In this review, we will be comparing SX-70 and ES30, two Center Channel speakers from Cambridge Audio and Polk Audio.
Let's have a brief look at the main features
of Cambridge Audio SX-70 and Polk ES30 first before getting into our more
detailed comparison.
| Key Specs | Cambridge Audio SX-70 | Polk ES30 |
|---|
| Brand | Cambridge Audio
United Kingdom · founded 1968 | Polk Audio
United States · founded 1972 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1" dome | 1" High-res dome |
|---|
| Woofer | 2 x 4" treated-paper | 2 x 5.5" mica-reinforced polypropylene Dynamic Balance |
|---|
| Frequency response | 65-22k Hz | 55-40k Hz |
|---|
| Sensitivity | 85 dB | 89 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 10-100 watts | 20-125 watts |
|---|
| Weight | 4.00kg / 8.8lbs | 8.64kg / 19lbs |
|---|
| Dimensions (H x W x D) | 5-7/16" x 14-1/4" x 9-3/4"
139.0 x 362.0 x 248.0mm | 7-1/2" x 20-1/16" x 10-5/8"
191.0 x 510.0 x 270.0mm |
|---|
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
Both SX-70 and ES30 are 2-way speakers.
Cambridge Audio SX-70Polk ES30
TweeterWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
Cambridge Audio SX-70 |
Polk ES30 |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
2 x 4-inch
|
2 x 5.5-inch
|
SX-70 features a 1" Silk dome Tweeter and 2 x 4" treated-paper Woofer. On the other hand, the ES30 features a 1" Terylene High-res dome Tweeter and 2 x 5.5" mica-reinforced polypropylene Dynamic Balance Woofer.
Frequency Response
SX-70 has a frequency range of 65-22k Hz whereas ES30 has a frequency range of 55-40k Hz. With a minimum frequency of 55Hz, the ES30 can go significantly deeper on the low side and provide stronger bass compared to the SX-70's min frequency of 65Hz.
The graph below depicts how these two speakers compare with the max, min and average Low Frequency values of other speakers in the Center Channel class in our database.
Low Frequency
Center Channel 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
SX-70 and ES30 have the same Impedance of 8 ohms but where they differ is the sensitivity levels. SX-70 sensitivity is rated at 85 dB and the ES30's is at 89 dB. This 4 dB difference makes the Polk ES30 a more sensitive speaker compared to Cambridge Audio SX-70, hence will play louder with the same amount of watts.
Sensitivity
Center Channel 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.
ES30 can handle a max power of 125 watts RMS, whereas SX-70 has a max power handling value of 100 watts RMS, 25 watts less than the ES30.
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
SX-70 features 5-Way post type posts and ES30 has a 5-Way post type posts. None of these speakers feature bi-amping/bi-wiring.
Polk ES30's 5-Way post terminals
Polk ES30 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 Cambridge Audio SX-70's and Polk ES30's external dimensions. Cambridge Audio SX-70 has external dimensions of 139.0 x 362.0 x 248.0mm (5-7/16 x 14-1/4 x 9-3/4inch) whereas Polk ES30 has external dimensions of 191.0 x 510.0 x 270.0mm (7-1/2 x 20-1/16 x 10-5/8inch).
Polk ES30 is clearly the larger of the two speakers. Its body is 148mm wider, 52mm taller and 22mm deeper than Cambridge Audio SX-70.
Size, drawn to scale
Both speakers and both views share one scale, so everything here is directly comparable. Hover a box for its dimensions.
One scale for both, standing on the same surface and pushed back to the same wall, so the deeper one visibly sticks out further.
Polk ES30 needs about 53% more floor or shelf area. Polk ES30 is 22mm deeper, so it stands that much further out from the wall. Polk ES30 is 52mm taller.
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 Cambridge Audio SX-70 is approximately 897.8cm2 / 139.2inch2 and base area of the Polk ES30 is approximately 1377.0cm2 / 213.4inch2. The SX-70 requires 35% less surface area than the ES30 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 Cambridge Audio SX-70 weighs 4.00kg / 8.8lbs and the Polk ES30 weighs 8.64kg / 19lbs. This makes the ES30 116% heavier than the SX-70.
Here is a comparison of how SX-70 and ES30's weights compare with the average, max and min weights in Passive Center Channel class.
Weight
All Center Channel Speakers
What's in the Box of Cambridge Audio SX-70?
Here are the items that are included inside the box of SX-70:
- Center-channel loudspeaker
- Grille
- 4 Self-adhesive rubber feet
- Installation Guide
What's in the Box of Polk ES30?
Here are the items that come with the ES30:
- Center-channel loudspeaker
- Grille (attached)
- 4 Self-adhesive rubber feet
- Owners Manual
- Online Product Registration
 Height |
139mm
vs
191mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
897cm2
vs
1377cm2
|
Takes less floor space |
 Price per pair* |
189USD
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 |
 Sensitivity |
89 dB
vs
85 dB
|
Play louder with same amount of amplification power |
 Woofer Size |
5.5 inches
vs
4 inches
|
Larger woofer |
|
Low Frequency Response |
55 Hz
vs
65 Hz
|
Generates deeper bass |
 High Frequency Response |
40k Hz
vs
22k Hz
|
Generates higher frequency |
| General |
Cambridge Audio SX-70 |
Polk Audio Signature Elite ES30 |
| Brand |
Cambridge Audio |
Polk Audio |
| Speaker Type |
Center channel speaker (Matte Black) |
Center channel speaker |
| Power Range |
10-100 watts |
20-125 watts |
| Sensitivity |
85 dB |
89 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
65-22k Hz |
55-40k Hz |
Drivers |
|
|
| Woofer Quantity |
2 |
2 |
| Woofer Size |
4" |
5.5" |
| Woofer Composition |
treated-paper |
mica-reinforced polypropylene Dynamic Balance |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
dome |
High-res dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Firing Direction |
n/a |
rear |
Physical Specs |
|
|
| Height |
139.0mm (5.5") |
191.0mm (7.5") |
| Width |
362.0mm (14.3") |
510.0mm (20.1") |
| Depth |
248.0mm (9.8") |
270.0mm (10.6") |
| Weight |
4.00kg (8.8lbs) |
8.64kg (19lbs) |
| Enclosure |
Acoustic Suspension |
Bass Reflex |
| Finish |
n/a |
MDF, Wood-grain vinyl |
| Available Colors |
Black |
Black, Walnut, White |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
No single best speaker here - they are built to different priorities, and the right one depends on your room, your amplifier and what you listen to.
| Area | Better | Why |
|---|
| Bass | B | Polk ES30 digs deeper - 55Hz against 65Hz. |
| Amplifier needs | B | Polk ES30 is more sensitive (89dB vs 85dB), so it goes louder on the same amplifier. |
| Headroom | B | Polk ES30 takes more power (125W vs 100W) - more in hand in a big room. |
| Size | depends | Cambridge Audio SX-70 is easier to place; Polk ES30 is bigger, which usually goes with fuller bass. Your room decides. |
| Cabinet | depends | Sealed vs Ported. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. Polk ES30 sits in a wider range (12 models), so a matched surround system is easier later. |
| Price | A | Cambridge Audio SX-70 is cheaper - $189 against $299, about 37% less. |
A Cambridge Audio SX-70 B Polk ES30
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 ES30 measures better, Cambridge Audio SX-70 costs about about 58% 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 65Hz anyway, which makes the cheaper Cambridge Audio SX-70 much easier to justify. Match it to your room: we rate Cambridge Audio SX-70 the better fit for near-field listening and a small room, and Polk ES30 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.