FEATURE: DIRECTIONAL AUDIO
time delay to each of those drivers”. Xavier Meynial, R&D manager at Active Audio, is ready to provide the maths: “For example, with a distance D and
a delay τ between adjacent drivers, the beam (at high frequencies) points in
direction θ such that
sin(θ)=c.τ/D; where c is the sound velocity. This old
technique has been widely used since the advent of digital delays.” In general, beam steering refers to the ability to control the sound from an array in the vertical pattern. Ateïs Europe’s Hans den Hertog observes that “with beam
beam steering modular line array, consisting of a base unit as a minimum and an extension unit, of which one or two can be added to the base unit. Meanwhile, all three models of the Meyer Sound CAL column array loudspeaker – CAL 32, CAL 64 and CAL 96 – offer beam steering and beam shaping, while CAL 64 and CAL 96 have beam splitting capabilities too.
BEAM
SHAPING Recent years have also seen an upswing in the
The new VUE Audiotechnik al-8 Compact Line Array System is fully compatible with the VUEPoint beam steering technology
steering, the azimuth can be steered towards the listening area. The simple arrays will have a fixed azimuth and can even be passive arrays, whereas the advanced arrays are active with DSP-controlled steering capabilities.” For the venue and installer, this heightened directivity of sound is likely to have acoustic and aesthetic advantages. “Now the array can be positioned vertically against a wall, or even recessed into the wall,” says van Raalte. “This is aesthetically more pleasing and, as a bonus, also reduces disturbing incoherent reflections from the rear wall.” There is no shortage of
currently available products with beam steering capabilities, although many manufacturers are eager to stress the variations that they claim make their products unique. So with VUE Audiotechnik’s VUEPoint beam steering technology, explains CEO and co-founder Ken Berger, there is the use of “industry- standard modelling tools along with the powerful DSP architecture that’s already built into every VUE line array system. This means that any VUE Audiotechnik line array already has the ability to be a digitally steerable line array if the user so chooses.” In Fohhn Audio’s Focus Series loudspeakers, the beam steering process sees each individual driver being controlled by its own amplifier and DSP channel. Bosch’s Vari-directional Array is a
www.installation-international.com
number of systems promoted as having
‘beam shaping’ capabilities. This technique, says Duran Audio’s senior R&D scientist/engineer, Evert Start, is “more versatile and complex” than beam steering, allowing the user to “change the shape of the lobe and completely tailor-make it to the audience area”. Such capabilities have made beam shaping particularly relevant to challenging spaces that call for very precise directivity of sound, such as houses of worship, airports and theatres. Meynial fills in some of the fine
detail: “Achieving constant SPL over a large audience area implies generating a ‘lobe’ with a specific asymmetrical shape which depends on the size and shape of the audience area, and the position of the array relative to the audience.” And there is a caveat here
regarding terminology. “The term ‘beam’ is often irrelevant here since it assumes far field (-6dB per doubling distance) while listeners are not in the far field,” says Meynial. “The key concept is rather that of the ‘wave front’ control popularised in the ’90s.” In addition to achieving a beam shape that delivers an equal sound at all listening positions, there is need also to consider “the loudness of the signal, which should be almost the same for all listening positions, avoiding hot spots”, notes van Raalte. “People close to the loudspeaker should not feel uncomfortable because the sound is too loud and for people far away it should not be too soft.” The solution, he adds, is
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