Sound Power Measurements Research Articles

Acoustic contributions and characteristics of floor treatments for elementary school classroom background noise levels

A two part investigation involving the effect of floor treatments on classroom background noise levels will be presented. Phase 1 determined the effects of hard versus soft flooring on overall speech and activity noise levels using long-term calibrated sound recordings in elementary classrooms. Two similar-sized classrooms were used: one with vinyl composition tile (VCT) flooring, and one with short-pile commercial carpeting. After parsing the recordings into separate segments of (a) teacher/student speech (alone), and (b) classroom activity noise, including footfalls, chair scrapes, and impacts (no speech), a significant decrease in overall levels was found in the carpeted rooms. Phase 2 determined the acoustical properties of nine different flooring materials ranging from resilient athletic floors to VCT to commercial carpeting. Sound absorption was measured following ISO 10534-2, while ISO 3741 sound power measurements were made while either (a) using a standard tapping machine, or (b) scraping a classroom chair back/forth over the floor surface in a reciprocating manner. In general, both carpet samples resulted in the lowest sound levels and the highest absorption. Relative performances of each material will be presented along with additional classroom usability factors, such as maintenance, cost and durability. [Work supported by Paul S. Veneklasen Research Foundation.]

Underwater measurement of narrowband sound power and directivity using Supersonic Intensity in Reverberant Environments

A laboratory underwater acoustic measurement technique, Supersonic Intensity in Reverberant Environments (SIRE), is developed analytically and validated experimentally and numerically. Unlike standard free or diffuse field techniques, SIRE enables the measurement of narrowband sound power and directivity in an environment with inexact field conditions. The technique takes advantage of underwater vector sensors, measuring only acoustic pressure and the normal component of particle velocity/acceleration, and supersonic wavenumber filtering in the near field of a source. The result is outward-propagating acoustic waves separated from interfering incoming and/or evanescent waves. The SIRE technique was experimentally applied to monopole and dipole sources and the results are compared with theory and standard methods. SIRE is shown to accurately measure radiated sound power to within the limits of ANSI S12.51 and to accurately measure the directivity indices of simple sources to within ±3dB. A coupled finite element/boundary element model of a point-driven, thin-walled cylinder is also developed to establish the limitations of the SIRE technique. The model results show that the measurement standoff distance should be less than the reciprocal of the largest wavenumber in the frequency band of interest. Furthermore, the maximum measurement grid spacing must be less than twice the standoff distance.

Research on the reverberation measuring technique of underwater directional sound sources

The radiated noise of underwater directional sound sources was generally measured in the corresponding ocean environmental condition. Influenced by the ocean environmental noise, the reflection of ocean bottom and ocean surface, it is very difficult to get the radiated sound power of underwater directional sound sources. Reverberation method used in the Architectural acoustics was taken in this paper for measuring the radiated sound power of underwater directional sound sources. It has been used in the radiated sound power measurement of underwater spherical sound sources, but never been used in underwater directional sound sources. The reverberant theoretical formula of directional sound sources was derived by introducing the directivity factor. The radiated sound power of directional sound sources such as dipole and the two same-phase sphere was measured. The measuring and analyzing results show that the reverberant radius of directional sound sources is related to directivity factor. With the directivity factor turns strong, the reverberant radius will become larger but the reverberant controlled area will become smaller, so the measurement range of spatial averaging will become small. The radiated sound power of directional sound sources such as dipole and two same-phase spheres can be measured by large-range of spatial averaging. The measurement techniques can apply to measure the radiated sound power of underwater complex sound sources.

Acoustic testing facilities at the Office of Mine Safety and Health Research

The National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) maintains a noise control program as part of its Hearing Loss Prevention Branch (HLPB). This program utilizes two large acoustic laboratories�a reverberation chamber and a hemi-anechoic chamber�to assist OMSHR engineers with the development and evaluation of noise controls. This paper discusses the design, instrumentation, and use of the NIOSH acoustics laboratories and the important role they play in noise control development and evaluation. The NIOSH reverberation chamber meets the absorption, reverberation time, and test room broadband qualification requirements specified in the ISO 3741/ANSI S12.51 acoustics standard for precision method sound power testing. As part of a qualification testing program, NIOSH conducted an uncertainty estimate for sound power level testing in the chamber. For an overall sound power measurement, this uncertainty estimate was 0.4 dB. The NIOSH hemi-anechoic chamber, which uses Eckel Industries SuperSoft Panels on the walls and ceiling, is used primarily for noise source identification to determine significant noise sources on equipment. Testing was completed to ensure that the chamber functions as a free-field. The SuperSoft panels met NIOSH requirements and the chamber was verified as a free-field per the test room qualification criteria set forth in ISO 3745.

