When measuring your speakers at listener place, the target curve is (or should be) slightly decreasing with frequency.
But what should be the slope of this falling curve ?
There is no single answer, it depends on the direct sound and on the diffuse field.
So it depends on your speakers, your room, your position : check it here but, take care, this is only an indication.
Corresponding measurement should be done with a long gating window of
200ms or more.
Frequency limits are normally 200Hz and 10kHz but this can be adapted
to each case.
For a shorter gating window or DRC, this calculated curve should be used with care:
ie for short time window of 20ms or less, that contains more
direct sound and less diffuse field, the measured curve is nearer to flat.
Common values for reverberation time at 200Hz : 0.3 for dry environnement, 0.5 is standard, 0.7 for live room
time at 10kHz : 0.2 for dry environnement, 0.3 is standard, 0.6 for live rooms
Common values for DI at 200Hz : 0 for omnidirectionnal, 1-2 for standard, 4.8 for open baffle
DI at 10kHz : 0 for omnidirectionnal (rare), 8 for standard, 15 for horns
The critical distance is where the level of direct soundfield and level of diffuse field are equal.
Critical distance at F1 : 0.8 m
Critical distance at F2 : 2.1 m
Target at F2 compared to F1 : -5.7 dB