OVERHEAD VERSUS LATERAL LOUDSPEAKER SYSTEM DESIGNS - CONSIDERATIONS FOR SPEECH INTELLIGIBILITY
S WISE · 2024
Much competent sound system design relies heavily on calculations based on the %ALCONS equation.This equation considers the level of rst arrival sound only (direct sound), and its relationships with the levels of the reverberant eld and background noise.This can overlook the sometimes non-linear nature of sound arrivals at the listener's ears, and the uneven arrival of reverberant sound.Designs whose calculations would appear to provide adequate intelligibility can produce results that are poor.This paper examines the effects of the interactions between widely spaced loudspeakers, the room environment and some basic principles of human sound perception.Simple systems are studied, allowing examination of the resulting direct sound, early re ection and long term energy distributions that result.Overhead and lateral sound system con gurations are considered and de ned, and advantages / disadvantages of these two basic system types are examined.Examples of successful and unsuccessful applications of each type of system are reviewed and key designparameters are af rmed. THE %ALCONS EQUATION -USE AND MISUSEThe %ALCONS equation is commonly used in various forms to predict speech intelligibility in noisy and reverberant spaces Like many acoustical equations, it is based on the statistical distribution of reverberant sound energy.In other words, it assumes an average and smoothly decaying room response over an audience area, providing a predictable result for most if not all listeners.This equation, and later developments of it, provides much useful insight into expected listener perception. it is especially helpful to the sound system designer in evaluating the limits of what can be accomplished using particular loudspeaker characteristics within an acoustic environment.Minimum requirements for noise and/or reverberation control are made evident.'But beware, %ALCONS does not tell the whole story, and can lead to complacency over other important design issues.This equation assumes that all of the important characteristics of the sound transmission process are constant or decaying smoothly with time, In some sound system / room con gurations this is essentially tnie, and in these cases calculating %ALCONS may be suf cient to provide con dence in the speech intelligibility of the system.Thisis usually the case where all of the sound from individual loudspeakers arrives within the early time period, and where later sound decays smoothly,