In this review, we will be comparing Airmotiv B2+ and R-51M, two Passive Bookshelf speakers from Emotiva and Klipsch.
Let's have a brief look at the main features
of Emotiva Airmotiv B2+ and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | Emotiva Airmotiv B2+ | Klipsch R-51M |
|---|
| Brand | Emotiva
United States · founded 2003 | Klipsch
United States · founded 1946 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 25×32 mm" folded ribbon | 1" Tractrix Horn |
|---|
| Woofer | 6.25" woven fiber cone | 5.25" Copper-spun IMG |
|---|
| Frequency response | 40-28k Hz | 62-21k Hz |
|---|
| Sensitivity | 86 dB | 93 dB |
|---|
| Impedance | 4 ohms | 8 ohms |
|---|
| Power range | Up to 125 watts | Up to 85 watts |
|---|
| Weight | 7.10kg / 15.6lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 12-3/4" x 8-1/2" x 11-1/2"
324.0 x 216.0 x 293.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the Emotiva Airmotiv B2+ 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* |
Emotiva Airmotiv B2+ |
Klipsch R-51M |
| Near-field |
Average |
Average |
| Small Room |
Good |
Good |
| Mid-size Room |
Average |
Average |
| Large Room |
Poor |
Poor |
| Very Large Room |
Bad |
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 Airmotiv B2+ and R-51M are 2-way speakers.
Emotiva Airmotiv B2+Klipsch 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 |
Emotiva Airmotiv B2+ |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
25×32 mm-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 6.25-inch
|
1 x 5.25-inch
|
Airmotiv B2+ features a 25×32 mm" folded ribbon Tweeter and 1 x 6.25" woven fiber cone Woofer with a Crossover frequency at 2000Hz. 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
Airmotiv B2+ has a frequency range of 40-28k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 40Hz, the Airmotiv B2+ can go significantly deeper on the low side and provide stronger bass compared to 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
Airmotiv B2+ is a 4 ohms speaker compared to the R-51M 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 Airmotiv B2+ can provide this impedance level.
These two speakers also have different sensitivity levels. Airmotiv B2+ sensitivity is rated at 86 dB and the R-51M's is rated at 93 dB. This 7 dB difference makes the Klipsch R-51M a more sensitive speaker compared to Emotiva Airmotiv B2+, 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.
Airmotiv B2+ can handle a max power of 125 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 40 watts less than the Airmotiv B2+.
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
Airmotiv B2+ features Binding post posts which make bi-amping or bi-wiring possible. R-51M has a Single Gold Plated Binding Posts - 5-way which doesn't feature bi-amping/bi-wiring.
Emotiva Airmotiv B2+'s Binding post terminals allows Bi-amping or bi-wiring
Klipsch R-51M's Single Gold Plated Binding Posts - 5-way terminals
Cabinet Type and Port Position
Both Airmotiv B2+ 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.
Emotiva Airmotiv B2+ 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 Emotiva Airmotiv B2+'s and Klipsch R-51M's external dimensions. Emotiva Airmotiv B2+ has external dimensions of 324.0 x 216.0 x 293.0mm (12-3/4-inch x 8-1/2-inch x 11-1/2-inch) whereas Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm (13.3 x 7.0 x 8.4inch).
Klipsch R-51M is 38mm narrower and 78mm less deeper than Emotiva Airmotiv B2+ but it is also 14mm taller.
Below you can see the front view size comparison of Emotiva Airmotiv B2+ and Klipsch R-51M in scale.
Comparison image of Emotiva Airmotiv B2+ 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 Emotiva Airmotiv B2+ is approximately 632.9cm2 / 98.1inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The Airmotiv B2+ requires 65% 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 Emotiva Airmotiv B2+ 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 Emotiva Airmotiv B2+ weighs 7.10kg / 15.6lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the Airmotiv B2+ 42% heavier than the R-51M.
Here is a comparison of how Airmotiv B2+ 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 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 |
125 watts
vs
85 watts
|
Handle more power from your amplifier |
 Woofer Size |
6.25 inches
vs
5.25 inches
|
Larger woofer |
|
Low Frequency Response |
40 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
28k Hz
vs
21k Hz
|
Generates higher frequency |
 Bi-Amping and Bi-Wiring |
Yes
vs
No
|
Allows bi-amping and bi-wiring connections |
 Height |
324mm
vs
338mm
|
Easier to fit in smaller spaces |
 Sensitivity |
93 dB
vs
86 dB
|
Play louder with same amount of amplification power |
 Nominal Impedance |
8 ohms
vs
4 ohms
|
Less selective with amplifiers |
 Base Surface Area |
382cm2
vs
632cm2
|
Takes less floor space |
 Price per pair* |
359USD
vs
499USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
Emotiva Airmotiv B2+ |
Klipsch Reference R-51M |
| Brand |
Emotiva |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
Up to 125 watts |
Up to 85 watts |
| Sensitivity |
86 dB |
93 dB |
| Impedance |
4 ohms |
8 ohms |
| Frequency Response |
40-28k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6.25" |
5.25" |
| Woofer Composition |
woven fiber cone |
Copper-spun IMG |
| Woofer Surround Material |
SBR |
Rubber |
| Tweeter Size |
25×32 mm" |
1" |
| Tweeter Type |
folded ribbon |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2000Hz |
1660Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
324.0mm (12.8") |
338.0mm (13.3") |
| Width |
216.0mm (8.5") |
178.0mm (7") |
| Depth |
293.0mm (11.5") |
215.0mm (8.5") |
| Weight |
7.10kg (15.6lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass reflex |
Bass Reflex |
| Finish |
HDF |
MDF/Wood-grain vinyl |
| Available Colors |
Black |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
n/a |
24-28" |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
Yes |
No |
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
No single best speaker here - they are built to different priorities, and the right one depends on your room, your amplifier and what you listen to.
| Area | Better | Why |
|---|
| Bass | A | Emotiva Airmotiv B2+ digs deeper - 40Hz against 62Hz. |
| Amplifier needs | B | Klipsch R-51M is more sensitive (93dB vs 86dB), so it goes louder on the same amplifier. |
| Amplifier match | B | Klipsch R-51M is the easier load at 8 ohms; the other is 4 ohms and wants an amplifier rated for it. |
| Headroom | A | Emotiva Airmotiv B2+ takes more power (125W vs 85W) - more in hand in a big room. |
| Size | depends | Klipsch R-51M is easier to place; Emotiva Airmotiv B2+ is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | A | Emotiva Airmotiv B2+: bi-amping. Emotiva Airmotiv B2+ sits in a wider range (9 models), so a matched surround system is easier later. |
| Price | B | Klipsch R-51M is cheaper - $359 against $499, about 28% less. |
A Emotiva Airmotiv B2+ 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?
Emotiva Airmotiv B2+ is ahead, but only on 1 of the measured areas, and it costs about 39% more. That is a lot of money for a narrow margin on paper - Klipsch R-51M looks like the sensible buy unless something else about the Emotiva Airmotiv B2+ appeals to you. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 62Hz anyway, which makes the cheaper Klipsch R-51M much easier to justify. In a large or open-plan room, Emotiva Airmotiv B2+ has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Klipsch R-51M 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.