Audio Video Poland – S400

Buchardt S400 – Uncompromising little ones .

More expensive, and so far the most expensive, speaker by young Danish audio brand shows that even such a small manufacturer is capable of creating something significant, even though soinconspicuous.

Buchardt Audio is one of those brands that emerged in recent years. It was created just over 5 years ago by Dane Mads Buchardt, an owner of internet store for hobbyists-amateurs, RABU Acoustics. Kasper Raun is responsible for acoustical projects – he’s an ex Dynaudio engineer. Those of you interested more in the beginnings and genesis of company’s emergence shall be pointed towards the review of cheaper S300 MkII model on our website

Despite of a small scale production, the company boasts an advanced laboratory equipment and also the fact that it is more flexible in terms of design than large and stale manufacturers.


The above mentioned S300 are utterly traditional in their construction – two drivers from SB Acoustics catalog, placed in cuboidal 15 liters cabinet with bass reflex. There are no secrets here, and the whole ‘work’ is done by a specific tuning of the whole thing – successful in our opinion, at least interesting for sure. Maybe not for everyone.

S400 is entirely different design, much more advanced, where two solutions can be found: not innovative by any means, but important in acoustical terms. The first one is a 170mm in diameter waveguide called Constant Directivity Control Waveguide, inside of which, a smaller than usual, 19mm tweeter is set. Today, such small tweeters are not too popular, which is caused by a fact that their loading capabilities are lower than that of larger tweeters (low thermal capacity of the reduced coil), and the frequency of mechanical resonance of the suspension system is higher. This in turn forces the use of higher crossover point, which is not exactly suited in a two way systems with 6 or 7 inch mid woofer drivers. Small tweeter has it certain advantages though. First and foremost its sound dispersion in high registers is better, and the smaller membrane’s mass enables higher level of detail.

In order to overcome the natural downsides of a small tweeter, the above mentioned waveguide is used. In a way it increases the driver’s sensitivity and lets it reproduce lower frequencies with lower distortions. Due to considerable depth of the waveguide, the membrane ceases to ‘see’ cabinet’s edges which eliminates diffraction. The main purpose of CDCW though is to adapt the directional characteristics of both, tweeter and mid bass, drivers. What does this mean exactly? Buchardt argues that, entirely not unfounded, a lot of contemporary speakers show good or very good results in on-axis measurements. Situation looks considerable worse in an off-axis setting (to the sides or above/below), where holes and large waves appear in the frequency response. These amplitude inconsistent sound waves with different lengths (frequencies) bounce off the walls in manner which is very hard to predict, which, in worst case scenario (large, flat and deflecting surfaces in non acoustically treated rooms), leads to sound coloration. When we add to that, that direct sound, in typical conditions, is responsible for only one eight of the entire sound reaching the listener, it becomes clear, that the off-axis behavior of a loudspeaker is very important. It needs to be explained that there are two schools of thought. One of them tries to maximally narrow down the directional characteristics (this situation is used in tube speakers and flat dipoles, for example electro- and magnetostats), and the second – one using more conventional speakers – tries to make them maximally homogenous. Buchardt belongs to the second camp. It goes without saying that when designing S400, Kasper Raun created an acoustic model based on 5402 measurement points, which were filled in by data retrieved from a 3D scanner analyzing forefront of a sound wave.

The design of tube, drivers and a crossover was subordinated to achieving almost monotonically falling directional characteristics on the sides of loudspeakers as well as homogenous sound power curve. These things are extremely difficult to achieve – much more complicated than achieving linearity of on-axis response.

Mid bass driver is an aluminum woofer 145mm in diameter (basket diameter is 170mm), made by SB Acoustics and custom tuned specifically for the demands of this loudspeaker. It is based on NAC series, which membranes with small grooves are brainchild of Ulrik Schmidt – the ‘father’ of Scan Speak Revelators’ membranes.

Short grooves are there to practically eliminate parasitic resonances which are characteristic to stiff metal membranes.

Instead of bass reflex port, a passive radiator was used – an oval membrane with dimensions of 125 x 200mm, also made by SB Acoustics, with an additional counterweight mounted on its back in order to achieve the appropriate tuning (38Hz). A passive radiator works, as far as the rule is concerned, in analogy to bass reflex, but it is free from some of its downsides – most of all it doesn’t introduce turbulent noise nor pipe resonances of the port (which are absent here). It can also be tuned more comfortably, there is no need for compromising moving of the port due to cabinet’s depth vs the magnet’s size etc.

Inverted tweeter and mid woofer layout is a result of the need for time coherence of both drivers. Despite considerable depth of the waveguide, the tweeter’s coil is much closer to the front wall than the coil of even deeper woofer. The height of stands should be chosen in a way that the listener’s ears are above the tweeter – more or less at the height of the woofer. In the case of conventional driver’s layout, in order to achieve similar effect, the stands would have to be unnaturally high (tweeters above the ears’ line) or the listening chair particularly low. Crossover has been built out of selected elements of really high quality. These are Bennic foil capacitors and big, wire air coils (photo on the side). Even at this price level manufacturers tend to use core coils which are suffering from problems connected to magnetic hysteresis. Relatively high, as far as small loudspeakers are concerned, efficiency of 88dB was achieved.

