Machinery Noise Research Articles

Improvement of Working Environment and Measurement Method for Machinery Noise

Improvement of Working Environment and Measurement Method for Machinery Noise

Response to air-cooling machinery noise: A preliminary study

People living close to commercial properties are often exposed to air-cooling machinery noise. Of primary concern is the awareness of tones in the sounds and how that awareness contributes to the overall annoyance experienced by people exposed to the noise. For noise control, it is most straightforward to control the strength of tonal contributions from components such as fans and compressors. For the class of machinery considered in this study, fan fundamentals are usually around 60 Hz and compressor fundamental frequencies are typically between 500 and 700 Hz. A preliminary study was carried out using 27 sounds that simulated a broad range of possible noises made by this type of air-cooling machinery. The sounds were presented to people who were asked to rate them in terms of tonality and annoyance. Tonality and annoyance ratings only increased when sounds contained at least one compressor tone above a certain threshold level. High correlations were found between objective metrics and the average of the subjects’ responses. Recommendations for future research include investigations into the individual effects of changing spectral balance, overall loudness, and tonal contributions for these types of sounds, because changing tonal levels alone affects all of these sound characteristics simultaneously.

Adaptive compensation of noise in a sonar system

The performance of a sonar system on a ship is strongly influenced or even limited by its own and other ship’s noise. Its own noise can have different sound sources. The engine causes disturbing line spectra, the auxiliary equipment can radiate both harmonic signals and white or colored noise signals. Due to the viscous flow during ship movement, disturbing noise can also arise. Interaction between the hydrodynamic flow and the whole ship structure can excite the ship’s own modes, which results in strong natural oscillations (flow noise-induced resonances). Additionally, other loud ships can disturb the sonar processing, too. An adaptive noise reduction method is presented. It is suited to reduce a ship’s own machinery noise, and, with slight variations, also jamming targets. The output of the adaptive method can be calculated in the time domain as well as in the frequency domain. Working in the time-domain, techniques are available which reduce the numerical expense, but some reasons suggest the calculation in the frequency domain. Calculations based on both simulated data and real data recorded at sea are presented.

Noise emission—A part of the risk assessment concerning the safety of machinery

ISO/IEC guide 51 describes safety aspects in products, processes, and services. EN 292/EN 414/EN 1050 describe the safety of machinery: concepts, general principles of design, and the risk assessment. For specific machinery groups standards on ISO or CEN level describe safety aspects, technical data or test methods. Problems with the implementation of noise into these standards are discussed because the reduction of emission of machinery (noise, vibration, toxic agents) has, until now, obviously been neglected, as it seems, due to the unsuitable approach of classical risk reduction. Therefore the European Machinery-Directive requires (i) a reduction of risks to the lowest possible level (ii) and the information of the user about existing residual risk. Thus machinery standards to reduce noise-emission must comprise (1) specified measuring procedures (yet existing to a large extent) including representative operating conditions for emission measurements, (2) collected emission values for each type of machinery in order to derive the state of the art, and (3) examples for noise reduction by design. Exemplary C-standards will be presented.

Hot new topics in ASA/ANSI standardization

The ASA Committee on Standards has many new work efforts underway. As chairman of the ANSI S12 committee (noise), this author is primarily versed in the hot new noise standards being developed. Hence, this paper will concentrate on noise standards. (The S12 committee can be considered the counterpart to ISO TC 43/SC 1 and concentrates on noise.) Several new efforts are underway in S-12, including (1) classroom acoustics, (2) room noise criteria, (3) model community noise ordinances, (4) community noise assessment, (5) consumer product noise labeling, and (6) in situ hearing protector measurements. In addition, there is a new effort in the S-3 committee (bioacoustics) dealing with warning signal definitions. Clearly, these new topics depart from many of the traditional standards topics such as measurement of workplace machinery noise or office and business equipment noise. Rather, these new work efforts concentrate on criteria development, measures to assess response to noise in various settings, or various human interactions with sound, etc. Several of these topics, such as community noise assessment, noise labeling, or hearing protector measurement, relate to ongoing international efforts. This paper will briefly describe the goals, progress, key contacts, and schedules for these work efforts.

Strategy policy of ISO/TC43 ‘‘Acoustics’’

The scope of ISO Technical Committee 43 ‘‘Acoustics,’’ together with its Subcommittees ‘‘Noise’’ and ‘‘Building Acoustics’’ comprises standardization in the whole field of acoustics, i.e., the measurement of sound, its generation, transmission, and reception as well as its effects on Man and the environment. Close liaison is maintained with related international and regional standardization committees, especially IEC/TC 29, which is responsible for electroacoustic standards. ISO standards elaborated by TC 43 are equally addressed to a variety of parties, such as industry, regulatory authorities, trade and consumer groups, research institutes, testing laboratories and consulting engineers, health and safety inspectors, audiologists, and communication experts. Representatives of these groups from 24 different countries contribute actively to its work. More than 120 standards have been published so far and the present program of work includes nearly 80 projects for new or revised standards. In the past few years, major emphasis was laid on the measurement of machinery noise and the measurement and rating of sound insulation in buildings and of building products, both in the context of recent regional legislation. Fields like environmental noise, transport noise, noise prediction, and simplified measurement methods for building acoustics are considered to be future priority areas.

