Study on the effect of sound duration on the annoyance of helicopter noise by applying a technique of time compression and expansion of sound signals

The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise.     

Fundamental frequency and sound pressure level of phonation in pathological states

The fundamental frequency (F₀) for the habitual pitch (F_0HAB), F₀ for the lowest physiological tone (F_0L), F₀ for the highest physiological tone (F_0H), F₀ range of phonation (F₀ Rg), sound pressure level (SPL) for habitual loudness (SPL_HAB), SPL for the softest tone (SPL_S), SPL for the loudest tone (SPL_L), and SPL range of phonation (SPL Rg) were measured in 40 normal adult subjects and 1,563 voice patients with varying diseases. F_0H, F₀ Rg, SPL_L, and SPL Rg were decreased in many disease groups. F_0HAB and F_0L varied. SPL_HAB and SPL_S were increased in some disease groups. F₀-related parameters reflected effects of treatments in the cases with polyp, Reinke's edema, epithelial hyperplasia, carcinoma, and paralysis. Effects of treatments were manifested in SPL-related parameters in the cases with nodule, polyp, carcinoma, and paralysis.     

Perceptual study of soundscapes in train stations

This paper presents a study on the perception of soundscapes in train stations. The two issues addressed by this study are (1) to show that people’s knowledge about the space typology that makes up a train station is also based on sound information, and (2) to show that this information is involved in the recognition of the type of space. This study is composed of two stages. In the first stage, two auditory experiments are performed on 66 soundscape samples recorded under natural conditions: (1) free categorization with verbalization and (2) forced-choice recognition. The statistical and lexical analysis of the first experiment reveals three main types of acoustical information: sound sources, human activities, and room effects. The results of the second experiment show that people were able to recognize the type of space (platform, hall, etc.) just by listening to its soundscape. Comparison between Experiments 1 and 2 reveals the auditory similarities of the soundscapes that were recognized as belonging to the same category. In the second step, an in situ questionnaire survey was carried out and confirms the laboratory results. Indeed, when travelers are asked to describe the soundscape of the space in which they are situated, they use the same kind of auditory similarities as those found in the experiments.     

US National Parks and management of park soundscapes: A review

For more than 17 years the US National Park Service has been developing the methods, processes and skills required to effectively manage the soundscapes of the National Parks. The author and his company have had the honor of providing technical acoustics related assistance throughout much of this period. This article presents his reflections on the process, its technical and political complexities, and provides what are hoped to be useful syntheses derived both from his experiences and from past and recent discussions with many of the participants. Specifically, the article describes the fundamental questions that need to be answered for management of natural soundscapes, the types of noise issues that arise in parks, the need for quantitative data, approaches to identifying, measuring and collecting those data, and a suggested approach for developing criteria designed to effectively manage sounds in natural areas.     

The effect of workmanship on the transmission of airborne sound through light framed walls

A study of the airborne sound transmission in a multi-tenanted building has shown that elements of the building which are nominally identical do not have the same acoustic performance. It was seen that some of this variation in performance could be attributed to visually-observable differences in the constructions. Some of the variation could not be explained however, and it was concluded that this variation was due to workmanship. The level of this variation was seen to be approximately 1 dB for a light steel framed construction. This variation is considerably less than that measured previously for a monolithic construction.     

A fast automatic calibration system for a sound level meter in an anechoic room

A fast automatic calibration system for a sound level meter in an anechoic environment has been developed. The precise and fast generation of the constant frequency-independent acoustic pressure field and reduction of digital voltmeter readout to sound pressure level were achieved by a newly designed software algorithm, assuming the system linearity. The performance test justified the assumed linearity, and showed that the searching speed was sufficiently fast within the small error limit.     

Field measurement of airborne sound insulation between rooms with non-diffuse sound fields at low frequencies

Procedures for the field measurement of airborne sound insulation between rooms with diffuse fields are described in International Standard ISO 140-4. However, many dwellings contain rooms with volumes less than 50 m³, where low frequency measurements are less reliable; hence there is a need for a measurement procedure to improve the reliability of field measurements in rooms with non-diffuse fields. Procedures are proposed for sound pressure level and reverberation time measurements for the 50, 63 and 80 Hz third octave bands. The sound pressure level measurement combines corner microphone positions with positions in the central region of each room. This provides a good estimate of the room average sound pressure level with significantly improved repeatability.     

