Sound Power Measurements Research Articles

Research on sound power measurement of multi-element ultrasonic focusing transducer based on cross-spectrum method.

In this paper, aiming at the problem that a multi-array focused ultrasonic transducer working in a high power range has a nonlinear influence on the measurement accuracy, a study of acoustic power measurement based on the near field cross-spectrum method was carried out. The focused acoustic field of a multi-array transducer was derived theoretically by combining the cross-spectrum method and the Westervelt nonlinear acoustic propagation equation. Finite element simulation was used to establish the model of the focused sound field of the multi-array transducer under different excitation conditions, and the influence law of each harmonic on the total sound power under specific excitation conditions was obtained. A cross-spectrum measurement system was built to scan the two near focusing planes under different excitation conditions. The total energy, each harmonic energy, and their proportion in the focusing region under the corresponding excitation were obtained through calculation and processing. The theoretical and simulation results were verified, and the harmonic energies were compensated in the calculation of the total ultrasonic power. The measurement results were compared with those obtained by radiation force balances. It was found that the maximum measurement deviation of compensated ultrasonic power was 7.89%, which met the requirements of acoustic measurement. The accuracy of the method and conclusion was verified under the power range of 10-60W.

Experimental and numerical validation of vibration-based sound power measurements of arbitrarily curved panels

Vibration-based sound power (VBSP) measurement methods are of interest due to their potential versatility in application compared to methods based on sound-pressure or sound-intensity. The VBSP method is based on the elementary radiator approach that relies on the acoustic radiation resistance matrix. Previous work has validated the form of the radiation resistance matrix for flat plates, cylindrical- and spherical-shells, and simple-curved plates. A form specific to arbitrarily curved structures has not been developed. Experimental VBSP measurements of two arbitrarily curved panels are shown to have excellent agreement with results from the ISO 3741 method. The VBSP method was applied by using the simple-curved plate form of the radiation resistance matrix and mapping each arbitrarily curved panel with a constant-radius curve fit. Numerical boundary element models, that inherently use the true form of the radiation resistance matrix, were also used to compute the sound power from the same curved panels. Surface velocity data from the numerical models were used to also compute sound power using the VBSP method with the simple-curved plate form of the radiation resistance matrix. Sound power results show excellent agreement between the numerical model and VBSP method. [Work supported by the National Science Foundation.]

Modeling a representative room to evaluate sound power measurement methods for ASTM ISR testing

ASTM ISR (Impact Sound Rating) test method suffers from non-reproducibility problems, especially in lower frequency bands in smaller rooms where the sound field is non-diffuse. The problem arises from the fact that Sound Pressure Level is measured in these rooms, which is dependent on the room dimensions if the sound field is non-diffuse due to low modal density. Currently, this non-diffusivity is ignored. We propose to measure sound power radiated from the ceiling instead of volume-averaged sound pressure level, which is independent of room dimensions regardless of the type of sound field in the receiving room. This study evaluates sixteen different ideas to measure sound power levels in the receiving rooms through a simulation model of a representative room using Simcenter 3D. Each method's pros and cons in the simulation are used to downselect methods to test in the field.

Sound power and sound energy measurements using an ellipsoidal measurement surface

To support purchasing low noise products, sound power and sound energy measurements of sufficient quality need to be routinely made by consumers on a global scale. Sound power measurements using ISO 3744, 3745, and 3746 are conducted in a free field using an acoustic far-field approximation of the intensity integrated over an enveloping measurement surface. Sound power and sound energy measurements generally use a hemispherical, parallelepiped, or cylindrical measurement surface. Those measurement surfaces have limitations and assume that the measurement points lie on the measurement surface often in preferred positions. An alternative approach is to choose microphone positions that optimally satisfy the assumptions of the measurement. The measurement surface should then be fit to the chosen microphone positions. Regression methodologies are available for fitting ellipsoids. The number of microphone positions can be as few as three to fit an ellipsoid. An ellipsoidal measurement surfaces can abut zero, one, two, or three orthogonal reflecting planes. Correction equations for the microphone locations and the angle errors for the microphone orientation and wave propagation direction are shown. This paper will present simulations of sound power, sound energy, and corrections for environmental reflections for ISO 3745 and other measurement surfaces.

