Sound Intensity Measurements Research Articles

Noise source identification on rolling tires by sound intensity measurement.

The sound radiation characteristics of actually rolling tires with three types of the tread patterns were measured by the 2-microphone sound intensity technique. The measure mentswere performed at a test course in Japan Automobile Research Institute, in which a special trailer equipped with an automatic microphone scanning system was used and the normal sound intensity distribution in a plane parallel to the sidewall of a tire was measured during actual running. The results show that it is possible to identify the source positions on a tire actually rolling on a road surface by means of the soundin tensity technique. In the case of a rib tire, the noise was mainly generated from the leading and the trailing edges, not from the contact patch, while in the case of a lug tire, the main source position was the contact patch. The noise radiation pattern varied according to the difference of tread pattern. Further, the sound power radiated by three kinds of tires were compared. A-weighted sound power level of the lug tire is the biggest among them.

Phase response measurement with the three-port two-microphone coupler

With the advent of sound intensity measurement, the need for a reliable and precise method for the assessment of phase response of microphones is evident. For national laboratories, a direct method is preferred. There are less time-consuming signal-processing techniques that are capable of measuring the phase response of microphones. However, for high-precision measurement, it is relatively difficult for national laboratories to verify or to substantiate the uncertainty of phase measuring techniques that involve inaccesible computational algorithms. The theory on precision phase measurement with the three-port two-microphone coupler [J. Acoust. Soc. Am. 71, 1276–1277 (1982)] is presented with experimental verification. The uncertainty of the method depends on the uncertainty of the phase measuring instrument. With a calibrated commercial phase meter, the uncertainty is typically 0.02 deg.

Noise and vibration characteristics of a 3kW class Stirling engine.

In recent years a wide variety of papers on the Stirling engine and its unique properties have been published. However, the available knowledge on noise and vibration characteristics of the Stirling engines is very limited. This paper presents experimental results which are useful in modifications for the engine parts influencing the noise and vibration characteristics of the reciprocating kinematic Stirling engines. In order to clarify the noise and vibration sources of a 3 kW class Stirling engine, the modal analysis for the engine parts and the measurement of sound intensity were examined. As a result, it became clear that the modifications for the combustion system and the driving system, particularly with respect to the crankshaft, are available for decrement of the engine noise and vibration. Through use of the proposed modifications, the 1987 engine noise was greatly decreased, and the 59 dB(A) noise level was measured under a normal driving condition.

The application of the sound-intensity technique to defect detection in rolling-element bearings

The two-microphone sound-intensity technique has been used for the detection of defects in radially loaded ball bearings. The difference in the sound-intensity levels measured for bearings with no defect and for those with intentionally introduced defects of different sizes in their elements under various operating conditions of loads and speeds is demonstrated. A change in the intensity frequency spectrum because of the defects is observed. The results show that the detectability of an outer-race defect is much better than that of an inner-race or ball defect. It is difficult to detect defects at lower speeds. Sound-pressure measurements were also performed for comparison, and it is shown that the detectability of defects by sound-intensity measurements is better than that by sound-pressure measurements.

Measurements of Structure-Borne Wave Intensity on Lightly Damped Pipes

Measurement of the structure-borne sound energy flow through pipes has been studied for the purpose of transmission path ranking. This paper describes the measuring methods for frequencies below the cut-off frequency of the n = 2 shell mode. The methods show a strong analogy with the two-microphone cross-spectral density method for airborne sound intensity measurements. Experiments on two lightly damped pipe sections of a cooling water circuit are used to illustrate some practical measuring aspects and some procedures for error analysis. Reasonably accurate measurements appear feasible, provided high quality instrumentation is used and the various wave types are separated carefully.

Low‐frequency sound intensity measurement and free‐field sound‐pressure propagation

Classical acoustical equations relate the sound power of a source to sound‐pressure level at a given distance from that source. Sound intensity of a source can be measured, sound power determined by integration over the radiation area, and the sound‐pressure levels at a distance from the source can be calculated. An assumption is made when the sound power to sound‐pressure calculation is made, that at low frequencies (20–100 Hz) the waves have propagated and the resultant sound‐pressure level is from the source. This work tests the reliability of that assumption. A speaker was suspended inside three different size boxes, and powered by a noise generator bandpassed at discrete frequencies. Sound intensity measurements were recorded near field at the same discrete frequency. Free‐field sound pressure measurements were then recorded at distances from the boxes. This paper reports the results of the measurements.

Architectural acoustics: The forgotten dimension

The basic considerations of architectural acoustics—isolation from unwanted noise and vibration, control of mechanical system noise, and room acoustics design—are all clearly exemplified in Sabine's design for Boston Symphony Hall. Opened in 1900, this hall is one of the outstanding successes in musical acoustics. Yet, as we approach the hundredth anniversary of Sabine's first experiments, acoustical characteristics remain one of the least considered aspects of building design. This is due, in part, to the difficulty of visualizing the acoustical outcome of design decisions, complicated by individual judgment as to what constitutes good acoustics. However, the lack of a comprehensive teaching program remains the dominant problem. Significant advances over the past 2 or 3 decades in measurement and evaluation have refined the ability to design predictability and to demonstrate acoustical concerns to others. New techniques such as sound intensity measurements, new descriptors for room acoustics phenomena, a...

