Sound Intensity Measurements Research Articles

On‐board sound intensity measurements and results in Florida.

This paper describes an investigation of on‐board sound intensity (OBSI) and concurrent wayside sound levels along multiple roadway surfaces in the state of Florida. By conducting concurrent sampling of the OBSI and wayside noise not only were insights into the pavement texture noise generation at the tire/pavement interface possible but direct comparisons allowed findings on the propagation characteristics as well. Measurement values, pavement rankings, multiple findings, and preliminary statistical modeling will be shown.

Noise dose for aquatic animals: Preliminary estimates for two seismic surveys.

In humans, a daily noise dose is defined and used to regulate noise exposure in the working environment. This is an integrated measure of sound intensity over the working day, typically 8 h in duration. When investigating behavioral effects on aquatic animals exposed to anthropogenic noise, a comparable measure would be valuable, especially when transient but powerful underwater noise sources such as seismic air‐guns and mid‐ and low‐frequency sonars are being used or are being considered for use. Here, an integrated noise dose measure is defined. Preliminary estimates of this noise‐dose measure are given for two different seismic surveys.

Diffraction based optical microelectromechanical systems microphone and its application to the measurement of sound intensity.

Diffraction based optical MEMS microphones and force feedback capabilities of these microphones are presented earlier [Bicen et al., J. Acoust. Soc. Am. 123, 3230 (2008)]. Further investigation is done in order to see the capabilities of these optical microphones in measuring the sound intensity. The biomimetic diaphragms of these microphones are designed for responding to pressure gradient which can be used for extracting the particle velocity required to measure the sound intensity. In order to show the velocity measuring capability of these microphones, an impedance tube method is used because the velocity and pressure at each point in the impedance tube can be found accurately. The comparison of the measured velocities and sound intensities with the optical microphone and commercially available sound intensity probes is presented. Model results are discussed in order to show the effect of the different mode shapes on the accuracy of the pressure gradient measurements. Optimization of these biomimetic diaphragms will result in the measurement of the sound intensity in a larger bandwidth without using any spacers and additional microphone adapters like in commercial sound intensity probes. [Work supported by National Institutes of Health (NIH) and the Catalyst Foundation.]

Normalization and calibration of microphones in sound-intensity probes

A system for normalizing and calibrating the microphones of a sound-intensity probe or a composite of such probes, with respect to a stable comparison microphone with known acoustical characteristics. Normalizing and calibrating are performed using an apparatus 57 consisting of a tube with a loudspeaker inserted in one end and a fixture for holding the microphones of the probe together with the comparison microphone in the other end. The comparison microphone has known acoustical characteristics supplied by the manufacturer. Two banks of quarter-wave resonators 83 and 84 are attached to the side of the tube to absorb standing waves. The sound-intensity probe can be either a two-microphone probe used for measuring a single component of the sound-intensity vector or a probe with four microphones in the regular tetrahedral arrangement used for measuring the full sound-intensity vector. The microphones in the probe are made to have a substantially identical response with the comparison microphone by determining the transfer functions between the microphones and the comparison microphone. The transfer functions and known acoustical characteristics of the comparison microphone are then used to correct the pressure measurements by the microphones, when they are used to measure sound intensity. This ensures that the sound-intensity measurements are accurate and that there is essentially no bias in determining the direction to a sound source from the direction of the sound-intensity vector.

Phase frequency responses of measurement microphones and their calibration.

For more than 20 years, comparison calibration of microphone phase responses has been a topic of interest. The interest grew up in the 1980s, when it became technically possible to design instruments for measurement of sound intensity and particle velocity. At that time, the calibration frequency range was limited by the first generation of comparison couplers, which typically worked up to 5 kHz. Since then, new applications and needs for wider frequency range or higher accuracy have occurred. Today phase response comparison calibration of half‐inch and quarter‐inch microphones can be made with couplers from below 20 Hz up to about 20 kHz. The uncertainty is estimated to about 0.010 deg between 20 and 500 Hz from where it increases to some tenths of a degree at 20 kHz. Microphone array applications require large numbers of microphones with essentially equal phase responses. This has increased the need for reference standards, whose absolute phase responses are known. The Danish Primary Laboratory of Acoustics calibrates such reference standards by the reciprocity method. This paper gives an overview of the spread of microphone phase responses, commonly required tolerances, phase calibration methods, and their uncertainties.

