Beam steering is the art of getting a line array to ‘steer’ its output to wherever you want it to go, and nowhere you don’t. It’s a technique and technology commonly employed in acoustically challenging and reverberant spaces like airports, public buildings, and houses of worship. The advantage it confers is to get the acoustic energy output by the array to land mainly on people’s ears, and not on reflective surfaces like walls and windows, which creates excess reverberation, comb filtering, and other artefacts that all lead to lower speech intelligibility. Market leaders in the field include Fohhn AG, Duran Audio, Renkus-Heinz, and Meyer Sound.
A bit of history – both line arrays and beam steering have been mathematically understood electroacoustic principles since the first edition of legendary engineer Harry F. Olson’s book ‘Acoustical Engineering’ hit the shelves in 1940. In the 1957 edition, he even explained in a diagram how digital beam steering would actually work. Unfortunately for Harry and the rest of us, the affordable DSP chips that actually make beam steering possible didn’t exist until the very late 1990s. Most beam steering arrays have emerged in the last decade, taking advantage of greater processing power at a lower cost.
How It Works
The principles by which a line array exerts pattern control are pretty simple, but involve a lot of side-effects to overcome and design compromises to make. Basically, how tall your array is divided by two will give you the wavelength of lowest frequency that it can vertically control, and how close your drivers are multiplied by two will give you the wavelength of the highest frequency it can vertically control. That seems straightforward, and until you realise that 20Hz has a wavelength of 15.25 metres and 20kHz a wavelength of 13 millimetres. Clearly, you can’t build a box that can vertically control frequencies across the full range of human hearing. Line array manufacturers have come up with a lot of workarounds, mainly involving waveguides, and deciding which frequencies they want to control and which ones they don’t.
Once you have your line array, beam steering is at once both simple and complicated. By delaying each individual driver and increasing the amounts of delay time as you go down the array (and employing some other sneaky phase and EQ settings), the acoustic result is very similar to what would happen if you’d just physically angled the whole array down (or up, if you increase delay for the bottom up). The calculations that the DSP does figure out exactly how much delay and what phase adjustments are needed in each driver’s signal to make certain frequencies either cancel or sum, and where in the loudspeaker’s coverage area this happens. Make them cancel at the top of the speaker’s coverage area and sum at the bottom, and it’s like you just tipped the whole array forward 30 degrees or so.
The reasons for employing this amount of processing and amp channels to solve an acoustic issue are usually architectural or visual. A beam steered column doesn’t have to be wide like a traditional point source box, can sit flat and unobtrusively wherever it is convenient, and then be digitally programmed to send the sound where it needs to go. This is especially important in reverberant yet sensitive and heritage-listed buildings like cathedrals, mosques, and synagogues. It’s also a major aesthetic consideration in sleek architect-designed spaces like airports and public buildings, where they never want to see loudspeakers, and there are few places to mount them amongst the steel and glass. Also cursed with longer than usual reverb times, steering is invaluable in these types of modern installs.
Manufacturers provide both predictive and control software for their beam steering column products, sometimes in the same package. Most control software enables you to upload a setting to a column, wait, and then hear the results. Fohhn is a little different – their package enables simple and totally real-time control, and you can simply drag a beam in the direction you want it to go and hear it change.
Not just for speech
Fohhn are also a little different to the other manufacturers in terms of where they see the market for beam steered columns. While covering the traditional ‘public address’ market with a huge array of options, Fohhn have also developed an entire line dedicated to full-range live music – the Focus Venue series. Effectively concert arrays without the signature ‘banana’ curve of other manufacturers, the Focus Venue range offer an easily rigged option for installed and touring systems. One of the really interesting things about them is the ease with which they sit either side of giant LED and projection screens due to their dimensions, all while delivering a massive full-range result. It’s not something engineers expect of a column array, and has the added advantage of being able to steer the sound around balconies and walls at a mouse click.