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6-2
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).
Use the steps below to calculate the number of speakers:
1. Determine the speaker-to-listener distance (D2).
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.
Speaker Design Method
Introduction
Step 1:
Room
Characteristics
Step 2:
Calculate the
Number of Speakers
Step 3:
Audio Power and
Individual Speaker
Wattage Tap
Step 4:
Model Design to
Predict Intelligibility
Step 5:
Verify Final
Installation