Ultrasonic Detection of Lubricating Film Collapse in Mechanical Seals

Mechanical seals generally fail as the result of the collapse of the lubricating film between the faces. In the present research, a system that detects the collapse of the lubricating film in a gas seal has been developed. The system uses an active ultrasonic transmission technique to monitor the fluid film. Sensors are placed behind each stator of a double mechanical seal. A series of ultrasonic sinusoidal wave packets is generated by one transducer while the second transducer monitors the signal transmitted through the seal interface. A weak transmitted signal indicates a continuous fluid film, while a strong transmitted signal indicates contact between the seal faces. The transmitted signal is relatively independent of the seal characteristics and operating conditions, and can be easily distinguished from machinery noise since its frequency and amplitude can be controlled. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

音の工学ヘの応用 音色の測定法・評価法

音の工学ヘの応用 音色の測定法・評価法

Annapolis Laboratory contribution to structureborne noise measurement and analysis

The Annapolis Laboratory of the Carderock Division of the Naval Surface Weapons Center has continually been in the forefront of the development of instrumentation and standards for the measurement and analysis of the structureborne noise generated by shipboard machinery. This effort included but was not limited to sensor mounting and calibration techniques, equipment mounting fixtures, analysis instrumentation, and criteria for permissible shipboard machinery noise levels. The Laboratory also established the Machinery Acoustic Data Information Center (MADIC), which provided the Navy’s only central source of such information for ship design and operational requirements. One of the results of this effort was MIL-STD-740, the military standard for machinery noise measurement procedures and criteria. An ASA/ANSI standard S2.16-1997, which was based upon MIL-STD-740, has recently been issued.

A practical method for predicting ship machinery noise

The development of a ship’s noise prediction method at Annapolis from 1960 to 1967 is reviewed. In 1960, the Noise Transmission Branch was exploring mechanical impedance measurement concepts. Numerous structureborne and waterborne tests were made on machines, foundations, flexible couplings and conduits in the laboratory as well as on the SS427. The effort was complicated because of the large number of matrix elements describing even a simple machine foundation and the problems in obtaining meaningful measurements using the state-of-the-art instrumentation. The team’s ivy tower collapsed by urgent requests to predict radiated noise from a whole ship to assist BUSHIPS in decision making. A prediction model was developed using the force transfer factor concept by Wright and Akey. Based on in-house measurements and estimates from available literature, each transmission path component was categorized as a single spectrum. Vibration levels for each machine type were fed into representations of its transmission path components: isolation mounts, foundation, flanking paths (piping, conduits, etc.), and the hull. The team ended up with a practical prediction scheme to aid in the preliminary design stages of new ships and in guiding priorities for future research in ship silencing.

Rattles and squeeze toys: a proposal for a noise test code (with low measurement uncertainty)

The new European Standard EN 71-1:1997 includes the presented measurement method for the determination of emission sound pressure levels of rattles and squeeze toys in order to declare and verify (check conformance with pertinent) noise emission values (limits). The toy industry has argued that reliable measurement methods are impossible to develop (since the noise of a toy depends on the operations of humans). They have also argued that restrictions (limits) on noise imply that toys must be manufactured with unrealistic margins because of the poor measurement uncertainty. This study, however, shows that it is possible to test rattles and squeeze toys by using human operators and still obtain reasonable values for the measurement uncertainty. The standard deviation of the measurement reproducibility will improve if several operators are used, and can be kept below 2 dB of the A-weighted sound exposure level (SEL or LpA,1s is) or Leq as well as of the C-weighted peak level Lpcpeak. This means that noise measurements on these toys can be performed with the same (or better) precision than the one obtained when applying ISO standards on machinery noise to verify conformance with EU directives on machinery safety (noise in the industry). The test method does not require expensive testing equipment; the measurements can be made in almost any ordinary room with some acoustical damping, using ordinary equipment for sound pressure level measurements.

An intensity-scaled stochastic signal processing of detecting machinery noise based on the vibration information under a background noise

An intensity-scaled stochastic signal processing of detecting machinery noise based on the vibration information under a background noise

Effects of Caffeine and Noise on Mood, Performance and Cardiovascular Functioning

An experiment was conducted to examine the effects of caffeine and noise on mood, mental performance and cardiovascular function. One hundred and six young adults (mean age 21·2 years) took part in the study. Subjects were assigned to one of six groups formed by combining noise/quiet and drink (caffeinated coffee, decaffeinated coffee and fruit juice) conditions. Subjects were familiarized with the tasks and then completed a pre-drink baseline session (conducted in the quiet). Subjects were then given either caffeinated coffee (1·5 mg/kg caffeine), decaffeinated coffee or fruit juice. Following consumption of the drink subjects were re-tested 1 h later, either in noise (75 dBA conglomerate noise, consisting of speech, music and machinery noise) or in quiet. The subjects exposed to noise felt more anxious and showed an increase in blood pressure. Their performance of a cognitive vigilance task also declined over time. There were no significant main effects of caffeine, although simple reaction time was quickest in the caffeinated coffee group. Caffeine did not modify the effects of noise on mood, cardiovascular functioning or sustained attention. Indeed, the only interaction between drinks and noise was found in recall and recognition memory tasks, with the caffeine/noise group having better memory performance than the decaffeinated/noise subjects. Overall, the results show that low levels of caffeine do not increase the behavioural and physiological changes observed in a stressful situation.

