scholarly journals Consumer-Grade Headphones for Children: Limited Effectiveness of “Level Limiters” When Used With Portable or Home Media Players

2019 ◽  
Vol 23 ◽  
pp. 233121651988923
Author(s):  
Michael A. Stone ◽  
Mark Harrison ◽  
Keith Wilbraham ◽  
Melanie Lough
Keyword(s):  
Sound Pressure ◽  
Standardized Test ◽  
Output Level ◽  
Laptop Computer ◽  
Limited Effectiveness ◽  
Listening Levels ◽  
Computer Based ◽  
Audio Output ◽  
Audio Interfaces ◽  
Field Sound

Consumer-grade headphones for children are frequently packaged or marketed with labels claiming incorporation of an output-level-limiting function. Six pairs of headphones, sold separately from devices with audio interfaces, were selected either from online recommendations or from “best rated” with a large online retailer, the opinions being expressed in 2018 to early 2019. The acoustic outputs in response to an internationally standardized test signal were measured through the ears of a head-and-torso simulator and referenced to equivalent A-weighted diffuse-field sound pressure levels. The headphones were tested with a variety of music capable sources found in a domestic environment, such as a mobile phone, tablets, laptop computer, and a home “hi-fi” CD player. To maintain likely homogeneity of the audio interface, the computer-based platforms were manufactured by either Apple™ or certified Android devices. One of the two Bluetooth-linked headphones exhibited level limiting with low distortion (i.e., a compression ratio well in excess of unity). None of the devices wired directly to an audio output performed distortionless level limiting: “limiting” was implemented by a reduction of sensitivity or mechanical limitations, so could be called “soft limiting.” When driven by a laptop or CD player, some were still capable of producing output levels well in excess of “safe-listening” levels of 85 dB(A). Packaging labels were frequently ambiguous and imprecise.

Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

2012 ◽  
Vol 217-219 ◽  
pp. 2590-2593 ◽  
Author(s):  
Yu Wang ◽  
Bai Zhou Li
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Low Frequency ◽  
Dipole Source ◽  
Fluctuating Pressure ◽  
Common Structure ◽  
Hydrodynamic Noise ◽  
Near Field Sound ◽  
Equivalent Sources ◽  
Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

scholarly journals A Tablet-Computer-Based Tool to Facilitate Accurate Self-Assessments in Third- and Fourth-Graders

2018 ◽  
Vol 13 (10) ◽  
pp. 225
Author(s):  
Denise Villanyi ◽  
Romain Martin ◽  
Philipp Sonnleitner ◽  
Christina Siry ◽  
Antoine Fischbach
Keyword(s):  
Reading Comprehension ◽  
Rating Scale ◽  
Assessment Tool ◽  
Standardized Test ◽  
Fourth Graders ◽  
Tablet Computer ◽  
School Students ◽  
Self Assessment ◽  
Computer Based ◽  
Self Assessments

Although student self-assessment is positively related to achievement, skepticism about the accuracy of students’ self-assessments remains. A few studies have shown that even elementary school students are able to provide accurate self-assessments when certain conditions are met. We developed an innovative tablet-computer-based tool for capturing self-assessments of mathematics and reading comprehension. This tool integrates the conditions required for accurate self-assessment: (1) a non-competitive setting, (2) items formulated on the task level, and (3) limited reading and no verbalization required. The innovation consists of using illustrations and a language-reduced rating scale. The correlations between students’ self-assessment scores and their standardized test scores were moderate to large. Independent of their proficiency level, students’ confidence in completing a task decreased as task difficulty increased, but these findings were more consistent in mathematics than in reading comprehension. We conclude that third- and fourth-graders have the ability to provide accurate self-assessments of their competencies, particularly in mathematics, when provided with an adequate self-assessment tool.

Reconstruction of the unsteady rotating forces of fan’s blade from far-field sound pressure

2014 ◽  
Vol 86 ◽  
pp. 126-137 ◽  
Author(s):  
Hassen Trabelsi ◽  
Majdi Abid ◽  
Mohamed Taktak ◽  
Tahar Fakhfakh ◽  
Mohamed Haddar
Keyword(s):  
Sound Pressure ◽  
Far Field ◽  
Field Sound

A study of brake disc modal behaviour during squeal generation using high-speed electronic speckle pattern interferometry and near-field sound pressure measurements

2000 ◽  
Vol 214 (3) ◽  
pp. 285-296 ◽  
Author(s):  
M Reeves ◽  
N Taylor ◽  
C Edwards ◽  
D Williams ◽  
C. H. Buckberry
Keyword(s):  
High Speed ◽  
Sound Pressure ◽  
Surface Deformation ◽  
Speckle Pattern ◽  
Near Field ◽  
Electronic Speckle Pattern Interferometry ◽  
Brake Disc ◽  
Pressure Measurements ◽  
Near Field Sound ◽  
Field Sound

The out-of-plane surface vibration of a brake disc during naturally excited squeal has been investigated using a combination of high-speed electronic speckle pattern interferometry (ESPI) and near-field sound pressure measurements. Both techniques provide visualization and quantification of the time-resolved surface velocity. A mathematical description of disc brake squeal modal behaviour is proposed that predicts accurately all of the experimentally observed interferometry and sound field measurements. The complex mode description proposed here is in agreement with that proposed by others for drum brake squeal. This assumes that two identical diametral modes are excited simultaneously, identical except for a spatial and temporal phase shift. The use of a near-field microphone array provided a convenient multipoint, non-contacting vibration probe which may find use in the study of other vibrations characterized by high surface amplitudes and efficient sound radiation. The high-speed ESPI provided a real-time visualization of surface deformation analogous to double- pulsed holographic interferometry, with the benefit of giving a true time series of the surface deformation during a single vibration cycle.

Prediction of Far-Field Sound Pressure of a Semisubmerged Cylindrical Shell With Low-Frequency Excitation

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
T. Y. Li ◽  
P. Wang ◽  
X. Zhu ◽  
J. Yang ◽  
W. B. Ye
Keyword(s):  
Cylindrical Shell ◽  
Free Surface ◽  
Sound Pressure ◽  
Acoustic Radiation ◽  
Phase Method ◽  
Far Field ◽  
Radiation Model ◽  
New Approaches ◽  
Modal Coupling ◽  
Field Sound

A sound–structure interaction model is established to study the vibroacoustic characteristics of a semisubmerged cylindrical shell using the wave propagation approach (WPA). The fluid free surface effect is taken into account by satisfying the sound pressure release condition. Then, the far-field sound pressure is predicted with shell's vibration response using the stationary phase method. Modal coupling effect arises due to the presence of the fluid free surface. New approaches are proposed to handle this problem, i.e., diagonal coupling acoustic radiation model (DCARM) and column coupling acoustic radiation model (CCARM). New approaches are proved to be able to deal with the modal coupling problem efficiently with a good accuracy at a significantly reduced computational cost. Numerical results also indicate that the sound radiation characteristics of a semisubmerged cylindrical shell are quite different from those from the shell fully submerged in fluid. But the far-field sound pressure of a semisubmerged shell fluctuates around that from the shell ideally submerged in fluid. These new approaches can also be used to study the vibroacoustic problems of cylindrical shells partially coupled with fluid.

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