In this review, we will be comparing Monitor XT30 and SX-70, two Center Channel speakers from Polk Audio and Cambridge Audio.
Let's have a brief look at the main features
of Polk XT30 and Cambridge Audio SX-70 first before getting into our more
detailed comparison.
| Key Specs | Polk XT30 | Cambridge Audio SX-70 |
|---|
| Brand | Polk Audio
United States · founded 1972 | Cambridge Audio
United Kingdom · founded 1968 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1" High-res dome | 1" dome |
|---|
| Woofer | 2 x 5.25" bi-laminate paper cone | 2 x 4" treated-paper |
|---|
| Frequency response | 55-40k Hz | 65-22k Hz |
|---|
| Sensitivity | 89 dB | 85 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | 30-200 watts | 10-100 watts |
|---|
| Weight | 5.91kg / 13lbs | 4.00kg / 8.8lbs |
|---|
| Dimensions (H x W x D) | 6-1/2" x 19-1/16" x 8-3/16"
166.0 x 485.0 x 208.0mm | 5-7/16" x 14-1/4" x 9-3/4"
139.0 x 362.0 x 248.0mm |
|---|
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
Both Monitor XT30 and SX-70 are 2-way speakers.
Polk XT30Cambridge Audio SX-70
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 XT30 |
Cambridge Audio SX-70 |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
2 x 5.25-inch
|
2 x 4-inch
|
Monitor XT30 features a 1" Terylene High-res dome Tweeter and 2 x 5.25" bi-laminate paper cone Woofer. On the other hand, the SX-70 features a 1" Silk dome Tweeter and 2 x 4" treated-paper Woofer.
Frequency Response
Monitor XT30 has a frequency range of 55-40k Hz whereas SX-70 has a frequency range of 65-22k Hz. With a minimum frequency of 55Hz, the Monitor XT30 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
Monitor XT30 and SX-70 have the same Impedance of 8 ohms but where they differ is the sensitivity levels. Monitor XT30 sensitivity is rated at 89 dB and the SX-70's is at 85 dB. This 4 dB difference makes the Polk XT30 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.
Monitor XT30 can handle a max power of 200 watts RMS, whereas SX-70 has a max power handling value of 100 watts RMS, 100 watts less than the Monitor XT30.
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
Monitor XT30 features 5-Way post type posts and SX-70 has a 5-Way post type posts. None of these speakers feature bi-amping/bi-wiring.
Polk XT30's 5-Way post terminals
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 XT30's and Cambridge Audio SX-70's external dimensions. Polk XT30 has external dimensions of 166.0 x 485.0 x 208.0mm (6-1/2 x 19-1/16 x 8-3/16inch) whereas 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).
Cambridge Audio SX-70 is 123mm narrower and 27mm shorter than Polk XT30 but it is also 40mm deeper.
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 XT30 needs about 12% more floor or shelf area. Cambridge Audio SX-70 is 40mm deeper, so it stands that much further out from the wall. Polk XT30 is 27mm 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 Polk XT30 is approximately 1008.8cm2 / 156.4inch2 and base area of the Cambridge Audio SX-70 is approximately 897.8cm2 / 139.2inch2. The Monitor XT30 requires 12% more surface area than the SX-70 which gives it a small disadvantage 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 XT30 weighs 5.91kg / 13lbs and the Cambridge Audio SX-70 weighs 4.00kg / 8.8lbs. This makes the Monitor XT30 48% heavier than the SX-70.
Here is a comparison of how Monitor XT30 and SX-70'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 Polk XT30?
Here are the items that are included inside the box of Monitor XT30:
- Center-channel loudspeaker
- Grille (attached)
- 4 Self-adhesive rubber feet
- Owners Manual
- Online Product Registration
- Wall-Mount Template
What's in the Box of Cambridge Audio SX-70?
Here are the items that come with the SX-70:
- Center-channel loudspeaker
- Grille
- 4 Self-adhesive rubber feet
- Installation Guide
 Max Input Power |
200 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 |
5.25 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 |
 Height |
139mm
vs
166mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
897cm2
vs
1008cm2
|
Takes less floor space |
 Price per pair* |
189USD
vs
199USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
Polk Audio Monitor XT30 |
Cambridge Audio SX-70 |
| Brand |
Polk Audio |
Cambridge Audio |
| Speaker Type |
Center channel speaker |
Center channel speaker (Matte Black) |
| Power Range |
30-200 watts |
10-100 watts |
| Sensitivity |
89 dB |
85 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
55-40k Hz |
65-22k Hz |
Drivers |
|
|
| Woofer Quantity |
2 |
2 |
| Woofer Size |
5.25" |
4" |
| Woofer Composition |
bi-laminate paper cone |
treated-paper |
| Tweeter Size |
1" |
1" |
| Tweeter Type |
High-res dome |
dome |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Firing Direction |
rear |
n/a |
Physical Specs |
|
|
| Height |
166.0mm (6.5") |
139.0mm (5.5") |
| Width |
485.0mm (19.1") |
362.0mm (14.3") |
| Depth |
208.0mm (8.2") |
248.0mm (9.8") |
| Weight |
5.91kg (13lbs) |
4.00kg (8.8lbs) |
| Enclosure |
Bass Reflex |
Acoustic Suspension |
| Available Colors |
Black |
Black |
| 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 | A | Polk XT30 digs deeper - 55Hz against 65Hz. |
| Amplifier needs | A | Polk XT30 is more sensitive (89dB vs 85dB), so it goes louder on the same amplifier. |
| Headroom | A | Polk XT30 takes more power (200W vs 100W) - more in hand in a big room. |
| Size | depends | Cambridge Audio SX-70 is easier to place; Polk XT30 is bigger, which usually goes with fuller bass. Your room decides. |
| Cabinet | depends | Ported vs Sealed. 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 XT30 sits in a wider range (9 models), so a matched surround system is easier later. |
| Price | evenly matched | Much the same money ($199 vs $189 a pair). |
A Polk XT30 B Cambridge Audio SX-70
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 XT30 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 a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 65Hz anyway, so judge these on the other rows instead. Match it to your room: we rate Polk XT30 the better fit for a mid-size room and a large room, and Cambridge Audio SX-70 for near-field listening and a small 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.