The cabinets are the only elements which have undergone a revision using spreadsheets. They were made out of 15mm thick MDF boards without internal bracing and it was damped using mineral wool. We were surprised by the lack of threaded sockets – metal screws go directly into MDF. In this class of loudspeakers, in our opinion, this is too far reaching cost saving. On the other hand there are high quality metal speaker terminals used.

As we have discussed all the technicalities now, we can talk a bit about the looks. S400 are small, neat and, in satin white, they present themselves really elegantly. I can hazard a risk by saying that there won’t be a single lady who won’t accept these in the salon or in the bedroom. Despite small measurements (36.5cm height, 18cm width and 24cm depth), Buchardts have their character – black drivers attract attention, forecasting strong sound. It is worth mentioning that there are no speaker grills in the box. (MS)


The history of majority of loudspeakers’ manufacturers is fairly similar. Someone was unhappy with products available on the market, had passion and an idea for sound. As far as the last factor is concerned, S400 are a testimony to uncompromising approach to sound. There is no place for compromises here – these bookshelves sound direct. Nothing is veiled, every detail, every rise, but also a fall, are visible first hand. Not only in the music itself, but also in the configuration of the equipment. Small Buchardts add very little from themselves, reproducing everything that gets sent to them via speaker cable.

Their first impression was the verve in which they picture the soundstage: broad, effortless and unbelievably precise. In a large scale music – symphonic and electronic – one can forget that bookshelf loudspeakers are listened to. To the same category belongs film music – in this case, immortal for me “Star Wars: A New Hope” in BlueSpec edition. The illusion of sitting in a concert hall is very convincing. In my 15 square meters room (25 square meters all together with an opening) I was unable to drive these loudspeakers in a way audible distortions were heard. They can, not only play loud, but at the same time they don’t lose the fundament in the low registers. Considering how controlled and energetic bass is, facilitated by the duo of driver and passive membrane, I am beginning to wonder why I still see so many bass reflex ports and pipes in the loudspeakers made by competition manufacturers.

S400 was tuned with a light emphasis on mid and higher bass, but a perfect impulse response was saved (passive membrane can be tuned in many different ways), achieving very good low registers’ extension for a loudspeaker of this size. They are not worried even by trance music. If someone wants to check the speed of these speakers, then it’s hard to find a better track for it than Blastoyz – “Mandala”. Electronic bass can be driven quicker and in more controlled fashion than the one recorded from an instrument. I always search for alternative methods of testing and this is one of the best of my findings.

In contrast to large scale recordings I reached for “Wallflower” by Diana Krall – to check how these small speakers cope with more intimate music. In this case the vocalist came closer, coming out before the speakers, which points to their ability of reproducing recordings of different character. Her voice was pronounced and clear as a crystal. The mid frequencies level of detail turned out to be perfect – those looking for smallest of details won’t be disappointed. Everything had its place and meaning.

High frequencies are particularly impressive – they are well resolved, natural and contain a lot of detail, which larger tweeters can lose. Buchardts are characterized by a light, well resolved and full of detail sound. The frequency response reminds a flattened letter “V”. Fans of overwhelming “honey” won’t be be happy here. Recordings for lower quality neither. As I mentioned these speakers are not forgiving for worse recordings. Mistakes in their execution are visible, unmasked by coloration or distortions.

As far as combining these speakers with electronics, they will also not like everything. Better results were achieved with Class D NAD M10 than with SOtM sMS200 streamer, Mytek Liberty or Naim NAP-100. For sure I would pair it with something more focussed on mid frequencies, which could do with a little bit more of weight in comparison to higher bass. This is rather a question of my preferences. Looking at cheaper devices Rega Brio-R or Pioneer A-50 come to mind.

Wide and deep soundstage are one of the advantages of using driver in a fitted waveguide. The second advantage is perfect directional characteristics, which, together with well tuned passive membrane, ensures very easy room placement of these speakers. Of course in a well chosen place they will sound their best, but put up against a wall or on a shelf they will surprise.


Compact bookshelf speakers with a great heart to sound. Even though they look inconspicuous, they can cause quite a stir even in a larger space. Their sound – glamorous, but not showy – it draws attention, and high level of quality of sound keeps us there for longer. Bold, direct, vivid – if that’s the speakers you are looking for, then these should be on your shortlist for listening session. Pairing with electronics requires a bit of attention in order to achieve beautiful effect. Great pairing would be with miniature NAD M10, but also with full size amplifiers, such as warm sounding Sugden or energetic Moon. Impressive, and at the same time, comforting is that how much of hard work and advanced technology have been invested in this seemingly humble project. It is good to know that there are manufacturers out there which invest time and resources in solutions not widely popular. We are waiting for more, and from what I have heard, something new is on the short term horizon. Full recommendation.

Final Score: 5 stars

Additional award: Audio Video Recommendation

Neutrality: 9.0

Slighty “V” shaped frequency response adds a bit of verve to the sound

Precision: 10.0

All I want these days

Musicality: 8.0

Open, very clean sound exposes advantages and disadvantages alike

Stereo imaging: 10.0


Dynamics: 9.0

A very good, quick loudspeaker

Bass: 9.0

Slightly emphasized, quick, powerful – as for this size of loudspeaker it is hard to expect more

Rating: 92%

Equipment Class:  B

Translated by

– Arkadiusz Miken Mikina –