Sound Intensity Technique Research Articles

Evaluation of Noise Performance of Multi-Lane Highways in the State of Qatar

In recent years, a growing number of people are complaining to transportation authorities for the traffic noise as a result of increased traffic volume on the highways. Therefore, transportation authorities are actively pursuing ways to reduce the traffic noise. In recent years, quieter pavement has become one of the cost-effective ways of sustainable highway noise reduction. However, for design and construction of quieter pavements, proper and accurate noise measurement is of paramount importance for evaluating the noise level of existing pavement as well as evaluating noise level of newly constructed pavements. In this study, the variation of noise level among different lanes of existing multi-lane highways in the State of Qatar was examined. Tire-pavement noise was measured by using onboard sound intensity (OBSI) technique. OBSI test results showed that highest noise level was observed at outer lane of multi­lane highways. This is probably due to the pavement distress caused by the heavy vehicle travelling at the outer lane of multi-lane highways.

Effects of Speed on Tire–Pavement Interaction Noise (Tread-Pattern–Related Noise and Non–Tread-Pattern–Related Noise)

ABSTRACT Tire noise is mainly generated from the interaction between tire and pavement. Different combinations of tire and pavement usually generate noise of different levels and different frequencies. For the same tire and same pavement, the most important factor influencing the noise level is vehicle speed. To provide a detailed description of the effects of speed on the noise generation, the present study investigates the tire noise of nineteen tires of the same size but with different tread patterns. The study includes the standard reference test tire and four other normal patterned tires running on a nonporous asphalt pavement using an on-board sound intensity (OBSI) technique. This OBSI system also has an optical sensor to monitor vehicle speed and to perform order-tracking analysis. The field tests were conducted under different vehicle speed values (72-105 km/h; i.e., 45-65 mph). The effects of speed on the noise spectrum and on the overall noise level have been analyzed. In addition, using the optical sensor signal, the tire noise related to the tire tread pattern has been isolated from noises from all other sources. The effects of speed on the separated signals have also been investigated. It was found that increasing speed increases the frequencies and levels of tread-pattern–related noise component, while for the noise component not related to the tread pattern, increasing speed only increases its amplitude, not its frequency. In addition, the noise generated at the trailing edge of the contact patch is more sensitive to the speed than the one at the leading edge.

Multi-Modal Acoustic Flow Decomposition Examined in a Hard Walled Cylindrical Duct

Abstract Flow fields could be of great interest in the study of sound propagation in aeroengines. For ducts with rigid boundaries, the fluid-resonant category may contribute significantly to unwanted noise. An understanding of the multi-modal propagation of acoustic waves in ducts is of practical interest for use in the control of noise in, for example, aero-engines, automotive exhaust and heating or ventilation systems. The purpose of our experiments was to test the acoustic energy transmission of duct modes based on studies carried out by the sound intensity technique. Sound intensity patterns in circular duct are discussed of modal energy analysis with particular reference to proper orthogonal decomposition and dynamic mode decomposition. The authors try to justify some advantages of the sound intensity experimental research in this area. In the paper, the wide-band sound signal propagated from source approximated with loudspeaker in hard-walled duct is imaged using a sound intensity - based approach. For a simple duct geometry, the sound intensity field is examined visually and by performing a modal decomposition greater insight into the acoustic structures is obtained. The image of sound intensity fields below and above “cut-off” frequency region are found to compare acoustic modes which might resonate in duct.

Numerical and experimental investigations on the acoustic power radiated by Aluminium Foam Sandwich panels

Aluminium Foam Sandwich (AFS) panels are a new class of flat structures, constituted by two aluminium layers with a core made by foamed aluminium. Their excellent combination of properties, arising from the metallic nature of the matrix and from the porosity behaviour of the foam core, guarantees high specific stiffness, thermal and acoustical isolation, as well as vibration damping. For these reasons, they are becoming more and more attractive in transportation engineering applications.In this work, numerical and experimental investigations on the acoustic power, radiated by Aluminium Foam Sandwich panels, are carried out. Two different Alulight® specimens, made of the same material but with different thickness and percentage of foam density, are investigated. A Finite Element model is used to estimate the distribution of velocity over the panel surface and, then, the radiated acoustic power is calculated through the discrete formulation of the Rayleigh integral for flat radiators. The numerical model is validated by means of experimental tests, performed by using a sound intensity technique.