The effect of sound intensity measurement parameters on sound power determination

Practical investigation of the repeatability of sound intensity measurements and the influence of some measurement parameters, such as the distance from the source, scanning pattern and speed, configuration of points and point density, on sound power determination has been presented. Two measurement methods, namely the scanning and the point methods, are compared. The measurements have been performed on a sound source in an ordinary room. Both the measurement methods show good repeatability but that of the point method is slightly better. Fairly accurate results are obtained at larger measurement distances from the source. Better results are obtained if a sufficient number of points are taken in the point method and if a slower speed and a smaller gap between sweeps is used in the case of the scanning method.

Sound intensity of the Comerford HVDC converter station

The author demonstrates acoustic intensity for in situ sound power measurements of converter-type transformers and rank-orders all other noise sources at the Comerford high-voltage DC converter station. The sound intensity measurement uses two closely-spaced, phase-matched pressure-sensitive microphones to approximate one component of the intensity vector. Measurements made at the Comerford station are used with geometrical considerations and Gauss' law to compute individual noise source strengths despite interference and reverberation. The data and analyses show that over 84% of the noise is radiated by harmonic filters. Another 12% can be traced to the converter transformers. The analysis also shows that noise levels increase in loaded vs. unloaded converter transformers by nearly four times. The results support the claim that sound intensity has applications in the power distribution industry as a diagnostic tool for quantifying transformer noise. The results also indicate where noise reduction efforts should be concentrated at the Comerford station.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sound Intensity Survey of the Comerford HVDC Converter Station

The purpose of this EPRI study is to demonstrate and deploy acoustic intensity for in-situ sound power measurements of converter-type transformers and to rank order all other noise sources at the Comerford High Voltage dc Converter Station. Sound intensity is a new technology using two closely-spaced and phase-matched, pressure-sensitive microphones to approximate one component of the intensity vector. Sound intensity measurements made at the Comerford station are used with geometrical considerations and Gauss' law to compute individual noise source strengths despite interference and reverberation. The data and analyses show that over 84% of the noise is radiated by the harmonic filters. Another 12% can be traced to the converter transformers. Our analysis also shows that noise levels increase in loaded versus unloaded converter transformers by nearly four times. The results support the claim that sound intensity has applications in the power distribution industry as a diagnostic tool for quantifying transformer noise. The results also indicate where noise reduction efforts should be concentrated at the Comerford station.

Review of ISO and ANSI standards for the determination of sound power levels of noise sources using sound intensity measurements

Sound intensity measurements can now be used to determine accurately the in situ sound power of machinery noise sources in the presence of high levels of background noise. Meetings of working group ISO/TC43/SC1/WG25 began in 1982 and a first draft standard was produced in late 1985. Meetings of working group ANSI S12-21 began in 1983 and produced first draft of a standard in 1984. The ANSI draft standard was circulated for balloting as a standard in 1987, and the ISO third draft was circulated in 1988. Although the ISO and ANSI drafts are similar, there are some differences. The ISO draft allows precision, engineering, and survey grade determinations and requires four indicators to be measured to decide the grade achieved. The ANSI draft only allows engineering determinations of sound power. The ISO draft only allows fixed point measurements, while the ANSI draft allows either fixed point or scanning measurements of intensity on a surface enclosing the source. Last year, 17 laboratories in North America took part in a round robin using the ANSI draft.

LITERATURE REVIEW: survey and analysis of the Shock and Vibration literature: Sound Intensity Measurement

LITERATURE REVIEW: survey and analysis of the Shock and Vibration literature: Sound Intensity Measurement

Estimating sound power from discrete measurements of sound intensity on a hemisphere

In theory, total sound power radiated from a noise source can be determined by integrating the normal component of sound intensity over an arbitrary enclosing surface S. In practice, one must settle for approximation, taking the sound power integral to be a weighted sum of intensity measurements at certain strategically located nodes, or meshpoints, on S. What are the strategic locations, what are the weights, and what level of accuracy can be expected? The present paper attempts to answer these questions for the particular experimental setup described in a recent publication [R. Hickling and L. N. Bolen, “Indoor system for efficient measurement of the sound power of light vehicles,” NCPA Rep. RH-01-88]. Here, S is a hemisphere H plus circular base B—the latter a physical boundary that is perfectly reflective. The mesh covers H but not B: it appears rectangular in cylindrical projection, with longitudes equally spaced. Strategic positioning is therefore a matter of latitude selection. Several schemes are discussed based on different notions of optimality, the means of calculating weights for each scheme are shown, and numerical evidence is compiled to indicate that levels of accuracy attainable, by applying the quadrature formulas to various test functions (chiefly monopoles). The rapid fluctuations that can occur in the sound intensity function and the reasons for this condition are also discussed.

