AES British Section lectures - February 2007
Experiments with a Multi-Element Steerable Loudspeaker Array
Laurie Fincham, THX
www.thx.com
On February 13th the UK Section of the AES hosted a lecture titled "Experiments with a Multi-Element Steerable Loudspeaker Array" by Laurie Fincham of THX. Laurie is very well know from his work as Technical Director at KEF and is currently the Chief Scientific Officer at THX.
Laurie started by pointing out that the massive improvements in video reproduction had not been replicated in loudspeaker design. Laurie started investigating line arrays to look into how the directivity of the loudspeaker affected the listening experience.
Laurie suggested the four characteristics of a good speaker were no undesirable loudspeaker/room interaction, stable imaging, an unlimited sweet spot and accurate sound timbre. Previous research has shown that accurate timbre reproduction is heavily influenced by the directivity of the loudspeaker, so line arrays were a good tool for investigating this.
Having justified the benefits of a phased arrays Laurie showed the THX design for a 1000 sq ft speaker array for cinemas which included the ability to send different sounds to different sections of the audience. Of course it was never built due to its complexity and cost.
Laurie discussed the various design parameters for line arrays and demonstrated a tool developed at THX for simulating line arrays before building them. He then went on to discuss the line arrays his research team have built. A row of metal dome tweeters are PCB mounted in the gap between offset pairs of mid-range slot-loaded transducers. Each transducer has its own DSP and amplifier. With the line array they can vary the beam width, do beam steering and beam overlays.
The main point Laurie wanted us to take away was that the problems we can see when measuring a system are sometimes automatically corrected by the brain (like room reflections). So modern correction techniques should be used with economy or risk hurting the sound more that helping it.
There followed a very convincing demonstration of a set of line arrays, demonstrated in both horizontal and vertical orientations, and a lively question and answer session. A recording of the lecture is available from the UK section website at www.aes.org/sections/uk/meetings/a0702.html.
Report by Tim Harris