English

The Direct Piercing Carved Wood Panel (DPCWP) installed in Masjid Abidin, Kuala Terengganu, is one example that carries much aesthetic and artistic value. The use of DPCWP in earlier mosques was envisaged to improve the intelligibility of indoor speech because the perforated panels allow some of the sound energy to pass through. In this paper, the normal incidence sound absorption coefficient of DPCWP with Daun Sireh motif, which is a form of floral pattern, is discussed. The Daun Sireh motif was chosen and investigated for 30%, 35%, 40%, and 45% perforation ratios. The simulations were conducted using BEASY Acoustic Software based on the boundary element method. The simulation results were compared with measurements obtained by using the sound intensity technique. An accompanying discussion on both the numerical and the measurement tendencies of the sound absorption characteristics of the DPCWP is provided. The results show that the DPCWP with Daun Sireh motif can act as a good sound absorber. © Universiti Malaysia Pahang.

Experimental Acoustic Flow Analysis Inside a Section of an Acoustic Waveguide

Abstract Noise propagation within ducts is of practical concern in many areas of industrial processes where a fluid has to be transported in piping systems. The paper presents experimental data and visualization of flow in the vicinity of an abrupt change in cross-section of a circular duct and on obstacles inside where the acoustic wave generates nonlinear separated flow and vortex fields. For noise produced by flow wave of low Mach number, laminar and turbulent flows are studied us- ing experimental sound intensity (SI) and laser particle image velocimetry (PIV) technique adopted to acoustics (A-PIV). The emphasis is put on the development and application of these methods for better understanding of noise generation inside the acoustic ducts with different cross-sections. The intensity distribution inside duct is produced by the action of the sum of modal pressures on the sum of modal particle velocities. However, acoustic field is extremely complicated because pressures in non-propagating (cut-off) modes cooperate with particle velocities in propagating modes, and vice versa. The discrete frequency sound is strongly influenced by the transmission of higher order modes in the duct. By under- standing the mechanism of energy in the sound channels and pipes we can find the best solution to noise abatement technology. In the paper, numerous methods of visualization illustrate the vortex flow as an acoustic velocity or sound intensity stream which can be presented graphically. Diffraction and scattering phenomena occurring inside and around the open-end of the acoustic duct are shown.

Sound radiation from Caribbean steelpans using nearfield acoustical holography

The sound-field of a Caribbean low tenor steelpan is examined using nearfield acoustical holography (NAH). The particular instrument, a Bertrand Kelman low tenor, has been previously examined in a single plane using a four microphone sound intensity technique. This paper will examine the sound radiation in a cuboid space enclosing the instrument at three frequencies. Presented will be the results of sound pressure level (SPL), active acoustic intensity (AI), and reactive acoustic intensity (RI) obtained through application of the NAH technique. The limitations of NAH when applied to an irregularly shaped object such as a tenor steelpan will also be presented.

Standardization of Measurement of Sound Insulatian in Buildings and of Building Elements Using Sound Intensity Technique

Standardization of Measurement of Sound Insulatian in Buildings and of Building Elements Using Sound Intensity Technique

Applications of 2-Microphone Sound Intensity Technique to Road Vehicle Noise

Applications of 2-Microphone Sound Intensity Technique to Road Vehicle Noise

Small-scale transmission loss facility for flat lightweight panels

The design, construction and qualification of a small-scale sound transmission loss (STL) facility are described. STL measurements were made using the sound intensity technique based on ASTM E 2249-02. The volume of the irregular-shaped reverberant source chamber was 15 m3, and the volume of the regular-shaped anechoic receiver chamber was 20 m3. The facility was tested between 315 Hz and 10 kHz. Good spatial diffusion, and good repeatability for same and repeat installations were demonstrated in the above frequency range. The results from the small-scale facility were compared to tests conducted at a full-scale facility. The STL values of flat, lightweight sandwich panels measured at the small-scale chamber were greater than those measured in the full-scale facility. However, the results from the small-scale facility showed trends that were consistent with the sandwich panel theory above 1 kHz. The results demonstrated that the small-scale STL facility could be successfully used for qualitative comparisons of lightweight, sandwich panels above 1 kHz

Squeal Noise in Disc Brakes and the Influence of Damping on the System Dynamic Stability