Automated sound power measurement system for indoor testing of motor vehicle noise

Indoor noise testing of motor vehicles poses advantages not offered by the conventional outdoor pass‐by test method. The sound power of a motor vehicle can be determined by measuring sound intensity over a surface enclosing the vehicle. Due to its geometric simplicity, a hemisphere was chosen for this purpose. In order to facilitate efficient measurement of sound intensity on a hemisphere, large enough to enclose an automobile situation on chassis dynamometer rolls, a special structure was designed to carry the intensity measurement probes. The structure was semicircular in shape made up of two concentric sections. The inner section with the measurement probes was hinged to the outer support structure such that it could be lowered into a position providing easy access to the microphones for calibration purposes. Truss sections were used in the construction of the microphone boom to present as small an interference to the sound field as possible. The entire structure was suspended at its apex and was drive...

Active and reactive, coherent and incoherent sound fields

The question of whether a given sound field can be characterized as active or reactive has received some attention for the past decade—mainly because the answer can be of vital importance in predicting the reliability of sound intensity measurements. This paper attempts to discuss these sound field characteristics from another viewpoint. The purpose of the paper is to demonstrate the relationship between certain measurable quantities, “sound field indicators”, and the characteristics of the sound field. Two new sound field indicators are proposed: the coherence between sound pressure and particle velocity, and the normalized complex intensity. Some other measures are also considered. The proposed indicators are examined theoretically and experimentally.

The properties of the estimation error of sound power measurement using sound intensity techniques

In this article, a general expression was derived for the sound intensity normal to a plane measurement surface caused by a plane distribution of monopole sources. A program was developed to calculate the ratio between the approximate sound power estimated from a finite number of measurements of sound intensity on a plane surface and the exact power passing through the same measurement area. The ratio, which is considered the estimation error of the sound power measurement, is affected by many factors such as the number of measurements, the distance between the source and the measurement surface, the locations of the sources with respect to the measurement points and the types of sources. The effects of these factors on the estimation error were investigated, and some error curves were plotted. By examining the error curves, it was found: (1) when the measurement surface has unit area, the estimation error decreases with an increase in the measurement distance and an increase in the number of sound intensity measurements; and (2) when the measurement surface is a surface enclosing the source, the estimation error depends on the total number of sound intensity measurements over the surface, and does not depend on the measurement distance or the number of measurements over each unit area. Some experimental tests were carried out to check the error curves for the case when the sound source is a monopole. The experimental results agreed well with the theoretical predictions.

A Sound Intensity Probe Using the Nonlinear Behaviors of Sound Wave

A sound intensity probe using the nonlinear behaviors of the sound wave is presented. The principle of the probe is theoretically discussed with regard to the variation and angular dependence of the phase velocity caused by the non-collinear interaction of sound waves. Two parametric receiving arrays whose probing waves propagate in opposite directions are applied to the sound intensity probe. The basic characteristics of the probe are observed, and the results support that the probe is applicable for the sound intensity measurements.

A brief summary of sound intensity measurements and their application to noise control

The two-microphone method of sound intensity measurement is reviewed. Principles of the technique, the measurement errors, instrumentation and the applications of sound intensity are described. The applications covered are the determination of the sound power, the noise source location, the transmission loss and the sound absorption coefficient.

Sound bridge localization in buildings by structure-borne sound intensity measurements

A localization procedure is described which permits fast and accurate localization of point-like sound bridges in buildings by means of measurements of the vibrational intensity at a few points on the wall or : floor. In a laboratory experiment a resolution of about 10 cm was achieved with seven points. Essential to the performance of the procedure are a favourable choice of the positions of the measurement points, a suitable weighting of the measured data, and a favourable choice of the band for the frequency average. Es wird ein Mesverfahren vorgestellt, das eine schnelle und genaue Lokalisierung von punktformigen Schallbrucken in Gebauden erlaubt. Gemessen wird die Korperschallintensitat an wenigen Punkten auf der Wand oder dem Fusboden. In einem Laborversuch wurde mit sieben Punkten eine Genauigkeit von ungefahr 10 cm erreicht. Wesentlich fur eine erfolgreiche Lokalisierung sind eine gunstige Auswahl der Mespunkte, eine geeignete Gewichtung der Mesergebnisse und eine gunstige Wahl des Frequenzbereichs fur die Mittelwertbildung.

Sound intensity measurements in a vehicle's interior sound field

Sound pressure and sound intensity in the passenger compartment of a vehicle with many standing waves are measured through piston‐plate excitation. These measurements provide the characteristics of attenuation in the free field near the sound source, which is found to be approximately −6 dB per doubling of distance. At a certain distance from the sound source, sound intensity shows an average sound‐pressure level between the maximum and minimum values in the passenger compartment. The reason for this is that, owing to the use of sound‐absorbing materials, the sound field does not consist only of standing waves, It is revealed that progressive waves dominate near the sound source. As a result, sound intensity measurements in passenger compartments provides the precise location and contribution of the sound source, even when booming sounds are present. Moreover, using the modal analysis method to investigate the behavior of the body vibration from the enforced point to the sound source is effective in improving the body structure for reducing passenger compartment noise levels.