Speaker Design Method

Introduction

Step 1:

Room

Characteristics

The steps below summarize the speaker system design method. Use these steps in conjunction with the Tyco Safety Products iTool (described later in this chapter).

Determine if the room requires advanced design methods. Some characteristics of a difficult location/space include:

•High Background Noise Levels (Greater than 80 dB).

•Large Spaces with High Ceilings (Greater than 15-foot high ceilings).

•Unique Room Shapes (Rooms with many different angles, spherical shapes, etc.).

•High Reverberation Times (T60 > 1.5).

	Step 2:	Use the steps below to calculate the number of speakers:
	Calculate the	1. Determine the speaker-to-listener distance (D2).
	Number of Speakers	1. Determine the speaker-to-listener distance (D2).
	Number of Speakers

Step 3:

Audio Power and

Individual Speaker

Wattage Tap

Step 4:

Model Design to Predict Intelligibility

Step 5:

Verify Final

Installation

2.Using D2 and the speaker's polar response, calculate the speaker's coverage area.

3.Select a layout pattern and calculate the number of speakers required for the area.

Use these steps below to determine the required audio power:

1.Using the speaker's sensitivity and speaker-to-listener distance, calculate the listener SPL for each of the wattage taps. Subtract the SPL variation based on the coverage pattern from Table 2-3.

2.Determine the SPL requirements by adding the required signal-to-noise ratio (usually 15dB) to the background noise levels.

3.From Step 1, select the wattage tap that satisfies the SPL requirements determined in Step 2.

4.Multiply the wattage tap selection by the number of speakers in the room to determine the total audio power required.

This optional step is recommended for areas of high reverberation or of complex geometry. Modern modeling tools such as EASE® from Renkus-Heinz and Modeler® from Bose use sophisticated ray-tracing algorithms to accurately predict intelligibility.

As part of system commissioning the audibility for every area must be verified. This can be accomplished with a simple SPL meter set to read decibels with the “A” weighted filters applied. The audibility of the primary evacuation signal is measured, typically a temporal coded horn or slow whoop horn is used. The audibility of emergency voice/alarm communications messages is typically not recorded due to the varying nature of speech.

6-2

Speaker Design Method

1. Determine the speaker-to-listener distance (D2).