In this review, we will be comparing Monitor XT12 and KUBE 8b, two Powered Subwoofer speakers from Polk Audio and KEF. Being Powered subwoofers, they both have built-in amplifiers so you don't need an external power amp or an integrated amp to power them. Let's have a brief look at the main features of Polk Monitor XT12 and KEF KUBE 8b first before getting into our more detailed comparison.
In the following sections, we will get into details in order to better understand how the Polk Monitor XT12 and KEF KUBE 8b compare and hopefully end up with enough arguments to decide which one of these subwoofers is the better choice for you.
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Drivers
The efficiency of a subwoofer is directly proportional to the total radiating are squared hence the woofer quantity and diameter.Both Polk Monitor XT12and KEF KUBE 8b have a single woofer setup however the Polk Monitor XT12's woofer is 12-inch whereas the KEF KUBE 8b features a 8-inch woofer.
Frequency Response
Monitor XT12 has a frequency range of 24-160 Hz whereas KUBE 8b has a frequency range of 34-140 Hz. With a minimum frequency of 24Hz, the Monitor XT12 can go significantly deeper on the low side and provide stronger bass compared to the KUBE 8b's min frequency of 34Hz.
Below graphs depict how these two speakers compare with the max, min and average values of the Min and Max Frequencies of other speakers in the Subwoofer class in our database.
Low Frequency
Subwoofer Speakers
High Frequency
Subwoofer Speakers
Cabinet Type
The Polk Monitor XT12 has a Bass Reflex type cabinet. Bass Reflex type subwoofers (aka Ported, Vented or Reflex Port) have enclosures that uses a port, hole or vent cut into the cabinet. Ported designs are generally more efficient than the Sealed designs. On the other hand the KEF KUBE 8b have Acoustic Suspension type enclosure. Acoustic Suspension aka Sealed type subwoofers have enclosures that are sealed hence no ports or holes exists on the cabinet. Sealed designs helps to provide more accurate and tight bass responses compared to ported designs.
Physical Specs
Size of a speaker can sometimes become 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 Monitor XT12's and KEF KUBE 8b's external dimensions. Polk Monitor XT12 has external dimensions of 418.0 x 408.0 x 485.0mm ( 16-7/16inch x 16-1/16inch x 19-1/16inch ) whereas KEF KUBE 8b has external dimensions of 294.0 x 296.0 x 339.0mm ( 11-9/16 x 11-5/8 x 13-5/16inch) .
Polk Monitor XT12 is clearly the larger of the two speakers. Its body is 112mm wider, 124mm taller and 146mm deeper than KEF KUBE 8b.
Below you can see the front view size comparison of Polk Monitor XT12 and KEF KUBE 8b in scale.
Comparison image of Polk Monitor XT12 and KEF KUBE 8b 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 Monitor XT12 is approximately 1978.8cm2 / 306.7inch2 and base area of the KEF KUBE 8b is approximately 1003.4cm2 / 155.5inch2. The Monitor XT12 requires 97% more surface area than the KUBE 8b which gives it a small disadvantage on placement in tight spaces.
Weight Comparison The weight of a subwoofer may become an important factor if you need to move and reposition the unit often to find the optimal positioning, also known as 'Subwoofer Crawling'. The Polk Monitor XT12 weighs 17.73kg / 39lbs and the KEF KUBE 8b weighs 11.36kg / 25lbs. This makes the Monitor XT12 56% heavier than the KUBE 8b.
Here is a comparison of how Monitor XT12 and KUBE 8b's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
What's in the Box of Polk Monitor XT12?
Here are the items that are included inside the box of Monitor XT12:
Black powered subwoofer6.5-feet AC power cordGrilleOwners ManualOnline registration card
What's in the Box of KEF KUBE 8b?
Here are the items that come with the KUBE 8b:
Powered subwoofer6.5-feet AC power cordSpeaker-level input blockUser ManualImportant Safety InformationWarranty Information
 Woofer Size |
12 inches
vs
8 inches
|
Larger woofer |
| Low Frequency Response |
24 Hz
vs
34 Hz
|
Generates deeper bass |
 High Frequency Response |
160k Hz
vs
140k Hz
|
Generates higher frequency |
 Price per pair* |
399USD
vs
600USD
|
costs less (*prices may change depending on the seller, location and time) |
 Height |
294mm
vs
418mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1003cm2 (296x339mm)
vs
1978cm2 (408x485mm)
|
Takes less floor space |
| General |
Polk Monitor XT12 |
KEF KUBE 8b |
| Brand |
Polk Audio |
KEF |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
50 watts |
300 watts |
| Frequency Response |
24-160 Hz |
34-140 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
50-watt RMS |
300-watt RMS |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
12" |
8" |
| Woofer Composition |
Bi-laminate paper |
Not given |
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
n/a |
40-140 Hz |
| Firing Direction |
front |
front |
Physical Specs |
|
|
| Height |
418.0mm (16.5") |
294.0mm (11.6") |
| Width |
408.0mm (16.1") |
296.0mm (11.7") |
| Depth |
485.0mm (19.1") |
339.0mm (13.3") |
| Weight |
17.73kg (39lbs) |
11.36kg (25lbs) |
| Enclosure |
Bass Reflex |
Acoustic Suspension |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
3 Years |
2 Years |
| Labor Warranty |
3 Years |
2 Years |