Sound Intensity Method Research Articles

A case study of flanking transmission through double structures

An investigation was carried out in a new house row having unsatisfactory sound insulation. The sound intensity method was found very valuable for ranking the room surfaces according to radiated sound power. Two different flanking paths were found. In both cases, identical double structures in adjacent dwellings caused overlapping resonance frequencies and strong flanking at these frequencies. For example, structure-borne flanking via the intermediate floor (160 mm concrete) caused poor sound insulation between living rooms. A light floor covering with a thin flexible blanket below it caused a natural resonance at 500 Hz. The flanking at the problematic frequency range could be reduced by 10 dB, changing the natural resonance frequency in the other dwelling. It can be concluded that symmetrical double structures in adjacent dwellings should be avoided unless experience (e.g. measurement in situ) proves otherwise.

Enhancing maximum measurable sound reduction index using sound intensity method and strong receiving room absorption.

The sound intensity method is usually recommended instead of the pressure method in the presence of strong flanking transmission. Especially when small and/or heavy specimens are tested, the flanking often causes problems in laboratories practicing only the pressure method. The purpose of this study was to determine experimentally the difference between the maximum sound reduction indices obtained by the intensity method, RI,max, and by the pressure method, Rmax. In addition, the influence of adding room absorption to the receiving room was studied. The experiments were carried out in an ordinary two-room test laboratory. The exact value of RI,max was estimated by applying a fitting equation to the measured data points. The fitting equation involved the dependence of the pressure-intensity indicator on measured acoustical parameters. In an empty receiving room, the difference between RI,max and Rmax was 4-15 dB, depending on frequency. When the average reverberation time was reduced from 3.5 to 0.6 s, the values of RI,max increased by 2-10 dB compared to the results in the empty room. Thus, it is possible to measure wall structures having 9-22 dB better sound reduction index using the intensity method than with the pressure method. This facilitates the measurements of small and/or heavy specimens in the presence of flanking. Moreover, when new laboratories are designed, the intensity method is an alternative to the pressure method which presupposes expensive isolation structures between the rooms.

A physical insight of the active control on sound source in a pipe

This paper is mainly intended to discuss the physical understanding of active control on the primary source in a pipe. The derivation of some acoustic fields involved, the measurement of the sound source impedance in either an active or non-active control situation by using a Helmholtz resonator, and the comparison between two results as obtained are included in this study. In order to demonstrate the feasibility of the measurement of source impedance using the Helmholtz resonator technique, this study also compares the acoustic power as obtained for a sound source in a semi-infinite pipe with that measured at the anechoic termination by means of a sound intensity method. The results as obtained by using the above two methods agree reasonably well.

SOUND INSULATION OF DOORS—PART 2: COMPARISON BETWEEN MEASUREMENT RESULTS AND PREDICTIONS

In the first part of this paper the prediction models for both structural and leak transmission of doors were presented [1]. In this second part, results are presented for tested models comprising nine steel passage doors and nine timber passage doors. The results are presented in a form of two practical case studies. All measurements were made by the two-microphone sound intensity method. The structural SRI of a door was determined when the door was properly tape-sealed. The predicted structural Rwwas on an average 1·0±1·5 dB higher than measuredRw of tape-sealed doors, the range of variation being −1…+3 dB (N=13). The average difference between the predicted and the measured SRI increased gradually with frequency from −3 up to +12 dB. The best structural solutions were those where two rigid panels formed a double panel without interpanel connections. The interpanel cavity was filled with sound-absorbing material which does not form rigid interpanel connections. Structures with previous descriptions were found to give 8–10 dB better values ofRw than structures comprising strong interpanel connections with the same mass. Gomperts' model for slit-shaped apertures predicted reasonably well the frequency behaviour of slit transmission when no seals were present (open apertures). When the door seams were sealed with rubber seals, the slits behaved in a more complex way probably because of the irregular shape of the slit. The total SRI of the door was calculated by the area-weighted sum of the predicted structural transmission and the predicted slit transmission. Approximating the slit transmission coefficient by Gomperts' model and predicting the structural transmission by Sharp's model produced a good overall prediction accuracy for the total SRI of the doors throughout the frequency range of interest.

Sound Radiation from Ventilation Aperture with Circular Thin Air Layer Setting Up Machinery Wall. Attenuation of DFN Radiated from Axial Flow Fan.

Purpose of this study is attenuation of sound radiated from ventilation apertures and holes setting up on all apparatus by using circular slit resonator. The circular slit resonator composed of thin air layer that is radial expansion with very short axial length was set up machinery wall. The circular thin air layer acts as an acoustic resiatance, inertance and capacitance. The noise was reduced greatly at a natural frequency of the circular thin air layer that shows symmetrical circular mode of standing wave. In this paper insertion loss, IL, of the circular slit resonator designing to reduce discreat frequency noise(DFN)radiated from axial flow fan was clarified on both experimental and theoretical studies. The insertion loss, IL, of the circular slit resonator was measured by using sound intensity method. IL indicates narrow peak at resonant frequency and it strongly depends on the slit depth and slit width. IL level increases with the slit width, thickness of resonator panel and separator. The prediction of IL by the calculation model is approximately accurate.