Squeal noise in vehicle disc brakes is perceived by consumers as both annoying and as an indication of a problem with the braking system, dramatically affecting quality, satisfaction ratings and warranty costs. Among the methods that have been used to control squeal noise, increasing the system damping has been shown to be very effective. The most commonly used method to increase system damping consists of attaching multi-layer laminates on the back of the brake pads. Such laminates, also known as brake shims, are composed of different layers of metal and viscoelastic materials. In this paper, the dynamics of a disc brake system are discussed. At first, the squeal noise mechanism is broken down and a simple analytical model is used to exemplify the modal coupling phenomenon and how damping affects it. A technique to measure brake system damping as a function of brake lining pressure and temperature is explained and the results with and without brake shims are discussed. One of the conditions believed necessary for the occurrence of squeal noise in some disc brake systems is related to the relative position of the rotor and pad critical mode shapes. This condition, addressed in some previous papers [1, 2], is also studied here by using the Sound Intensity technique. Measurement of the properties of viscoelastic materials as a function of temperature and frequency is discussed. Results are shown for different materials (rubber, acrylic and silicone). Modal damping is also measured for different brake shim configurations as a function of braking temperature and lining pressure using the above mentioned technique. It was found that the modal coupling plays an important role in noise generation for certain brake system designs. For the brake system analyzed, the anti-nodes of the rotor mode related to the squeal frequency are fixed in space, i.e., they no longer rotate, remaining in the same position along the rotor diameter. Also, measuring system damping can be effectively used in the design and selection of brake shim configurations. However, in practice, the technique presented in this paper showed the best results for specific squeal noise problems where rotor and pad bending modes are the main root cause of the noise.

A STUDY ON THE STRUCTUREBORNE NOISE OF HYDRAULIC GEAR PUMPS

The main source of vibration and noise in hydraulic systems is the flow ripple at the pump output which interacts with the downstream components and generates pressure ripple in the current, structureborne noise in mechanical parts and airborne noise in the environment. The present research was suggested by the observation that some peaks in the airborne noise spectrum of a specific pump family were within a frequency range far from those typically related with the fluidborne or structureborne noise; unfortunately, in that range the human ear does not filter the noise efficiently. In general, the investigation of the interaction between fluidborne noise and structurebornenoise can be carried through both “macro-analysis” techniques (sound emission analysis, pressure ripple measurement, modal analysis, etc.) and “micro-analysis” techniques (contact mechanics of gears, performance of the bearing system, etc.). The present research started from a “macro” approach inclusive of the modal analysis of a gear pump, the measurement of its pressure ripple and its acoustic mapping though the sound intensity technique. Currently, the focus is on the “micro” approach and specially on the investigation of the elasto-hydrodynamic bearing performance in view of deriving the influence of the bearing geometry on the overall structureborne noise.

An Experimental Study on Sound Radiation Characteristics of Radial Tires for Vehicles, Due to Excitation

Vibration characteristics of a tire play an important role to judge a ride comfort ability and sound quality for a vehicle. In this study, the experimental investigation on the sound radiation of a radial tire has been examined. Based on the sound intensity techniques, the sound pressure field and the sound radiation are measured. It turns out that air pressure in tire, tread patterns, and aspect ratio of the tire governs the sound radiation characteristics. Then a numerical analysis for the tire element is conducted. During analysis, the tire element is modeled as an elastic ring. The comparison shows that the numerical output correlates to the experimental data.

Measurement of transmission loss trends for orthotropic sandwich panels at a subscale facility

Interior noise studies in airplanes have identified floors as one of the primary noise paths. The acoustic barrier properties of floor panels are typically quantified by sound transmission loss (STL) measurements. A subscale transmission loss suite consisting of a reverberant room and an anechoic room was constructed and qualified to study the relative transmission loss trends of orthotropic sandwich panels used in airplane floors. A host of material combinations accounting for a variety of mechanical properties were tested for their acoustic performance. The transmission loss measurements were based on a sound intensity technique (ASTM E 2249-02) and a sound pressure technique (SAE J 1400-90). The results from these two techniques were compared to results from a full-scale accredited facility using the two-reverberation room method (ASTM E 90-02). The STL trends for orthotropic sandwich panels from the sub-scale facility were comparable to trends from the full-scale facility between 315 and 5000 Hz. The measurements permitted a ranking of several standard floor panels with respect to acoustic performance. [Support for this research from Mervyn C. Gill Foundation is gratefully acknowledged.]

Analysis of engine front noise using sound intensity techniques

This paper describes the investigation of the mechanisms of engine front noise generation and the corresponding countermeasures employed in the development of a diesel engine. According to the analysis of acoustic signals and vibration signals measurement, an investigation of the noise source identification in a diesel engine is presented, and that the noise level of the diesel is comprehended. With the sound intensity method, the major sources of the exterior radiation noise of the engine front are surveyed. The research provides the reliable basis for the engineering practice to reduce vehicle noise level. Furthermore, the measuring data of the acoustic signals are compared by measuring noise from surface vibration, and the results are valid.

