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The Percentile Frequency method originated in an attempt to quantify the frequency content of door slam sounds. The method is based on the Specific Loudness Patterns of Zwicker Loudness. Zwicker states that the area of the Specific Loudness Pattern is proportional to the total loudness. The method summarizes each Pattern as seven frequencies identifying the contributions of fixed percentages of the total area (i.e. 10%, 20%, 30%, 50%, 70%, 80% and 90%). Applying the method to each Pattern in a time series generates a family of curves representing the change in relative frequency content with time. The process, in effect, normalizes the frequency content of the impulse for loudness and reduces the data to a two dimensional plot. On a Percentile Frequency plot a simple impulse appears as a pattern of “nested, inverted check marks.” More complicated impulses, such as rattles, have more complicated shapes that are still “nested” together.

Damping treatments are widely used in passenger vehicles, but the knowledge of damping treatments is often fragmentary in the industry. In this study, vibro-acoustics behavior of a set of vehicle floor and dash panels with various types of damping treatments was investigated. Sound transmission loss, sound radiation efficiency as well as damping loss factor were measured. The damping treatments ranged from laminated steel construction (thin viscoelastic layer) and doubler plate construction (thick viscoelastic layer) to less structural “bake-on” damping and self-adhesive aluminum foil-backed damping treatments. In addition, the bare vehicle panels were tested as a baseline and the fully carpeted floor panel was tested as a reference. The test data were then examined together with analytical modeling of some of the test configurations. As expected, the study found that damping treatments add more than damping. They also add mass and change body panel stiffness.