Arraying Loudspeaker Systems - Page 2

Before I continue this paper on loudspeaker placement within an array, I would suggest that you read the article on decibels in this publication, as it will prepare you for the following discussion. It would be impossible to address or cover every possible variation of church sanctuaries, so the following information is meant to be used as a guideline as to what to take into account when arraying individual loudspeaker components. There are some small church sanctuaries that can be accommodated by a single loudspeaker enclosure. Usually such a sanctuary is not very deep and not too wide, and a single loudspeaker can indeed cover the majority of the congregation.

Check out the aspect ratio of such a room:
In this case the loudspeaker enclosure has a ninety-degree horizontal angle of coverage as far as the high frequency horn's coverage capability. Notice that it doesn't cover the entire first pew on the left and right sides. This may be acceptable because the members of the congregation seated there could probably hear and understand a sermon delivered from the pulpit without a sound system. If, however, in some room of similar dimension, it is deemed necessary to cover this small zone, that is not in the main FOH (Front of House) systems pattern of coverage; the way to go about this is with what are referred to as near field "fill speakers."

The Peavey Impulse Six would do a good job in this instance. When employing a fill loudspeaker, the power amplifier driving these speakers must have the ability to set the gain or level for these speakers. The proper adjustment is to have the level all the way down, have a listener sit in the area to be covered, and slowly increase the level of the gain control of the amplifier until it is just noticeable that the speaker is on.

A fill loudspeaker by virtue of it's intended use should not be so in level that anyone seated outside the intended area of coverage can tell that the "fill" loudspeaker is on.

Another consideration in a small church such as this is the angle of coverage in the vertical plane that the loudspeaker offers. Many of our enclosures have a nominal ninety-degree horizontal by a forty-five degree vertical angle of coverage. A typical coverage pattern with a single loudspeaker with a forty-five degree vertical angle of coverage is shown below:

The room in these examples is 40 ft. long by 25 ft. wide by 16 ft. high.

What happens when the room is much longer and a single loudspeaker enclosure does not have enough vertical coverage pattern to do the job? The answer is to employ two enclosures, one for the Far Field and one for the Near Field. The Inverse Square Law says that the direct sound field emanating from a sound source will vary in level with the inverse of the square of the distance away from the source. Or on the decibel scale it becomes simpler, as sound drops in level -6 dB, each time you double the distance away from the source.

The important thing to consider here is that the loudspeaker that is intended to cover the first one-third of the congregation must be reduced in level.

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