Technical Note: Influence of the Frame on the Sound Reduction Index of a Window

The Sound Reduction Index of 1.2 × 1.2 m windows composed of two identical pivoting leaves of three different thickness of laminated glass and inserted in two different frames (aluminium and PVC) had been measured using pressure and sound intensity techniques. The Sound Reduction Index has been also predicted. These results have allowed us to compare the relative importance of the frame acoustic isolation effectiveness against the glass pane effectiveness in order to achieve an overall window Sound Reduction Index.

Normal-incidence sound absorption measurement of a perforated panel using a sound-intensity technique: Theoretical versus experimental

A direct-piercing carved-wood panel (DPCWP) is a form of wood carving that allows air to pass through the panel easily. In Malaysia, DPCWPs are available with various perforation ratios, patterns, and elements, and are typically used as part of a wall partition for an enclosed room. It helps in providing natural ventilation, besides it is believed to be able to act as a sound absorber. Circular perforated panels are the simplest form of DPCWP available. It was found out that normal-incidence sound-absorption performance of perforated panels can be measured reliably using a sound-intensity measurement technique. In this paper, normal-incidence sound-absorption measurement of a perfortated panel using fixed-point scanning will be discussed. Close correlations were obtained from 250 Hz to 4 kHz between theoretical and measured sound absorption. Factors contributing toward sound intensity measurement reliability, primarily through its sound quality indicators such as F1, F2, F3, and F4, and the effect of measurement distance will be thoroughly discussed. This finding suggests that the sound intensity measurement technique can be used to measure normal-incidence sound-absorption performance of DPCWP reliably.

Normal incidence sound absorption coefficient measurement using sound intensity technique: An accuracy investigation

Sound absorption data are required in specifying and proposing the correct materials for room acoustic treatment. However, there are instances where noncommon materials such as direct piercing carved wood panels (dpcwps) are used without sound absorption data. Sound absorption measurements obtained using an impedance tube and reverberation chamber are not accurate for dpcwp. This is primarily because the wall backing the dpcwp during the measurements constitutes the carved surface, which does not exist in actual installation. Therefore, an alternative measurement technique using a sound intensity measurement technique is more appropriate for dpcwp. This paper focuses on experimental methodology where various aspects need to be taken into consideration to achieve accurate results. Various criteria affecting measurement instruments’ capabilities and other factors affecting sound intensity measurement accuracy will be discussed. Sound absorption measurement was conducted on three different perforation panels which resemble dpcwp and it was found that the sound absorption measured with a deviation from an average value of −5.59% to 5.95% can be achieved, and is particularly accurate.

The sound-field characterisation of a power transformer

In order to effectively suppress the noise radiation from large electrical power transformers, both the structure-borne and air-borne sound fields need to be characterised. The characterisation can be made either from theoretical predictions or by in-situ measurements. This paper presents the study of the sound radiation from a large power transformer in a substation. The radiation pattern can be predicted from the measured acceleration distribution and the predicted value is not affected by other noise sources. Alternatively, the farfield sound pressure level can be predicted from the sound pressure level measured at NEMA locations. Both the near- and far-field power radiation can be in-situ measured using the sound intensity technique. It is shown that both the vibration of a transformer tank wall and the radiated noise consist of a series of tonal components mainly at the first few harmonic frequencies of 100 Hz. Also, the neglect of the noise radiation from the transformer (top and bottom) lids does not affects the accuracy of the transformer radiation characterisation.

Assessment of tire/pavement interaction noise under vehicle passby test conditions using sound intensity measurement methods

Over the past several years, sound intensity measurement methods have become an increasing valuable tool in isolating tire/pavement interaction noise when a vehicle is tested under full throttle acceleration conditions such as the ISO 362 R15 procedure. Several investigations have been conducted and reported which demonstrate the relationship between ‘‘on-board’’ sound intensity measured close to a tire contact patch and the sound pressure level measured by a stationary microphone 7.5 m away from the line of travel of the vehicle. Using these relationships, the contribution of tire/pavement noise can be assessed relative to other noise sources associated with a vehicle under acceleration as measured at 7.5 m. In this application, it has been determined that some tires can produce significantly higher noise levels under the torque of acceleration than under cruise conditions. Sound intensity has also been used to separate sound propagation from sound generation effects in the assessment of test surfaces such as those specified by SAE and ISO. This paper reviews the various applications of sound intensity in the assessment of tire/pavement interaction noise issues related to vehicle passby noise, the implication of recent findings on noise reduction strategies, and the potential for standardization of sound intensity techniques.