A complete three-dimensional sound intensity sensor integrated on a single chip

Complete characterization of a sound field requires measurement of both sound pressure and particle velocity. In this paper, we present a three-dimensional acoustic particle velocity sensor chip. Furthermore, a sound pressure sensor was integrated on the same chip, enabling three-dimensional sound intensity measurements. The integration of multiple sensors on a single silicon chip results in highly reproducible sensors and a very small sensor-to-sensor distance allowing for accurate single-point measurements. The latter is demonstrated by measurement of the 3D particle velocity field of a very small (1 × 1 mm2) sound source.

3-D Sound Intensity Measurements: Accuracy Enhancements With Virtual-Instrument-Based Technology

This paper describes a method that allows accuracy and bandwidth enhancements in 3D sound intensity measurements. Commercial 3D probes are usually set up with three mutually perpendicular 1D p-p probes and, thus, arranged with six microphones; although sound intensity can be calculated with 15 independent pairs of transducers, only the three "primary" pairs that are aligned with the coordinate system axes. The other 12 "secondary" pairs consist of mutually perpendicular microphones, which are placed at a distance that is radic2 times shorter than the primary one. The main idea of the proposed method is to average the intensity that is measured on primary and secondary pairs. This leads to a larger bandwidth, thanks to the shorter separating distance between secondary pairs. The intrinsic p-p method high- frequency sensitivity loss is partially recovered, starting from the theoretical plane wave expression. Measurements of different axes are weighted with coefficients that are computed by optimizing the measurement uncertainty. Errors that are due to the metrological characteristics of the transducers and the effects of environmental conditions are compensated. Experimental results showed that a p-p probe arranged with half-inch microphones that are placed at a distance of 50 mm allows reliable measurements up to 2.5 kHz, whereas a commercial probe bandwidth with the same configuration is usually 1250 Hz.

Array based measurement of radiated and absorbed sound intensity components

Calibration of energy flow models for cabin environments requires tools able to measure the energy flow between the sub-systems of the models. Here we shall specifically consider the energy flow between acoustic energy in the cabin and vibration energy in the panels. Sound intensity measurement, for example with a two-microphone intensity probe, can provide the total sound intensity at some distance from panels. It cannot resolve, how much of the intensity is due to radiation from the surface and how much is due to absorption of energy from the sound field. And it cannot provide the information right on the panel surface, leading to a degraded resolution. The ability to distinguish between radiated and absorbed intensity is important for energy flow modeling, and for identification of the areas where noise energy enters the cabin. The present paper describes some work done to measure the radiated and absorbed intensity components by the use of a double layer microphone array. Two measurements are performed: A measurement of surface absorption coefficient and an operational measurement. Non-locally reacting surfaces represent a particular challenge, the handling of which will be discussed. Results from both loudspeaker measurements and in-flight measurements will be presented.

Evaluation of the ASTM Standard Reference Test Tire for purposes of standardized measurement of on‐bound tire/pavement noise

Currently in the US, efforts are underway to develop standard methods for on‐board sound intensity (OBSI) measurement of tire/pavement noise. Up until recently, the default standard tire was the Goodyear Aquatred 3 tire originally selected due to its apparent similarity to Tire A specified in the ISO CPX procedure. Because of longer‐term availability, the ASTM Standard Reference Test Tire (SRTT) is the primary candidate for replacement of the Aquatred 3. Issues of concern for the SRTT include tire‐to‐tire variation, the relation of the SRTT to previously used reference tire, and the period required for stable test tires. To address tire‐to‐tire variability, six SRTT's were tested on variety of asphalt (AC) and Portland cement concrete (PCC) surfaces. These included four new tires and two that had been in use for some time. Two of the new tires were retested with increasing use to examine any break‐in period effect. For comparison, the older Aquatred 3 was also tested on these same surfaces using both OBSI and controlled pass‐by measurements. The results of these measurements are presented along with their implication to for reference tire selection.

Cyclic Sound Intensity and Source separation from NAH measurements on a Diesel engine

Noise source separation and acoustic imaging are two research fields of interest in car industry. For this, RENAULT (French car manufacturer) and the University of Technology of Compiegne (UTC, France) are conducting an original study aiming to couple these fields to solve in an efficient way engine NVH problems. Previously, in the first part of this study, combustion noise separation on Diesel engine radiation was implemented from classical sound intensity measurements. The separation, based on Wiener filtering, was performed by taking advantage from the cyclostationary property of engine signals. The second part, presented here, aims to overcome the main shortcoming of the method: time‐consuming measurements. Our method is then applied to Near‐field Acoustic Holography that is faster and more adapted to an industrial context. Source separation is implemented to complete global radiation maps by specific‐source radiation maps such as combustion and other sources radiating in low frequencies since NAH per...

