In this review, we will be comparing S20 and LS50, two Passive Bookshelf speakers from Polk Audio and KEF.
Let's have a brief look at the main features
of Polk S20 and KEF LS50 first before getting into our more
detailed comparison.
| Key Specs | Polk S20 | KEF LS50 |
|---|
| Brand | Polk Audio
United States · founded 1972 | KEF
United Kingdom · founded 1961 |
|---|
| Design | 2-way | 2-way |
|---|
| Uni-Q driver | — | 11th Generation Uni-Q |
|---|
| Tweeter | 1" Soft-Dome | 1" Vented dome |
|---|
| Woofer | 6.5" Mica-reinforced polypropylene | 5.25" Magnesium/aluminum alloy |
|---|
| Frequency response | 39-40k Hz | 79-28k Hz |
|---|
| Sensitivity | 88 dB | 85 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 20-125 watts | 25-100 watts |
|---|
| Weight | 7.73kg / 17lbs | 7.20kg / 15.8lbs |
|---|
| Dimensions (H x W x D) | 14.8" x 8.5" x 13.7"
376.0 x 216.0 x 350.0mm | 11.8" x 7.8" x 10.9"
302.0 x 200.0 x 278.0mm |
|---|
What size room are the Polk S20 and KEF LS50 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 S20 |
KEF LS50 |
| 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.
Drivers
Both S20 and LS50 are 2-way speakers.
Polk S20KEF LS50
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 S20 |
KEF LS50 |
|
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 LS50 features a 1" Aluminum Vented dome Tweeter and 1 x 5.25" Magnesium/aluminum alloy Woofer with a Crossover frequency at 2200Hz.
Frequency Response
S20 has a frequency range of 39-40k Hz whereas LS50 has a frequency range of 79-28k Hz. With a minimum frequency of 39Hz, the S20 can go significantly deeper on the low side and provide stronger bass compared to the LS50's min frequency of 79Hz.
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
S20 and LS50 have the same Impedance of 8 ohms but where they differ is the sensitivity levels. S20 sensitivity is rated at 88 dB and the LS50's is at 85 dB. This 3 dB difference makes the Polk S20 a more sensitive speaker compared to KEF LS50, 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.
S20 can handle a max power of 125 watts RMS, whereas LS50 has a max power handling value of 100 watts RMS, 25 watts less than the S20.
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
S20 features Post type posts and LS50 has a Post type posts. None of these speakers feature bi-amping/bi-wiring.
KEF LS50's Post terminals
Cabinet Type and Port Position
Both S20 and LS50 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
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 S20's and KEF LS50'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 KEF LS50 has external dimensions of 302.0 x 200.0 x 278.0mm (11.8 x 7.8 x 10.9inch).
Polk S20 is clearly the larger of the two speakers. Its body is 16mm wider, 74mm taller and 72mm deeper than KEF LS50.
Below you can see the front view size comparison of Polk S20 and KEF LS50 in scale.
Comparison image of Polk S20 and KEF LS50 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 KEF LS50 is approximately 556.0cm2 / 86.2inch2. The S20 requires 36% more surface area than the LS50 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 Polk S20 and KEF LS50 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 KEF LS50 weighs 7.20kg / 15.8lbs. This makes the S20 7% heavier than the LS50.
Here is a comparison of how S20 and LS50'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 loudspeakers
- 2 Grilles (attached)
- 8 Self-adhesive rubber feet
- Owners Manual
- Online Product Registration
What's in the Box of KEF LS50?
Here are the items that come with the LS50:
- 2 Bookshelf loudspeakers
- 2 Foam port plugs
- 8 Self-adhesive rubber feet
- Owner's Manual
- Warranty Registration Card
 Max Input Power |
125 watts
vs
100 watts
|
Handle more power from your amplifier |
 Sensitivity |
88 dB
vs
85 dB
|
Play louder with same amount of amplification power |
 Woofer Size |
6.5 inches
vs
5.25 inches
|
Larger woofer |
|
Low Frequency Response |
39 Hz
vs
79 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
28k Hz
|
Generates higher frequency |
 Price per pair* |
299USD
vs
1300USD
|
costs less (*prices may change depending on the seller, location and time) |
 Height |
302mm
vs
376mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
556cm2
vs
756cm2
|
Takes less floor space |
| General |
Polk Audio Signature S20 |
KEF LS50 |
| Brand |
Polk Audio |
KEF |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-125 watts |
25-100 watts |
| Sensitivity |
88 dB |
85 dB |
| Impedance |
8 ohms |
8 ohms |
| Impedance |
n/a |
3.2 ohms |
| Frequency Response |
39-40k Hz |
79-28k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6.5" |
5.25" |
| Woofer Composition |
Mica-reinforced polypropylene |
Magnesium/aluminum alloy |
| Woofer Surround Material |
Butyl rubber |
Rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Soft-Dome |
Vented dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2500Hz |
2200Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
376.0mm (14.8") |
302.0mm (11.9") |
| Width |
216.0mm (8.5") |
200.0mm (7.9") |
| Depth |
350.0mm (13.8") |
278.0mm (10.9") |
| Weight |
7.73kg (17lbs) |
7.20kg (15.8lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
Polymer/Lacquer |
| Available Colors |
Black, Walnut, Brown Walnut |
Black, High Gloss Piano Black, High Gloss Piano White |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
24-28" |
18-28" |
| Grille |
Yes |
n/a |
| 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 - KEF LS50 costs roughly 4.3x what Polk S20 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 S20 digs deeper - 39Hz against 79Hz. |
| Amplifier needs | A | Polk S20 is more sensitive (88dB vs 85dB), so it goes louder on the same amplifier. |
| Headroom | A | Polk S20 takes more power (125W vs 100W) - more in hand in a big room. |
| Size | depends | KEF LS50 is easier to place; Polk S20 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. KEF LS50 sits in a wider range (10 models), so a matched surround system is easier later. |
| Price | A | Polk S20 is cheaper - $299 against $1,300, about 77% less; arguably a different class. |
A Polk S20 B KEF LS50
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 S20 is the easier recommendation: it leads on most of the measured areas and costs less. Take KEF LS50 if its size, looks or fit in your room suit you better. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 79Hz anyway, so judge these on the other rows instead. Match it to your room: we rate Polk S20 the better fit for a mid-size room and a large room, and KEF LS50 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.