In this review, we will be comparing S15 and RTi A1, two Passive Bookshelf speakers by Polk Audio.
Let's have a brief look at the main features
of Polk S15 and Polk RTi A1 first before getting into our more
detailed comparison.
| Key Specs | Polk S15 | Polk RTi A1 |
|---|
| Brand | Polk Audio
United States · founded 1972 | Polk Audio
United States · founded 1972 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1" Dome | 1" Dome |
|---|
| Woofer | 5.25" Mica-reinforced polypropylene | 5.25" Polymer composite |
|---|
| Frequency response | 50-40k Hz | 60-26k Hz |
|---|
| Sensitivity | 88 dB | 89 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 20-100 watts | 20-125 watts |
|---|
| Weight | 5.90kg / 13lbs | 5.44kg / 12lbs |
|---|
| Dimensions (H x W x D) | 12.0" x 7.4" x 10.2"
304.8 x 190.0 x 260.4mm | 12.0" x 7.3" x 11.5"
304.8 x 187.5 x 292.1mm |
|---|
What size room are the Polk S15 and Polk RTi A1 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 RTi A1 |
| 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 RTi A1 are 2-way speakers.
Polk S15Polk RTi A1
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 RTi A1 |
|
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 RTi A1 features a 1" silk polymer composite Dome Tweeter and 1 x 5.25" Polymer composite Woofer with a Crossover frequency at 1900Hz.
Frequency Response
S15 has a frequency range of 50-40k Hz whereas RTi A1 has a frequency range of 60-26k Hz. With a minimum frequency of 50Hz, the S15 can go significantly deeper on the low side and provide stronger bass compared to the RTi A1's min frequency of 60Hz.
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 RTi A1 have the same Impedance of 8 ohms but where they differ is the sensitivity levels. S15 sensitivity is rated at 88 dB and the RTi A1's is at 89 dB. This 1 dB difference makes the Polk RTi A1 a more sensitive speaker compared to Polk S15, 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.
RTi A1 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 RTi A1.
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
RTi A1 features Pair of Dual 5-way Binding Posts - Gold-Plated posts which make bi-amping or bi-wiring possible. S15 has a Pair of Binding Posts - Gold Plated which doesn't feature bi-amping/bi-wiring.
Cabinet Type and Port Position
S15 has a rear firing port whereas RTi A1 has a back and front firing ports.
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 RTi A1'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 RTi A1 has external dimensions of 304.8 x 187.5 x 292.1mm (12.0 x 7.3 x 11.5inch).
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 RTi A1 is approximately 547.7cm2 / 84.9inch2. The S15 requires 10% less surface area than the RTi A1 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 RTi A1 weighs 5.44kg / 12lbs. This makes the S15 8% heavier than the RTi A1.
Here is a comparison of how S15 and RTi A1'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 RTi A1?
Here are the items that come with the RTi A1:
- 2 Cherry bookshelf speakers
- 2 Self-tapping screws
- 8 Self-adhesive rubber feet
- Owner's Manual
- Template
- Online registration sheet
- Polk Audio product brochure
 Low Frequency Response |
50 Hz
vs
60 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
26k Hz
|
Generates higher frequency |
 Base Surface Area |
494cm2
vs
547cm2
|
Takes less floor space |
 Price per pair* |
259USD
vs
382USD
|
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 |
 Sensitivity |
89 dB
vs
88 dB
|
Play louder with same amount of amplification power |
 Bi-Amping and Bi-Wiring |
Yes
vs
No
|
Allows bi-amping and bi-wiring connections |
| General |
Polk Audio Signature S15 |
Polk Audio RTi A1 |
| Brand |
Polk Audio |
Polk Audio |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-100 watts |
20-125 watts |
| Sensitivity |
88 dB |
89 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
50-40k Hz |
60-26k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5.25" |
5.25" |
| Woofer Composition |
Mica-reinforced polypropylene |
Polymer composite |
| Woofer Surround Material |
Butyl rubber |
Butyl rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Dome |
Dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2500Hz |
1900Hz |
| Firing Direction |
rear |
back and front |
Physical Specs |
|
|
| Height |
304.8mm (12") |
304.8mm (12") |
| Width |
190.0mm (7.5") |
187.5mm (7.4") |
| Depth |
260.4mm (10.3") |
292.1mm (11.5") |
| Weight |
5.90kg (13lbs) |
5.44kg (12lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
Real wood veneer |
| Available Colors |
Black, Walnut, Brown Walnut |
Black, Cherry |
| Mounting Bracket |
Keyhole |
Keyhole |
| Recommended Stand Height |
24-30" |
28-36" |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
No |
Yes |
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
A generation apart: Polk S15 is the newer design, against a 2008 model. Newer is not automatically better, but the older one is more likely to be discounted or near run-out.
| Area | Better | Why |
|---|
| Bass | A | Polk S15 digs deeper - 50Hz against 60Hz. |
| Amplifier needs | evenly matched | Similar sensitivity (88dB vs 89dB) - both want much the same power. |
| Headroom | B | Polk RTi A1 takes more power (125W vs 100W) - more in hand in a big room. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | B | Polk RTi A1: bi-amping. |
| Price | A | Polk S15 is cheaper - $259 against $382, about 32% less. |
A Polk S15 B Polk RTi A1
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 RTi A1 is ahead, but only on 1 of the measured areas, and it costs about 47% more. That is a lot of money for a narrow margin on paper - Polk S15 looks like the sensible buy unless something else about the Polk RTi A1 appeals to you. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 60Hz anyway, so judge these on the other rows instead. Match it to your room: we rate Polk S15 the better fit for near-field listening and a small room, and Polk RTi A1 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.