Uncertainty of sound power measurements of a reference sound source using the AHRI Standard 230 sound intensity method

The uncertainty of determining the sound power of HVAC equipment using the AHRI Standard 230 sound intensity measurement method is presented. Measurements of six different reference sound sources (RSS) at four different laboratories, by nineteen different individuals with four different instrumentation systems are presented. From 2004 through 2020, these measurements were performed as part of a training program at Johnson Controls HVAC test laboratories to qualify technicians and engineers on the use of sound intensity instrumentation. The results illustrate the reproducibility of sound intensity measurements using the scanning method of AHRI Standard 230.

On the acoustic effects of sonic crystals in heat exchanger arrangements

Heat exchangers can be found in a large number of technical systems and installations. They are usually operated in combination with other machines, such as axial fans, in order to remove or supply heat to a system. The heat exchanger can influence the existing flow field and thus lead to increased noise emission from fans located downstream of the heat exchanger. This can be observed, for example, in air conditioning units in which axial fans operate in combination with heat exchangers. Even though this mechanism is known, it is not yet understood how the heat exchanger affects the sound propagation of the sound produced by the downstream machine. For example, the heat exchanger may lead to a change in directional characteristics or specific frequencies may be attenuated. In order to better understand the interaction of the heat exchanger with the sound field, sound power measurements were carried out on various heat exchangers and the sound propagation was simulated numerically. It was shown that the sound attenuation due to the interaction with the periodic tube array is detectable in heat exchangers and that this leads to a sound reduction at the Bragg frequency. Based on its filling factor, the heat exchanger can reduce the sound propagation in certain frequency bands by up to 10 dB if the geometrirical properties are selected suitably. The simulations of a single unit cell confirm in very good agreement with the experimental results. This allows the conclusion that the approach presented in this paper is a cost-effective way to model acoustic effects of heat exchangers. Furthermore, sound attenuation effects by the heat exchanger were caused by thermoviscous effects on the cooling fins and dimensions of the heat exchanger housing.

Calibration of sound power sources: Current status and new developments.

Reference sound sources used in sound power measurements are currently calibrated according to well-documented techniques. Low frequency limitations and solely broadband analysis restrict the applicability of these methods. The concept of traceability is introduced to overcome these deficiencies. This study presents the calibration of reference sound sources through a measurement chain, which is based on the substitution method. The applicability of the substitution method extends to sound intensity measurements and narrowband frequency analysis. A specially designed apparatus allows the detection of the sound field over a fully scanned hemisphere. The results of the apparatus are comparable to the results of the existing methods. The substitution method reduces the required corrections, which are presented. The sound power levels are supplemented by a transparent uncertainty budget, which allows the estimation of each uncertainty component individually. The comparison between the methods is also given in terms of a confidence interval.

Sound power of vibrating cylinders using the radiation resistance matrix and a laser vibrometer

Research has shown that using acoustic radiation modes combined with surface velocity measurements provide an accurate method of measuring the radiated sound power from vibrating plates. This paper investigates the extension of this method to acoustically radiating cylindrical structures. The mathematical formulations of the radiation resistance matrix and the accompanying acoustic radiation modes of a baffled cylinder are developed. Computational sound power calculations using the vibration-based radiation mode (VBRM) method and the boundary element method are then compared and shown to have good agreement. Experimental surface velocity measurements of a cylinder are taken using a scanning laser Doppler vibrometer and the VBRM method is used to calculate sound power. The results are compared to sound power measurements taken using ISO 3741.

