In this review, we will be comparing R-51M and R-51PM, two Bookshelf speakers by Klipsch The main difference between these two speakers is that the Klipsch R-51PM is a Powered speaker which means that it has a built-in amplifier inside the speaker body so you don't need an external power amp or an integrated amp whereas the Klipsch R-51M is a Passive speaker so has to be matched with an amplifier to get any sound from it. Let's have a brief look at the main features
of Klipsch R-51M and Klipsch R-51PM first before getting into our more
detailed comparison.
Klipsch R-51M Key Specs
- 2-way Design
- 1" Tractrix Horn Tweeter
- 5.25" Copper-spun IMG Woofer
- 62-21k Hz Frequency Response
- 93 dB Sensitivity
- Impedance: 8ohms
- Power Range:Up to 85watts
- Weight:5.00kg
- Dimensions (H x W x D): 338.0" x 7.0" x 8.4"( 338.0 x 178.0 x 215.0mm )
Klipsch R-51PM Key Specs
- 2-way Design
- 120-watt RMS( 240-watt Peak) Integrated Amplifier
- 1.0" Tractrix Horn Tweeter
- 5.25" Copper-spun IMG Woofer
- 68-21k Hz Frequency Response
- 24-bit Max Depth / 96 kHz Max Sample Rate
- Built-in 3.0 Bluetooth
- Weight:4.80kg
- Dimensions (H x W x D): 330.2" x 7.0625" x 10.25"( 330.2 x 179.4 x 260.3mm )
R-51M and R-51PM are members of Klipsch's Reference (R) Bookshelf series of speakers. Below you can find the loudspeakers from this series.
Klipsch Reference (R) Bookshelf Series History
|
Model |
Body |
Frequency |
Sensitivity | Impedance | Woofer |
 |
Klipsch R-51M
|
Bookshelf |
62-21k Hz |
93 dB | 8Ω |
1 x 5.25"
|
 |
Klipsch R-41M
|
Bookshelf |
68-21k Hz |
90 dB | 8Ω |
1 x 4"
|
In the following sections, we will get into more detail in order to better understand how the Klipsch R-51M and Klipsch R-51PM compare and hopefully end up with enough arguments to decide which one of these loudspeakers is the better choice for you.
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Drivers
Both R-51M and R-51PM are 2-way speakers.
| Driver |
Klipsch R-51M |
Klipsch R-51PM |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1.0-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 5.25-inch
|
R-51M features a 1" Tractrix Horn Tweeter and 1 x 5.25" Copper-spun IMG Woofer with a Crossover frequency at 1660Hz. On the other hand, the R-51PM features a 1.0" Aluminum LTS Tractrix Horn Tweeter and 1 x 5.25" Copper-spun IMG Woofer with a Crossover frequency at 1663Hz.
Frequency Response
R-51M has a frequency range of 62-21k Hz whereas R-51PM has a frequency range of 68-21k Hz. With a minimum frequency of 62Hz, the R-51M can go significantly deeper on the low side and provide stronger bass compared to the R-51PM's min frequency of 68Hz.
Below graphs depict how these two speakers compare with the max, min and average values of the Min and Max Frequencies of other speakers in the Bookshelf class in our database.
Low Frequency
Bookshelf Speakers
High Frequency
Bookshelf Speakers
None of these speakers achieves full range experience which is commonly agreed as 20Hz-20kHz. In order to achieve lower lows / deeper bass, we recommend you pair these with a subwoofer. Visit our Powered Subwoofers section to find out more about the available options.
Cabinet Type and Port Position
Both R-51M and R-51PM 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
Size of a speaker can sometimes become an important decision factor due to space constraints or in some cases purely for esthetic reasons. In this section, we are going to compare Klipsch R-51M's and Klipsch R-51PM's external dimensions. Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm ( 13.3 x 7.0 x 8.4inch) whereas Klipsch R-51PM has external dimensions of 330.2 x 179.4 x 260.3mm ( 13 x 7.0625 x 10.25inch) .
Klipsch R-51M is 1.4mm narrower and 45.3mm less deeper than Klipsch R-51PM but it is also 7.8mm taller.
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 Klipsch R-51M is approximately 382.7cm2 / 59.3inch2 and base area of the Klipsch R-51PM is approximately 467.0cm2 / 72.4inch2. The R-51M requires 18% less surface area than the R-51PM which gives it a small advantage on placement in tight spaces.
What's in the Box of Klipsch R-51M?
Here are the items that are included inside the box of R-51M:
2 Bookshelf loudspeakers 2 Grilles (installed) 8 Self-adhesive rubber feet Quick Setup Guide Important Safety Instructions Warranty Information
What's in the Box of Klipsch R-51PM?
Here are the items that come with the R-51PM:
Powered speaker (right)Passive speaker (left)2 Grilles68-inch AC power cordRemote control2
Low Frequency Response 
Base Surface Area 
Price per pair* 
Speaker Type 
Height 
3.5mm Connection 
RCA Connection