MartinLogan Revamped Grotto Line Digs Deep with 1kW 12" & 15" Subwoofers

MartinLogan Digs Deep with Revamped Grotto Line of Subs

MartinLogan has impressed us with their subwoofers in our recent reviews of the Dynamo 12 and Abyss 10. The new refresh of the Dynamo and Abyss series was greatly improved over their predecessor subwoofer lines. Now, MartinLogan looks to be giving the same treatment to their Grotto series, which last used that name in 2007 with the Grotto i. However, MartinLogan is taking the Grotto name way past the caliber of subwoofers that the older Grotto subs were. The older Grotto subs were sealed 10” models with 250 to 300 watt amplifiers. The new Grotto subs have a 12” driver and a 15” driver, with both drivers loading dual passive radiators. What is more is that these new models are powered by a 1,000-watt RMS amplifier. Those are some monster specs that make the older Grotto subs seem quaint by comparison.

In addition to much beefier specs, the newer Grotto subs also benefit from advances in technology in the seventeen years since the last Grotto sub. The new Grotto subs use a highly sophisticated 500MHz DSP system with 64-bit resolution and a plethora of features made possible by digital signal processing. The Grotto subs have a wireless transmitter and receiver, so no cables are needed to connect the sub to the system. They are also compatible with Anthem’s ARC room correction, so those who have an ARC calibration mic and a PC can load an equalization profile that compensates for the room’s acoustics. The new Dynamo and Abyss subs that we reviewed also had the same system, and our testing has shown them to work quite well. The new Grotto subs have extensive app control that has some useful features in addition to typical subwoofer controls, such as a tone generator, different listening modes, and ARC Genesis activation.

MartinLogan Grotto Design Details

On paper, the build quality of the Grotto subs looks to be substantial. We have a 12” sub with an 82 lbs. weight and a 15” sub with a 118 lbs. weight; that is some serious heaviness given the size of the driver used. This is especially true since these subs use passive radiators, which would not add a lot of mass to the overall weight. They use 1” MDF panels and look to keep the same level of build quality as the Abyss 10 and Dynamo 12, and that means they will be built like boulders. Much like the Abyss subs, the Grotto 12 has a center brace as well as reinforced driver baffles, and the Grotto 15 uses two center support braces. The Grotto subs also have vibration-damping feet that can use rubber tips for hard floors and spiked tips for carpeted surfaces.

As with the Abyss 10, the new Grotto subs keep the same passive radiator orientation, where the radiators are mounted on opposite side panels. That is a good thing because the layout of the radiators in these subs is the best way to do passives, in my opinion. The main advantage is that since the oscillation of each radiator is negated by the other, they will cancel out each other’s momentum, thereby eliminating any rocking motion that they could impart on the enclosure. Furthermore, MartinLogan has wisely decided to use two passive radiators instead of one long-throw radiator, as older designs have done. Long-throw radiators have historically had reliability issues. They also had a lot of mass in motion, and that could lead to a lot of vibration in the cabinet. Indeed, older designs with heavy radiators could ‘walk’ the sub out of place due to the radiator’s vibrations. The design of the new Grottos looks more like MartinLogan’s current Abyss subs but scaled up to 12” and 15” versions.

The drivers are fed 1,000 watts RMS of amplification courtesy of a class-D amplifier that MartinLogan terms the ‘Magnitude MT-2kW’, so they are sure to be beefy drivers. One trick in having drivers be able to handle so much power is not making them overly heavy by giving them a ton of voice coil mass. That can really hurt driver sensitivity. If MartinLogan has found a good balance here, these subs could be absolute monsters. The drivers use an aluminum unibody cone, which can act as a heatsink to help disperse heat.

What’s especially cool is that the Grotto subs should be able to produce a ton of deep bass without needing a gigantic cabinet. Passive radiators function much like ports, except they don’t need all of the extra internal volumetric area that ports do. They can give you the deep bass output without the huge size. They also will not have the problems that some ports can have, such as chuffing or pipe resonances.

On the other hand, passive radiators do have their own compromises, such as the weight of the radiators being much heavier than the weight of the air within a port, and thus their reaction time will not be as quick. This can be mitigated by having the tuning frequency of the radiator be too low for lightning-quick reactions to matter. A few milliseconds of delay at 20Hz isn’t going to be noticed by anyone. And while radiators may not be susceptible to port turbulence or pipe resonances, they can have their own noises, such as surround flutter. That can be taken care of by simply engineering them well. From our review of the Abyss 10, we know that MartinLogan can make a good passive radiator, and we expect that to be the case with the new Grotto subs.

MartinLogan Gratto Initial Impressions

Gene and Don had the chance to hear the revamped Grotto subwoofers in action at Audio Advice Live 2025 and walked away genuinely impressed by their depth and control. MartinLogan’s new 12” and 15” models promise serious low-end extension with the precision the brand is known for, making them equally at home in dedicated theaters or high-performance music systems. The Grotto 12 is priced at $2.4k, while the Grotto 15 comes in at $2.8k, with availability expected soon. Stay tuned to Audioholics for more coverage—and hopefully a full review once we get them in for testing.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.