Review: Buchardt Audio S400 MKII

Upgraded success

Buchardt Audio has updated their best passive speaker. The difference is profound.

Published 29 August 2023 - 8:00 am
Buchardt Audio S400 MKII
John Hvidlykke

Danish Buchardt Audio is a small speaker company that for several years consisted solely of the founder, Mads Buchardt. Nevertheless, for almost 10 years, Mads and his team have succeeded in selling loudspeakers globally. The recipe has been low prices in relation to performance, thanks in part to direct mail order sales without distributors. This makes it a little harder to hear them in advance, but the company offers free shipping and 30 days free returns – anywhere in the world.

The speakers are available in a beautiful wood finish. But can also be purchased in black and white if preferred. (Photo: Buchardt Audio)

Buchardt Audio S400 MKII is an updated version of the S400, which we have previously reviewed. But since there are supposedly major improvements in the MKII version, we gave it another go on the test bench.

One of the things Buchardt’s speakers have become known for is their ability to deliver deep bass from small cabinets. The S400 MKII is roughly the size of a shoebox, but nevertheless promises a frequency range down to 33 Hz (-3 dB).

Genuine wood

The cabinets on the test samples were black lacquered, but are also available in white, as well as walnut and light oak. Real wood veneers add 5-10 percent to the price. But it’s great to see that speakers can once again be allowed to look like speakers instead of having to be as unnoticeable as possible.

The configuration is almost identical to the original S400. Photo: Buchardt Audio)

The configuration is almost identical to the original S400, but the 6″ midwoofer has been replaced with a version with a paper cone instead of an aluminium one. The tweeter is the same three-quarter-inch textile dome mounted in a large waveguide. The tweeter is placed below the midwoofer.

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On the back of the cabinet, you find a large oval slave unit that covers most of the back of the rear panel, as well as a pair of banana/screw terminals that seem seriously beefy considering the price range. The enclosure is surprisingly lightweight. The weight is only 7.5kg each. Since the diaphragms move a lot when playing deep bass, it’s a good idea to mount the speakers on stands with spikes to avoid rattling noises due to vibrations.

As mentioned, the biggest difference between the two versions of the S400 is the crossover. And they’ve used really nice components where it counts: Heavy-duty air coils and solid MKP film capacitors from Jantzen. This is not commonplace in loudspeakers at this price.

The crossover is new – and packed with high-quality components (Photo: Buchardt Audio)

The sound quality

The changes have paid off: The Buchardt Audio S400 MKII is a completely different speaker than its predecessor (which, it should be noted, was also very good sounding).

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Buchardt Audio S400 plays music excellently, it is extremely decor-friendly - and it plays bass in a way that should not have been possible in a passive speaker of that size.

Whereas the sound image of the original S400 was very forward and close, with an acoustic stage in front of the speakers, the sound image in the S400 MKII is more rearward, and you get more of an experience of listening through a “window” in the wall behind the speakers.

Here, a rather large and deep acoustic scene is presented – as long as there is room information for it present in the recording. The soundstage easily extends far beyond the other side of the speakers in width.

A set of stands can be purchased (Photo: Buchardt Audio)

The small speakers shine, for example, on a track like the Telarc version of Johann Strauss’ Banditen Galopp with the Cincinnati Pops. Both in terms of the concert hall atmosphere, where you can easily sense the depth and width of the large room. And when it comes to the dynamic impressor effects in the form of whiplash and deep timpani blasts. I haven’t heard any other passive speaker of this size reproduce such deep bass. And do it pretty accurately, too. I’ve definitely heard deep bass that was more distinct and dry. But that was from big speakers with big diaphragms and massive magnets.

Requires a powerful amplifier

Buchardt Audio recommends combining the S400 MKII with amplifiers of 40 W to 200 W. This can work if you’re into chamber music in small rooms. But those small boxes really like plenty of power. To get such deep bass in a cabinet the size of a shoebox, you need to use units with heavy diaphragms and a long excursion. And the price for that is inevitably low efficiency. In this case, a sensitivity of 87 dB. The S400 MKII ideally requires an amplifier with high output power and a high damping factor to control the heavy bass system. The NAD C298 power amplifier I hooked them up to has both and costs as much as the speakers.

The transition between the six-inch woofer and the very small three-quarter-inch dome is completely smooth. The large waveguide certainly helps the unit to work down to 1,800 Hz without losing momentum.

The tweeter with its large waveguide is located below the woofer. (Photo: Buchardt Audio)

If I had to put my finger on it, on some tracks you can experience a slight tendency to yawning around two kilohertz. Possibly a horn effect from the large waveguide.


The Buchardt S400 MKII is in a price range where there are quite a few competitors. The Revival Audio Atalante 3 costs only a little more and is exemplary neutral – but delivers not nearly as deep bass. The Bowers & Wilkins 705 S3 impresses with dynamics, but has a somewhat lacklustre bass response. And the JBL L82 Classic brings a rock vibe to the living room.

The oval shaped passive radiator takes up the majority of the back. The terminals are of great quality for the price (Photo: Buchardt Audio)


The Buchardt Audio S400 MKII is a really successful small speaker at a price that most certainly can be called reasonable. As Buchardt has made it their trademark, it reproduces deep bass to a degree that should be impossible in a passive speaker of this size. The changes compared to the first version have, in this tester’s opinion, been a great improvement that has clearly lifted the perspective capabilities. And that’s without actually increasing the price. For the price, the S400 MKII is a speaker that should be on every hi-fi buyer’s checklist. At least if you’re not also a fan of low-powered single ended valve and class A amplifiers. Because you will need plenty of power.

(Photo: Buchardt Audio)

Buchardt Audio S400 MKII

We think

The astonishingly deep bass is the speaker's best party trick. The upgraded crossover has done wonders for ambience reproduction. Requires an amplifier with plenty of power and a generous power supply. But then they sing.

Among the best in its class

Big sound in a flexible format

Wall art with sound

Punches above its weight class

Finally truly wireless

Sublime music presenter in 70s disguise

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