In this review, we will be comparing LSX II and Navis ARB-51, two Powered Bookshelf speakers from KEF and ELAC. 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 KEF LSX II and ELAC Navis ARB-51 first before getting into our more
detailed comparison.
| Key Specs | KEF LSX II | ELAC Navis ARB-51 |
|---|
| Brand | KEF
United Kingdom · founded 1961 | ELAC
Germany · founded 1926 |
|---|
| Design | 2-way | 3-way |
|---|
| Built-in amplifier | 200-watt RMS | 300-watt RMS (600-watt peak) |
|---|
| Uni-Q driver | 11th Generation Uni-Q | — |
|---|
| Tweeter | 0.75" Hard-Dome | 1" Soft-Dome |
|---|
| Midrange | — | 4" |
|---|
| Woofer | 4.5" Magnesium/Aluminium alloy | 5.25" Aluminum |
|---|
| Frequency response | 54-28k Hz | 44-28k Hz |
|---|
| Max depth / sample rate | 24-bit / 384 kHz | — |
|---|
| Bluetooth | Built-in 4.2 | Optional |
|---|
| App control | Yes | — |
|---|
| Weight | 3.60kg / 7.9lbs | 8.10kg / 17.8lbs |
|---|
| Dimensions (H x W x D) | 9.5" x 6.1" x 7.1"
240 × 155 × 180 mm | 13.8125" x 7.5625" x 11.3125"
350.8 x 192.1 x 287.3mm |
|---|
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
One of the fundamental differences between these two speakers is that LSX II is a 2-way design whereas the Navis ARB-51 is a 3-way speaker. 3-way designs utilize a midrange driver in addition to the tweeter and woofer on 2-way designs. Designing a crossover for a 3-way speaker is a complicated process and generally increases the overall cost of the speaker.
KEF LSX IIELAC Navis ARB-51
TweeterMidrangeWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
KEF LSX II |
ELAC Navis ARB-51 |
|
Driver Setup
|
2-way
|
3-way
|
|
Tweeter
|
0.75-inch
|
1-inch
|
|
Midrange
|
- |
1 x 4-inch |
|
Woofer
|
1 x 4.5-inch
|
1 x 5.25-inch
|
LSX II features a 0.75" Aluminum Hard-Dome Tweeter and 1 x 4.5" Magnesium/Aluminium alloy Woofer. On the other hand, the Navis ARB-51 features a 1" Fabric Soft-Dome Tweeter, a 4" Midrange and 1 x 5.25" Aluminum Woofer.
Frequency Response
LSX II has a frequency range of 54-28k Hz whereas Navis ARB-51 has a frequency range of 44-28k Hz. With a minimum frequency of 44Hz, the Navis ARB-51 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 LSX II and Navis ARB-51 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.
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 KEF LSX II's and ELAC Navis ARB-51's external dimensions. KEF LSX II has external dimensions of 240 × 155 × 180 mm (9.5 × 6.1 × 7.1 inch) whereas ELAC Navis ARB-51 has external dimensions of 350.8 x 192.1 x 287.3mm (13.8125 x 7.5625 x 11.3125inch).
ELAC Navis ARB-51 is clearly the larger of the two speakers. Its body is 37.1mm wider, 110.8mm taller and 107.3mm deeper than KEF LSX II.
Below you can see the front view size comparison of KEF LSX II and ELAC Navis ARB-51 in scale.
Comparison image of KEF LSX II and ELAC Navis ARB-51 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 KEF LSX II is approximately 279.0cm2 / 43.2inch2 and base area of the ELAC Navis ARB-51 is approximately 551.9cm2 / 85.5inch2. The LSX II requires 49% less surface area than the Navis ARB-51 which gives it a small advantage 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 KEF LSX II and ELAC Navis ARB-51 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 KEF LSX II weighs 3.60kg / 7.9lbs and the ELAC Navis ARB-51 weighs 8.10kg / 17.8lbs. This makes the Navis ARB-51 125% heavier than the LSX II.
Here is a comparison of how LSX II and Navis ARB-51's weights compare with the average, max and min weights in Powered Bookshelf class.
Weight
All Bookshelf Speakers
What's in the Box of KEF LSX II?
Here are the items that are included inside the box of 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
What's in the Box of ELAC Navis ARB-51?
