Sound pressure

About: Sound pressure is a research topic. Over the lifetime, 14165 publications have been published within this topic receiving 143027 citations. The topic is also known as: acoustic pressure & instantaneous sound pressure.

Transfer function method of measuring in‐duct acoustic properties. I. Theory

Abstract: The theory of a transfer function method of measuring normal incident in‐duct acoustic properties is presented. In this method, a broadband stationary random acoustic wave in a tube is mathematically decomposed into its incident and reflected components using a simple transfer‐function relation between the acoustic pressure at two locations on the tube wall. The wave decomposition leads to the determination of the complex reflection coefficient from which the complex acoustic impedance and the sound absorption coefficient of a material and the transmission loss of a silencer element can be determined. Also presented are the theories of two techniques for improving transfer function estimates: a sensor‐switching technique for automatic system calibration and a coherence function technique for signal enhancement.

Engineering Noise Control: Theory and Practice, Third Edition

Abstract: Fundamentals and Basic Terminology Introduction Noise-Control Strategies Acoustic Field Variables Wave Equations Mean Square Quantities Energy Density Sound Density Sound Power Units Spectra Combining Sound Pressures Impedance Flow Resistance The Human Ear Brief Description of the Ear Mechanical Properties of the Central Partition Noise Induced Hearing Loss Subjective Response to Sound Pressure Level Instrumentation for Noise Measurement and Analysis Microphones Weighting Networks Sound Level Meters Classes of Sound Level Meter Sound Level Meter Calibration Noise Measurements Using Sound Level Meters Time-Varying Sound Noise Level Measurement Data Loggers Personal Sound Exposure Meter Recording of Noise Spectrum Analysers Intensity Meter Energy Density Sensors Sound Source Localization Criteria Introduction Hearing Loss Hearing Damage Risk Hearing Damage Risk Criteria Implementing a Hearing Conservation Program Speech Interference Criteria Psychological Effects of Noise Ambient Noise Level Specification Environmental Noise Level Criteria Environmental Noise Level Surveys Sound Sources and Outdoor Sound Propagation Introduction Simple Source Dipole Source Quadruple Source (Far-Field Approximation) Line Source Piston in an Infinite Baffle Incoherent Plane Radiator Directivity Reflection Effects Reflection and Transmission at a Plane/Two Media Interface Sound Propagation Outdoors, General Concepts Sound Power, its Use and Measurement Introduction Radiation Impedance Relation between Sound Power and Sound Pressure Radiation Field of a Sound Source Determination of Sound Power Using Intensity Measurements Determination of Sound Power Using Surface Vibration Measurements Some Uses of Sound Power Information Sound in Enclosed Spaces Introduction Low Frequencies Bound between Low-Frequency and High-Frequency Behavior High Frequencies, Statistical Analysis Transit Response Porous Sound Absorbers Panel Sound Absorbers Flat and Long Rooms Applications of Sound Absorption Auditorium Design Partitions, Enclosures and Barriers Introduction Sound Transmission through Partitions Noise Reduction vs Transmission Loss Enclosures Barriers Pipe Lagging Muffling Devices Introduction Measures of Performance Diffusers as Muffling Devices Classification of Muffling Devices Acoustic Impedance Lumped Element Devices Reactive Devices Lined Ducts Duct Bends or Elbows Unlined Ducts Effect of Duct End Reflections Duct Break-Out Noise Line Plenum Attenuator Water Injection Directivity of Exhaust Duct Vibration Control Introduction Vibration Isolation Types of Isolators Vibration Absorbers Vibration Neutralizers Vibration Measurement Damping of Vibrating Surfaces Measurement of Damping Sound Power and Sound Pressure Level Estimation Procedures Introduction Fan Noise Air Compressors Compressors for Chillers and Refrigeration Units Cooling Towers Pumps Jets Control Valves Pipe Flow Boilers Turbines Diesel and Gas-Driven Engines Furnace Noise Electric Motors Generators Transformers Gears Transportation Noise Practical Numerical Acoustics Introduction Low-Frequency Region High-Frequency Region: Statistical Energy ANalysis

Holograms for acoustics.

Abstract: Holograms for sound waves, encoded in a 3D printed plate, are used to shape sound fields that can be used for the contactless manipulation of objects. Sound, especially ultrasound, can be used for contactless manipulation of objects in liquid and air, a phenomenon with applications in medical imaging, non-destructive testing and metrology. Usually, the desired sound field is shaped with arrays of transducers that must be carefully connected and controlled. Here Peer Fischer and colleagues describe a relatively simple technique for creating acoustic holograms and demonstrate their potential for use in matter manipulation. The acoustic holograms are encoded in a polymer plate by 3D printing and then used to shape a sound field that can be used for contactless manipulation of objects. The method can produce complex fields with reconstruction degrees of freedom two orders of magnitude greater than existing approaches. Because the holograms are inexpensive and fast to make, the method could be widely adopted to enable new applications with ultrasound manipulation. Holographic techniques are fundamental to applications such as volumetric displays1, high-density data storage and optical tweezers that require spatial control of intricate optical2 or acoustic fields3,4 within a three-dimensional volume. The basis of holography is spatial storage of the phase and/or amplitude profile of the desired wavefront5,6 in a manner that allows that wavefront to be reconstructed by interference when the hologram is illuminated with a suitable coherent source. Modern computer-generated holography7 skips the process of recording a hologram from a physical scene, and instead calculates the required phase profile before rendering it for reconstruction. In ultrasound applications, the phase profile is typically generated by discrete and independently driven ultrasound sources3,4,8,9,10,11,12; however, these can only be used in small numbers, which limits the complexity or degrees of freedom that can be attained in the wavefront. Here we introduce monolithic acoustic holograms, which can reconstruct diffraction-limited acoustic pressure fields and thus arbitrary ultrasound beams. We use rapid fabrication to craft the holograms and achieve reconstruction degrees of freedom two orders of magnitude higher than commercial phased array sources. The technique is inexpensive, appropriate for both transmission and reflection elements, and scales well to higher information content, larger aperture size and higher power. The complex three-dimensional pressure and phase distributions produced by these acoustic holograms allow us to demonstrate new approaches to controlled ultrasonic manipulation of solids in water, and of liquids and solids in air. We expect that acoustic holograms will enable new capabilities in beam-steering and the contactless transfer of power, improve medical imaging, and drive new applications of ultrasound.

Transformation of sound pressure level from the free field to the eardrum in the horizontal plane.

Abstract: Measurements of pressure transformation, azimuthal dependence, interaural level difference, and ear canal pressure distribution from 12 studies are brought together in a common framework The pool of data covers 100 subjects, the majority male, measured in five countries over a 40‐yr period Logical procedures are developed to identify the surfaces which best fit these essentially three‐dimensional distributions of data, making allowance for the many disparities between studies Sheets of data are presented showing transformation to the eardrum, azimuthal dependence, and interaural difference as functions of frequency from 02 to 12 kHz at 45° intervals in azimuth Other sheets show azimuthal dependence and interaural difference as functions of azimuth at 24 discrete frequencies The logical procedures, data presentations, and review of disparities lead to the construction of self‐consistent families of curves best fitting the data and showing the average sound pressure transformation from the free field to the human eardrum as a function of frequency at 15° intervals in azimuth Possible explanations of differences between studies are suggested