In this review, we will be comparing Motion XT B100 and R3, two Passive Bookshelf speakers from MartinLogan and KEF.
Let's have a brief look at the main features
of MartinLogan Motion XT B100 and KEF R3 first before getting into our more
detailed comparison.
| Key Specs | MartinLogan Motion XT B100 | KEF R3 |
|---|
| Brand | MartinLogan
United States · founded 1982 | KEF
United Kingdom · founded 1961 |
|---|
| Design | 2-way | 3-way |
|---|
| Uni-Q driver | — | 12th Generation Uni-Q |
|---|
| Tweeter | 1.25 x 2.4" Folded Motion XT | 1" Dome |
|---|
| Midrange | — | 5" |
|---|
| Woofer | 6.5" Kevlar | 6.5" Hybrid aluminum |
|---|
| Frequency response | 45-25k Hz | 52-28k Hz |
|---|
| Sensitivity | 93 dB | 87 dB |
|---|
| Impedance | 4 ohms | 8 ohms |
|---|
| Power range | 20-250 watts | 15-180 watts |
|---|
| Weight | 9.30kg / 20.5lbs | 13.55kg / 29.8lbs |
|---|
| Dimensions (H x W x D) | 14-1/2" x 8" x 12-1/2"
368 x 203 x 318mm | 16-5/8" x 7-13/16" x 13-1/4"
423.0 x 199.0 x 337.0mm |
|---|
What size room are the MartinLogan Motion XT B100 and KEF R3 speakers good for?
The size of the room in which you are planning to use these loudspeakers is an important decision
factor. Here we have compared their suitability to various sizes of environments considering their size
and max power parameters:
| Listening Environment* |
MartinLogan Motion XT B100 |
KEF R3 |
| Near-field |
Poor |
Poor |
| Small Room |
Poor |
Average |
| Mid-size Room |
Good |
Good |
| Large Room |
Good |
Average |
| Very Large Room |
Average |
Poor |
(* Approximate Room sizes: Small < 100sq. ft / 9 m2,
Mid-size: 100-220 sq. ft / 9-20 m2, Large 220-400 sq. ft / 20-36 m2, Very Large: >
400 sq. ft / 36 m2.
Average Floor Height: 9" / 2.7m. Typical room sizes differ from country to country, and the actual
listening experience changes depending on floor height, room shape, surface materials, listening
position, speaker locations, etc.)
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 Motion XT B100 is a 2-way design whereas the R3 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.
MartinLogan Motion XT B100KEF R3
TweeterMidrangeWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
MartinLogan Motion XT B100 |
KEF R3 |
|
Driver Setup
|
2-way
|
3-way
|
|
Tweeter
|
1.25 x 2.4-inch
|
1-inch
|
|
Midrange
|
- |
1 x 5-inch |
|
Woofer
|
1 x 6.5-inch
|
1 x 6.5-inch
|
Motion XT B100 features a 1.25 x 2.4" Folded Motion XT Tweeter and 1 x 6.5" Kevlar Woofer with a Crossover frequency at 2600Hz. On the other hand, the R3 features a 1" aluminum Dome Tweeter, a 5" Midrange and 1 x 6.5" Hybrid aluminum Woofer with a Crossover frequency at 400Hz and 2900Hz.
Frequency Response
Motion XT B100 has a frequency range of 45-25k Hz whereas R3 has a frequency range of 52-28k Hz. With a minimum frequency of 45Hz, the Motion XT B100 can go significantly deeper on the low side and provide stronger bass compared to the R3's min frequency of 52Hz.
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.
Impedance and Sensitivity
Motion XT B100 is a 4 ohms speaker compared to the R3 which has a nominal impedance of 8 ohms. Lower impedance speakers, especially the ones that are rated at 4 ohms may put more pressure on the amplifier unit especially when played at high volume levels, so make sure the amp you pair with the Motion XT B100 can provide this impedance level.
These two speakers also have different sensitivity levels. Motion XT B100 sensitivity is rated at 93 dB and the R3's is rated at 87 dB. This 6 dB difference makes the MartinLogan Motion XT B100 a more sensitive speaker compared to KEF R3, hence will play louder with the same amount of watts.
Sensitivity
Bookshelf Speakers
Power Range
Power
range is the range of input power in watts RMS that a loudspeaker is designed to handle. Staying
within that range gives nominal performance; driving the speaker beyond its maximum wattage can damage it.
Motion XT B100 can handle a max power of 250 watts RMS, whereas R3 has a max power handling value of 180 watts RMS, 70 watts less than the Motion XT B100.
Note that higher power handling does not make a speaker louder: that depends mainly on
sensitivity and impedance. The calculator below shows how loud each of these actually plays
on a real amplifier.
Which plays louder on your amplifier?
Starting with a popular amplifier - change it to the one you own, or any you are
considering, and watch both numbers move.
MartinLogan Motion XT B100
Input Type and Bi-Amping / Bi-Wiring
Both Motion XT B100 and R3 features dual binding post speaker terminals for bi-amping or bi-wiring.
