Seismion Reactio 2

REVIEW
Ed Selley
Oct 20, 2025

The principles of isolating audio equipment and decoupling it from its immediate surroundings are well understood. They have been a meaningful part of system building for many years. For the most part, isolation platforms are passive devices, relying on some form of dampening material between the platform surface and what it is placed on. Some of these can be comparatively sophisticated in terms of how they go about this process. It wasn’t too many issues ago I was looking at magnetic levitation. Yet, it is passive, nevertheless.

The Reactio 2 from Seismion takes an entirely different approach to the business of isolating components. The Hannover-based company specializes in building isolation devices for scientific and engineering applications where mechanical isolation is vital. This is not merely desirable. Rather than employing a passive system, they have developed an active system. It measures external vibration and applies specific counteraction based on those measurements.

Sensitive sensors

This is achieved by extremely sensitive piezoelectric sensors, which detect any external vibrations. An all-analogue electronic control circuit generates the required compensation forces to a top plate. This top plate is large enough to support most bits of audio equipment it is likely to encounter. The 65kg weight handling should be sufficient for most components. An XL version is available with a higher weight handling still. This would be sufficient to isolate a complete rack if you were inclined to do so.

One other aspect of the Seismion’s design is going to be appealing to anyone looking for a means of isolating a turntable. When the device is powered up, the Reactio establishes a ‘baseline’ for external interference. It then judges the weight and balance of the device on the top plate and self-levels it. Seismion claims that the measurement is accurate to a repeatability of 25 µm, which is likely to be better than what most of us will achieve with a spirit level.

No less usefully, if you need to adjust the device placed on the Seismion, the top plate can be locked. This means the sensitive hardware inside isn’t put under any unwanted strain. This also speaks to a certain confidence on Seismion’s part. They believe you will hear the benefits of what their equipment can do when it is powered on. Power is supplied via an external PSU. The platform is locked and leveled via a single button on the front.

Unobtrusive

While the engineering involved is unquestionably thorough, the Reactio 2 is not the most spectacular-looking object you can lavish the best part of ten grand on. It’s unobtrusive to the point of dull. While it unquestionably feels well-made, it doesn’t have the gloriously overbuilt feel we can associate with the high end. Nevertheless, with Seismion claiming -10dB of noise reduction from 1Hz (and up to 20dB by 5Hz), you’d need to be very confident in a passive system to claim anything similar.

For testing the Seismion, I elected to make use of the various turntables I had on hand. They are the most receptive devices to isolation. Valve-based electronics would also benefit, but none were available simultaneously. The most testing has been done with a Rega Planar 10 on account of its design. Beyond a tiny degree of pliancy in the feet, the Planar 10 is entirely rigid and designed for use on a wall shelf. Parking it on my rack near a speaker on one side yields respectable but not outstanding performance.

Tightening up

Placing the Rega on the locked Seismion has the immediate benefit of tightening up the bass response. The massive drum used in the ‘Sort of Revolution’ on Fink’s Wheels Turn Beneath my Feet [Ninja Tune] gains both depth and definition. This improvement is repeatable across both percussive and non-percussive bass. The Reactio 2 is providing a degree of decoupling in all states.

Switching the platform on makes a significant and immediate change. What is interesting is that the point where the Seismion makes the most profound difference is the upper midrange. With Christine and the Queen’s Chris [Because Music], where vocals are competing with heavyweight electronic underpinnings, the result is dramatic. With no outside interference hitting the cartridge, the jump in tonal realism, detail, and three-dimensionality is significant. This particular Planar 10 has been on hand since 2019, and I can confidently say that I’ve not heard it perform better than this.

More pliant

Running the same tests with an AVID Ingenium Twin (also unsuspended but with more pliant feet) reveals a similar benefit. The reduction in interference affecting the playing surface enables both cartridges in use on the AVID to achieve considerable gains in clarity and realism. Interestingly, the AVID does not demonstrate the same improvements in its bass response. This might be due to the role its feet play in its overall performance. The final turntable used, a Vertere MG-1 MkII, yields the most mixed results. Unlike the other two designs, the Vertere has internal isolation, which is partly in conflict with the Seismion. The benefits to vocal and instrumental performance are still readily apparent, but some of the flow and rhythmic energy of the Vertere is lost when the Reactio 2 is powered up.

While it might be best not to view the Seismion as a panacea, the effect on unsuspended turntables is genuinely impressive. The price gap between the Planar 10 and the Vertere in the configuration they were tested in is around ten grand, or the price of the Reactio 2. The platform narrows the gap between them to something approaching subjective preference. For turntables of this nature, the effect is sufficiently big that, even at its significant asking price, the Seismion is something you should consider as an upgrade path. This is the cleverest and most carefully thought-out device of its type I have yet to test. It offers huge system upgrade potential.

Read more about Session’s approach to active isolation here.