nc�ve soundthat colours that of the drivers.

Figure 41. CFD model showing the effect of the computer-op�mised port flaregeometry on air turbulence

Figure 39. Measured surface velocity of cabinet wall outside midrange enclosure in
R11 Meta comparing the standing wave leakage with and without acous�c damping

Figure 39 shows a comparison of the velocity of thecabinet side wall of an R11 Meta outside the midrange
enclosure when foam is added while Figure 40 shows
the associated frequency response of the midrange(without crossover) where the successful treatment of
the standing waves is observable and the loss in lowfrequency response is minimal.

Figure 40. Measured frequency response of the midrange in R11 Meta (no crossover)comparing the standing wave leakage with and without acous�c damping (at 1m
distance)

16

Since the introduc�on of LS50, and improved during thedevelopment of the Reference Series, a mechanism has
been devised in which the wall of the tubular portsec�on is made from a flexible rubber that allows thewall to expand with the acous�c pressure of the port
resonances. Since rubber has high internal damping, itdissipates energy away from these resonances. This
results in a reduced acous�c output of the port
resonances, while the low-frequency behaviour of theport remains unaffected. Figure 43 shows themechanism of resonance damping through port flexible
walls.

Figure 42. System output simula�on showing the effect of op�mised port loca�on
on standing wave leakage

Figure 43. Pressure of the first resonance in a port with rigid walls (top) and flexible
walls (bo�om)

Crossover
The primary role of a crossover filter network is tocombine the output of the different drivers in a
speaker such that the transi�on between them issmooth in magnitude and phase and that they work intheir intended frequency range away from damage anddistor�on.

17

However, to maximise the communica�on of spa�alcues in a recording that enhances the realis�cpercep�on of the stereo image by the listener, aspeaker’s frequency response must be designed to besmooth on-axis as well as off-axis, both ver�cally andhorizontally. This is so that the room’s early reflectedsound has a tonal balance that is not abruptly dissimilar
to the speaker’s direct sound.
Therefore, a secondary but equally important func�onof the crossover is to help ensure this smooth transi�onoccurs in all direc�ons, not only on the speaker’s frontal
axis.

then rotated on a turntable and the measurement isrepeated every few degrees. This results in a sphere of
frequency response data that can be fed into thecomputer model and post-processed to produce
relevant acous�c metrics. These metrics then inform thecrossover design in terms of how the speaker’s
individual driver outputs are combined.
Figure 45 shows the crossover topology used across theseries consis�ng of a three-way network, except for R8
Meta which uses a different 2-way topology op�mised
for Dolby Atmos®.

To design such a crossover, it is necessary to simulate it
first through a virtual computer model of the crossovernetwork and feed it with measurements of the
impedance and anechoic frequency response of the LF,
MF and HF sec�ons playing individually.

smoother ver�cal and horizontal direc�vity averages.
These curves are special averages of the speaker’s offaxis response. As an example, Figures 46 and 47 show acomparison of the balance between R3 (2018) and R3
Meta, where a smoother result has been achieved.
The R3 Meta is a special case within the range as the LF
sec�on does not form a symmetrical arrangement
around the Uni-Q, since it has only one LF driver. For thisreason, the Uni-Q is mounted close to the top edge ofthe enclosure, and this results in a dip in its acous�cpower direc�vity index just above 2kHz. Designing acrossover considering only the axial responsesmoothness would result in a corresponding bump in the
acous�c power average. The studied approach,however, allows a dip in the axial response, priori�sing asmooth power average. This represents the approachrefined during the development of Reference Meta [8]as well as extensive listening tests in different rooms.

Figure 46. Axial frequency response, acous�c power average and acous�c power
average direc�vity index of R3 (2018) (red) vs. R3 Meta (blue)

System THD Performance
The aggregate outcome of the improvements outlined in
the previous sec�ons can be somewhat summarised in
the system’s total harmonic distor�on. Figure 48 shows
a comparison of THD (%) at 90dB SPL matched at 500Hz
at 1m distance between R11 (2018) and R11 Meta. The
full audible frequency band is shown to highlight theresults from the mul�ple improvements in the system.

Figure 45. Main crossover topology for R Series with MAT (3-way models)The new topology simplifies the tweeter filter toimprove the system’s direc�vity, uses a single seriescapacitor C2 in the MF branch, and only uses C3 in the
LF branch in some models to help tailor their direc�vity
across LF to MF.

