TABLE OF CONTENTS Due to the spatial variation of sound pressure in a space, or vibration over a surface, we almost always need to measure temporal and spatial average levels.
The temporal and spatial average sound pressure level in a room is usually referred to as the average sound pressure level. Temporal and spatial average values for sound pressure and velocity levels don't tend to use different symbols; they simply use L P and L v respectively, and rely on accompanying text to make it clear.
For N individual measurement positions, where L eq ,n is measured at each position, the temporal and spatial average level is
| (3.18) |  |
For sound pressure, spatial averaging can also be carried out with a continuously moving microphone. In this case, L p is equal to the measured L eq.
The sample standard deviation, s dB, can be calculated using
| (3.19) |  |
Calculation of confidence intervals requires knowledge of the probability distribution for the variable of interest; this variable is usually the sound pressure level or the velocity level. Exact probability distributions will vary and are rarely known (Lyon, 1969). For mean-square pressure, a gamma distribution applies to the source room and a log-normal distribution can be assumed in the receiving room (Section 1.2.7.9). For mean-square velocity, it is also reasonable to assume a log-normal distribution (Section 2.7.6). Therefore, it can be assumed that the spatial variation of sound pressure levels and vibration levels in decibels is described by...
