The TiMax Concept

The human hearing system is binaural. This gives people the ability to hear multiple sounds via two separate aural receptors and thus draw clearer conclusions about the positions of the sources of the sound. Listeners make judgements about the distance of the sound source and their acoustic environment based on their perception of echoes and reverberation and the frequency-dependent absorption characteristics of reflective surfaces within the environment. The main clues to localisation of sound are provided not only by differences in sound levels but also by soundwave arrival times at the ears. These differences allow people to "focus" their hearing onto what is of interest to them and to filter out what is not (this has been aptly named the Cocktail-Party Effect).

Delivering sound to an auditorium from a large stereo loudspeaker system prevents the audience in most listening positions (i.e. off-centre) from properly localising anything other than extreme panoramic information in the sound mix. This is because the sound from the closer loudspeaker stack will arrive at a listener's ear before the sound from the more distant loudspeaker. The psychoacoustic law of Precedence, sometimes known as "Haas-effect" after its originator, dictates that for a sound coming from two or more speakers the listener will perceive the sound as coming from the closer loudspeaker due to its earlier arrival time, in many cases even if the more distant sound is louder due to the effect of a panpot. Thus an audience member's perception of stereo imaging in a stereo sound mix will only be as good as their proximity to the centre line of the room dictates.

The way to deal with this is to implement a Source-Oriented Reinforcement ("SOR") system, which, as well as achieving the desired even distribution of sound level over a large listening area, will also maintain directional information about multiple sound sources, so that the "audio position" of a presenter, actor, musical instrument, recorded program channel or special effect sample authentically matches the actual, "visual position" or required contextual localisation. This outcome reduces listener stress and improves intelligibility and hence message impact for all audience members, as well as typically widening the 'sweet spot' for creative panoramic or spatial information in the sound mix to over 90 per cent of the audience listening positions.

The principle reason why SOR works is its exploitation of natural ways of hearing. An SOR system utilises a special type of multichannel audio matrix which gives every audio source it's own unique level and delay setting with respect to every loudspeaker, which allows every sound source to be independently and identically localised for every audience member. Stereo music reproduction from a distributed SOR loudspeaker system is achieved by using the delay matrix to feed several loudspeakers with both channels of the stereo signal, but delayed and summed so as to maintain the left and right perspective of the two signals for all listening positions.

The same idea can be used to reproduce pre-recorded film surround sound material; each of the five signals intended for the L, C, R, Ls and Rs loudspeakers can be fed into the matrix and the signals delay-matrixed such that a distributed system gives a better delivery of spatial information for all audience members by creating a "virtual" surround sound environment rather than relying on a conventional "discrete" surround configuration. SOR techniques have been used for top international productions of musicals, plays, arena operas, concerts, dance clubs and artists, special effects soundscapes, as well as many major corporate promotional events. Although very different in application and outcome, typically their shared agenda is audience immersion and message impact, often with the addition of enhanced panoramic surround and animated audio effects.

We have learned quite a lot over the years, especially since digital processes have allowed us to measure and adjust at a more detailed level, about how speaker drivers and loading devices interact with each other and their enclosures, about how these enclosures subsequently interact when arrayed together, and how this integrated system interacts with the spaces and environments that we place them in. In recent years the smart money has begun to include psychoacoustics in their sound design deliberations, in acknowledgement of the inescapable symbiosis between Speakers, Spaces and Senses.