Figure 44. Representa�on of the measurement data acquisi�on system in KEF’s
anechoic chamber

Figure 44 shows a 3D representa�on of themeasurement data acquisi�on system used in KEF’s
anechoic chamber. An array of omnidirec�onal
microphones captures the anechoic frequency responseof the speaker at various ver�cal angles. The speaker is

The tweeter series capacitor (C1) has been upgraded toa be�er design Polypropylene film one with a thicker
film, lower resistance contact layer (schoopage), lower
resistance terminals and a thicker outer damping layer.
Where possible, air core inductors have been used andall cored inductors have a laminated steel core of a
specially selected grade to reduce THD.
In R Series with MAT the overall frequency response anddirec�vity smoothness have been further improved. To
improve direc�vity, priority has been assigned toobtaining a smoother acous�c power average and18

The measurements show the reduced harmonic
distor�on across the high frequency band covered by
the tweeter, the very low distor�on across the midrange
passband (~0.1%), the disappearance of the glitch at
950Hz associated with the MF suspension resonance,
the suppression of the bump around 250Hz due to thelower distor�on midrange motor and a broad
improvement to the LF sec�on mainly due to thecrossover design.

Figure 47. Horizontal (top) and ver�cal (bo�om) response average of R3 (2018) (red)vs. R3 Meta (blue)

Summary
The R Series was originally introduced as a more
affordable op�on to the Reference Series while directly
benefi�ng from the research conducted during thedevelopment of KEF’s highest performance ranges.
The R Series with MAT carries on this legacy byintegra�ng numerous acous�c innova�ons, resul�ng in
objec�vely be�er performance in the laboratory and a

Figure 48. Comparison of THD (%) between R11 (2018) (red) and R11 Meta (blue) at
90dB SPL matched at 500Hz at 1m

19

more realis�c and engaging musical reproduc�on experiencein the listening room.
This paper aims to provide insight into the development
process of these innova�ons by explaining their engineeringand suppor�ng its arguments with results from computer
simula�ons and laboratory measurements.
The tweeter metamaterial absorber, innova�ve drivers,
enclosure acous�cal behaviour, and new crossover filter
networks together combine to result in a loudspeaker range
with a much higher capability for faithful and engaging
musical reproduc�on.

References[1]“The Reference (White Paper).” KEF R&D,
Apr. 2014. [Online][2]“R Series 2018 (White Paper).” KEF R&D, Oct.
2018. [Online][3]

M. Dodd and J. Oclee-Brown, “A New Methodology
for the Acous�c Design of Compression Driver
Phase Plugs with Radial Channels”, 125th Audio
Eng. Soc. Conven�on, 2008

[4]

S. Degraeve and J. Oclee-Brown, “Metamaterial
Absorber for Loudspeaker Enclosures”, 148th Audio
Eng. Soc. Conven�on 2020

[5]

“LS50 Collec�on (White Paper).” KEF R&D, Sep.
2020 [Online][6]

M. Dodd, “Optimum Diaphragm and Waveguide
Geometry for Coincident source Drive Units”,
121st Audio Eng. Soc. Conven�on 2006

[7]

“Blade/The Reference with MAT (White Paper).”
KEF R&D, Feb. 2022. [Online][8]“LS50 (White Paper).” KEF R&D, Sep. 2011.
[Online]20

21

R11 Meta
Three-way Floorstanding Loudspeaker

R11 Meta Spinorama

Technical Specifica�ons
SystemDrive units

Three-way bass reflex
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone
Bass Drivers:

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on
2nd & 3rd harmonics (90dB, 1m)

Maximum output

R Series Meta
Model Informa�on, Specifica�ons andMeasurements22

LF: 4 x 165mm (6.5 in.)hybrid aluminium cone
30Hz - 50kHz
26Hz
46Hz - 28kHz
330Hz, 2.5kHz
15-300W
90dB<1% 33Hz and above<0.5% 80Hz - 20kHz(Peak sound pressure level at
1m with pink noise)

113dB

Impedance

4 Ω (min. 3.2 Ω

WeightDimensions with plinth(H x W x D)

36.5kg (80.5 lbs)
1296 x 311 x 384 mm(51.0 x 12.2 x 15.1 in.)

R11 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

23

R7 Meta

R5 MetaThree-way Floorstanding Loudspeaker

Three-way Floorstanding Loudspeaker

R7 Meta Spinorama

R5 Meta Spinorama

Technical Specifica�ons

Technical Specifica�ons
SystemDrive units

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on
2nd & 3rd harmonics (90dB, 1m)

Maximum output

SystemThree-way bass reflex
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone

Drive units

Three-way bass reflex
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone

Bass Drivers:

Bass Drivers:

LF: 2 x 165mm (6.5 in.)hybrid aluminium cone
33Hz - 50kHz

LF: 2 x 130mm (5.25 in.)hybrid aluminium cone
38Hz - 50kHz

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on

27Hz
48Hz - 28kHz
400Hz, 2.4kHz
15-250W
88dB<1% 76Hz and above<0.5% 110Hz - 20kHz(Peak sound pressure level at
1m with pink noise)