Vocal efficiency in tracheoesophageal phonation

Objective Voice rehabilitation after total laryngectomy is challenging. In order to investigate and understand the function of the neoglottis sophisticated measurements need to be made. During voice production, aerodynamic energy is transformed into sound energy. In non-laryngectomized patients, the voice production efficiency is called the vocal efficiency. Vocal efficiency is an indication of how efficient the transformation of energy takes place. Vocal efficiency is calculated by dividing the output sound power by the aerodynamic power. Patients and methods In a group of eight laryngectomees with tracheoesophageal voice, we measured aerodynamic and acoustic quantities and calculated vocal efficiency. We used a computer setup with airflow transducers, pressure transducers, mikrotip transducers and sound intensity measurement to allow calculation of the needed parameters. Results The tables show the results of the power used and produced in various phonatory tasks. Relatively high levels of aerodynamic power are interpreted as increased effort to speak. Conclusion The aerodynamic power is an indication of the effort needed for voice generation. The efficiency of TE-voice production is lower compared to laryngeal voice production but does show an increase when sound intensity increases, a known phenomenon in healthy laryngeal voice production.

An investigation into the relationship between sound intensity and normal surface velocity

The analysis of sound characteristics using boundary element methods (BEM) requires accurate sound source data of normal surface velocity or pressure as boundary conditions. However, direct measurements of normal surface velocity are not easily acquired while sound intensity measurements are relatively easy to obtain. In this study the relationship between near field sound intensity and normal surface velocity is investigated. The study first considers correlated and uncorrelated sound sources in the frequency range of 63 to 1000 Hz. A matrix of sound intensity measurements on well-distributed points in the near field of the sound source is collected. A model of the relationship between sound intensity and volume velocity is developed and used to compute the normal surface velocity of the sound source from sound intensity measurements. The normal surface velocities are then used as the boundary conditions for a BEM model of the sound source that predicts the sound intensity at the original measurement points. The measured and predicted values are compared in order to validate the model. The differences of predicted and measured sound intensities that are within ±3 dB are considered sufficiently accurate.

Phonometrical precision measurements during a high end classical music live recording and four standardized recording systems’ signal comparison

Discographical sound recording process is very seldom accompanied by real sound pressure, intensity and level measurements. Usually available data are often referred to mathematical extrapolations calculated on sound recording audio signals. This article investigates the situation defined as ‘‘real’’ from a scientifical point of view, having as a referring base a Swedish precision sound level meter fresh from calibration, during the stereophonic multichannel live recording session of the Philharmonische Camerata Berlin. Comparison among reference signal and eight high quality microphone capsules signals coming from four different stereophonic standardized microphone systems devoted to discographical purpose recording (XY, ORTF, Binaurale and AB) shows big differences among the respective signals and the same recording spot measurement system position. It is noticeable how differences even higher than 6 dB can make microphone positioning particularly critical. A standardizing method is proposed.

Sound source location and quantification using arrays of vector probes

Method and apparatus for locating and quantifying sound sources using an array of acoustic vector probes ( 200 ). Signals received at the probes are converted to digital form and fed into a digital signal processor ( 400 ) which computes the sound pressure and the sound-intensity vector at each probe. The set of sound-intensity vectors measured by the array provides a set of directions to a sound source ( 100 ) whose approximate spatial coordinates are determined using a least-squares triangulation formula. The sound-intensity vectors also determine sound-power flow from the source. In addition sound pressure measured by the probes can be phased to form a sensitivity beam ( 250 ) for scanning a source. Sound-intensity measurements made concurrently can be used to determine the spatial coordinates of the part being scanned and the sound power radiated by that part. Results are displayed on a computer screen or other device ( 500 ) permitting an operator to interact with and control the apparatus. Additional related features and methods are disclosed.