From statistical room acoustics and acoustic intensity to spatial audio

Jiri Tichy was my graduate student advisor at Penn State. Jiri introduced me to statistical room acoustics and sound power measurements using a single pressure microphone in a reverberation room. From there we moved on to the measurement of sound power using acoustic intensity. We developed spatial microphone array probes with 2–4 microphones that measured the complex vector acoustic intensity in one to three dimensions. After graduation, the fundamentals developed analyzing the estimation of the complex acoustic intensity were applied to the development of a spherical microphone array that realized any first-order superdirectional directivity pattern pointing in any direction. It later became clear that higher-order arrays were needed to achieve higher directional gain. This led to the development of the Eigenmike® spherical microphone array with 32 pressure microphones and capable of 4th order spherical harmonic decomposition of the sound field. This array is finding application into AR/VR and statistical room acoustic analysis … bringing the technology full circle. I am incredibly lucky and grateful to have had Jiri as my mentor. He showed me how to look at acoustics problems and set the foundations of the many acoustic signal processing areas I have worked on in my career.

Psychoacoustic and noise annoyance of hard disk drive affects acoustic ergonomics and emotional wellness of consumers

Human hearing is a complex system due to the highly nonlinear nature of human ears. The ears perform many tasks simultaneously from identifying sound direction, estimating a distance from a sound source, masking of sound, and evaluating the noise. The objective sound power measurement is unable to convince the subjective nature of sound evaluation. Psychoacoustic measures such as sharpness, roughness, loudness, and fluctuation strength begin to show importance in understanding the quality of the sound from small interior such as Hard Disk Drive (HDD), which present in the most mobile consumer laptop. Two sets of jury tests have been performed to quantify the degree of HDD noise annoyance with psychoacoustic on broader age groups. The results indicate that the psychoacoustic have a close relationship with the HDD noise annoyance and age groups. The effect of laptop HDD on the user's emotional perceptions of different sound events caused by HDD's shows some participants are feeling less calm, annoyed, and excited as compared to before the jury tests.

Sampling procedures on reception plates to quantify structure-borne sound power from machinery

Experimentally validated models of a heavyweight reception plate using finite element methods (FEM) have been used to assess reception plate measurements of structure-borne sound power injected by single- and multiple-contact, broadband sources. Measurements and FEM indicated high velocity levels near corners and edges of the plate; hence the reception plate power was underestimated by up to ≈9 dB below 100 Hz when using velocity measurements in the central zone of the plate. To avoid this problem, a sampling strategy was developed using an area-weighting approach for the velocity measurements. Measurement of the reception plate power using the area-weighted velocity level gave errors that were less than 2 dB between 20 Hz and 2 kHz for both single- and multiple-contact sources. FEM simulations also identified an additional measurement constraint for a multiple-contact source representing white goods with either zero-phase or random-phase relationships between the four contact points. As the actual phase relationship is rarely known, potential bias can be avoided by excluding positions in the area between the contacts (typically the area underneath a machine) along with those within the estimated reverberation distance from each contact point.

A low-frequency sound power measurement technique based on the separation of near-field acoustic energy flux in a non-anechoic tank

To determine the radiated sound power of an underwater sound source below the first resonance frequency in a non-anechoic tank, a sound intensity measurement technique based on separating near-field acoustic energy flux is proposed. A theoretical analysis of vibration and acoustic radiation of underwater structures shows that the variation in the radiation impedance of the sound source in the given frequency band is much smaller than the mechanical impedance, and the vibration state of the sound source changes negligibly compared with that of the sound source in the free field. This theoretical analysis is verified experimentally. Based on this analysis, the acoustic energy flux is determined at various locations on the enveloping surface by first measuring the near-field sound pressure and the normal component of the particle velocity on the surface. The efflux and influx sound energies at an enveloping surface are separated to obtain the free-field radiated sound power of the source to be tested. This approach is tested by measuring the low-frequency radiated sound power of an underwater transducer source in a glass tank. The test results show that the maximum difference between the sound power measured in the glass tank and that measured in the anechoic tank is less than 0.8 dB.

