Fortunately, multiple sound sources do not automatically increase the sound level in an exponential manner, but multiple sound sources do create a "cluttered" acoustic environment.

Determine the Background Noise sound level by looking at the digital screen on a Sound Level Meter (SLM). Note the predominant decibel level at a point in time. It is the nature of sound that it quickly decays and a new sound event is registered on the SLM screen. Practice with the SLM so that you get a feel for the fluctuations in acoustic environments and the delay that occurs when the meter displays the reading.

For the purposes of the FHI, a general measure of the background noise is the target.