In this review, we will be comparing S20 and Uni-Fi BS U5 Slim, two Passive Bookshelf speakers from Polk Audio and ELAC.
Let's have a brief look at the main features
of Polk S20 and ELAC Uni-Fi BS U5 Slim first before getting into our more
detailed comparison.
| Key Specs | Polk S20 | ELAC Uni-Fi BS U5 Slim |
|---|
| Brand | Polk Audio
United States · founded 1972 | ELAC
Germany · founded 1926 |
|---|
| Design | 2-way | 3-way |
|---|
| Tweeter | 1" Soft-Dome | 1" soft dome |
|---|
| Midrange | — | 4" |
|---|
| Woofer | 6.5" Mica-reinforced polypropylene | 5.25" Aluminum |
|---|
| Frequency response | 39-40k Hz | 46-25k Hz |
|---|
| Sensitivity | 88 dB | 85 dB |
|---|
| Impedance | 8 ohms | 4 ohms |
|---|
| Power range | 20-125 watts | 40-140 watts |
|---|
| Weight | 7.73kg / 17lbs | 7.50kg / 16.5lbs |
|---|
| Dimensions (H x W x D) | 14.8" x 8.5" x 13.7"
376.0 x 216.0 x 350.0mm | 13-3/8" x 7-1/16" x 12-7/8"
340.0 x 180.0 x 328.0mm |
|---|
What size room are the Polk S20 and ELAC Uni-Fi BS U5 Slim 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 |
ELAC Uni-Fi BS U5 Slim |
| Near-field |
Poor |
Poor |
| Small Room |
Average |
Average |
| Mid-size Room |
Good |
Good |
| Large Room |
Average |
Average |
| Very Large Room |
Poor |
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
One of the fundamental differences between these two speakers is that S20 is a 2-way design whereas the Uni-Fi BS U5 Slim is a 3-way speaker. 3-way designs utilize a midrange driver in addition to the tweeter and woofer on 2-way designs. Designing a crossover for a 3-way speaker is a complicated process and generally increases the overall cost of the speaker.
Polk S20ELAC Uni-Fi BS U5 Slim
TweeterMidrangeWoofer
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 |
ELAC Uni-Fi BS U5 Slim |
|
Driver Setup
|
2-way
|
3-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
1 x 4-inch |
|
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 Uni-Fi BS U5 Slim features a 1" soft dome Tweeter, a 4" Midrange and 1 x 5.25" Aluminum Woofer.
Frequency Response
S20 has a frequency range of 39-40k Hz whereas Uni-Fi BS U5 Slim has a frequency range of 46-25k Hz. With a minimum frequency of 39Hz, the S20 can go significantly deeper on the low side and provide stronger bass compared to the Uni-Fi BS U5 Slim's min frequency of 46Hz.
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 is a 8 ohms speaker compared to the Uni-Fi BS U5 Slim which has a nominal impedance of 4 ohms. Lower impedance speakers, especially the ones that are rated at 4 ohms may put more pressure on the amplifier unit especially when played at high volume levels, so make sure the amp you pair with the Uni-Fi BS U5 Slim can provide this impedance level.
These two speakers also have different sensitivity levels. S20 sensitivity is rated at 88 dB and the Uni-Fi BS U5 Slim's is rated at 85 dB. This 3 dB difference makes the Polk S20 a more sensitive speaker compared to ELAC Uni-Fi BS U5 Slim, 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.
Uni-Fi BS U5 Slim can handle a max power of 140 watts RMS, whereas S20 has a max power handling value of 125 watts RMS, 15 watts less than the Uni-Fi BS U5 Slim.
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 Uni-Fi BS U5 Slim has a Post type posts. None of these speakers feature bi-amping/bi-wiring.
ELAC Uni-Fi BS U5 Slim's Post terminals
Cabinet Type and Port Position
Both S20 and Uni-Fi BS U5 Slim 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 ELAC Uni-Fi BS U5 Slim'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 ELAC Uni-Fi BS U5 Slim has external dimensions of 340.0 x 180.0 x 328.0mm (13-3/8 x 7-1/16 x 12-7/8inch).