MartinLogan Motion XT B100's Custom 5-way bi-wire tool-less binding posts terminals allows Bi-amping or bi-wiring
Cabinet Type and Port Position
Both Motion XT B100 and R3 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 R3 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 MartinLogan Motion XT B100's and KEF R3's external dimensions. MartinLogan Motion XT B100 has external dimensions of 368 x 203 x 318mm (14-1/2-inch x 8inch x 12-1/2inch) whereas KEF R3 has external dimensions of 423.0 x 199.0 x 337.0mm (16-5/8 x 7-13/16 x 13-1/4inch).
MartinLogan Motion XT B100 is 55mm shorter and 19mm less deeper than KEF R3 but it is also 4mm wider.
Below you can see the front view size comparison of MartinLogan Motion XT B100 and KEF R3 in scale.
Comparison image of MartinLogan Motion XT B100 and KEF R3 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 MartinLogan Motion XT B100 is approximately 645.5cm2 / 100.1inch2 and base area of the KEF R3 is approximately 670.6cm2 / 103.9inch2. The Motion XT B100 requires 4% less surface area than the R3 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 MartinLogan Motion XT B100 and KEF R3 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 MartinLogan Motion XT B100 weighs 9.30kg / 20.5lbs and the KEF R3 weighs 13.55kg / 29.8lbs. This makes the R3 46% heavier than the Motion XT B100.
Here is a comparison of how Motion XT B100 and R3's weights compare with the average, max and min weights in Passive Bookshelf class.
Weight
All Bookshelf Speakers
MartinLogan Motion XT B100
What's in the Box of KEF R3?
Here are the items that come with the R3:
- 2 Bookshelf loudspeakers
- 2 Grilles
- 2 Foam port plugs
- 8 Self-adhesive rubber feet
- User Manual
- Warranty Information
 Max Input Power |
250 watts
vs
180 watts
|
Handle more power from your amplifier |
 Sensitivity |
93 dB
vs
87 dB
|
Play louder with same amount of amplification power |
 Low Frequency Response |
45 Hz
vs
52 Hz
|
Generates deeper bass |
 Height |
368mm
vs
423mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
645cm2
vs
670cm2
|
Takes less floor space |
 Price per pair* |
1598USD
vs
2200USD
|
costs less (*prices may change depending on the seller, location and time) |
 Driver Setup |
3-way
vs
2-way
|
Have a dedicated mid-range driver |
 Nominal Impedance |
8 ohms
vs
4 ohms
|
Less selective with amplifiers |
 High Frequency Response |
28k Hz
vs
25k Hz
|
Generates higher frequency |
| General |
MartinLogan Motion® XT B100 |
KEF R3 |
| Brand |
MartinLogan |
KEF |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-250 watts |
15-180 watts |
| Sensitivity |
93 dB |
87 dB |
| Impedance |
4 ohms |
8 ohms |
| Impedance |
n/a |
3.2 ohms |
| Frequency Response |
45-25k Hz |
52-28k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6.5" |
6.5" |
| Woofer Composition |
Kevlar |
Hybrid aluminum |
| Woofer Surround Material |
Rubber |
Rubber |
| Tweeter Size |
1.25 x 2.4" |
1" |
| Tweeter Type |
Folded Motion XT |
Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
5" |
| Crossover Frequency |
2600Hz |
400Hz and 2900Hz |
| Firing Direction |
rear |
rear |
| Suggested Break-in Period |
Allow 72 hours of break-in |
n/a |
Physical Specs |
|
|
| Height |
368.0mm (14.5") |
423.0mm (16.7") |
| Width |
203.0mm (8") |
199.0mm (7.8") |
| Depth |
318.0mm (12.5") |
337.0mm (13.3") |
| Weight |
9.30kg (20.5lbs) |
13.55kg (29.8lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
MDF/Wood veneer |
MDF/Lacquer |
| Available Colors |
Gloss Black, Walnut, and Satin White |
Black Gloss, White Gloss, Walnut |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
24-28" |
n/a |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
Yes |
Yes |
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
A generation apart: MartinLogan Motion XT B100 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 | A | MartinLogan Motion XT B100 digs deeper - 45Hz against 52Hz. A subwoofer would even that out. |
| Amplifier needs | A | MartinLogan Motion XT B100 is more sensitive (93dB vs 87dB), so it goes louder on the same amplifier. |
| Amplifier match | B | KEF R3 is the easier load at 8 ohms; the other is 4 ohms and wants an amplifier rated for it. |
| Headroom | A | MartinLogan Motion XT B100 takes more power (250W vs 180W) - more in hand in a big room. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | depends | MartinLogan Motion XT B100: bi-amping; KEF R3: bi-amping. |
| Price | A | MartinLogan Motion XT B100 is cheaper - $1,598 against $2,200, about 27% less. |
A MartinLogan Motion XT B100 B KEF R3
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?
MartinLogan Motion XT B100 is the easier recommendation: it leads on most of the measured areas and costs less. Take KEF R3 if its size, looks or fit in your room suit you better. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 52Hz anyway, so judge these on the other rows instead. Match it to your room: we rate MartinLogan Motion XT B100 the better fit for a large room and a very large room, and KEF R3 for a small room.
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.