Acoustic characteristics of floor treatments for elementary school classrooms

Phase 1 of this study [J. Acoust. Soc. Am. 129(4), 2523 (2011)], determined the effects of hard versus soft flooring on overall speech and activity noise levels in elementary classrooms. A significant decrease in overall levels was found in carpeted rooms. This phase sought to investigate a range of floor materials and their pertinent properties. Nine different floor materials were mounted to 3 in. concrete slabs and evaluated using a battery of acoustic, impact, and chair scrape tests. Tested materials included vinyl composition tile, resilient rubber athletic flooring (virgin, blended/synthetic, and recycled), polyurethane, vinyl cushion tufted textile carpet, and rubber-backed commercial nylon carpet. Impedance tube measurements of sound absorption were made using International Organization for Standardization (ISO) 10534-2, while sound power measurements according to ISO 3741 were made while either (a) tapping on each mounted sample with a standard tapping machine or (b) while reciprocating an elementary classroom chair back and forth to produce repeatable scraping sounds. In general, the two carpet samples resulted in the lowest sound levels and the highest absorption. The relative performance of each material will be presented along with a discussion of additional usability factors, such as maintenance, cost, and durability. [Work supported by Paul S. Veneklasen Research Foundation.]

An equipment manufacturer's perspective of acoustical standards

As an HVAC manufacturer, it is our goal to create safe, comfortable, and efficient environments (i.e., classrooms, health care facilities, offices, etc.). Standards are useful in gaining agreement regarding the appropriate sound levels for these spaces and establishing how to verify that these levels are met. Regular interaction and participation in writing the standards helps to ensure that all are aware of the requirements and it also allows participants to provide input on what is practical. Participating in the process also helps to prevent adversarial relations between the parties involved in the design and use of the equipment. Standards also provide the technical basis for which manufacturers and customers can make a valid comparison of different products. The information provided is useful in the design process. Sound power of the equipment is a commonly used metric. Standardizing sound power measurement methods reduces the customer's risk by making sure the published sound levels are representative of the equipment as it is intended and gives a defined expectation of repeatability. Thus, participating in the standards process, we help to ensure that the measurement methods are practical for the intended equipment.

Transmission loss measurements using a scanned array nearfield acoustical holography system in an anechoic/reverberation facility. Part II. Comparison of transmission loss methods.

Transmission loss is an important metric used to assist in the selection of materials for noise control and design. In order to assess and improve the performance of transmission loss measurements, two different techniques were compared: traditional microphone and/or matched pair microphone intensity anechoic chamber‐side techniques, and nearfield acoustical holography techniques. Intensity and sound power measurements using traditional methods were made on a test panel installed in an anechoic‐reverb facility transmission loss window, then repeated using a conformal nearfield microphone array and nearfield acoustical holography processing techniques. The full vectored intensity components were used to assess the radiation characteristics of the test panel. This assessment quantifies the acoustics as panel radiation, flanking path contamination, and boundary effects. Data are presented to qualify the best estimate for transmission loss by rejecting contamination. Also, the dynamic range of the transmission loss measurement is compared between traditional and nearfield acoustical holography techniques with high transmission loss panel samples.

Transmission loss measurements using a scanned array nearfield acoustical holography technique in an anechoic/reverberation facility. Part I. Measurement methodology.

Transmission loss is an important metric when used to assist in the selection of materials for noise control and design. In order to assess and improve the performance of transmission loss measurements, two different techniques were compared: traditional microphone and/or matched pair microphone intensity anechoic chamber chamber‐side techniques, and nearfield acoustical holography (NAH) techniques. Intensity and sound power measurements using traditional methods were made on a test panel installed in an anechoic‐reverb facility transmission loss window, then repeated using a conformal nearfield microphone array and nearfield acoustical holography processing techniques. In order to process the data with the relative phase between microphones preserved, a set of stationary reference signals was used. A number of spectral preprocessing techniques and reference combinations are presented. The nearfield acoustical holography processing methodology is also presented with an emphasis on data quality and error reduction.

Rocket noise predicton models: An update.

