dB re what? The theshold of hearing I_0=10^-12 watts/m^2 or I_0=1 watt/m^2?

SL=10log_10(I/I_0),

so:

I=I_0 10^{SL/10}.

What intensity to you mean?2.) A person standing 4.0 m from a wall shouts such that the sound strikes the wall with an intensity of 2.5 x 10 x 10 W/m . Assuming that the wall absorbs 20% of the incident energy and reflects the rest, what is the sound intensity level just before and after the sound is reflected?

I=2.5 x 10^-3 W/m^2 and I=2 x 10^-3 W/m^2

SL=10 log_10 (2.5 x 10^-3) dB re 1 w/m^2

and

SL=10 log_10 (2 x 10^-3) dB re 1 w/m^2

RonL