In this review, we will be comparing S15 and S20, two Passive Bookshelf speakers by Polk Audio.
Let's have a brief look at the main features
of Polk S15 and Polk S20 first before getting into our more
detailed comparison.
| Key Specs | Polk S15 | Polk S20 |
|---|
| Brand | Polk Audio
United States · founded 1972 | Polk Audio
United States · founded 1972 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1" Dome | 1" Soft-Dome |
|---|
| Woofer | 5.25" Mica-reinforced polypropylene | 6.5" Mica-reinforced polypropylene |
|---|
| Frequency response | 50-40k Hz | 39-40k Hz |
|---|
| Sensitivity | 88 dB | 88 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 20-100 watts | 20-125 watts |
|---|
| Weight | 5.90kg / 13lbs | 7.73kg / 17lbs |
|---|
| Dimensions (H x W x D) | 12.0" x 7.4" x 10.2"
304.8 x 190.0 x 260.4mm | 14.8" x 8.5" x 13.7"
376.0 x 216.0 x 350.0mm |
|---|
S15 and S20 are members of Polk Audio's Signature S series of speakers. Below you can find the loudspeakers from this series.
What size room are the Polk S15 and Polk S20 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 S15 |
Polk S20 |
| Near-field |
Average |
Poor |
| Small Room |
Good |
Average |
| Mid-size Room |
Average |
Good |
| Large Room |
Poor |
Average |
| Very Large Room |
Bad |
Poor |
(* 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 S15 and S20 are 2-way speakers.
Polk S15Polk S20
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 S15 |
Polk S20 |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 6.5-inch
|
S15 features a 1" Terylene Dome Tweeter and 1 x 5.25" Mica-reinforced polypropylene Woofer with a Crossover frequency at 2500Hz. On the other hand, the S20 features a 1" Terylene Soft-Dome Tweeter and 1 x 6.5" Mica-reinforced polypropylene Woofer with a Crossover frequency at 2500Hz.
Frequency Response
S15 has a frequency range of 50-40k Hz whereas S20 has a frequency range of 39-40k Hz. With a minimum frequency of 39Hz, the S20 can go significantly deeper on the low side and provide stronger bass compared to the S15's min frequency of 50Hz.
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
S15 and S20 have the same Impedance of 8 ohms and their sensitivity is also same at 88 dB.
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 S15 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
S15 features 5-way post type posts and S20 has a 5-way post type posts. None of these speakers feature bi-amping/bi-wiring.
Cabinet Type and Port Position
Both S15 and S20 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 S15's and Polk S20's external dimensions. Polk S15 has external dimensions of 304.8 x 190.0 x 260.4mm (12.0 x 7.4 x 10.2inch) whereas Polk S20 has external dimensions of 376.0 x 216.0 x 350.0mm (14.8 x 8.5 x 13.7inch).
Polk S20 is clearly the larger of the two speakers. Its body is 26mm wider, 71.2mm taller and 89.6mm deeper than Polk S15.
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 S15 is approximately 494.8cm2 / 76.7inch2 and base area of the Polk S20 is approximately 756.0cm2 / 117.2inch2. The S15 requires 35% less surface area than the S20 which gives it a small advantage on placement in tight spaces.
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 S15 weighs 5.90kg / 13lbs and the Polk S20 weighs 7.73kg / 17lbs. This makes the S20 31% heavier than the S15.
Here is a comparison of how S15 and S20'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 S15?
Here are the items that are included inside the box of S15:
- 2 Bookshelf loudspeakers
- 2 Grille (attached)
- 8 Self-adhesive rubber feet
- Wall-mount template
- Owners Manual
- Online Product Registration
What's in the Box of Polk S20?
Here are the items that come with the S20:
- 2 Bookshelf loudspeakers
- 2 Grilles (attached)
- 8 Self-adhesive rubber feet
- Owners Manual
- Online Product Registration
 Mounting Bracket |
Yes
vs
No
|
Allows mounting on walls |
 Height |
304mm
vs
376mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
494cm2
vs
756cm2
|
Takes less floor space |
 Price per pair* |
259USD
vs
299USD
|
costs less (*prices may change depending on the seller, location and time) |
 Max Input Power |
125 watts
vs
100 watts
|
Handle more power from your amplifier |
 Woofer Size |
6.5 inches
vs
5.25 inches
|
Larger woofer |
|
Low Frequency Response |
39 Hz
vs
50 Hz
|
Generates deeper bass |
| General |
Polk Audio Signature S15 |
Polk Audio Signature S20 |
| Brand |
Polk Audio |
Polk Audio |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-100 watts |
20-125 watts |
| Sensitivity |
88 dB |
88 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
50-40k Hz |
39-40k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
6.5" |
| Woofer Composition |
Mica-reinforced polypropylene |
Mica-reinforced polypropylene |
| Woofer Surround Material |
Butyl rubber |
Butyl rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Dome |
Soft-Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2500Hz |
2500Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
304.8mm (12") |
376.0mm (14.8") |
| Width |
190.0mm (7.5") |
216.0mm (8.5") |
| Depth |
260.4mm (10.3") |
350.0mm (13.8") |
| Weight |
5.90kg (13lbs) |
7.73kg (17lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
Meddite MDF |
| Available Colors |
Black, Walnut, Brown Walnut |
Black, Walnut, Brown Walnut |
| Mounting Bracket |
Keyhole |
No |
| Recommended Stand Height |
24-30" |
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 |
Siblings in Polk Audio's Signature S series, so they share a family sound. It comes down to size, output and price.
| Area | Better | Why |
|---|
| Bass | B | Polk S20 digs deeper - 39Hz against 50Hz. |
| Amplifier needs | evenly matched | Similar sensitivity (88dB vs 88dB) - both want much the same power. |
| Headroom | B | Polk S20 takes more power (125W vs 100W) - more in hand in a big room. |
| Size | depends | Polk S15 is easier to place; Polk S20 is bigger, which usually goes with fuller bass. Your room decides. |
| Price | A | Polk S15 is cheaper - $259 against $299, about 13% less. |
A Polk S15 B Polk S20
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?
The usual trade-off: Polk S20 measures better, Polk S15 costs about about 15% more% less. Whether that gap is worth the money is the call only you can make - and in a normal room it is often smaller than the numbers suggest. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 50Hz anyway, which makes the cheaper Polk S15 much easier to justify. Match it to your room: we rate Polk S15 the better fit for near-field listening and a small room, and Polk S20 for a mid-size room and a large 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.