Bandwidth extension of intensity-based sound power estimates

The traditional method for intensity-based sound power estimates often used in engineering applications is limited in bandwidth by microphone phase mismatch at low frequencies and by microphone spacing at high frequencies. To overcome these limitations, the Phase and Amplitude Gradient Estimator (PAGE) method [Gee, Neilsen, Sommerfeldt, Akamine, and Okamoto, J. Acoust. Soc. Am. 141(4), EL357-EL362 (2017)] is applied to sound power for a reference sound source, a blender, and a vacuum cleaner. Sound power measurements taken according to ISO 3741:2010 (2010) are compared against traditional- and PAGE-processed intensity-based sound power estimates measured according to ANSI S12.12-1992 (R2017). While the traditional method underestimates the sound power at the spatial Nyquist frequency by 7-10 dB, the PAGE-based sound power is accurate up to the spatial Nyquist frequency, and above when phase unwrapping is successful.

Experimental validation of determining sound power using acoustic radiation modes and a laser vibrometer

The theoretical development for computing sound power using acoustic radiation modes is well documented. However, an experimental validation and comparison with other sound power measurement standards over a wide frequency range has not been presented. This paper compares experimental results from an acoustic-radiation-modes-based sound power measurement method to results obtained using ISO 3741 in two scenarios. First, sound power measurement results from a single simply-supported baffled panel are compared. A comparison of sound power measurements of two simply-supported baffled panels is then presented. Results between the two methods for the single panel show a maximum one-third octave band difference of 2.2 dB between 200 Hz and 4 kHz with an overall difference of 1.7 dB. For the two-panel system, the maximum one-third octave band difference is 1.6 dB with an overall difference of 0.7 dB. It is also shown that in the two-panel case, the sound power from each panel can be measured individually using the acoustic radiation modes approach and summed to obtain the overall sound power as measured using ISO 3741.

Blinkies: Open Source Sound-to-Light Conversion Sensors for Large-Scale Acoustic Sensing and Applications

We propose an open source hardware platform called Blinky, a sound-to-light conversion sensor that harvests sound power at low-rate and conveniently. Blinkies are made up of a central processing unit connected to two microphones and a few light-emitting devices, are powered by a battery, and protected by a robust enclosure. Distributed in space and combined with a conventional video camera, they allow to practically sense sound power over a very large area without hassle. We give a comprehensive overview of the proposed system and its potential applications. We describe the hardware design and trade-offs made. We provide a model for the channel between sound power measurements and signal acquired by the video camera. Because each sensor is potentially affected by a different attenuation due to the channel, we propose a calibration procedure to restore the scale of the measurements. The effectiveness of the calibration is validated in an experiment. Finally, we demonstrate sound source localization using a hundred-and-one actual Blinkies in highly reverberent environment.

Extending bandwidth for sound power measurements

Sound power is often measured using the intensity-based engineering standard ANSI S12.12-1992. Traditional methods for intensity-based sound power estimation are limited in bandwidth at low frequencies by phase mismatch between microphones and at high frequencies by microphone spacing—with errors occurring well below the spatial Nyquist frequency. The PAGE (Phase and Amplitude Gradient Estimation) method has been used to extend the bandwidth of intensity calculations [Gee et al., J. Acoust. Soc. Am. 141(4), EL357–EL362 (2017)]. This paper examines the efficacy of the PAGE method to overcome bandwidth limitations in estimating sound power. Specifically, the sound fields from three sources—a blender, a vacuum cleaner, and a dodecahedron speaker—were measured according to ANSI S12.12-1992. The sound power was computed for each source using both the traditional and PAGE methods. The resulting intensity-based sound power estimates are compared against sound power measurements obtained according to the scientific-grade ISO 3741:1999 standard. The PAGE method increases the bandwidth over which reliable estimates are achievable for intensity-based sound power estimates, even exceeding the spatial Nyquist frequency when phase unwrapping is successful. Thus, using existing equipment, industry professionals can extend the bandwidth of sound power estimates with the PAGE method. [Work supported by NSF.]