Polk S20 is clearly the larger of the two speakers. Its body is 36mm wider, 36mm taller and 22mm deeper than ELAC Uni-Fi BS U5 Slim.
Below you can see the front view size comparison of Polk S20 and ELAC Uni-Fi BS U5 Slim in scale.
Comparison image of Polk S20 and ELAC Uni-Fi BS U5 Slim 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 ELAC Uni-Fi BS U5 Slim is approximately 590.4cm2 / 91.5inch2. The S20 requires 28% more surface area than the Uni-Fi BS U5 Slim 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 ELAC Uni-Fi BS U5 Slim 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 ELAC Uni-Fi BS U5 Slim weighs 7.50kg / 16.5lbs. This makes the S20 3% heavier than the Uni-Fi BS U5 Slim.
Here is a comparison of how S20 and Uni-Fi BS U5 Slim'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 ELAC Uni-Fi BS U5 Slim?
Here are the items that come with the Uni-Fi BS U5 Slim:
- 2 Bookshelf loudspeakers
- 2 Grilles
- Operating Instructions
 Sensitivity |
88 dB
vs
85 dB
|
Play louder with same amount of amplification power |
 Nominal Impedance |
8 ohms
vs
4 ohms
|
Less selective with amplifiers |
 Woofer Size |
6.5 inches
vs
5.25 inches
|
Larger woofer |
|
Low Frequency Response |
39 Hz
vs
46 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
25k Hz
|
Generates higher frequency |
 Price per pair* |
299USD
vs
735USD
|
costs less (*prices may change depending on the seller, location and time) |
 Max Input Power |
140 watts
vs
125 watts
|
Handle more power from your amplifier |
 Driver Setup |
3-way
vs
2-way
|
Have a dedicated mid-range driver |
 Height |
340mm
vs
376mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
590cm2
vs
756cm2
|
Takes less floor space |
| General |
Polk Audio Signature S20 |
ELAC Uni-Fi BS U5 Slim |
| Brand |
Polk Audio |
ELAC |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
20-125 watts |
40-140 watts |
| Sensitivity |
88 dB |
85 dB |
| Impedance |
8 ohms |
4 ohms |
| Frequency Response |
39-40k Hz |
46-25k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6.5" |
5.25" |
| Woofer Composition |
Mica-reinforced polypropylene |
Aluminum |
| Woofer Surround Material |
Butyl rubber |
Rubber |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
Soft-Dome |
soft dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
4" |
| Crossover Frequency |
2500Hz |
n/a |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
376.0mm (14.8") |
340.0mm (13.4") |
| Width |
216.0mm (8.5") |
180.0mm (7.1") |
| Depth |
350.0mm (13.8") |
328.0mm (12.9") |
| Weight |
7.73kg (17lbs) |
7.50kg (16.5lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
Meddite MDF |
MDF/Vinyl |
| Available Colors |
Black, Walnut, Brown Walnut |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
24-28" |
24-31" |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
No |
No |
Other |
|
|
| Parts Warranty |
5 Years |
3 Years |
| Labor Warranty |
5 Years |
3 Years |
These sit in different price classes - ELAC Uni-Fi BS U5 Slim costs roughly 2.5x 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 46Hz. A subwoofer would even that out. |
| Amplifier needs | A | Polk S20 is more sensitive (88dB vs 85dB), so it goes louder on the same amplifier. |
| Amplifier match | A | Polk S20 is the easier load at 8 ohms; the other is 4 ohms and wants an amplifier rated for it. |
| Headroom | evenly matched | Similar power handling (125W vs 140W). |
| Size | depends | ELAC Uni-Fi BS U5 Slim is easier to place; Polk S20 is bigger, which usually goes with fuller bass. Your room decides. |
| Price | A | Polk S20 is cheaper - $299 against $735, about 59% less; arguably a different class. |
A Polk S20 B ELAC Uni-Fi BS U5 Slim
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 ELAC Uni-Fi BS U5 Slim 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 46Hz anyway, so judge these on the other rows instead. In a large or open-plan room, Polk S20 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, ELAC Uni-Fi BS U5 Slim is the easier speaker to get right.
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.