A note on SPL calculations for multiple speakers.
Posted: Wed Jun 03, 2020 5:49 am
I've seen a few people on here adding 6dB per doubling of boxes and trying then to subtract only 3dB per doubling of distance because "It's a 'line array".
This is not correct.
Firstly the -3dB per doubling of distance only applies a few metres away from the speakers unless the array is "floor to ceiling" indoors, but a vertical stack of say 4 boxes outdoors starts obeying the -6dB rule within a few rows of audience.
Secondly, assuming the -3dB/doubling distance rule did apply, the 6dB/doubling cabs is a FAR FIELD result, and then you ADD 3dB per halving of distance, rather than saying this much SPL at 1 metre and subtracting 3dB per doubling of distance.
Thirdly for mids/highs cabs, the +6dB/doubling cabs doesn't apply once you get above the kick bass and lower mid frequencies. For higher frequencies it's probably around 3dB. You might need to re-EQ your cabs to compensate for this.
Not following these rules will cause you to overestimate the SPL capability of your rig over distance.
This is not correct.
Firstly the -3dB per doubling of distance only applies a few metres away from the speakers unless the array is "floor to ceiling" indoors, but a vertical stack of say 4 boxes outdoors starts obeying the -6dB rule within a few rows of audience.
Secondly, assuming the -3dB/doubling distance rule did apply, the 6dB/doubling cabs is a FAR FIELD result, and then you ADD 3dB per halving of distance, rather than saying this much SPL at 1 metre and subtracting 3dB per doubling of distance.
Thirdly for mids/highs cabs, the +6dB/doubling cabs doesn't apply once you get above the kick bass and lower mid frequencies. For higher frequencies it's probably around 3dB. You might need to re-EQ your cabs to compensate for this.
Not following these rules will cause you to overestimate the SPL capability of your rig over distance.