The standardized equal loudness contours identify the non-linearities of the human auditory system using simple sinusoidal input signals. The graphical illustration of auditory performance trends provides a visual representation of these non-linearities with respect to both frequency and amplitude across the range of auditory perception. Metrics such as the A-Weighting filter approximate one generalized curve shape, in an effort to quantify measured values in a manner that represents the perception of the measured sound. With the release of the ISO226:2003 version of the standard, the most recent version of the equal loudness contours provide an improved contour set with more refined shapes and steeper slopes. The purpose of this study is to investigate the performance of the A-weighting function compared to the updated curves of the equal loudness contours. Included is an examination and discussion of the appropriateness of the continued use of the existing A-Weighting filter. Given the overall un-hyperbolic shape and flattening of the equal loudness contours as the amplitude of the noise increases, the A-weighted results visually identify the areas of weakness associated with a constant filter approach. This visual examination easily identifies the strengths of each approach as well as the deviations from anticipated outcomes.
Graphic Processor Units (GPUs) on the latest models of computer graphic cards generate significant amounts of heat. In fact, the required dissipation rate is so large that cooling fans mounted on heat-sinks must be used to maintain satisfactory GPU temperatures. The packaging of these fans is small and similar designs have been used for cooling of electronic packaging for decades. The appropriate application of these fans as well as their optimal design for minimal noise generation and maximum air movement has not kept pace with that of large industrial sized fans. Where space limitations allow and heat transfer requirements dictate, blower type fans are implemented because they are capable of delivering relatively high flow rates in high impedance environments when they are compared to more traditional axial flow fans. The operation of these blower fans, particularly at high speeds, results in the generation of noise which is experienced by the user. Both computer manufacturers and consumers alike have deemed this noise to be excessive and annoying. The fan model predictions and the operational reality of the higher fan speeds needed to deliver increased air flow both lead to the reality of higher noise levels. The purpose of this study was to experimentally investigate the realized thermal and acoustic performance of a blower style fan-sink mounted on an advanced graphics port (AGP) card. The goal of this investigation was to determine what thermal benefits of higher flow rate are realized by the blower fan at the expense of increased noise emissions. The experimental results of thermal measurement results spanning the operating speed of the fan are presented and accompanied by the noise data. These data include both traditional acoustic analysis techniques using sound pressure and power level measurements as well as psychoacoustic metrics. The result of the thermal testing suggests that the rate of improvement in thermal performance decreases as the blower fan speed increases. As expected, an increase in noise level was also observed. Of particular interest were the results of the psychoacoustic analysis which indicate a similar detrimental effect with increased fan speed for some metrics, while other metrics indicate no change across the operating speed range of the blower fan.
While noise levels are most often quantified using physical quantities including A-weighted sound pressure level, these metrics do not adequately represent the human perception of the noise. For this, loudness is a more appropriate acoustic metric as it describes the perceived acoustic intensity of a sound. Given that real sounds are often unsteady, a most useful loudness calculation will also account for the perceptional phenomena of time and temporal masking. One such model is the DIN 45631-A1. However, this standard takes a less common approach in that it does not fully describe a methodology to calculate the unsteady loudness. It instead offers a more general procedure along which it provides open-ended checks and balances for verifying the progress through the various calculation steps. The caveat of this is that while conditions specified by this standard may be satisfied, it has been suggested that varying results may be achieved due to the procedure’s open architecture. Using several commercial software applications which purport to follow the DIN standard, this study investigated several of these commercial applications and compared the calculated results for several common time varying inputs to determine the extent to which compliance with DIN 45631-A1 results in identical loudness scores.
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