5.4.2 Maximum far-field on-axis SPL Calculations
Simplified maximum far-field on-axis spl estimates for a single column may be made
using the following simple arithmetic and look-up tables . . .
Far-field Sound Pressure Level (spl) = A minus B minus C
where A = the effective source spl referred to 1m distance
B = the radial attenuation with distance
C = excess air attenuation
(A) - The effective source spl is calculated for far-field estimates only (in practice,
large array outputs do not integrate as close as 1m).
This “source spl” will depend on the W8L Series model’s maximum spl, the
number of cabinets and the splay angle between the cabinets. W8L Series
cabinets have a nominal vertical MF & HF coverage of 7.5° so calculations
have been restricted to 8 cabinets for 1° splay and 4 cabinets for 2° splay on
the assumption that progressive curvature arrays start with minimal splay at
the top for far-field projection, increasing towards the bottom. 0° (straight)
arrays are calculated for up to 16 cabinets as curvature losses are not
applicable.
See look-up table below.
(B) - Radial attenuation is the reduction in sound pressure due to the radial
expansion of the wavefront. This attenuation varies from 3dB per doubling of
distance in the nearfield to 6dB per doubling in the farfield and depends on
the length of the array.
See look-up table below.
(C) - Excess air attenuation is caused by air absorption. It is heavily dependent on
humidity and temperature and is worse at mid and high frequencies.
See look-up table below.
Value of A
Quantity
(splayed at 0°)
W8L
Max dB spl
cont. pk
W8LC
Max dB spl
cont. pk
W8LM
Max dB spl
cont. pk
1 134 140 129 135 125 131
2 140 146 135 141 131 137
4 146 152 141 147 137 143
6 150 156 145 151 141 147
8 152 158 147 153 143 149
10 154 160 149 155 145 151
12 156 162 151 157 147 153
14 157 163 152 158 148 154
16 158 166 153 159 149 155
Effective source spl (referred to 1m) vs model & quantity
To Next Page
Loading...
Need help?
General