111dB

Impedance
WeightDimensions with plinth(H x W x D)

2nd & 3rd harmonics (90dB, 1m)

Maximum output

29Hz
52Hz - 28kHz
400Hz, 2.7kHz
15-200W
87dB<1% 75Hz and above<0.5% 110Hz - 20kHz(Peak sound pressure level at
1m with pink noise)

110dB

4 Ω (min. 3.2 Ω)

Impedance

4 Ω (min. 3.2 Ω)

29.3kg (64.6 lbs)
1109 x 311 x 384 mm(43.7 x 12.2 x 15.1 in.)

WeightDimensions with plinth(H x W x D)

24.5kg (54.0 lbs)
1025 x 272 x 344 mm(42.2 x 10.7 x 13.5 in.)R7 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

24

R5 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

25

R3 Meta

R6 MetaThree-way Bookshelf Loudspeaker

Three-way Centre Loudspeaker

R3 Meta Spinorama

R6 Meta Spinorama

Technical Specifica�ons

Technical Specifica�ons
SystemDrive units

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on
2nd & 3rd harmonics (90dB, 1m)

Maximum output

Three-way bass reflex
Uni-Q Driver Array:

System

HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone

Drive units

Three-way bass reflex
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone

Bass Driver:Bass Drivers:

LF: 165mm (6.5 in.)hybrid aluminium cone
38Hz - 50kHz

LF: 2 x 165mm (6.5 in.)hybrid aluminium cone
55Hz - 50kHz

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on

30Hz
58Hz - 28kHz
420Hz, 2.3kHz
15-180W
87dB<1% 73Hz and above<0.5% 90Hz - 20kHz(Peak sound pressure level at
1m with pink noise)

110dB

Impedance
WeightDimensions with plinth(H x W x D)

2nd & 3rd harmonics (90dB, 1m)

Maximum output

40Hz
65Hz - 28kHz
550Hz, 2.4kHz
15-250W
88dB<1% 65Hz and above<0.5% 93Hz - 20kHz(Peak sound pressure level at
1m with pink noise)111dB

4 Ω (min. 3.2 Ω)

Impedance

4 Ω (min. 3.2 Ω)

12.4kg (27.3 lbs)
422 x 200 x 336 mm(16.6 x 7.9 x 13.2 in.)

WeightDimensions with plinth(H x W x D)

17.8kg (39.2 lbs)
200 x 625 x 339 mm(7.9 x 24.6 x 13.3 in.)R3 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

26

R6 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

27

R2 Meta

R8 MetaThree-way Centre LoudspeakerTwo-way surround/Dolby Atmos
Loudspeaker

R2 Meta Spinorama

Technical Specifica�ons

Technical Specifica�ons
SystemDrive units

SystemThree-way bass reflex
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF: 125 mm (5 in.)aluminium cone

Drive units

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on
2nd & 3rd harmonics (90dB,
1m)
Maximum output(Peak sound pressure level at
1m with pink noise)
ImpedanceBass Drivers:

Frequency range free-field(-6dB)
Typical in-room bass
response (-6dB)
Frequency response(±3dB)
Crossover frequencies
Recommended amplifier
power
Sensi�vity (2.83V/1m)
Harmonic distor�on
2nd & 3rd harmonics (90dB, 1m)

Maximum output

LF: 2 x 130mm (5.,25 in.)hybrid aluminium cone
58Hz - 50kHz
43Hz
67Hz - 28kHz
560Hz, 2.5kHz
15-200W
87dB<1% 84Hz and above<0.5% 95Hz - 20kHz(Peak sound pressure level at
1m with pink noise)

110dB

Impedance

4 Ω (min. 3.2 Ω)

WeightDimensions with plinth(H x W x D)

15.4kg (34.0 lbs)
175 x 550 x 309 mm(6.9 x 21.7 x 12.2 in.)

WeightDimensions with plinth(H x W x D)

R2 Meta direc�vity contours - horizontal (top) and ver�cal (middle) - andimpedance (bo�om)

Two-way closed box
Uni-Q Driver Array:
HF: 25 mm (1 in.) aluminium
dome with MAT
MF/LF: 130 mm (5.25 in.)aluminium cone
88Hz - 19.5kHz
97Hz - 17.5kHz
2.6kHz25-150W
85dB<1% 220Hz and above<0.5% 320Hz - 20kHz
106dB
4 Ω (min. 3.2 Ω)
4.5kg (9.9 lbs)
174 x 175 x 259 mm(6.9 x 6.9 x 10,2 in.)R8 Meta impedance

28

29