Tyco 579-769 Layout Pattern Selection Guide, SPL Variation by Layout Pattern, 2x Edge-to-Edge

Speaker Basics, Continued

Power Rating	Speakers used for emergency voice/alarm communication system are wired as “Constant Voltage”
	systems, where the maximum power output of the amplifier is obtained at a certain speaker
	voltage, such as 25 V or 70.7 V. The power output of a speaker, and thus the resulting SPL is
	controlled by wattage taps on the speakers themselves. The minimum wattage tap for a
	UL Standard 1480 listed speaker is 1/4 W. For example, the Simplex 4902 Series speakers have
	wattage taps in 3 dB increments: 1/4 W, 1/2 W, 1 W and 2 W. Each wattage tap doubles the
	power delivered by the speaker, and so increases the SPL output by 3 dB for each increasing tap.
	An increase of 3 dB is considered a just noticeable increase in SPL, changing the wattage tap from
	1/4 W to 2 W increases the perceived loudness by slightly less than double.
Speaker Layouts	Many rooms require more than one speaker, the question then becomes, “how many speakers do I
	need, and how far apart should they be placed?” The answer invariably is “that depends.” There are
	many layout patterns to choose from, each suitable for different room geometries, background noise
	and reverberation times. See Table 2-2 “Layout Pattern Selection Guide” for some recommendations.
	The most common layout pattern is the rectangular pattern shown in Figure 2-7 below.

Table 2-2. Layout Pattern Selection Guide

Pattern	Description
2x Edge-to-	Not recommended except for
	tone only signaling or small rooms with
Edge
	low noise and low reverberation.
	Uses fewer speakers than Edge-to-
1.4x Edge-to-	Edge pattern. Only appropriate for
Edge	rooms with low noise and low
	reverberation.
Edge-to-Edge	Preferred layout pattern for most
	areas.
Minimum	Use with areas of high reverberation
Overlap	and/or high ceilings.
	For the worst areas, generally provides
	excellent intelligibility for even difficult
	areas. Use with caution, this type of
Full Overlap	pattern can result in lower than
	expected intelligibility due to multiple
	speaker interaction. Modeling is
	recommended for areas that would
	need this layout pattern.

Table 2-3. SPL Variation by Layout Pattern

Speaker Layout	Increase in SPL	Variation in
	Over Single
Pattern		Coverage
	Speaker
2x Edge-to-Edge	0.2 dB	–10.4 dB
1.4x Edge-to-	0.4 dB	–6.8 dB
Edge
Edge-to-Edge	0.7 dB	–4.4 dB
Minimum Overlap	2.0 dB	–2.0 dB
Full Overlap	5.2 dB	–1.4 dB

	Speaker layout patterns
	(rectangular placement)
	1.4x Edge-to-Edge
2x Edge-to-Edge
Edge to Edge	Minimum Overlap	Full Overlap
(Standard layout )

Figure 2-7. Speaker Layout Patterns

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