Martin Audio W8L Longbow Application Manual page 27

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