The Design Philosophy Behind
An Open Baffle Line Array Loudspeaker

A developmental project of a hi-fi loudspeaker based on the open baffle approach

© Oliver Mertineit  < oliver.mertineit@ymail.com >

The best way of sound radiation is controlled angular dispersion over the entire listening range of frequencies

Only a loudspeaker which is able to radiate the whole range of relevant frequencies with even angular dispersion will sound equally well at different listening positions. A loudspeaker coming close to this design goal will reach the level of performance it is designed for even when placed in living rooms which are shaped and arranged differently.

A dipole line source has the advantage of maintaining a larger ratio of direct-to reflected sound especially at larger listening distances. Thereby the contribution of the listening room, which is far from ideal in most living room environments, is minimized. It was in this background that research was initiated into evolving a line array with an open baffle design as a means to realizing the reproduction of uncoloured sound at a high level of fidelity and realism. There could be as many opinions about which loudspeaker enclosure is best as there are designers. But in the ultimate test of listening, one thing becomes painfully obvious-- the best enclosure is no enclosure at all.

The best loudspeaker enclosure is no enclosure at all

Enclosures tend to colour and in many ways distort the sound they deliver. Even the most ideally built enclosure has Helmholtzian resonances and material resonances that add to the reproduced sound, ruining its fidelity. The 'sympathetic' vibrations of the enclosure are known to at times to drown out the sound of the drivers even. This being the state of affairs, ways must be devised to address such problems at their very source.

'Dipol-08' by design avoids these pitfalls as it does away with the traditional enclosure --completely. Surely open baffle loudspeakers are no longer a curiosity. They have evolved into mature systems and quite a few manufacturers offer open baffle models. But here again large baffles, or 'wings' on the baffles, contribute to colourations and detract from the aesthetics.

The ideal loudspeaker is said to be made up from a single sound source

The ideal Loudspeaker mostly has been conceptualized as a point source of absolute coherence in reproduction. Achieving this ideal has occupied designers pursuing many exotic techniques with varying degrees of success. As an approach to this ideal notion, 'Dipol-08' represents a virtually coherent sound source made up from a multitude of small and identical transducers. This way the inevitable drawbacks present with large speaker cones are circumvented, which again would cause sound discoloration. Six selected high quality full-range transducers are driven in a novel manner to make up a line source, which adapts its effective length according to the wavelength radiated. Even the mid and upper bass range, which contribute to spatial imaging, is radiated from the line array. Only below 70 Hz the system is crossed over to a dedicated subwoofer --which works as a dipole radiator too-- thereby being able to reproduce organ pedal tones with lifelike realism and without booming or any tendency to causing listener fatigue.

The best is when form follows function

The 'Dipole-08' base is a massive, decoupled inertial damper. Rising stele-like from the base to the full height of the speaker is a 'spine' of natural rock, chosen for its mass, rigidity and damping qualities --not to speak of the aesthetics of a well-appointed living room. The motor/magnet assemblies of the drivers are rigidly held in space by the rock 'spine'. Special damping and mounting techniques hold the 160 cm tall, but 19 cm narrow baffle in front of the drivers in a vibration-free manner to project the sound into the room evenly and with an accuracy and sweetness that approaches a live presentation. Voices and instruments achieve a rare clarity and 'life' that recreate the recorded reality. Imaging is solid and wide, not only in the traditional 'sweet spot', but over a much wider area.

Unwanted vibrations of the baffle or the box are the bugbear of conventional designs. Ideally the vibrating 'cone' or 'dome' of the driver is the only part that should contribute to the wave patterns broadcast into the listening room. In practice, however, quite often the baffles and boxes can be shown to have significant 'roles' in establishing the 'tone' of a speaker. In other words, we will often be listening to the speaker, baffle, box and all, and not to the sound that is reproduced.

In the 'Dipol-08' radical design measures preserve the 'purity' of the drivers and banish unwanted vibrations. The only part that vibrates and produces sound here is precisely the one that is designed to do so--the diaphragm or the 'cone' of the driver, and absolutely nothing else. The tall and narrow open baffle enforces a sound radiation distributed evenly over the entire spectrum, thereby minimizing lobing in the horizontal plane. Musical instruments and voices keep their typical timbre in every pitch. The listener is free to choose the recordings to listen to, without taking “the loudspeakers favourite music” into account.

The result is a loudspeaker reproducing music and not itself

The absence of cavities and obstacles to sound generation and propagation ensures a sound that is 'pure' and which is freed from the loudspeaker, thereby letting the music flow in its emotional expression and rhythm. While detail is audible in high resolution, it is not imposed on the listener, rather  musical detail is felt and experienced in the whole living room.

Music of a rare 'purity' , 'emotion' and 'life' envelopes the listener so naturally that the speakers themselves, quite uncannily, 'disappear'. The 'Dipol-08' makes no claims to 'character'. They are as 'characterless' and transparent as we could make them, and so the only 'colour' that you experience comes from the music. Perhaps for the first time the listener has a choice of just listening to the music of his choice and surely not to the speakers!

'Dipol-08' is no longer prototype, but has become a mature and proven system.