Estimating the acoustic power of sources in semi-reverberant enclosures using generalized energy density

Sound power measurements of acoustic sources are typically performed in anechoic or reverberation chambers using acoustic pressure according to international standards. The anechoic chamber creates a free-field environment where the sound power is estimated from the squared pressure integrated over some enveloping surface. The reverberation chamber produces diffuse-field conditions, where sound power is proportional to the spatially averaged squared pressure. Since most acoustic sources exist in rooms that are neither anechoic nor entirely reverberant, it is desirable to estimate the sound power within these non-ideal, semi-reverberant spaces. In such environments, the direct and reverberant energies each contribute to the total measured field. If the kinetic and potential components of acoustic energy density are weighted appropriately, the spatial variation of the field can be significantly reduced compared to squared pressure. This generalized energy density allows an adaptation of the sound power formulation by Hopkins and Stryker to be used to make an efficient and accurate in situ sound power estimate of a noise source in a non-ideal acoustical environment. Since generalized energy density optimizes the spatial uniformity of the field, fewer measurement positions are needed compared to traditional standards. The experimental results and practical limitations of this method will be discussed.

Referee whistles Part II—Outdoor sound power assessment

Referee whistles have been suggested as a significant contributor to noise-induced hearing loss. Thirteen models of sport whistles were tested for sound power with a 3-m hemispherical array of 19 microphones. The whistler produced nine tweets of low, medium, and high effort with two samples of each whistle model. Sound power levels ranged between 74 and 115 dB re 1 pW. The low, medium, and high effort tweets had average power levels of 85 ± 6 dB, 100 ± 6 dB, and 110 ± 4 dB, respectively. Preliminary damage-risk analysis of the whistle impulses yield varied estimates for the allowable number of tweets before auditory damage might be expected. For the Auditory Hazard Assessment Algorithm, between 4 and 66 tweets may exceed the daily exposure threshold. Based upon the amount of eight-hour equivalent A-weighted energy, approximately 120 to 500 tweets would exceed the daily 85 dBA exposure limit. The directivity of the sound power measurements will also be examined, and risk of hearing loss will be discussed.

How to create an advanced acoustical test and research laboratory in 5 months

This paper will take you through the need, design, building, and testing of a state of the art acoustical testing and research facility in a 5 month period. We will discuss the increasing need for wide frequency bandwidth measurements of absorption, transmission loss, very low level sound power measurements, and high resolution measurement of the directivity of speakers and diffusers. We will also look at the limits of standard laboratories and observe what changes are needed to extend those abilities and limits. At the end of the paper, we can look at the end result measurements of these facilities to see how close to design and performance the lab approached.This paper will take you through the need, design, building, and testing of a state of the art acoustical testing and research facility in a 5 month period. We will discuss the increasing need for wide frequency bandwidth measurements of absorption, transmission loss, very low level sound power measurements, and high resolution measurement of the directivity of speakers and diffusers. We will also look at the limits of standard laboratories and observe what changes are needed to extend those abilities and limits. At the end of the paper, we can look at the end result measurements of these facilities to see how close to design and performance the lab approached.

Effects of a finite size reflecting disk in sound power measurements

In practical sound power measurements in an anechoic room, a baffle sometimes has to be used to support the sound source under test so that the anechoic room can be used as a hemi-anechoic room by laying a reflecting plane. To understand the effects of a finite size reflecting plane on measurements quantitatively, this paper investigates the effects of a disk on sound power measurements by formulating an exact solution to the problem based on the spheroidal wave functions. Three practical measurement cases are considered and the correction terms for the cases are presented based on numerical simulations. Experiments are conducted to validate the analytical solutions and numerical results.