# Sound intensity levels lab report

OBJECTIVE

The purpose of this experiment is to:

1. 1) measure sound intensity levels (SIL) in decibels (dB) and verify that an increase in SIL, eg. when
two sources are played simultaneously, are a result of adding individual intensities (in W/m2),
and not by adding the SILs directly.
2. 2) establish a relationship between SIL (dB) and distance (m).

METHOD

Two sound sources of the same frequency are played individually, and then simultaneously, while the
SIL (dB) are measured using calibrated sound level meters (SLMs) tuned to the A-weighting setting. The
A-weighting setting sets a filter on the SLMs to make them mimic the characteristics of the human ear.

Data is gathered on a table, suggested by Table 1 below.

Table 1: Suggested table for gathering the data

ANALYSIS

1. 1) Generate a new table, converting all the SIL (dB) from Table 1 to intensity (W/m2), and call this
Table 2 from this point forward. A suggested format for Table 2 is shown below.
2. 2) Add the intensities for source A and for source B along the same locations, and put the values on
an additional column on Table 2. This will be the theoretical (or accepted value) for calculating
the error in this experiment.
3. 3) Calculate the error in your experimental value for intensity IA+B (dB), using IA + IB (dB) as the
accepted value, and record them on the last column of Table 2.
Table 2: Suggested table for Analysis
4. 4) Plot a graph of SIL (dB) vs. distance (m) for source A, and another one for source B. (You may
have a hard time drawing both on the same axes, so it’s okay to have 2 separate graphs). Try to
draw a smooth curve joining the points on both graphs.
5. 5) What is the trend that is seen in both graphs as distance from the source increases?
 Location # rA (m) rB (m) SILA (dB) SILB (dB) SILA+B (dB)
 Location # IA (W/m2) IB (W/m2) IA+B (W/m2) IA + IB (W/m2) Error (%)

2

1. 6) Theoretically, what happens to the intensity (W/m2) of a sound when the distance is doubled?
2. 7) Theoretically, what happens to the SIL (dB) of a sound when the distance is doubled?
3. 8) a) From your first graph of SIL (dB) vs distance (m) for source A, calculate the change in the SIL
(dB) for source A as the distance doubles from r = 2 m to r = 4 m.
b) From your second graph of SIL (dB) vs distance (m) for source B, calculate the change in the
SIL (dB) for source B as the distance doubles from r = 3 m to r = 6 m. You will have to estimate
the values of the SIL (dB) at r = 3 m and r = 6 m from the graph after you have drawn a smooth
curve joining the points.
4. 9) Do these estimates of the change in SIL (dB) values match with the theoretical predictions
drawn in Q #7 above?
5. 10) Suggest the sources of error in this experiment (do not write “human error”!), any precautions
that can be taken, and any improvements that can be made to reduce the errors while taking the
measurements.

table has been completed for the sound intensity levels, i will attach, please graph the points.

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