In this review, we will be comparing Grotto 12 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 12 and Polk Monitor XT12 first before getting into our more detailed comparison.
The sections below take each area in turn: driver and amplifier, frequency response, physical size and connectivity.
Drivers
The efficiency of a subwoofer is directly proportional to the total radiating are squared hence the woofer quantity and diameter.MartinLogan Grotto 12and Polk Monitor XT12 have the same driver set up: Both subwoofers have 1 x 12" drivers.
Frequency Response
Grotto 12 has a frequency range of 22-120 Hz whereas Monitor XT12 has a frequency range of 24-160 Hz. With a minimum frequency of 22Hz, the Grotto 12 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 12 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
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 MartinLogan Grotto 12's and Polk Monitor XT12's external dimensions. MartinLogan Grotto 12 has external dimensions of 452.0 x 454.0 x 454.0mm (17-13/16 x 17-7/8 x 17-7/8inch) 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).
Polk Monitor XT12 is 46mm narrower and 34mm shorter than MartinLogan Grotto 12 but it is also 31mm 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.
Near-identical footprints. Polk Monitor XT12 is 31mm deeper, so it stands that much further out from the wall. MartinLogan Grotto 12 is 34mm 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 MartinLogan Grotto 12 is approximately 2061.2cm2 / 319.5inch2 and base area of the Polk Monitor XT12 is approximately 1978.8cm2 / 306.7inch2. The Grotto 12 requires 4% 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 12 weighs 37.40kg / 82.3lbs and the Polk Monitor XT12 weighs 17.73kg / 39lbs. This makes the Grotto 12 111% heavier than the Monitor XT12.
Here is a comparison of how Grotto 12 and Monitor XT12's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
 Low Frequency Response |
22 Hz
vs
24 Hz
|
Generates deeper bass |
 Passive Radiator |
2 x 12-inch
vs
None
|
Increases the bass performance |
 High Frequency Response |
160 Hz
vs
120 Hz
|
Generates higher frequency |
 Height |
418mm
vs
452mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1978cm2
vs
2061cm2
|
Takes less floor space |
 Price per pair* |
399USD
vs
2300USD
|
costs less (*prices may change depending on the seller, location and time) |
Size, drawn to scale
Both subwoofers 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 floor and pushed back to the same wall, so the bigger one visibly takes more of the room.
Near-identical footprints. Polk Monitor XT12 stands 31mm further into the room. MartinLogan Grotto 12 is 34mm taller.
| General |
MartinLogan Grotto 12 |
Polk Monitor XT12 |
| Brand |
MartinLogan |
Polk Audio |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
1000 watts |
50 watts |
| Frequency Response |
22-120 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 |
12" |
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 |
452.0mm (17.8") |
418.0mm (16.5") |
| Width |
454.0mm (17.9") |
408.0mm (16.1") |
| Depth |
454.0mm (17.9") |
485.0mm (19.1") |
| Weight |
37.40kg (82.3lbs) |
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 |
A sealed subwoofer against a ported one. That is the most consequential line on this page: it decides how the bass rolls off, how it behaves in a small room, and how much output you get for the size of the box.
| Area | Better | Why |
|---|
| Bass depth | evenly matched | Effectively the same reach (22Hz vs 24Hz). |
| Amplifier power | A | MartinLogan Grotto 12 has the bigger amplifier - 1000W against 50W RMS, about 13dB more on tap. In a large room that is headroom before the DSP starts limiting. |
| Driver area | evenly matched | Near-identical radiating area (12" against 12"). |
| Enclosure | depends | MartinLogan Grotto 12 is sealed - a sealed box rolls off gently and is usually the easier one to integrate in a small or awkward room; Polk Monitor XT12 is ported - a ported box gives more output low down for its size, at the cost of a steeper roll-off below tuning. Neither is better in the abstract; ported tends to suit films and sealed tends to suit music, and both generalisations have exceptions. |
| Price | B | Polk Monitor XT12 costs less - $399 against $2,300, about 83% less. |
A MartinLogan Grotto 12 B Polk Monitor XT12
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 subwoofers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
MartinLogan Grotto 12 is ahead, but on only 1 of the measured areas, and it costs about 5.8x the price. Polk Monitor XT12 is the sensible buy unless your room is large enough to need the extra. Films or music? If this is mainly a home cinema, Polk Monitor XT12 will hit harder for the money; if it is mainly for music in a normal-sized room, MartinLogan Grotto 12 is usually the easier one to make sound right. Two small subwoofers beat one big one in most rooms - a pair evens out the room modes in a way no single box can, whatever its specs. At $399 each, two Polk Monitor XT12 cost about $798 against $2,300 for one of the other, which is worth a thought.
One thing outweighs everything above: where the subwoofer stands. Room modes can add or remove 10dB or more at a given seat, which is far larger than any difference on this page. Before spending more, try the sub in two or three positions - the crawl test, where you put it in the listening seat and crawl the room to find where the bass sounds best, costs nothing and usually beats an upgrade.