This paper summarizes revised or improved elements of rocket engine noise prediction models including overall sound power for rocket, noise source locations in undeflected/deflected rocket exhausts, sound power and/or pressure spectrum, and directivity for the rocket noise sources at, and after, launch with emphasis on locations on the launch tower. Finally, influence of the flow deflector and water injection on the rocket noise levels is considered. The data presented are from a number of previously published reports by the author, and others, including Eldred, Crocker, and Potter. The sound power of the rocket is predicted by a Lighthill theory‐consistent model as proportional to a flow‐dependent multiplier corresponding to the ratio of flow mechanical power at the supersonic core tip to mechanical power at nozzle exit. Data from 27 measurements of sound power of jets and rockets covering a range from 135 to 200 dB re 1 PW show a prediction accuracy of +/−2.8 dB. The model is a more robust approach to r...

Characterisation of valves as sound sources: Fluid-borne sound

The sound pressure level in receiving rooms, caused by taps at the ends of pipe systems, is considered. The structure-borne sound power, from the pipes to the supporting wall, was obtained from intensity measurement of the fluid-borne sound power of the tap. The fluid-borne sound power is combined with a ratio of structure-borne sound power to fluid-borne sound power, obtained from laboratory measurements of similar pipe assemblies. Alternatively, a reception plate method is proposed, which avoids the necessity for intensity measurements. The structure-borne power into walls, to which the pipe work is attached, provides input to the standard building propagation model, which yields the predicted sound pressure level in the adjacent room.

Investigation of Noise Sources on a Series Hybrid Transmission

Advanced hydrostatic transmissions and hydraulic hybrids show potential in new market segments such as commercial vehicles and passenger cars. Such new applications regard low noise generation as a high priority, thus, demanding new quiet hydrostatic transmission designs. The aim of this paper is to investigate noise sources on a series hybrid transmission through simulation and measurements. A model has been developed to capture the interaction of a pump and motor working in a hydrostatic transmission and to predict overall noise sources. The model describes dynamics of the system by coupling lumped parameter pump and motor models with a one-dimensional unsteady compressible transmission line model including a dynamic model of an accumulator. A semi-anechoic chamber has been designed and constructed for sound intensity measurements that can be used to derive sound power. Sound power measurements were conducted on a series hybrid transmission test bench inside the semi-anechoic chamber in order to study the relationship between sound power and two types of noise sources, fluid and structure borne. The focus of these measurements was to investigate the impact of an accumulator in the high pressure line as well as the influence of varying high pressure line length. Results show a strong influence of changing line length and the addition of an accumulator on pressure ripple, but with little impact on sound power. A high correlation was found between sound power levels and control moment amplitudes on the swash plate. This study demonstrates the usefulness of predicting transmission noise sources, and how this information is beneficial in the design process of a transmission.

Outdoor sound power calibration of reference sound sources.

Methods and procedures for outdoor sound power measurement for reference sound sources according to ISO 6926/ANSI 12.5 are discussed. This method assures no low‐frequency cutoff of the sound power determination. A quiet outdoor site with a sealed surface of suitable radius, clear of structures and trees is required. Measurement plan‐positions are marked on the surface. Equipment components are prepared in advance for efficient deployment. Weather forecasts are used to determine day or night measurement periods that are free of rain and wind. When ready, site barometric pressure, dry bulb temperature, and wet bulb temperature are measured. The microphone height and the 2 m radius are positioned with a fixture. Sound pressure level data are acquired at all microphone positions, serially if necessary. Sound power results are corrected to standard conditions. High‐frequency results are corrected for humidity as it affects sound absorption by air. Results obtained over several years and at a variety of temperatures are discussed.

Sound intensity radiated by Gaohu

Gaohu is one of the main bowed stringed instruments used in Guangdong music and Chinese native Orchestra. However its sound intensity has never been carefully measured. In this paper the sound power measurements of Gaohu were performed in a reverberation chamber according to the Chinese national standard. Two qualified musicians performed on their own instruments. The mean sound power levels and the dynamic ranges of Gaohu were investigated by four channel acoustic measuring equipments when single notes, music scale and melodies were performed under pp, mp, f and ff dynamics. Great differences were found when Gaohu performed single notes, while the sound power levels were quite close when music scale were performed under f dynamic to those when melodies were performed under normal dynamic mark, the sound power levels of Gaohu when music scale was performed under f dynamics were suggested as the typical and representative value of the sound intensities of Gaohu instrument.

