In this review, we will be comparing S15 and Q150, two Passive Bookshelf speakers from Polk Audio and KEF.
Let's have a brief look at the main features
of Polk S15 and KEF Q150 first before getting into our more
detailed comparison.
| Key Specs | Polk S15 | KEF Q150 |
|---|
| Design | 2-way | 2-way |
|---|
| Uni-Q driver | — | 11th Generation Uni-Q |
|---|
| Tweeter | 1" Dome | 1" Dome |
|---|
| Woofer | 5.25" Mica-reinforced polypropylene | 5.25" Aluminum |
|---|
| Frequency response | 50-40k Hz | 51-28k Hz |
|---|
| Sensitivity | 88 dB | 86 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 20-100 watts | 10-100 watts |
|---|
| Weight | 5.90kg / 13lbs | 5.60kg / 12.3lbs |
|---|
| Dimensions (H x W x D) | 12.0" x 7.4" x 10.2"
304.8 x 190.0 x 260.4mm | 11.9" x 7.0" x 10.9"
303.0 x 180.0 x 278.0mm |
|---|
What size room are the Polk S15 and KEF Q150 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 |
KEF Q150 |
| Near-field |
Average |
Average |
| Small Room |
Good |
Good |
| Mid-size Room |
Average |
Average |
| Large Room |
Poor |
Poor |
| Very Large Room |
Bad |
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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through our links. As an Amazon Associate I earn from qualifying purchases.
Drivers
Both S15 and Q150 are 2-way speakers.
Polk S15KEF Q150
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 |
KEF Q150 |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5.25-inch
|
1 x 5.25-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 Q150 features a 1" vented aluminum Dome Tweeter and 1 x 5.25" Aluminum Woofer with a Crossover frequency at 2500Hz.
Frequency Response
S15 has a frequency range of 50-40k Hz whereas Q150 has a frequency range of 51-28k Hz. With a minimum frequency of 50Hz, the S15 can go slightly deeper then the Q150's min frequency of 51Hz.
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 Q150 have the same Impedance of 8 ohms but where they differ is the sensitivity levels. S15 sensitivity is rated at 88 dB and the Q150's is at 86 dB. This 2 dB difference makes the Polk S15 a more sensitive speaker compared to KEF Q150, 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.
Both handle the same maximum of 100 watts RMS, though S15 is rated 20-100 watts and Q150 10-100 watts.
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 Post type posts and Q150 has a Post type posts. None of these speakers feature bi-amping/bi-wiring.
KEF Q150's Post terminals
Cabinet Type and Port Position
Both S15 and Q150 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.
KEF Q150 Port
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 KEF Q150'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 KEF Q150 has external dimensions of 303.0 x 180.0 x 278.0mm (11.9 x 7.0 x 10.9inch).
KEF Q150 is 10mm narrower and 1.8mm shorter than Polk S15 but it is also 17.6mm deeper.
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 KEF Q150 is approximately 500.4cm2 / 77.6inch2. The S15 requires 1% less surface area than the Q150 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 KEF Q150 weighs 5.60kg / 12.3lbs. This makes the S15 5% heavier than the Q150.
Here is a comparison of how S15 and Q150'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 KEF Q150?
Here are the items that come with the Q150:
- 2 Bookshelf loudspeakers
- 2 Foam port plugs
- 8 Self-adhesive rubber feet
- Owner's Manual
- Warranty Registration Card
 Sensitivity |
88 dB
vs
86 dB
|
Play louder with same amount of amplification power |
 Low Frequency Response |
50 Hz
vs
51 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
28k Hz
|
Generates higher frequency |
 Mounting Bracket |
Yes
vs
No
|
Allows mounting on walls |
 Base Surface Area |
494cm2
vs
500cm2
|
Takes less floor space |
 Price per pair* |
259USD
vs
600USD
|
costs less (*prices may change depending on the seller, location and time) |
 Height |
303mm
vs
304mm
|
Easier to fit in smaller spaces |
| General |
Polk Audio Signature S15 |
KEF Q150 |
| Brand |
Polk Audio |
KEF |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-100 watts |
10-100 watts |
| Sensitivity |
88 dB |
86 dB |
| Impedance |
8 ohms |
8 ohms |
| Impedance |
n/a |
3.7 ohms |
| Frequency Response |
50-40k Hz |
51-28k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
5.25" |
| Woofer Composition |
Mica-reinforced polypropylene |
Aluminum |
| Woofer Surround Material |
Butyl rubber |
Rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Dome |
Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2500Hz |
2500Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
304.8mm (12") |
303.0mm (11.9") |
| Width |
190.0mm (7.5") |
180.0mm (7.1") |
| Depth |
260.4mm (10.3") |
278.0mm (10.9") |
| Weight |
5.90kg (13lbs) |
5.60kg (12.3lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
MDF/Vinyl-wrapped |
| Available Colors |
Black, Walnut, Brown Walnut |
Black, Walnut, White |
| Mounting Bracket |
Keyhole |
No |
| Recommended Stand Height |
24-30" |
18-24" |
| 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 - KEF Q150 costs roughly 2.3x what Polk S15 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 |
evenly matched |
Much the same reach (50Hz vs 51Hz). |
| Amplifier needs |
A |
Polk S15 is more sensitive (88dB vs 86dB), so it goes louder on the same amplifier. |
| Headroom |
evenly matched |
Similar power handling (100W vs 100W). |
| Size |
depends |
Similar cabinet size - neither is easier to fit. |
| Price |
A |
Polk S15 is cheaper - $259 against $600, about 57% less; arguably a different class. |
A Polk S15
B KEF Q150
depends neither is better in the abstract - it turns on your room, placement 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 S15 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 your amplifier is modest, vintage or valve-based, Polk S15 is the safer partner - the other will want more current or more watts to sound its best. Think about the whole system, not just the speakers: the roughly $341 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
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.