Percentile Frequency Method for Evaluating Impulsive Sounds

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. Applying this understanding to practical problems, the method has been used to visually show the progress of a project to reduce rattles occurring in door slam sounds. The method also has been used to quantify the low pitched “thump” of a door slam sound. In addition, a further extension of the method has been successful in differentiating high pitched door latch closing sounds. By incorporating these techniques into a general door slam sound test, it should be possible to evaluate objectively for rattles, latch sound, and “thump” as well as loudness.