Statistical properties of kinetic and total energy densities in reverberant spaces

Many acoustical measurements, e.g., measurement of sound power and transmission loss, rely on determining the total sound energy in a reverberation room. The total energy is usually approximated by measuring the mean-square pressure (i.e., the potential energy density) at a number of discrete positions. The idea of measuring the total energy density instead of the potential energy density on the assumption that the former quantity varies less with position than the latter goes back to the 1930s. However, the phenomenon was not analyzed until the late 1970s and then only for the region of high modal overlap, and this analysis has never been published. Moreover, until fairly recently, measurement of the total sound energy density required an elaborate experimental arrangement based on finite-difference approximations using at least four amplitude and phase matched pressure microphones. With the advent of a three-dimensional particle velocity transducer, it has become somewhat easier to measure total rather than only potential energy density in a sound field. This paper examines the ensemble statistics of kinetic and total sound energy densities in reverberant enclosures theoretically, experimentally, and numerically.

The variance of the discrete frequency transmission function of a reverberant room

This paper first shows experimentally that the distribution of modal spacings in a reverberation room is well modeled by the Rayleigh or Wigner distribution. Since the Rayleigh or Wigner distribution is a good approximation to the Gaussian orthogonal ensemble (GOE) distribution, this paper confirms the current wisdom that the GOE distribution is a good model for the distribution of modal spacings. Next this paper gives the technical arguments that the author used successfully to support the pragmatic arguments of Baade and the Air-conditioning and Refrigeration Institute of USA for retention of the pure tone qualification procedure and to modify a constant in the International Standard ISO 3741:1999(E) for measurement of sound power in a reverberation room.

Sound power emitted by a pure-tone source in a reverberation room

Energy considerations are of enormous practical importance in acoustics. In "energy acoustics," sources of noise are described in terms of the sound power they emit, the underlying assumption being that this property is independent of the particular environment where the sources are placed. However, it is well known that the sound power output of a source emitting a pure tone or a narrow band of noise actually varies significantly with its position in a reverberation room at low frequencies, and even larger variations occur between different rooms. The resulting substantial uncertainty in measurements of sound power as well as in predictions based on knowledge of sound power is one of the fundamental limitations of energy acoustics. The existing theory for this phenomenon is fairly complicated and has only been validated rather indirectly. This paper describes a far simpler theory and demonstrates that it gives predictions in excellent agreement with the established theory. The results are confirmed by experimental results as well as finite element calculations.

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.

측정방법별 가전제품의 음향파워레벨

As the economy has grown and the main industry in Korea has been changed from secondary industry to tertiary industry, the importance of indoor environment has been a matter of common concern, in which one of the main concerns is to improve the indoor acoustic conditions. However, even though this is required more than before, there are no measures to protect the human being from the noise of electric home appliances. This is owing to the absence of the data about sound power level of electric home appliances. So, we investigate the sound power level of them and analyze the acoustical characteristics of each one. First, we tried to investigate the sound power measurement method of each electric home appliance. After it we test the sound power level of them. From the survey, we can know that the vacuum cleaner is the most noisy electric home appliance, and the refrigerator is the least noisy one. This results will help us predict the indoor noise level using the basic data of sound power level.

DVM-13 AIRFLOW INDUCED VIBRO-ACOUSTICS ANALYSIS OF HDD(Drive Mechanisms IV,Technical Program of Oral Presentations)

This paper studies airflow induced vibro-acoustics of HDD numerically and experimentally. The noise contribution from airflow is characterized and investigated through sound power measurements in a full anechoic chamber. A methodology is developed to simulate airflow induced noise for acoustic optimization of future products.

Uncertainty of sound power levels determined following Air Conditioning Heating and Refrigeration Institute Standard 220.

As part of the AHRI, ASA‐ANSI, and ISO standard development processes, the uncertainty of sound power measurements needs to be quantified for inclusion in sound power standards. A study of three reverberation rooms with volumes of 140, 280, and 560 cm3 was undertaken. Sound power levels for two noise sources (a horizontal shafted reference sound source and a leaf blower) were determined using ARI Standard 220. Variables investigated include source location, source orientation, room conditions, source operating characteristics, and microphone traverse length. The frequency range of interest was 25 Hz–10 kHz. Measurements were repeated and the order of tests was randomized. Of particular interest was the difference between the 140‐ft3 room and the other rooms to confirm the room qualification process required by ARI Standard 220 because the 140‐ft3 room does not meet the ARI Standard 220 qualification process but does meet the requirements in ISO 3741. This work will be helpful in understanding the sources of variation and allow for a starting point for determining if improvements are needed and if so what factors should be considered.