Specifications

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
near-field to 6dB per doubling in the far-field 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°)
Longbow
Max dB spl
W8LC
Max dB spl
W8LM
Max dB spl
cont.
pk
cont.
pk
cont.
pk
1 142 148 129 135 125 131
2 148 154 135 141 131 137
4 154 160 141 147 137 143
6 158 164 145 151 141 147
8
160
166
147
153
143
149
10 162 168 149 155 145 151
12 164 170 151 157 147 153
14 165 171 152 158 148 154
16 166 172 153 159 149 155
Effective source spl (referred to 1m) - at 0° splay - vs model & quantity
All material © 2007. Martin Audio Ltd. Subject to change without notice.