In this review, we will be comparing Duetto and LSX II, two Powered Bookshelf speakers from Sonus faber and KEF. Being Powered speakers, they both have built-in amplifiers so you don't need an external power amp or an integrated amp to power them.
Let's have a brief look at the main features
of Sonus faber Duetto and KEF LSX II first before getting into our more
detailed comparison.
| Key Specs | Sonus faber Duetto | KEF LSX II |
|---|
| Brand | Sonus faber
Italy · founded 1983 | KEF
United Kingdom · founded 1961 |
|---|
| Design | 2-way | 2-way |
|---|
| Built-in amplifier | 700-watt RMS | 200-watt RMS |
|---|
| Uni-Q driver | — | 11th Generation Uni-Q |
|---|
| Tweeter | 1.1" Soft-Dome | 0.75" Hard-Dome |
|---|
| Woofer | 5.25" Paper-Pulp | 4.5" Magnesium/Aluminium alloy |
|---|
| Frequency response | 37-30k Hz | 54-28k Hz |
|---|
| Max depth / sample rate | 24-bit / 192 kHz | 24-bit / 384 kHz |
|---|
| Bluetooth | Built-in 5.0 | Built-in 4.2 |
|---|
| App control | Yes | Yes |
|---|
| Weight | 6.80kg / 15lbs | 3.60kg / 7.9lbs |
|---|
| Dimensions (H x W x D) | 13.4375" x 8.3125" x 11.0625"
342.0 x 212.0 x 281.0mm | 9.5" x 6.1" x 7.1"
240 × 155 × 180 mm |
|---|
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
Both Duetto and LSX II are 2-way speakers.
Sonus faber DuettoKEF LSX II
TweeterWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
Sonus faber Duetto |
KEF LSX II |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1.1-inch
|
0.75-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 4.5-inch
|
Duetto features a 1.1" Silk Soft-Dome Tweeter and 1 x 5.25" Paper-Pulp Woofer. On the other hand, the LSX II features a 0.75" Aluminum Hard-Dome Tweeter and 1 x 4.5" Magnesium/Aluminium alloy Woofer.
Frequency Response
Duetto has a frequency range of 37-30k Hz whereas LSX II has a frequency range of 54-28k Hz. With a minimum frequency of 37Hz, the Duetto can go significantly deeper on the low side and provide stronger bass compared to the LSX II's min frequency of 54Hz.
The graph below depicts how these two speakers compare with the max, min and average Low Frequency values of other speakers in the Bookshelf class in our database.
Low Frequency
Bookshelf Speakers
Neither pair reaches down to 20Hz, the usual definition of full-range, which is normal for speakers of this size. If you want the bottom octave for movies or bass-heavy music, add a subwoofer to whichever you choose. Visit our Powered Subwoofers section to find out more about the available options.
Cabinet Type and Port Position
Both Duetto and LSX II have rear firing ports. Rear ported speakers generally need more room between the backside of the speaker and the wall compared to sealed and front/bottom ported speakers. Placing the speakers too close to the walls may cause the bass to sound boomy.
If you are limited in space and can't get the speakers away from the backwall, check our Speakers with Front Firing Ports page.
Sonus faber Duetto Port
KEF LSX II Port
Physical Specs
The size of a speaker can sometimes be an important decision factor due to space constraints or in some cases purely for esthetic reasons. In this section, we are going to compare Sonus faber Duetto's and KEF LSX II's external dimensions. Sonus faber Duetto has external dimensions of 342.0 x 212.0 x 281.0mm (13.4375inch x 8.3125inch x 11.0625inch) whereas KEF LSX II has external dimensions of 240 × 155 × 180 mm (9.5 × 6.1 × 7.1 inch).
Sonus faber Duetto is clearly the larger of the two speakers. Its body is 57mm wider, 102mm taller and 101mm deeper than KEF LSX II.
Below you can see the front view size comparison of Sonus faber Duetto and KEF LSX II in scale.
Comparison image of Sonus faber Duetto and KEF LSX II Size and External Dimensions
Base Surface Area Comparison
Base surface area of a loudspeaker may become a determining factor when the space in your room or desk is limited.
The base surface area of the Sonus faber Duetto is approximately 595.7cm2 / 92.3inch2 and base area of the KEF LSX II is approximately 279.0cm2 / 43.2inch2. The Duetto requires 114% more surface area than the LSX II which gives it a small disadvantage on placement in tight spaces.