Effects of Caffeine and Noise on Mood, Performance and Cardiovascular Functioning

An experiment was conducted to examine the effects of caffeine and noise on mood, mental performance and cardiovascular function. One hundred and six young adults (mean age 21·2 years) took part in the study. Subjects were assigned to one of six groups formed by combining noise/quiet and drink (caffeinated coffee, decaffeinated coffee and fruit juice) conditions. Subjects were familiarized with the tasks and then completed a pre-drink baseline session (conducted in the quiet). Subjects were then given either caffeinated coffee (1·5 mg/kg caffeine), decaffeinated coffee or fruit juice. Following consumption of the drink subjects were re-tested 1 h later, either in noise (75 dBA conglomerate noise, consisting of speech, music and machinery noise) or in quiet. The subjects exposed to noise felt more anxious and showed an increase in blood pressure. Their performance of a cognitive vigilance task also declined over time. There were no significant main effects of caffeine, although simple reaction time was quickest in the caffeinated coffee group. Caffeine did not modify the effects of noise on mood, cardiovascular functioning or sustained attention. Indeed, the only interaction between drinks and noise was found in recall and recognition memory tasks, with the caffeine/noise group having better memory performance than the decaffeinated/noise subjects. Overall, the results show that low levels of caffeine do not increase the behavioural and physiological changes observed in a stressful situation. © 1997 John Wiley & Sons, Ltd.

Inverse and Reciprocity Methods for Machinery Noise Source Characterization and Sound Path Quantification Part 2: Transmission Paths

This article and the foregoing companion article 1 are concerned with the experimental analysis of machinery noise control problems. Although the general approach, in terms of a source transmission path receiver scheme, is well-known, this is not the case with the manner in which source modelling is handled. The noise control problems of interest here, are dealing with a multitude of simultaneous sources or with a single noise source like a machine, with a multitude of partial sources and 'parallel' transmission paths. The analysis models which are considered are limited to systems with supposedly linear behaviour, i.e. to systems for which output responses may be modelled as a linear superposition of all contributions of the partial sources and transmission paths. Then in loose mathematical terms, for example, the following model equation applies: m partial sources:

Sound quality design to improve noise of construction machinery

Sound quality design to improve noise of construction machinery

Sound Field Assessment by Measurement of Sound Pressure Distribution Close to Machine Noise Source. (Estimation of Normal Particle Velocity at an Aperture by Single-Plane Sound Pressure Measurement).

For the assessment of machinery noise, we describe a method of estimating the normal particle velocity distribution from a sound pressure distribution measured at a single aperture close to the sound source based on near acoustic holography(NAH). In NAH, it is required that the distance between the surface of the sound source and the measurement aperture is one-tenth of a wavelength. In practice, the distance between the machinery and the measurement aperture is too large for NAH because of the 3-dimensional features of the machine, so this method is investigated under the condition that the sound pressure is measured at about one wavelength from the sound source. The size of the measurement aperture was determined to be 1m×1m. Through investigation by simulation, it has been shown that the effect of evanescent waves should be taken into consideration. Experimental verification shows that this method can be practically applied in echoic situations.

Inverse and Reciprocity Methods for Machinery Noise Source Characterization and Sound Path Quantification Part 1: Sources

A conventional approach for the analysis of noise control problems uses the source-transmission path-receiver scheme. In many situations this type of analysis is complicated by the fact that there is a multitude of simultaneous sources. Moreover, even for a single noise source like a machine, there can be a multitude of partial sources and parallel transmission paths. Therefore, the development of cost-effective noise reduction strategies often requires detailed knowledge of the contributions of the partial sources and transmission paths to the radiated sound at distant receiver positions. Generally speaking, this type of analysis requires a system modelling in terms of inputs I, which genuinely characterize the sources themselves and of output-input ratios O/I. These latter are transfer functions TF, which characterize the transmission paths. Such an analytical approach facilitates the effective specification of required noise source quietening and of improved sound or vibration isolation in one or more paths. The treatments in this article will be limited to systems with supposedly linear behaviour, i.e. to systems for which the output response may be modelled as a linear superposition of all contributions of the partial sources and transmission paths. Then in loose mathematical terms the following model equations apply:

Psychological evaluation of sound quality of machinery noise

Psychological evaluation of sound quality of machinery noise

Procedure for the improvement of sound quality of machinery noise

Procedure for the improvement of sound quality of machinery noise