In this review, we will be comparing Grotto 15 and Monitor XT12, two Powered Subwoofer speakers from MartinLogan and Polk Audio. 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 MartinLogan Grotto 15 and Polk Monitor XT12 first before getting into our more detailed comparison.
In the following sections, we will get into details in order to better understand how the MartinLogan Grotto 15 and Polk Monitor XT12 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 MartinLogan Grotto 15and Polk Monitor XT12 have a single woofer setup however the MartinLogan Grotto 15's woofer is 15-inch whereas the Polk Monitor XT12 features a 12-inch woofer.
Frequency Response
Grotto 15 has a frequency range of 20-120 Hz whereas Monitor XT12 has a frequency range of 24-160 Hz. With a minimum frequency of 20Hz, the Grotto 15 can go slightly deeper then the Monitor XT12's min frequency of 24Hz.
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 MartinLogan Grotto 15 has a Acoustic Suspension type cabinet. 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. On the other hand the Polk Monitor XT12 have Bass Reflex type enclosure. 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.
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 MartinLogan Grotto 15's and Polk Monitor XT12's external dimensions. MartinLogan Grotto 15 has external dimensions of 522.0 x 554.0 x 554.0mm ( 20-9/16 x 21-13/16 x 21-13/16inch) whereas 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 ) .
MartinLogan Grotto 15 is clearly the larger of the two speakers. Its body is 146mm wider, 104mm taller and 69mm deeper than Polk Monitor XT12.
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 MartinLogan Grotto 15 is approximately 3069.2cm2 / 475.7inch2 and base area of the Polk Monitor XT12 is approximately 1978.8cm2 / 306.7inch2. The Grotto 15 requires 55% more surface area than the Monitor XT12 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 MartinLogan Grotto 15 weighs 53.50kg / 117.7lbs and the Polk Monitor XT12 weighs 17.73kg / 39lbs. This makes the Grotto 15 202% heavier than the Monitor XT12.
Here is a comparison of how Grotto 15 and Monitor XT12's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
 Woofer Size |
15 inches
vs
12 inches
|
Larger woofer |
| Low Frequency Response |
20 Hz
vs
24 Hz
|
Generates deeper bass |
 Passive Radiator |
2 x 15-inch
vs
None
|
Increases the bass performance |
 High Frequency Response |
160k Hz
vs
120k Hz
|
Generates higher frequency |
 Height |
418mm
vs
522mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1978cm2
vs
3069cm2
|
Takes less floor space |
 Price per pair* |
399USD
vs
2800USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
MartinLogan Grotto 15 |
Polk Monitor XT12 |
| Brand |
MartinLogan |
Polk Audio |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
1000 watts |
50 watts |
| Frequency Response |
20-120 Hz |
24-160 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
1000-watt RMS |
50-watt RMS |
| Watts Peak (Max) |
2000-watt RMS |
n/a |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
15" |
12" |
| Woofer Composition |
Aluminium |
Bi-laminate paper |
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
35–120Hz |
n/a |
| Firing Direction |
n/a |
front |
Physical Specs |
|
|
| Height |
522.0mm (20.6") |
418.0mm (16.5") |
| Width |
554.0mm (21.8") |
408.0mm (16.1") |
| Depth |
554.0mm (21.8") |
485.0mm (19.1") |
| Weight |
53.50kg (117.7lbs) |
17.73kg (39lbs) |
| Enclosure |
Acoustic Suspension |
Bass Reflex |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
|
3 Years |
| Labor Warranty |
|
3 Years |