Aerodynamic and Sound Intensity Measurements in Tracheoesophageal Voice

Background: In laryngectomized patients, tracheoesophageal voice generally provides a better voice quality than esophageal voice. Understanding the aerodynamics of voice production in patients with a voice prosthesis is important for optimizing prosthetic designs and successful voice rehabilitation. Objectives: To measure the aerodynamics and sound intensity in tracheoesophageal voice production. Study Design and Methods: We built a special setup, which consisted of a Pentium 200 MHz computer with an AD-DA interface card and Labview 4.01 software. In an oral/nasal mask we constructed several mass flow sensors and a microphone. This measured both the oral airflow and the level of sound. For the measurement of endotracheal pressure, which is the driving force behind the airflow, we used a transducer which was connected to the tracheostoma. The endoesophageal pressure was measured at the level of the prosthesis in the esophagus by a Mikrotip transducer. Using this we could determine how much the voice prosthesis contributes to the overall pressure drop of the phonatory tract. Furthermore, the average airflow rate as a function of the sound pressure levels could be determined. Results: In our population, 6 out of 7 patients showed a positive relationship between trans-source airflow and generated sound intensity. We compared our prosthesis pressure drop values with in vitro data and found that there are some differences, possibly due to difference in age of the prosthesis and physiological circumstances in vivo. The overall contribution of the voice prosthesis to the airway resistance depends on the level of phonation and the type of device. In our patient group it is apparent that the pharyngoesophageal (PE) segment has the greatest share of the total pressure drop, especially at higher airflow rates. We measured a 27% pressure drop in airflow over the voice prosthesis. Different tracheostoma occlusion methods did not have any effect on the aerodynamics and sound intensity. One patient that had had a jejunal graft for reconstruction showed, not unexpectedly, extremely different aerodynamic values. We were unable to define optimal airflow rates or optimal resistance values for sound production in the PE segment. Conclusion: The aerodynamic characteristics of voice production in laryngectomized patients with voice prostheses are determined by both prosthetic factors and PE segment tissue factors. In our patient group the PE segment is responsible for the greatest pressure drop. We found no significant difference in pressure drop and sound intensity for different tracheostoma occlusion methods.

A numerical investigation of the influence of windscreens on measurement of sound intensity

Sound intensity probes are often used with windscreens to minimize the effect of noise caused by airflow. A theoretical and experimental study of the effect of windscreens on p-p intensity probes published ten years ago concluded that windscreens give rise to underestimation of the sound intensity at low frequencies in strongly reactive sound fields. The theoretical part of this study was based on the assumption of a windscreen of infinite extent. In this paper windscreens of realistic size and shape are dealt with by means of a coupled boundary element model for the windscreen and the surrounding air. The error of the estimated intensity caused by the windscreen is calculated under a number of sound field conditions of varying reactivity. It is shown that the resulting error can be much larger than the intensity itself in a very reactive sound field. It is also shown that the shape and size of the windscreen has a significant influence on the error.

Ultrasonic control of ceramic membrane fouling: Effect of particle characteristics

In this study, the effect of particle characteristics on the ultrasonic control of membrane fouling was investigated. Ultrasound at 20 kHz was applied to a cross-flow filtration system with γ-alumina membranes in the presence of colloidal silica particles. Experimental results indicated that particle concentration affected the ability of ultrasound to control membrane fouling, with less effective control of fouling at higher particle concentrations. Measurements of sound wave intensity and images of the cavitation region indicated that particles induced additional cavitation bubbles near the ultrasonic source, which resulted in less turbulence reaching the membrane surface and subsequently less effective control of fouling. When silica particles were modified to be hydrophobic, greater inducement of cavitation bubbles near the ultrasonic source occurred for a fixed concentration, also resulting in less effective control of fouling. Particle size influenced the cleaning ability of ultrasound, with better permeate recovery observed with larger particles. Particle size did not affect sound wave intensity, suggesting that the more effective control of fouling by large particles was due to greater lift and cross-flow drag forces on larger particles compared to smaller particles.

SOUND PRESSURE LEVEL OF ADVERTISEMENT CALLS OF ALYTES CISTERNASII AND ALYTES OBSTETRICANS (ANURA, DISCOGLOSSIDAE)

(2006). SOUND PRESSURE LEVEL OF ADVERTISEMENT CALLS OF ALYTES CISTERNASII AND ALYTES OBSTETRICANS (ANURA, DISCOGLOSSIDAE) Bioacoustics: Vol. 16, No. 1, pp. 27-37.

Visualization of reflected sound in enclosed space by sound intensity measurement

Visualization of reflected sound in enclosed space by sound intensity measurement

Reducing the noise emitted from a domestic clothes-drying machine

In recent years the development of large household appliances has increasingly focused on the reduction of noise. In this paper we report on attempts to reduce the sound-power level of an existing clothes dryer by investigating the aerodynamic noise sources. The critical points were determined on the basis of spatial sound-intensity measurements and sound-pressure-level spectra measurements. The changes to produce the modified dryer, version I, involved corrections to the secondary-flow fan's inlet region. For version II a different design of the heat exchanger was considered. For this, a measurement station was set up in order to analyze the aerodynamic properties of heat exchangers. The velocity and the acoustic properties of the heat exchangers were measured to help in the selection of the heat exchanger in accordance with the aeroacoustics theory that connects turbulent fluctuations and noise generation. After performing all the modifications, the A - weighted total sound-power level was reduced from 76.0 to 66.5 dB for left rotation and from 73.8 to 64.7 dB for right rotation.