In this review, we will be comparing S20 and R-51M, two Passive Bookshelf speakers from Polk Audio and Klipsch. Let's have a brief look at the main features
of Polk S20 and Klipsch R-51M first before getting into our more
detailed comparison.
What size room are the Polk S20 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:
In the following sections, we will get into more detail in order to better understand how the Polk S20 and Klipsch R-51M 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 S20 and R-51M are 2-way speakers.
| Driver |
Polk S20 |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 6.5-inch
|
1 x 5.25-inch
|
S20 features a 1" Terylene Soft-Dome Tweeter and 1 x 6.5" Mica-reinforced polypropylene Woofer with a Crossover frequency at 2500Hz. 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
S20 has a frequency range of 39-40k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 39Hz, the S20 can go significantly deeper on the low side and provide stronger bass compared to the R-51M's min frequency of 62Hz.
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.
Impedance and Sensitivity
S20 and R-51M have the same Impedance of 8 ohms but where they differ is the sensitivity levels. S20 sensitivity is rated at 88 dB and the R-51M's is at 93 dB. This 5 dB difference makes the Klipsch R-51M a more sensitive speaker compared to Polk S20, 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. While using an amplifier within this range ensures the nominal performance , inputting a power that is higher than the max wattage can result in a damaged speaker.
S20 can handle a max power of 125 watts RMS from the amp the whereas R-51M has a max power handling value of 85 watts RMS, 40 watts less than the S20.
Keep in mind that a higher max power handling value doesn't necessarily make that a louder speaker
compared to a lower max handling speaker. Loudness or the sound level is also impacted by parameters
such as Impedance, sensitivity and system efficiencies.
Input Type and Bi-Amping / Bi-Wiring
S20 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.
Klipsch R-51M's Single Gold Plated Binding Posts - 5-way terminals
Cabinet Type and Port Position
Both S20 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
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 Polk S20's and Klipsch R-51M's external dimensions. Polk S20 has external dimensions of 376.0 x 216.0 x 350.0mm ( 14.8 x 8.5 x 13.7inch) whereas Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm ( 13.3 x 7.0 x 8.4inch) .
Polk S20 is clearly the larger of the two speakers. Its body is 38mm wider, 38mm taller and 135mm deeper than Klipsch R-51M.
Below you can see the front view size comparison of Polk S20 and Klipsch R-51M in scale.
Comparison image of Polk S20 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 Polk S20 is approximately 756.0cm2 / 117.2inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The S20 requires 98% more surface area than the R-51M which gives it a small disadvantage on placement in tight spaces.
Here is an 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 Polk S20 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 Polk S20 weighs 7.73kg / 17lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the S20 55% heavier than the R-51M.
Here is a comparison of how S20 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 Polk S20?
Here are the items that are included inside the box of S20:
2 Bookshelf loudspeakers2 Grilles (attached)8 Self-adhesive rubber feetOwners ManualOnline Product Registration
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 |
6.5 inches
vs
5.25 inches
|
Larger woofer |
| Low Frequency Response |
39 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
21k Hz
|
Generates higher frequency |
 Sensitivity |
93 dB
vs
88 dB
|
Play louder with same amount of amplification power |
 Height |
338mm
vs
376mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
382cm2 (178x215mm)
vs
756cm2 (216x350mm)
|
Takes less floor space |
| General |
Polk Audio Signature S20 |
Klipsch Reference R-51M |
| Brand |
Polk Audio |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-125 watts |
Up to 85 watts |
| Sensitivity |
88 dB |
93 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
39-40k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6.5" |
5.25" |
| Woofer Composition |
Mica-reinforced polypropylene |
Copper-spun IMG |
| Woofer Surround Material |
Butyl rubber |
Rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Soft-Dome |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2500Hz |
1660Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
376.0mm (14.8") |
338.0mm (13.3") |
| Width |
216.0mm (8.5") |
178.0mm (7") |
| Depth |
350.0mm (13.8") |
215.0mm (8.5") |
| Weight |
7.73kg (17lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
MDF/Wood-grain vinyl |
| Available Colors |
Black, Walnut, Brown Walnut |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
24-28" |
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 |