Sound power measurements at low frequencies

The sound power level of a sound source is usually determined by sound intensity or sound-pressure measurements either in a free-field environment or in enclosures. Although these measurements provide good comparable results for the middle- and high-frequency range, there are large discrepancies at low frequencies. Using the sound intensity method as reference, it can be shown that these discrepancies are systematic. In the case of measuring sound pressure in a free field, they are due to the near-field error depending on the distance of the measurement surface to the source. Measuring sound pressure in enclosures—especially in rooms with hard walls—interference effects cause a change in the sound power output of the source, depending on the distance of the source to the room boundaries. The effects described above have been investigated theoretically and the results have been confirmed by accurate measurements.

A study on the sound radiation characteristics of conventional railway by sound intensity method

A study on the sound radiation characteristics of conventional railway by sound intensity method

The Estimation of the Sound Power Radiating from a Peripherally Fixed Rectangular Plate Subjected to Acoustic Excitation. 1st Report, Derivation of Estimation Formulae and Application to a Plate Subjected to a Normal Plane Acoustic Wave Excitation.

This paper describes the estimation method of sound power radiating from a peripherally fixed rectangular plate which is subjected to a sound excitation. The forced vibration of the plate which is excited by a distributed force has been theoretically solved by using modal analysis with Rayleigh-Ritz method. The basic equation for estimation has then been shown, and the equations of the frequency response of three parameters-total loss factor, radiation loss factor and input power for estimating sound power-have been derived. For a practical instance, the sound power radiating from a peripherally fixed rectangular steel plate, which was excited by the normal plane acoustic wave, has been estimated. The estimated frequency responses of the sound radiation power coincided well with the measured values obtained by the sound intensity method. This proposed method is hence effective to estimate the sound power radiating from a plate subjected to an acoustic excitation.

Test procedure and automatic system for sound insulation measurement using the sound intensity method

Test procedure and automatic system for sound insulation measurement using the sound intensity method

Estimation and Measurement of the Sound Power Radiated from a Circular Plate with a Solid Shaft and a Solid Cylinder. 2nd Report. Estimation and Measurement of Sound Radiation Power.

In this paper we describe the estimation result of sound power radiated from a circular plate with a solid shaft and a solid cylinder, which is a simple model of an aircraft gear blank and is excited axially, radially or three dimensionally. The three parameters for estimation, the radiation loss factor, the driving point mobility and the total loss factor, were calculated according to the formulae derived in the first paper. Using these calculated parameters and measured excitation force spectrums, the sound powers radiated due to the excitations were estimated and compared to the measured values obtained by means of the sound intensity method. The estimated frequency spectrums of sound radiation power coincided with the measured values. Consequently, the estimation theory and the associated formulae are valid.

音響・振動インテンシティ法によるエネルギー場の可視化 ( 可視化技術 : 音を見る・音で見る)

音響・振動インテンシティ法によるエネルギー場の可視化 ( 可視化技術 : 音を見る・音で見る)

Modal analysis of a circular plate with a solid shaft and a solid cylinder and estimation of radiating sound power

The natural modes of flexural vibration of a circular plate with a solid shaft and a solid cylinder, which is a simple model of aircraft gears, were theoretically analyzed with a new method proposed by the authors. The calculated natural frequencies and mode shapes coincided well with the values measured by experimental modal analysis. Using the calculated natural frequencies and mode shapes, the three parameters required for the estimation of radiating sound power—total loss factor, radiation loss factor, and driving point mobility—were calculated, and then the radiating sound power from the circular plate was estimated by the estimation theory proposed by the authors in other papers. The frequency response of the estimated sound power coincided well with the values measured by the sound intensity method.

Measurement of spatial impulse responses with a Soundfield Microphone

Concert hall designers have a keen interest in measuring the spatial evolution of sound fields. So far, 3-D impulse responses have been measured with sound intensity methods, with tetrahedral microphone arrays, and with large microphone arrays. These methods are very sensitive to phase, and therefore to particulars of microphone construction and analysis bandwidth. In this paper a method is proposed for capturing the spatial impulse response of a room by means of orthogonal cosine directivity microphones. Tests have been done with a simple figure-eight/omni microphone pair oriented in three directions, one after the other, as well as with a purpose-built Soundfield microphone. Impulse responses are captured for each of the X, Y, Z, and omni (Soundfield B-format) channels. The directional impulse responses are then cross correlated with the omni impulse response to construct ‘‘direction cosines’’ of strength with respect to the listener position, over time. Data can be mapped graphically in 3-D space to visualize the evolution of the sound field; the degree of scatter in the data represents diffuseness. In addition to graphics, convincing three-dimensional auralizations have been performed with soundfield impulse responses.

