In this review, we will be comparing Grotto 15 and KF92, two Powered Subwoofer speakers from MartinLogan 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 MartinLogan Grotto 15 and KEF KF92 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 KEF KF92 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.MartinLogan Grotto 15 and KEF KF92 have a totally different setup: the MartinLogan Grotto 15 features 1 x 15-inch drivers whereas the KF92 features 2 x 9-inch drivers.
Frequency Response
Grotto 15 has a frequency range of 20-120 Hz whereas KF92 has a frequency range of 11-200 Hz. With a minimum frequency of 11Hz, the KF92 can go significantly deeper on the low side and provide stronger bass compared to the Grotto 15's min frequency of 20Hz.
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
Both MartinLogan Grotto 15 and KEF KF92 have Acoustic Suspension type cabinets. 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 MartinLogan Grotto 15's and KEF KF92'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 KEF KF92 has external dimensions of 353.0 x 331.0 x 362.0mm ( 13-7/8 x 13 x 14-1/4inch) .
MartinLogan Grotto 15 is clearly the larger of the two speakers. Its body is 223mm wider, 169mm taller and 192mm deeper than KEF KF92.
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 KEF KF92 is approximately 1198.2cm2 / 185.7inch2. The Grotto 15 requires 156% more surface area than the KF92 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 KEF KF92 weighs 20.05kg / 44.1lbs. This makes the Grotto 15 167% heavier than the KF92.
Here is a comparison of how Grotto 15 and KF92's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
 Woofer Size |
15 inches
vs
9 inches
|
Larger woofer |
 Passive Radiator |
2 x 15-inch
vs
None
|
Increases the bass performance |
| Number of Woofers |
2
vs
1
|
More woofers |
| Low Frequency Response |
11 Hz
vs
20 Hz
|
Generates deeper bass |
 High Frequency Response |
200k Hz
vs
120k Hz
|
Generates higher frequency |
 Height |
353mm
vs
522mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1198cm2
vs
3069cm2
|
Takes less floor space |
 Price per pair* |
2000USD
vs
2800USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
MartinLogan Grotto 15 |
KEF KF92 |
| Brand |
MartinLogan |
KEF |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
1000 watts |
1000 watts |
| Frequency Response |
20-120 Hz |
11-200 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
1000-watt RMS |
1000-watt RMS |
| Watts Peak (Max) |
2000-watt RMS |
n/a |
Drivers |
|
|
| Woofer Quantity |
1 |
2 |
| Woofer Size |
15" |
9" |
| Woofer Composition |
Aluminium |
Hybrid aluminum |
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
35–120Hz |
n/a |
Physical Specs |
|
|
| Height |
522.0mm (20.6") |
353.0mm (13.9") |
| Width |
554.0mm (21.8") |
331.0mm (13") |
| Depth |
554.0mm (21.8") |
362.0mm (14.3") |
| Weight |
53.50kg (117.7lbs) |
20.05kg (44.1lbs) |
| Enclosure |
Acoustic Suspension |
Acoustic Suspension |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
|
2 Years |
| Labor Warranty |
|
2 Years |