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Church Sound: Principles Of Room Acoustics And Sound System Interaction

The bottom line is sound system design is equally as important as room acoustics

By Vance Breshears October 1, 2012

The acoustical characteristics of any room are determined by its architecture. Room architecture consists of room size, room shape and room finishes.

This means that room size, shape and finishes determine the room acoustics.

The first factor affecting room acoustics, room size, is usually determined by the number of seats needed for the room and the layout of those seats. 

The aspect ratio (ratio of the ceiling height to room width to the room length) is also a critical factor in the room’s acoustic functionality. 

Each of these factors should be carefully planned early in the design process to minimize potential acoustical problems.

The second factor in determining the room acoustics is the room shape.

Frequently, rooms are designed in a fan shape with a curved back wall and wrap-around seating. This type of room design generally creates a dramatic and inherent problem when it comes to focusing sound.

When designing a room, plan a room shape that does not include concave or focusing wall or ceiling shapes, parallel wall surfaces, or extremely large continuous surfaces. The room shape should reflect sound into areas that will not create acoustical problems.

With regard to room shape and how sound behaves as it bounces around the room, we want to provide early reflected sound energy to the seating areas and eliminate late reflections that are perceived as an echo. 

Whether sound arrives early or late in time is relative to how long after the direct sound it arrives.

In general, the larger the room, the farther sound has to travel to be reflected, and the later it arrives back at a listener.

The later it arrives back at the listener, the more it sounds like an echo and the more it distracts the listener and causes intelligibility problems.

The third element that determines the room acoustics is the room finishes.  Whether a surface will reflect sound, absorb sound, or reflect it in all different directions (diffuse sound) are all contributing factors to the acoustics.

Since we’re looking for early energy, not late energy, we will generally want the surfaces close to listeners to be hard or reflective and the surfaces far from listeners to be soft or absorptive. This is just the opposite of what happens in most rooms. 

A typical room is designed so absorptive surfaces, such as carpeting and padded pews or chairs, are closest to listeners, while reflective surfaces, such as walls and ceilings, are farthest from listeners.

This creates an environment where there is little early reflected sound energy and excessive late sound energy.

Ideally, we want the surfaces close to the listener to be reflective (for example, hard flooring instead of carpet beneath seats) and the surfaces far away to be more absorptive.  This will create a more acoustically balanced room.

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