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Sound In Live Event Production

A long-standing question, sometimes attributed to the 18th century philosopher George Berkeley, asks: "If a tree falls and no-one is there to hear it, does it make a sound?"

This appears to address a distinction (if there is one) between the external world and our perception of it, which is indeed a question for philosophers. A fundamental part of the question, however, is one of definition: what is sound? If it consists entirely of vibrations or oscillations in pressure, then the tree makes a sound. If it consists entirely of auditory experience, then the tree cannot make a sound without a listener.

The Shorter Oxford English Dictionary offers us: (1) "The sensation produced in the ear or other organ of hearing by the vibration of the surrounding air or other medium; that which is or may be heard; the phenomenon of vibration by which this is produced. Also, pressure waves outside the range of audible frequencies, as infrasound, ultrasound." If we take that definition, it isn't exclusively one thing or the other: it is either, or both.

Most of what is said in this section addresses the mechanics of sound ("the phenomenon of vibration") and the means by which we quantify and produce it, although the page on Loudness contains a few points that might sit more comfortably under "auditory experience".

It contains information about:

The Decibel

The Decibel is a basic mathematical tool commonly used for comparing sound levels (either in the form of sound pressure, or in other units of measurement commonly used in live sound reinforcement). It enables us to convert diverse units of measurement into a single common currency. Every piece of equipment in a PA system has an effect on signal level (either overall, or at a particular range of frequencies). The decibel is used to describe what is happening to signal level, irrespective of the unit of measurement.


Phase relationships have a fundamental role in sound propagation. This section offers some background information about how phase relationships in multiple loudspeaker systems affect overall system performance.

PA System Design

This addresses the fundamental requirements of sound systems: what is the PA System trying to achieve (what should it be designed to do)?


Everybody has heard something that was ‘too loud’, or struggled to hear something that wasn't loud enough. What is loudness? How should a sound system affect it?

The Law

What does the law have to say about sound?

If you wait long enough, this section will almost certainly have more to say about sound. If you have a particular question about it that isn't answered anywhere here, please feel free to ask us.