In this review, we will be comparing Motion 4i and Motion 15i, two Passive Bookshelf speakers by MartinLogan.
Let's have a brief look at the main features
of MartinLogan Motion 4i and MartinLogan 15i first before getting into our more
detailed comparison.
| Key Specs | MartinLogan Motion 4i | MartinLogan 15i |
|---|
| Brand | MartinLogan
United States · founded 1982 | MartinLogan
United States · founded 1982 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1 x 1.4" Folded Motion Ribbon | 1.0 x 1.4" Folded Motion |
|---|
| Woofer | 4" | 5.25" Aluminum |
|---|
| Frequency response | 70-23k Hz | 60-25k Hz |
|---|
| Sensitivity | 90 dB | 92 dB |
|---|
| Impedance | 4 ohms | 5 ohms |
|---|
| Power range | — | 20-200 watts |
|---|
| Weight | 2.72kg / 6lbs | 5.40kg / 11.9lbs |
|---|
| Dimensions (H x W x D) | 12-11/16" x 5-11/16" x 5-11/16"
322.3 x 144.5 x 144.5mm | 11.4" x 6.8" x 9.4"
290.0 x 173.0 x 240.0mm |
|---|
Motion 4i and Motion 15i are members of MartinLogan's Motion series of speakers. Below you can find the loudspeakers from this series.
MartinLogan Motion Series
History
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
Both Motion 4i and Motion 15i are 2-way speakers.
MartinLogan Motion 4iMartinLogan 15i
Woofer
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 4i |
MartinLogan 15i |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1 x 1.4-inch
|
1.0 x 1.4-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 4-inch
|
1 x 5.25-inch
|
Motion 4i features a 1 x 1.4" Folded Motion Ribbon Tweeter and 1 x 4" Woofer. On the other hand, the 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.
Frequency Response
Motion 4i has a frequency range of 70-23k Hz whereas Motion 15i has a frequency range of 60-25k Hz. With a minimum frequency of 60Hz, the Motion 15i can go significantly deeper on the low side and provide stronger bass compared to the Motion 4i's min frequency of 70Hz.
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 4i is a 4 ohms speaker compared to the Motion 15i which has a nominal impedance of 5 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 4i can provide this impedance level.
These two speakers also have different sensitivity levels. Motion 4i sensitivity is rated at 90 dB and the Motion 15i's is rated at 92 dB. This 2 dB difference makes the MartinLogan 15i a more sensitive speaker compared to MartinLogan Motion 4i, hence will play louder with the same amount of watts.
Sensitivity
Bookshelf Speakers
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 4i features Custom 5-way tool-less binding posts type posts and Motion 15i has a Custom 5-way tool-less binding posts type posts. None of these speakers feature bi-amping/bi-wiring.
MartinLogan 15i's Custom 5-way tool-less binding posts terminals
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 4i's and MartinLogan 15i's external dimensions. MartinLogan Motion 4i has external dimensions of 322.3 x 144.5 x 144.5mm () whereas MartinLogan 15i has external dimensions of 290.0 x 173.0 x 240.0mm (11.4 x 6.8 x 9.4inch).
MartinLogan Motion 4i is 28.5mm narrower and 95.5mm less deeper than MartinLogan 15i but it is also 32.3mm taller.
Below you can see the front view size comparison of MartinLogan Motion 4i and MartinLogan 15i in scale.
Comparison image of MartinLogan Motion 4i and MartinLogan 15i 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 4i is approximately 208.8cm2 / 32.4inch2 and base area of the MartinLogan 15i is approximately 415.2cm2 / 64.4inch2. The Motion 4i requires 50% less surface area than the Motion 15i 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 4i and MartinLogan 15i 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 4i weighs 2.72kg / 6lbs and the MartinLogan 15i weighs 5.40kg / 11.9lbs. This makes the Motion 15i 99% heavier than the Motion 4i.
Here is a comparison of how Motion 4i and Motion 15i'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 come with the Motion 15i:
- Bookshelf loudspeaker
- Grille
- 4 Rubber feet
- Users Manual
- Warranty/Registration Information
 Base Surface Area |
208cm2
vs
415cm2
|
Takes less floor space |
 Sensitivity |
92 dB
vs
90 dB
|
Play louder with same amount of amplification power |
 Nominal Impedance |
5 ohms
vs
4 ohms
|
Less selective with amplifiers |
 Woofer Size |
5.25 inches
vs
4 inches
|
Larger woofer |
|
Low Frequency Response |
60 Hz
vs
70 Hz
|
Generates deeper bass |
 High Frequency Response |
25k Hz
vs
23k Hz
|
Generates higher frequency |
 Height |
290mm
vs
322mm
|
Easier to fit in smaller spaces |
| General |
MartinLogan Motion 4i |
MartinLogan Motion 15i |
| Brand |
MartinLogan |
MartinLogan |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Sensitivity |
90 dB |
92 dB |
| Impedance |
4 ohms |
5 ohms |
| Frequency Response |
70-23k Hz |
60-25k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
4" |
5.25" |
| Woofer Composition |
|
Aluminum |
| Woofer Surround Material |
n/a |
Rubber |
| Tweeter Size |
1 x 1.4" |
1.0 x 1.4" |
| Tweeter Type |
Folded Motion Ribbon |
Folded Motion |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
n/a |
2700Hz |
| Firing Direction |
n/a |
rear |
| Suggested Break-in Period |
n/a |
Allow 72 hours of break-in at 90 dB |
Physical Specs |
|
|
| Height |
322.3mm (12.7") |
290.0mm (11.4") |
| Width |
144.5mm (5.7") |
173.0mm (6.8") |
| Depth |
144.5mm (5.7") |
240.0mm (9.4") |
| Weight |
2.72kg (6lbs) |
5.40kg (11.9lbs) |
| Enclosure |
|
Bass Reflex |
| Finish |
Piano Lacquer |
MDF/Lacquer |
| Available Colors |
Gloss Black |
Gloss Black, Matt White, Red Walnut |
| Mounting Bracket |
|
No |
| Recommended Stand Height |
n/a |
26-28" |
| Grille |
n/a |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
n/a |
No |
Other |
|
|
| Parts Warranty |
5 Yrs w/ Registration |
5 Years |
| Labor Warranty |
5 Yrs w/ Registration |
5 Years |
Siblings in MartinLogan's Motion series, so they share a family sound. It comes down to size, output and price.
| Area | Better | Why |
|---|
| Bass | B | MartinLogan 15i digs deeper - 60Hz against 70Hz. |
| Amplifier needs | B | MartinLogan 15i is more sensitive (92dB vs 90dB), so it goes louder on the same amplifier. |
| Amplifier match | B | MartinLogan 15i is the easier load at 5 ohms; the other is 4 ohms and wants an amplifier rated for it. |
| Size | depends | MartinLogan Motion 4i is easier to place; MartinLogan 15i is bigger, which usually goes with fuller bass. Your room decides. |
A MartinLogan Motion 4i B MartinLogan 15i
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 15i has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 70Hz anyway, so judge these on the other rows instead. In a large or open-plan room, MartinLogan 15i has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, MartinLogan Motion 4i 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.