Linn Exaktbox Sub

The Exaktbox Sub is the component that makes subwoofer integration in a Linn Exakt active system genuinely seamless — not approximately seamless, not acceptable at low volumes and problematic under dynamic load, but phase-linear from the crossover point all the way to 0Hz, in a way that no analogue crossover can achieve. Adding a subwoofer to a high-quality stereo system is harder to do well than most people expect, and the reason for that difficulty is not the subwoofer. It is the crossover. Every analogue crossover introduces phase shift at and around the crossover frequency — a region of the bass where main speakers and subwoofer are pulling in different directions rather than integrating as a single coherent system. The result is bass that sounds thickened, slowed, or disconnected from the music, regardless of how capable the subwoofer itself may be. The Exaktbox Sub eliminates that problem entirely, by replacing the analogue crossover with a digital one, processed in the mathematical domain at Akurate DAC level, inside the Exakt signal chain.

Why Digital Crossover Integration Is Transformative

The distinction between an analogue crossover and the digital crossover inside the Exaktbox Sub is not a matter of degree. It is a matter of physics. An analogue crossover — whether passive, inside a loudspeaker cabinet, or active, in a dedicated outboard unit — cannot achieve phase-linear behaviour at and around the crossover frequency. The gradual phase rotation introduced by analogue filter components is inherent to their electrical behaviour and cannot be designed away, only managed. The consequences are audible: bass that is slightly late relative to the main speakers, a crossover region where phase relationships are ambiguous, and an integration that convinces only until the music demands precision timing and rhythmic clarity.

A digital crossover operates in the mathematical domain. Inside the Exaktbox Sub, the crossover calculation is applied to the digital signal before DAC conversion — at a precision that no passive component can approach, with phase behaviour that is precisely and completely controlled. The result is a crossover point at which main speakers and subwoofer are genuinely time-aligned, contributing to the bass register with the same phase relationships they would have if they were a single, continuous driver. The bass is not merely louder or deeper — it is more precisely timed, more rhythmically convincing, and more accurately integrated with the rest of the frequency range.

Additionally, the Exaktbox Sub allows the time-of-flight relationship between main speakers and subwoofer to be configured independently — accounting for the physical difference in distance between the listening position and the main speakers versus the subwoofer, which is typically positioned differently in the room. Failing to correct for this timing difference is one of the most consistently overlooked aspects of subwoofer setup, and one of the most consequential. The Exaktbox Sub corrects for it precisely, because it is processing the signal in the digital domain, where timing corrections are applied mathematically rather than approximated with physical adjustments.

Akurate DAC Level Processing

The Exaktbox Sub provides two channels of Akurate-level DAC processing. The same DAC standard that defines the Akurate Exaktbox and Akurate DSM is applied to the subwoofer signal — not a compromised conversion stage, not a separately specified sub-quality output, but full Akurate DAC quality across both channels. The output is a line-level analogue signal, delivered via balanced XLR or unbalanced phono, to the subwoofer's own amplification. The Exaktbox Sub is therefore compatible with any subwoofer with a line-level input — the integration it provides is a function of the Exakt crossover and DAC quality, not of any restriction on the subwoofer's own amplifier or driver.

Configuration Options

The Exaktbox Sub supports two operating modes — stereo and mono — to suit both the subwoofer configuration and the room:

Stereo subwoofer operation: Two independent subwoofer channels, one for left bass and one for right bass, preserve full stereo imaging in the bass register. On well-recorded material with genuine stereo bass information, this configuration is audible and worthwhile.

Mono subwoofer operation: Both channels summed and fed to a single subwoofer. This is the more common configuration in practice, and is appropriate for the majority of rooms and subwoofer positions.

The Exaktbox Sub connects to the Linn DSM via two Exakt Link inputs and outputs via balanced XLR or unbalanced phono to the subwoofer. It requires an Exakt-capable Linn DSM as the source component. If your current DSM does not carry Exakt capability, discuss the upgrade options with us before purchasing.

Technical Specifications

Who Is It For?

The Exaktbox Sub is the correct and purpose-built solution for any Linn Exakt system owner who wants to add a subwoofer and wants the integration done properly — with phase-linear crossover behaviour, precise time alignment, and Akurate DAC quality on the subwoofer signal. It is equally relevant for anyone who has already tried to integrate a subwoofer into a high-quality stereo system using conventional analogue crossover methods and found the result unconvincing: the Exaktbox Sub explains why, and resolves it definitively. It is an Exakt product, and it requires Exakt infrastructure — an Exakt-capable Linn DSM is the necessary foundation. If your system already includes the Linn Klimax System Hub or is built around the Linn 360 Active Loudspeaker, the Exaktbox Sub integrates seamlessly into the existing Exakt framework.

Buying from Martins Hi-Fi

Martins Hi-Fi has been in Norwich since 1968. Elizabeth Gould runs the business today, and we stock only brands we have heard properly and stand behind.

Exakt subwoofer integration — particularly the crossover frequency, the time-of-flight calibration, and the interaction with Space Optimisation — benefits significantly from dealer involvement. We can configure the Exaktbox Sub correctly for your room and your system, and demonstrate the difference that properly executed digital subwoofer integration makes compared to conventional analogue methods.

When you get in touch, you'll be speaking with Dave, Chris and Tim — experienced specialists who can advise on this product and your whole system.

Contact us at info@martinshifi.co.uk, call 01603 627010, or WhatsApp on 07554 687137. You can read more about how we work on our Why Martins Hi-Fi page. We are at 85–91 Ber Street, Norwich, NR1 3EY.