KEF Kube 15 MIE subwoofer review

KEF asks only 1,300 euros for its new Kube 15 MIE – the flagship of a whole family of subwoofers, whose models differ only in size. Or so it seems. Tested at 1,300 euros.

KEF has equipped all four new subwoofers with powerful electronics and offers them at attractive prices. Especially the largest of the four new subwoofers, the Kube 15 MIE, has something to offer: a 38cm woofer – what a dream!

Physics explains it: When transmitting deep tones, the sound is known to be transmitted through air pressure fluctuations, and a lot of air volume needs to be moved. A generously dimensioned “pump” is extremely useful. The 38cm – or 15-inch in American terms – is not without reason, a standard in professional sound technology. The 45cm (18-inch) woofer is rarer, the 30cm (12-inch) woofer is considered the “smaller”, though still powerful and more domesticated “brother.”

A subwoofer with a 38cm woofer means serious business. So does the Kube 15, the top model of the cubical series from the English county of Kent.

It’s quite a “beast” with 27.5 kilograms and nearly 52 centimeters edge length. Definitely not for small rooms or hiding places. From an ambiance perspective, the opposite of “mini” and a certain challenge.

Here, a front-firing, particularly long-throw driver is used, meaning the construction of the voice coil, diaphragm, magnetic drive, and centering is designed to ensure a strong movement, i.e., a strong linear displacement backwards and forwards.

The entire Kube series, all models, uses a 300-watt amplifier in energy-efficient Class-D technology, whose DSP is precisely tuned to the parameters of the used driver to achieve optimal results. This precise tuning of all components is called the Music Integrity Engine by the British traditional manufacturer and is combined with Intelligent Bass Extension (iBX). By the way, KEF deliberately chose a sealed instead of a bass-reflex cabinet as the base.

Kube MIE Subwoofer Series
The newly available Kube series starts with the 8 MIE, featuring an 8-inch/20cm woofer for 650 euros, and progresses through the 10 MIE and 12 MIE to the 15 MIE.

Although a bass-reflex design potentially goes deeper into the basement, a sealed volume provides enormous spring or shock absorption due to its enclosed air cushion. After all, the air cannot escape – unlike through a reflex tunnel, a transmission line, or even an extruded passive membrane.

Precision Through Air Suspension

The so-called air cushion stiffness generally leads to increased precision with particularly well-defined, punchy, neutral, and “fast” bass. Not without reason are most classic British monitor speakers built this way. They wanted to achieve the cleanest, most balanced result and be as flexible as possible regarding positioning. Therefore, they also dispensed with a physically effective downfire arrangement of the driver. Why the impressive driver is shielded from view by a surround covering remains a secret of the developers.

A powerful amplifier, however, can ensure that even in the depth of the bass cellar, atmosphere is created in the airtight sealed cabinet via EQ. Power then replaces volume, but the Kube 15 also has that. The iBX approach, as it is called here, is the manufacturer’s expertise, and the apparent development goal with the Kube 15, balancing precision and depth, is excellently achieved.

KEF-KUBE-8-MIE rear view
The KEF offers RCA inputs and high-level inputs via terminals, along with phase and level controls.

The Brits specify a depth of 20 Hertz (at a 3-decibel drop) and a maximum level of 116 decibels. That should always be enough. The performance is correspondingly assertive and convincing, musically sovereign, in the cinema, for example, in “The Expendables” brutally real and gripping. We wouldn’t have thought that something like this would be possible at this price.

Attractive Price Point

At around 1,300 euros, the Kube 15 is not exactly cheap but remains pleasantly affordable and was consistently designed to meet high musical and cinematic demands. If we recall the subwoofer test, we reported that placement in the corner always saves power, as acoustic amplification effects through boundary surfaces can be used, which no longer need to be additionally provided by electronic power. To keep the bass power under control, KEF offers three explicit placement options in the room, on a wall, in a cabinet, or in a “corner,” which the owner sets as presets. That helps, and you can hear it.

A Kube electronics called Smart-Connect automatically detects whether the subwoofer is connected via RCA (mono) or two cables (stereo) and adjusts its basic sensitivity accordingly. Additionally, it can also be connected via high-level inputs using speaker cables. We would like to make a bit of criticism here, as the mentioned high-level inputs are essentially a kind of plug-in terminal, into which the customer first has to apply rather thin cables, which one would actually call fiddling.

Every Kube becomes a wireless subwoofer with the optionally available, cleverly attachable KW1 adapter, particularly with the appropriate KEF active speaker sets, such as LS50 Wireless II or LSX II – latency-free and via app control – very powerful combinations can be achieved. In fact, with the KEF active sets, seamless integration can be achieved, which is hard to top without integrated room calibration.

Direct connection to third-party satellite speakers via an integrated crossover, whether active or passive, is not provided, at least not in the form of a sub/sat system. But of course, independent support of the lower ranges is always possible, and here the KEF makes a very good impression, for example, on a monitor-like Spendor S3/5 or the very dynamic Canton Reference 9 with the sonorous Leonard Cohen.

So, this KEF Kube 15 is explicitly a powerful tool to generate pressure, space, and even extreme bass levels in impressively high quality. Not just in entry-level systems. In this context, the moderate price is surprisingly reasonable, with no doubt.


We listened with: Leonard Cohen: “You Want It Darker,” Films: “The Expendables,” “Dune,” “Nobody”

KEF Kube 15 MIE Verdict

An extremely confident and nearly perfect active subwoofer that delivers top-notch results at a surprisingly affordable price.

8.5 Total Score
Editor choice KEF Kube 15 MIE

The performance almost makes the jaw drop. This subwoofer is exceptionally balanced despite all its power and force and also masters finer nuances. It enhances even high-quality floor-standing speakers in the lowest ranges. However, the best performance is achieved with current active KEF satellites and the corresponding app.

  • Extremely deep, powerful, and well-controlled bass. Suitable for both music and cinema.
  • Very voluminous and spacious sound, with drivers almost invisible.
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KEF Kube 15 MIE subwoofer: Price Comparison

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KEF Kube 15 MIE 15 Inch 300 Watt Powered Subwoofer...
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  1. […] the KEF Kube 15 MIE, with its massive 15-inch driver, the KEF KC92, the flagship of KEF’s new subwoofer lineup, […]

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