A measurement method of an oblique-incidence absorption coefficient

It is said that the road surface has significant effects on road noise. For a proper evaluation of the effect of the road surface, it is important to develop a measurement method of the absorption coefficient for oblique as well as vertical incidence. A measurement method was developed that can be used in a hemianechoic room. A long strip of test material approximately 2 m in length and 0.5 m in width is placed on the floor of the room. A test noise is generated by a line array of loudspeakers which is placed above the floor and parallel to the test material. The distance from the material to the loudspeaker array is approximately 2 m. The position of the loudspeaker array is moved on the circumference so that the incidence angle may be changed while keeping the radius constant. The incident power is measured beforehand in an anechoic room which is proportional to the sound pressure squared. The absorbed power is measured by use of the sound intensity method. The measurement points of the intensity are on a smaller semicircle (approximately 0.5 m) with the same center as the test material. The absorption coefficient is given by the ratio of the absorbed power to the incident power.

Plate-damping measurements in a single reverberation room

Laboratory measurements on the damping components of a plate in a single conventional reverberation room by the sound intensity method are presented. A mobile anechoic chamber is placed at the most optimal position inside the reverberation room to meet this purpose. The specimen is placed in the opening of the anechoic chamber. The damping components of the plate can be determined by measurement of the sound pressure levels in the reverberation room and behind the specimen in the anechoic chamber, the reverberation time, the sound absorption coefficient of the specimen, and the velocity of the plate. Comparisons of the experimental results of the present method with other methods show good agreement.

舶用大型主機の放射音パワー評価法

Sound power evaluation methods are investigated numerically and experimentally. Sound measurement in ship's engine room is under very inferior condition because the engine is installed in such a small place. There are two methods to evaluate sound power; sound pressure based method and sound intensity method. The investigation shows that the former method has a inferiority in the precision, especially in the decision of environment correction factor, and the latter method is not practical for a large marine engine. As a result, the hybrid method which has both precision and practicality is proposed.

Estimation and Measurement of the Sound Power Radiating from a Circular Plate with a Solid Shaft Subjected to a Three-Dimensional Load

The overall aim of this research is to establish an effective method for accurately estimating the airborne noise power radiating from gear blanks. For this purpose, the basic theory for estimating the frequency response of radiating sound power was proposed in a previous paper, and was applied to a circular plate with a solid shaft subjected to an axial load, in which the circular plate was a simple model of gear blanks. In this paper the basic theory is extended to circular plates excited three-dimensionally, similar to that for helical gears. The theory includes the rigid-body modes of vibration as well as the natural modes of flexural vibration of the circular plates. The estimated sound powers agreed well with the values measured by the sound intensity method. Also, an interesting result is obtained ; sound power radiating from a circular plate with a helical tooth is proportional to sin2β, where β is the helix angle. In other words, the axial force has large influence on the sound power radiated due to the rigid-body and flexural vibrations of the circular plate.

Performance evaluation of a three dimensional intensity probe.

A three dimensional intensity probe using four microphones is proposed. Four microphones are placed at apexes of a regular tetrahedron. One is placed in the front and three others consisting a vertical regular triangle are in the back. The microphones are attached at the tips of parallel thin tubes. The microphone arrangement is not the conventional face to face type. The aim of this type of microphone arrangement is to design a sound intensity probe with a simple structure, which is essential for reducing the diffraction problem. Algorithms for three dimensional intensity components from cross spectra are given as well as for leakage components. Measurements of sensitivity characteristics in an anechoic room using two types of probes with 60mm and 20mm microphone separations show that sensitivity fluctuations are small enough (less than 1dB) for the practical application of the sound intensity method. The leakage errors of approximately 5%(-13dB) seem also acceptable. The measurement results indicate that sensitivity and leakage errors will become smaller if a more ideal plane wave field in an anechoic room is achieved.

Sound Radiation Characteristics of Lightweight Roof Constructions Excited by Rain

In order to investigate the sound radiation characteristics of lightweight roof constructions when excited by rainfall, an artificial rainfall apparatus was constructed to simulate natural rainfall conditions. From the measurement results, it can be seen that the facility developed is practically applicable for the examination of the sound radiation characteristics of rain noise. It was therefore used in the measurement of sound power of 20 lightweight roofs. In addition, the relationship between sound power level and sound transmission loss measured by the sound intensity method was investigated statistically. As a result, it has been shown that a linear relationship exists between them and there is a possibility of estimating the sound power level from the transmission loss.

Sound transmission loss measurements using the sound intensity technique Part 1: The effects of reverberation time

Two simplified geometric models have been considered to illustrate some characteristics of the sound intensity field in an enclosure and the results indicate that the sound intensity field is not affected by the reverberant component for distances from a source much greater than the reverberation radius (obtained from consideration of the sound pressure field) of the enclosure. The effects of reverberation time in the receiving room on sound transmission loss measurements using the sound intensity technique have been investigated. Six different reverberant conditions, ranging from 0·6 to 4·2 s at 500 Hz, have been used. Results indicate that the sound intensity measurements are virtually independent of the reverberant conditions (as illustrated by the simplified geometric models) provided that the pressure-intensity index of the measurements does not exceed the dynamic capability of the sound intensity measuring system. It has also been found that the pressure-intensity index of the measurements can be reduced by either increasing the distance of measurements from the test specimen or by reducing the reverberation time in the receiving room. A global indicator based on the pressure-intensity index has been formulated and is shown to be able to indicate the degree of agreement between sound transmission loss measurements determined using the conventional sound pressure and sound intensity methods.