In this review, we will be comparing Grotto 15 and A120P, two Powered Subwoofer speakers from MartinLogan and JBL. 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 JBL Stage A120P 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.Both MartinLogan Grotto 15and JBL Stage A120P have a single woofer setup however the MartinLogan Grotto 15's woofer is 15-inch whereas the JBL Stage A120P features a 12-inch woofer.
Frequency Response
Grotto 15 has a frequency range of 20-120 Hz whereas A120P has a frequency range of 32-150 Hz. With a minimum frequency of 20Hz, the Grotto 15 can go significantly deeper on the low side and provide stronger bass compared to the A120P's min frequency of 32Hz.
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 JBL Stage A120P have Bass reflex type enclosure.
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 15's and JBL Stage A120P'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 JBL Stage A120P has external dimensions of 415.0 x 393.0 x 475.0mm (16-5/16 x 15-7/16 x 18-11/16inch).
MartinLogan Grotto 15 is clearly the larger of the two speakers. Its body is 161mm wider, 107mm taller and 79mm deeper than JBL Stage A120P.
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.
MartinLogan Grotto 15 needs about 64% more floor or shelf area. MartinLogan Grotto 15 is 79mm deeper, so it stands that much further out from the wall. MartinLogan Grotto 15 is 107mm 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 15 is approximately 3069.2cm2 / 475.7inch2 and base area of the JBL Stage A120P is approximately 1866.8cm2 / 289.4inch2. The Grotto 15 requires 64% more surface area than the A120P 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 JBL Stage A120P weighs 18.68kg / 41.1lbs. This makes the Grotto 15 186% heavier than the A120P.
Here is a comparison of how Grotto 15 and A120P'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
32 Hz
|
Generates deeper bass |
 Passive Radiator |
2 x 15-inch
vs
None
|
Increases the bass performance |
 High Frequency Response |
150 Hz
vs
120 Hz
|
Generates higher frequency |
 Height |
415mm
vs
522mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1866cm2
vs
3069cm2
|
Takes less floor space |
 Price per pair* |
300USD
vs
2800USD
|
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.
MartinLogan Grotto 15 needs about 64% more floor area. MartinLogan Grotto 15 stands 79mm further into the room. MartinLogan Grotto 15 is 107mm taller.
| General |
MartinLogan Grotto 15 |
JBL Stage A120P |
| Brand |
MartinLogan |
JBL |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
1000 watts |
250 watts |
| Frequency Response |
20-120 Hz |
32-150 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
1000-watt RMS |
250-watt RMS |
| Watts Peak (Max) |
2000-watt RMS |
500-watt RMS |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
15" |
12" |
| Woofer Composition |
Aluminium |
Polycellulose |
| 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") |
415.0mm (16.3") |
| Width |
554.0mm (21.8") |
393.0mm (15.5") |
| Depth |
554.0mm (21.8") |
475.0mm (18.7") |
| Weight |
53.50kg (117.7lbs) |
18.68kg (41.1lbs) |
| Enclosure |
Acoustic Suspension |
Bass reflex |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
|
1 Year |
| Labor Warranty |
|
1 Year |
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 | A | MartinLogan Grotto 15 goes deeper - 20Hz against 32Hz. Under 20Hz is felt more than heard - the bottom of a pipe organ and the bottom of a film mix. |
| Amplifier power | A | MartinLogan Grotto 15 has the bigger amplifier - 1000W against 250W RMS, about 6dB more on tap. In a large room that is headroom before the DSP starts limiting. |
| Driver area | A | MartinLogan Grotto 15 moves more air: 15" against 12" is 1.56x the cone area, not the 1.25x the diameters suggest. More area means the same output with less excursion, and less distortion with it. |
| Enclosure | depends | MartinLogan Grotto 15 is sealed - a sealed box rolls off gently and is usually the easier one to integrate in a small or awkward room; JBL Stage A120P 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. |
| Speaker-level inputs | A | MartinLogan Grotto 15 takes a speaker-level connection as well as line level. That is what lets it work with an integrated amplifier or a vintage receiver that has no subwoofer output at all. |
| Cabinet size | depends | JBL Stage A120P is about 52% smaller by volume. In a subwoofer that is a real trade rather than a preference: box volume is how you get output low down without a bigger amplifier. |
| Price | B | JBL Stage A120P costs less - $300 against $2,800, about 89% less. |
A MartinLogan Grotto 15 B JBL Stage A120P
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?
The usual trade-off: MartinLogan Grotto 15 measures better, JBL Stage A120P costs about 89% less. In a normal room, placement will make a bigger difference than the gap between these two. Films or music? If this is mainly a home cinema, JBL Stage A120P will hit harder for the money; if it is mainly for music in a normal-sized room, MartinLogan Grotto 15 is usually the easier one to make sound right. Check your amplifier first: if it has no subwoofer or preamp output, MartinLogan Grotto 15 is the only one of these two you can connect at all.
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.