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A simple method for measuring the peak linear excursion capability (Xmax) of loudspeaker drive units is presented. The method measures the acoustic amplitude modulation of a small high-frequency signal by a very low-frequency signal. The low-frequency signal is increased to produce a target peak-to-peak modulation. A physical measurement of the peak-to-peak diaphragm excursion is made and defined to be twice Xmax.

Unacceptable distortion, sounding like a “blat” on bass notes was reported for some models of 4 X 6-inch loudspeakers in certain 1992 prototype vehicles. A study was initiated to find the cause of this distortion and to develop a specification to limit it to acceptable values. The cause of the distortion was determined to be a rapid increase in suspension stiffness at large cone excursion. The specification is based on the sum of the weighted acoustic amplitudes of the 4th through 10th harmonics of a sine wave input at 8.0 volts.

This paper presents a brief overview of the Common Launch Acceptability Region Approach (CLARA) problem and the history of efforts within the Air Force and SAE to address it. An SAE Task Group has produced top level requirements and a proposed CLAR Methodology consisting of three components (Truth Model, Coefficient Generator and LAR Generator) that provides a solution to the multiple LAR implementation problem. This proposed CLAR methodology fulfills the key requirement of a LAR algorithm that is to be common to all applications and allows updates via tables of coefficients requiring the validation of only those coefficients and not the algorithm. This paper also presents the status of trade studies being conducted by the CLARA TG on mathematical algorithms required to implement the methodology. A key step in these trade studies is development of the appropriate metrics and analysis tools with which to judge alternative algorithms.

Vehicle operation noise, even in the quietest cars, produces high sound pressure levels (SPL) at very low frequencies. This noise masks desired signals in and above this frequency range. A blind subjective test, using ten listeners, was undertaken to determine a frequency response equalization curve that would compensate for this noise under specific but realistic conditions. Starting with a 4 dB full-band level increase, an average of 40 listener responses showed a gentle rise in bass reaching an additional 4 dB at 50 Hz.

The consumer's listening test is the ultimate test of a sound system. During product development, listening tests must be carefully controlled if they are to produce useful data. Prejudiced or biased listeners are the most frequent cause of poor or misleading data from these tests. This paper describes methods of eliminating the effects of listener bias by using double-blind techniques.

A body of listening test techniques which produces consistant rankings of sound systems is presented. Sufficient detail is generated in the course of the prescribed listening evaluation to direct engineering changes to the system. A two dimensional weighting system (performance and usage) is used to determine a single-number rating.

A loudspeaker's low frequency parameters can be accurately estimated by measuring individual components without the need to assemble them into a working unit. Using this development approach, much time can be saved by optimizing one component at a time rather than building an entire speaker for each iteration. To do this, one must be able to measure the relevant physical characteristics of each component (the electro-mechanical parameters). It is also necessary to be able to predict electro-acoustic performance from the electro-mechanical parameters.

The objective of this study was to optimize the occupant restraint systems for a light tactical vehicle in frontal crashes. A combination of sled testing and computational modeling were performed to find the optimal seatbelt and airbag designs for protecting occupants represented by three size of ATDs and two military gear configurations. This study started with 20 sled frontal crash tests to setup the baseline performance of existing seatbelts, which have been presented previously; followed by parametric computational simulations to find the best combinations of seatbelt and airbag designs for different sizes of ATDs and military gear configurations involving both driver and passengers. Then 12 sled tests were conducted with the simulation-recommended restraint designs. The test results were further used to validate the models. Another series of computational simulations and 4 sled tests were performed to fine-tune the optimal restraint design solutions.

Low-frequency range extension of loudspeakers by alignments which include passive electrical components was first studied by Benson and more recently by Von Recklinghausen. The present work uses a computer model to test the practicality of representative designs. A third-order alignment is found to have considerable merit. Measurements of real systems are presented.

Delayed arrivals of a stereo source are manipulated to suppress undesirable vehicle cabin acoustics and replace them with optimum acoustics for reproduction of commercial recordings. These optimum playback acoustics are derived from concert hall and listening room measurements. An experimental vehicle sound system implementing these concepts is described.

It has been know for many years that the highest level of audio performance is achieved at the hands of an expert tuning engineer. It is recently that automotive signal processing options have become overwhelming in their number and variety. In addition, the number of vehicles using model-specific equalization has grown with the introduction of digital signal processing (DSP). It has been observed that much engineering time is consumed before arriving at the perfect tuning. To make the process a bit more “cookbook,” a structured approach is presented.