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This paper discusses a project that was begun shortly before an unexpected retirement opportunity appeared that limits the possibilities for follow-up work. Some simple measurements of impulsive sounds were made in an anechoic room to investigate concerns that room alterations for sound transmission loss testing had introduced what appeared to be some reflecting surfaces in the room. The impulsive sound tests confirmed that the alterations had indeed introduced reflections into the room. Ways to reduce those reflections were developed and confirmed. However, the test results also raise concerns about reflections from the perforated metal wedges used in the original room design. An important first question is how do these reflections affect the results of sound quality work performed in this type of room?

This paper discusses a partially completed project that was begun shortly before an unexpected retirement opportunity appeared that limits the possibilities for follow-up work. The project was to investigate the pitch of door closing “thump.” The impetus for the investigation was a paper by Gardner and Magnasco. Their paper described an instantaneous frequency decomposition method that they used in the study of bird song and human speech. Bird song or speech may not seem to be closely linked to measuring door closing thump but the speed with which the frequencies in door closing sounds change is not that different from the speed of frequency change in bird song or speech. Two questions that immediately arise are can Gardner and Magnasco's technique resolve the low frequency components that occur in door closing sounds and, if so, do they relate to human perception of thump?

In recent years a predominant strategy for setting sound quality (SQ) requirements has been the sensory correlation approach (also called sensory evaluation or sensory science). Some users of this approach have reported their progress in numerous papers. Other SQ practitioners have made presentations on specific topics that show the linkage to music and musical notation. These specific links point to an alternative general strategy - “the Music Analogy for Sound Quality.” This paper begins by comparing the general methods of the music analogy and sensory correlation. Some major differences will be identified and implications discussed. Some existing specific tools for the music analogy will be identified as well as some gaps that need to be filled. Finally, reasons will be presented concerning why the music analogy should be considered when developing sound quality requirements.

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.

One task of sound quality engineering is to find of links between engineering measures and human perceptions of sound. Over the years, several papers have been presented at SAE N&V conferences concerning the sound quality of electrical motor sounds in automotive applications. Many papers have focused on the variation in motor speed during system operation. While some papers have suggested that a useful measure for slow variations is fluctuation strength, other papers suggest measures for dealing with non-periodic variations or the general trend in motor speed. Both sets of papers tend to describe the changes in terms of percentage of a statistic of the motor speed. While percentage is a useful engineering approach, it may not be the best way to relate how the changes will be perceived by a human listener. The alternate approach described here offers formulae, in units of scale-steps or cents, to describe the changes based on the link between engineering measures and music.

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.

Sound Quality work often seeks to bridge the gap between human perception and objective noise measurements. Sometimes a Sound Quality requirement is a concept, such as Pitch, that can have many meanings depending on the type of sound under consideration. The idea of impulsive sounds having indefinite pitch may be unfamiliar to the engineering world, but the field of music has used the idea for decades if not centuries. Indefinite pitch may be of value in Sound Quality work, especially when dealing with door closing sounds. No instrumentation yet exists to measure objectively the indefinite pitch of impulsive sounds. However, a pitch matching technique using sine wave bursts is described which allows the indefinite pitch of impulsive sounds to be measured by ear. Some limitations of the method are discussed as well as the need for basic psychoacoustical research on the topic of indefinite pitch.

The common occurrence of impulsive sounds in automobiles and the recent emphasis on producing vehicles with a “quality sound” has increased the need for a method for measuring the pitch of impulsive sounds. Using Zwicker’s Loudness Patterns as a basis, a data reduction method was developed which summarizes the frequency content of each pattern. The method yields time varying quantities called Percentile Partial Loudness Frequencies from a time series of Loudness Patterns. Several “simple” impulsive sounds, representing a range of pitches, were investigated using this method. Visual inspection of the results has identified trends which seem to rank the impulsive sounds in agreement with subjective pitch rankings of a listening jury. In addition, the method appears to be capable of ranking the early portion of the impulse as a sharp or dull attack. Further investigations are needed to confirm these observations and refine the technique.

Because of the multitude of impulsive sounds that can occur in automobiles it would be valuable to have a method for evaluating these sounds that relates well to customer response. Loudness Calculation based on ISO 532 Method B ( Zwicker' s method) was investigated for its potential as such a method. Problems occurred in obtaining valid 1/3 octave band spectra from conventional real time analyzers for the input to the calculation routine. A conflict arises between the short averaging times needed to track the impulse and the uncertainty principle (BT product rule) for the lower frequency bands. Since Zwicker' s method is based on critical bands, a four-pass analysis procedure was devised using an external filter set for the width of a critical band. The calculation routine was modified to directly accept critical band data.