Here are the items that come with the Navis ARB-51:
- 2 Powered bookshelf loudspeakers
- Two 8-feet AC power cords
- Operating Instructions
 Handheld Remote |
Yes
vs
No
|
Control the speaker by the included RC |
 App-Based Control |
Apple iOS, Android
vs
None
|
Control the speaker via an app |
 Height |
240mm
vs
350mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
279cm2
vs
551cm2
|
Takes less floor space |
 Price per pair* |
1299USD
vs
1998USD
|
costs less (*prices may change depending on the seller, location and time) |
 Ethernet Connection |
Yes
vs
No
|
High quality streaming over Ethernet |
 USB Port |
USB-C (connects to your computer)
vs
No
|
USB port adds flexibility |
 3.5mm Connection |
Yes
vs
No
|
Connection via 3.5mm AUX input |
 Digital Input |
Optical
vs
No
|
Connect digital inputs directly |
 HDMI Input |
ARC
vs
No
|
Connect HDMI sources directly |
 Subwoofer Output |
Wired
vs
No
|
Pair your speakers with external subwoofer |
 Driver Setup |
3-way
vs
2-way
|
Have a dedicated mid-range driver |
 Woofer Size |
5.25 inches
vs
4.5 inches
|
Larger woofer |
|
Low Frequency Response |
44 Hz
vs
54 Hz
|
Generates deeper bass |
 RCA Connection |
Yes
vs
No
|
Connection via RCA input |
 XLR Connection |
Yes
vs
No
|
Connection via XLR input |
| General |
KEF LSX II |
ELAC Navis ARB-51 |
| Brand |
KEF |
ELAC |
| Speaker Type |
Powered Stereo Speakers |
Powered Stereo Speakers |
| Frequency Response |
54-28k Hz |
44-28k Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
200-watt RMS |
300-watt RMS |
| Watts Peak (Max) |
n/a |
600-watt RMS |
| Max Bit Depth |
24-bit |
n/a |
| Max Sample Rate |
384 kHz |
n/a |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
4.5" |
5.25" |
| Woofer Composition |
Magnesium/Aluminium alloy |
Aluminum |
| Woofer Surround Material |
Rubber |
n/a |
| Tweeter Size |
0.75" |
1" |
| Tweeter Type |
Hard-Dome |
Soft-Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
4" |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
240.0mm (9.4") |
350.8mm (13.8") |
| Width |
155.0mm (6.1") |
192.1mm (7.6") |
| Depth |
180.0mm (7.1") |
287.3mm (11.3") |
| Weight |
3.60kg (7.9lbs) |
8.10kg (17.8lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Available Colors |
Carbon Black, Mineral White, Cobalt Blue, Lava Red, and Soundwave |
n/a |
| Mounting Bracket |
No |
No |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Aux Inputs |
3.5mm |
XLR, RCA |
| USB Port |
USB-C (connects to your computer) |
No |
| Phone Input |
No |
No |
| Subwoofer Output |
Wired |
No |
| Digital Input |
Optical |
No |
| HDMI Input |
ARC |
No |
| Headphone Jack |
No |
No |
| Ethernet Port |
Yes |
No |
Other |
|
|
| Parts Warranty |
1 Year |
3 Years |
| Labor Warranty |
1 Year |
3 Years |
A generation apart: KEF LSX II is the newer design, against a 2018 model. Newer is not automatically better, but the older one is more likely to be discounted or near run-out.
| Area | Better | Why |
|---|
| Bass | B | ELAC Navis ARB-51 digs deeper - 44Hz against 54Hz. |
| Built-in power | B | ELAC Navis ARB-51 has the bigger amplifier (300W vs 200W RMS). |
| Connections | A | KEF LSX II adds Wi-Fi, streaming, HDMI and digital inputs. |
| Size | depends | KEF LSX II is easier to place; ELAC Navis ARB-51 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | A | KEF LSX II: a sub output. KEF LSX II sits in a wider range (10 models), so a matched surround system is easier later. |
| Price | A | KEF LSX II is cheaper - $1,299 against $1,998, about 35% less. |
A KEF LSX II B ELAC Navis ARB-51
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and your own room settle it. 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, ELAC Navis ARB-51 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.