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Squeal noise generation during braking is a complicated dynamic problem which automobile manufacturers have confronted for decades. Customer complaints result in significant yearly warranty costs. More importantly, customer dissatisfaction may result in rejection of certain brands of brake systems. In order to produce quality automobiles that can compete in today's marketplace, the occurrence of disc brake squeal noise must be reduced. The addition of a constrained layer material to brake pads is commonly utilized as a means of introducing additional damping to the brake system. Additional damping is one way to reduce vibration at resonance, and hence, squeal noise. The simulation of braking events in dynamometers has typically been the preferred insulator selection process. However, this method is costly, time consuming and often does not provide an insight into the mechanism of squeal noise generation. This work demonstrates the use of modal analysis techniques to select brake dampers for reducing braking squeal. The proposed methodology reduces significantly the insulator selection time and allows an optimized use of the brake dynamometer to validate selected insulators

The National Institute for Occupational Safety and Health and the Environmental Protection Agency sponsored the completion of an interlaboratory study to compare two fitting protocols specified by ANSI S12.6-1997 (R2002) [(2002). American National Standard Methods for the Measuring Real-Ear Attenuation of Hearing Protectors, American National Standards Institute, New York]. Six hearing protection devices (two earmuffs, foam, premolded, custom-molded earplugs, and canal-caps) were tested in six laboratories using the experimenter-supervised, Method A, and (naive) subject-fit, Method B, protocols with 24 subjects per laboratory. Within-subject, between-subject, and between-laboratory standard deviations were determined for individual frequencies and A-weighted attenuations. The differences for the within-subject standard deviations were not statistically significant between Methods A and B. Using between-subject standard deviations from Method A, 3-12 subjects would be required to identify 6-dB differences between attenuation distributions. Whereas using between-subject standard deviations from Method B, 5-19 subjects would be required to identify 6-dB differences in attenuation distributions of a product tested within the same laboratory. However, the between-laboratory standard deviations for Method B were -0.1 to 3.0 dB less than the Method A results. These differences resulted in considerably more subjects being required to identify statistically significant differences between laboratories for Method A (12-132 subjects) than for Method B (9-28 subjects).

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A new hybrid simulation method for room acoustics is presented. It is grounded on two well known numerical simulation techniques for room acoustics. The hybrid method takes geometric acoustics for granted and uses an improved version of the classical ray-tracing technique for computing the specular reflections and a slightly modified energy transition method for simulating the diffuse reflections. The impulse responses (IRs) are then computed by superposition of the specular and diffuse ones. The reverberant part of the IRs gains a much more realistic aspect than the one obtained from either ones method alone. Both the ray-tracing technique and the energy transition method are reviewed and some improved features are discussed. The sound source and the receiver modeling are presented, including a new method for simulating the head related transfer functions (HRTFs), and based on the wavelet technique, which provides a shorter time computation of the binaural impulse responses for auralization purposes. In a companion paper, entitled Hybrid method for numerical simulation of room acoustics: Part 2 - Validation of the computational code RAIOS 3, a validation of the method in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones