In this review, we will be comparing Motion 15i and R-51M, two Passive Bookshelf speakers from MartinLogan and Klipsch.
Let's have a brief look at the main features
of MartinLogan 15i and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | MartinLogan 15i | Klipsch R-51M |
|---|
| Brand | MartinLogan
United States · founded 1982 | Klipsch
United States · founded 1946 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1.0 x 1.4" Folded Motion | 1" Tractrix Horn |
|---|
| Woofer | 5.25" Aluminum | 5.25" Copper-spun IMG |
|---|
| Frequency response | 60-25k Hz | 62-21k Hz |
|---|
| Sensitivity | 92 dB | 93 dB |
|---|
| Impedance | 5 ohms | 8 ohms |
|---|
| Power range | 20-200 watts | Up to 85 watts |
|---|
| Weight | 5.40kg / 11.9lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 11.4" x 6.8" x 9.4"
290.0 x 173.0 x 240.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the MartinLogan 15i and Klipsch R-51M 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 15i |
Klipsch R-51M |
| Near-field |
Poor |
Average |
| Small Room |
Average |
Good |
| Mid-size Room |
Good |
Average |
| Large Room |
Average |
Poor |
| Very Large Room |
Poor |
Bad |
(* 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
Both Motion 15i and R-51M are 2-way speakers.
MartinLogan 15iKlipsch R-51M
TweeterWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
MartinLogan 15i |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1.0 x 1.4-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 5.25-inch
|
Motion 15i features a 1.0 x 1.4" Folded Motion Tweeter and 1 x 5.25" Aluminum Woofer with a Crossover frequency at 2700Hz. On the other hand, the R-51M features a 1" Tractrix Horn Tweeter and 1 x 5.25" Copper-spun IMG Woofer with a Crossover frequency at 1660Hz.
Frequency Response
Motion 15i has a frequency range of 60-25k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 60Hz, the Motion 15i can go slightly deeper then the R-51M's min frequency of 62Hz.
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 15i is a 5 ohms speaker compared to the R-51M which has a nominal impedance of 8 ohms.
These two speakers also have different sensitivity levels. Motion 15i sensitivity is rated at 92 dB and the R-51M's is rated at 93 dB. This 1 dB difference makes the Klipsch R-51M a more sensitive speaker compared to MartinLogan 15i, 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 15i can handle a max power of 200 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 115 watts less than the Motion 15i.
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.
Input Type and Bi-Amping / Bi-Wiring
Motion 15i features Single Gold Plated Binding Posts - 5-way type posts and R-51M has a Single Gold Plated Binding Posts - 5-way type posts. None of these speakers feature bi-amping/bi-wiring.
MartinLogan 15i's Custom 5-way tool-less binding posts terminals
Klipsch R-51M's Single Gold Plated Binding Posts - 5-way terminals
Cabinet Type and Port Position
Both Motion 15i and R-51M 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.
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 15i's and Klipsch R-51M's external dimensions. MartinLogan 15i has external dimensions of 290.0 x 173.0 x 240.0mm (11.4 x 6.8 x 9.4inch) whereas Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm (13.3 x 7.0 x 8.4inch).
MartinLogan 15i is 5mm narrower and 48mm shorter than Klipsch R-51M but it is also 25mm deeper.
Below you can see the front view size comparison of MartinLogan 15i and Klipsch R-51M in scale.
Comparison image of MartinLogan 15i and Klipsch R-51M 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 15i is approximately 415.2cm2 / 64.4inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The Motion 15i requires 8% more surface area than the R-51M 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 MartinLogan 15i and Klipsch R-51M 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 15i weighs 5.40kg / 11.9lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the Motion 15i 8% heavier than the R-51M.
Here is a comparison of how Motion 15i and R-51M's weights compare with the average, max and min weights in Passive Bookshelf class.
Weight
All Bookshelf Speakers
What's in the Box of MartinLogan 15i?
Here are the items that are included inside the box of Motion 15i:
- Bookshelf loudspeaker
- Grille
- 4 Rubber feet
- Users Manual
- Warranty/Registration Information
What's in the Box of Klipsch R-51M?
Here are the items that come with the R-51M:
- 2 Bookshelf loudspeakers
- 2 Grilles (installed)
- 8 Self-adhesive rubber feet
- Quick Setup Guide
- Important Safety Instructions
- Warranty Information
 Max Input Power |
200 watts
vs
85 watts
|
Handle more power from your amplifier |
 Low Frequency Response |
60 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
25k Hz
vs
21k Hz
|
Generates higher frequency |
 Height |
290mm
vs
338mm
|
Easier to fit in smaller spaces |
 Sensitivity |
93 dB
vs
92 dB
|
Play louder with same amount of amplification power |
 Nominal Impedance |
8 ohms
vs
5 ohms
|
Less selective with amplifiers |
 Base Surface Area |
382cm2
vs
415cm2
|
Takes less floor space |
 Price per pair* |
359USD
vs
900USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
MartinLogan Motion 15i |
Klipsch Reference R-51M |
| Brand |
MartinLogan |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-200 watts |
Up to 85 watts |
| Sensitivity |
92 dB |
93 dB |
| Impedance |
5 ohms |
8 ohms |
| Frequency Response |
60-25k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
5.25" |
| Woofer Composition |
Aluminum |
Copper-spun IMG |
| Woofer Surround Material |
Rubber |
Rubber |
| Tweeter Size |
1.0 x 1.4" |
1" |
| Tweeter Type |
Folded Motion |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2700Hz |
1660Hz |
| Firing Direction |
rear |
rear |
| Suggested Break-in Period |
Allow 72 hours of break-in at 90 dB |
n/a |
Physical Specs |
|
|
| Height |
290.0mm (11.4") |
338.0mm (13.3") |
| Width |
173.0mm (6.8") |
178.0mm (7") |
| Depth |
240.0mm (9.4") |
215.0mm (8.5") |
| Weight |
5.40kg (11.9lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
MDF/Lacquer |
MDF/Wood-grain vinyl |
| Available Colors |
Gloss Black, Matt White, Red Walnut |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
26-28" |
24-28" |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
No |
No |
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
These sit in different price classes - MartinLogan 15i costs roughly 2.5x what Klipsch R-51M 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 | evenly matched | Much the same reach (60Hz vs 62Hz). |
| Amplifier needs | evenly matched | Similar sensitivity (92dB vs 93dB) - both want much the same power. |
| Amplifier match | B | Klipsch R-51M is the easier load at 8 ohms. |
| Headroom | A | MartinLogan 15i takes more power (200W vs 85W) - more in hand in a big room. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. MartinLogan 15i sits in a wider range (18 models), so a matched surround system is easier later. |
| Price | B | Klipsch R-51M is cheaper - $359 against $900, about 60% less; arguably a different class. |
A MartinLogan 15i B Klipsch R-51M
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. Match it to your room: we rate MartinLogan 15i the better fit for a mid-size room and a large room, and Klipsch R-51M for near-field listening and a small room. Think about the whole system, not just the speakers: the roughly $541 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
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.