Here is another comparison that shows both speakers on a BDI Octave Media Cabinet, next to a standard size amplifier and turntable in scale:
Size Comparison image of Sonus faber Duetto and KEF LSX II on a Media Console
Weight Comparison The weight of a loudspeaker can become an important factor if you need to move and reposition the unit often. Weight of a speaker can also "sometimes" be an indicator of the rigidity of the enclosure and the quality of the internal components used. The Sonus faber Duetto weighs 6.80kg / 15lbs and the KEF LSX II weighs 3.60kg / 7.9lbs. This makes the Duetto 89% heavier than the LSX II.
Here is a comparison of how Duetto and LSX II's weights compare with the average, max and min weights in Powered Bookshelf class.
Weight
All Bookshelf Speakers
What's in the Box of Sonus faber Duetto?
Here are the items that are included inside the box of Duetto:
- 2 Wireless powered speakers
- 2 Grilles
- Two 6.5-feet AC power cords
- Remote control
- Quick Start Guide
- Safety Instructions
What's in the Box of KEF LSX II?
Here are the items that come with the LSX II:
- 2 Wireless powered speakers
- Two 6.5-feet AC power cords
- 10-feet Cat-6 interconnect speaker cable
- Remote control
- 2 AAA batteries
- Quick Start Guide
- Important Safety Information
- Warranty Information
- Maintenance Guide
 Woofer Size |
5.25 inches
vs
4.5 inches
|
Larger woofer |
|
Low Frequency Response |
37 Hz
vs
54 Hz
|
Generates deeper bass |
 High Frequency Response |
30k Hz
vs
28k Hz
|
Generates higher frequency |
 RCA Connection |
Yes
vs
No
|
Connection via RCA input |
 Height |
240mm
vs
342mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
279cm2
vs
595cm2
|
Takes less floor space |
 Price per pair* |
1299USD
vs
3999USD
|
costs less (*prices may change depending on the seller, location and time) |
 3.5mm Connection |
Yes
vs
No
|
Connection via 3.5mm AUX input |
| General |
Sonus faber Duetto |
KEF LSX II |
| Brand |
Sonus faber |
KEF |
| Speaker Type |
Powered Stereo Speakers |
Powered Stereo Speakers |
| Frequency Response |
37-30k Hz |
54-28k Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
700-watt RMS |
200-watt RMS |
| Max Bit Depth |
24-bit |
24-bit |
| Max Sample Rate |
192 kHz |
384 kHz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
4.5" |
| Woofer Composition |
Paper-Pulp |
Magnesium/Aluminium alloy |
| Woofer Surround Material |
n/a |
Rubber |
| Tweeter Size |
1.1" |
0.75" |
| Tweeter Type |
Soft-Dome |
Hard-Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
342.0mm (13.5") |
240.0mm (9.4") |
| Width |
212.0mm (8.3") |
155.0mm (6.1") |
| Depth |
281.0mm (11.1") |
180.0mm (7.1") |
| Weight |
6.80kg (15lbs) |
3.60kg (7.9lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Available Colors |
Black,Walnut |
Carbon Black, Mineral White, Cobalt Blue, Lava Red, and Soundwave |
| Mounting Bracket |
No |
No |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Aux Inputs |
RCA |
3.5mm |
| USB Port |
Service only |
USB-C (connects to your computer) |
| Phone Input |
No |
No |
| Subwoofer Output |
mono-RCA |
Wired |
| Digital Input |
Optical |
Optical |
| HDMI Input |
eARC |
ARC |
| Headphone Jack |
No |
No |
| Ethernet Port |
Yes |
Yes |
Other |
|
|
| Parts Warranty |
2 Yrs (3 Yrs registered) |
1 Year |
| Labor Warranty |
2 Yrs (3 Yrs registered) |
1 Year |
These sit in different price classes - Sonus faber Duetto costs roughly 3.1x what KEF LSX II does. Expect it to lead on paper; the question is whether the gap is audible enough in your room to be worth it.
| Area | Better | Why |
|---|
| Bass | A | Sonus faber Duetto digs deeper - 37Hz against 54Hz. |
| Built-in power | A | Sonus faber Duetto has the bigger amplifier (700W vs 200W RMS). |
| Connections | evenly matched | The same set of inputs and streaming options. |
| Size | depends | KEF LSX II is easier to place; Sonus faber Duetto is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Sonus faber Duetto: a sub output; KEF LSX II: a sub output. |
| Price | B | KEF LSX II is cheaper - $1,299 against $3,999, about 68% less; arguably a different class. |
A Sonus faber Duetto B KEF LSX II
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
The usual trade-off: Sonus faber Duetto measures better, KEF LSX II costs about about 3.1x the price% less. Whether that gap is worth the money is the call only you can make - and in a normal room it is often smaller than the numbers suggest. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 54Hz anyway, which makes the cheaper KEF LSX II much easier to justify. In a large or open-plan room, Sonus faber Duetto has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, KEF LSX II is the easier speaker to get right.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.