In this review, we will be comparing XT15 and R-51M, two Passive Bookshelf speakers from Polk Audio and Klipsch.
Let's have a brief look at the main features
of Polk XT15 and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | Polk XT15 | Klipsch R-51M |
|---|
| Brand | Polk Audio
United States · founded 1972 | Klipsch
United States · founded 1946 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1" Soft-Dome | 1" Tractrix Horn |
|---|
| Woofer | 5.25" Bi-laminate paper | 5.25" Copper-spun IMG |
|---|
| Frequency response | 48-40k Hz | 62-21k Hz |
|---|
| Sensitivity | 86 dB | 93 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 30-150 watts | Up to 85 watts |
|---|
| Weight | 4.09kg / 9lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 10-5/8" x 6-9/16" x 7-3/16"
270.0 x 167.0 x 183.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the Polk XT15 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* |
Polk XT15 |
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.
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Drivers
Both XT15 and R-51M are 2-way speakers.
Polk XT15Klipsch 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 |
Polk XT15 |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 5.25-inch
|
XT15 features a 1" Soft-Dome Tweeter and 1 x 5.25" Bi-laminate paper Woofer. 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
XT15 has a frequency range of 48-40k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 48Hz, the XT15 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
XT15 and R-51M have the same Impedance of 8 ohms but where they differ is the sensitivity levels. XT15 sensitivity is rated at 86 dB and the R-51M's is at 93 dB. This 7 dB difference makes the Klipsch R-51M a more sensitive speaker compared to Polk XT15, 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.
XT15 can handle a max power of 150 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 65 watts less than the XT15.
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
XT15 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
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 Polk XT15's and Klipsch R-51M's external dimensions. Polk XT15 has external dimensions of 270.0 x 167.0 x 183.0mm (10-5/8 x 6-9/16 x 7-3/16inch) 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 clearly the larger of the two speakers. Its body is 11mm wider, 68mm taller and 32mm deeper than Polk XT15.
Below you can see the front view size comparison of Polk XT15 and Klipsch R-51M in scale.
Comparison image of Polk XT15 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 XT15 is approximately 305.6cm2 / 47.4inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The XT15 requires 20% less surface area than the R-51M 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 Polk XT15 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 XT15 weighs 4.09kg / 9lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the R-51M 22% heavier than the XT15.
Here is a comparison of how XT15 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 XT15?
Here are the items that are included inside the box of XT15:
- 2 Bookshelf loudspeakers
- 2 Grilles (attached)
- 8 Self-adhesive rubber feet
- Owners Manual
- Online 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 |
150 watts
vs
85 watts
|
Handle more power from your amplifier |
 Low Frequency Response |
48 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
21k Hz
|
Generates higher frequency |
 Height |
270mm
vs
338mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
305cm2
vs
382cm2
|
Takes less floor space |
 Price per pair* |
199USD
vs
359USD
|
costs less (*prices may change depending on the seller, location and time) |
 Sensitivity |
93 dB
vs
86 dB
|
Play louder with same amount of amplification power |
| General |
Polk Audio Monitor XT15 |
Klipsch Reference R-51M |
| Brand |
Polk Audio |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
30-150 watts |
Up to 85 watts |
| Sensitivity |
86 dB |
93 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
48-40k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
5.25" |
| Woofer Composition |
Bi-laminate paper |
Copper-spun IMG |
| Woofer Surround Material |
Rubber |
Rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Soft-Dome |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
n/a |
1660Hz |
| Firing Direction |
n/a |
rear |
Physical Specs |
|
|
| Height |
270.0mm (10.6") |
338.0mm (13.3") |
| Width |
167.0mm (6.6") |
178.0mm (7") |
| Depth |
183.0mm (7.2") |
215.0mm (8.5") |
| Weight |
4.09kg (9lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
MDF, Vinyl |
MDF/Wood-grain vinyl |
| Available Colors |
Black |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
28-32" |
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 - Klipsch R-51M costs roughly 1.8x what Polk XT15 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 | A | Polk XT15 digs deeper - 48Hz against 62Hz. |
| Amplifier needs | B | Klipsch R-51M is more sensitive (93dB vs 86dB), so it goes louder on the same amplifier. |
| Headroom | A | Polk XT15 takes more power (150W vs 85W) - more in hand in a big room. |
| Size | depends | Polk XT15 is easier to place; Klipsch R-51M is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. Polk XT15 sits in a wider range (9 models), so a matched surround system is easier later. |
| Price | A | Polk XT15 is cheaper - $199 against $359, about 45% less; arguably a different class. |
A Polk XT15 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?
Polk XT15 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 62Hz anyway, so judge these on the other rows instead. Match it to your room: we rate Polk XT15 the better fit for a mid-size room and a large room, and Klipsch R-51M for near-field listening and a small room.
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.