Effects of signal processing on the measurement of maximum sound pressure levels

Maximum sound pressure levels are commonly used for environmental noise and building acoustics measurements. This paper investigates the signal processing errors due to Fast or Slow time-weighting detectors when combined with octave band filters, one-third octave band filters or an A-weighting filter. For 6th order Butterworth CPB filters the inherent time delay caused by the phase response of filters is quantified using three different approaches to establish the following rules-of-thumb: (1) time-to-gradient/amplitude matching occurs when Bt ≈ 1, (2) time-to-peak matching occurs when Bt ≈ 2 and (3) time-to-settle matching occurs when Bt ≈ 4 for octave band filters, and when Bt ≈ 3 for one-third octave band filters. Four different commercially-available sound level meters are used to quantify the variation in measured maximum levels using tone bursts, half-sine pulses, ramped noise and recorded transients. Tone bursts indicate that Slow time-weighting is inappropriate for maximum level measurements due to the large bias error. The results also show that there is more variation between sound level meters when considering Fast time-weighted maximum levels in octave bands or one-third octave bands than with A-weighted levels. To reduce the variation between measurements with different sound level meters, it is proposed that limits could be prescribed on the phase response for CPB filters and A-weighting filters.     

The design and evaluation of an auditory way-finding system in a train station

Previous studies have shown that auditory cues contribute to the identification of several components of a public space such as the volume, but also the type of activity to which the space is dedicated. This paper demonstrates that solutions to improve way-finding in a public place can be based on providing additional auditory information. A methodical approach in three phases is proposed and applied in the case of a train station. First, problems encountered by travellers in a train station are identified by way of an ergonomic study under real conditions with recruited travellers. The results reveal three kinds of problems: orientation errors, lack of confirmation of direction, and lack of information about the remaining distance to be covered. In the second phase, functional and environmental specifications were developed in order to create sound signals for each identified problem. A sound designer proposed several non-speech sound signals based on two schemas: a pair of sounds for the orientation and confirmation functions, and a timeline sequence for the remaining distance. Finally, in the third phase, the sound signals were installed in the train station using an experimental broadcasting system and were evaluated in a second ergonomic study using the same method. The results show that the number of orientation errors decreased and that participants felt more confident during their walk. Sound signals for the orientation and confirmation functions were understood and used by the participants. However, the timeline sequence signalling remaining distance was not understood.     

Determination of the sound power levels emitted by various vehicles using a novel testing method

This paper presents a new and efficient method to determine sound power levels (PWLs). PWLs, generally used for modeling outdoor sound simulations, are obtained from sounds that are emitted by various types of vehicles and cause road traffic noise. Other models, such as HARMONOISE and the ASJ Model, are also based on PWLs. However, a more efficient method is required for determining PWLs from sound pressure levels (SPLs) that typically are measured by field testing and evaluating the influence of different vehicles and road surfaces. The statistical pass-by (SPB) of ISO 11819-1 is used for SPL measurements; however, numerous SPBs must be carried out to reduce measurement uncertainty as well as to satisfy requirements related to meteorological conditions and background noise. In order to alleviate this problem and to make the determination of PWLS more efficient, a testing approach is presented that uses both the novel close proximity (NCPX) method and the pass-by method to determine PWLs.     

The effect of multiple branches on sound propagation in long enclosures

Since the classical room acoustics can not be used for long enclosures due to the inhomogeneous sound field, much work has been carried out recently to investigate the sound propagation in long enclosures, which are helpful to the acoustic design of practical long enclosures, such as the high-speed railway tunnels. However, most of these works focuses on the straight long enclosures without branches or with one branch. In this paper, the effects of the multiple branches on sound propagation of long enclosures are studied. The sound pressure level (SPL) attenuation, early decay time (EDT), and reverberation time (T30) of long enclosures with multiple branches have been investigated by physical scale models based acoustic experiments. Several interesting results have been obtained concerning the sound propagation of long enclosures with multiple branches. It shows that the sound field of long enclosures with multiple branches is more complex and inhomogeneous than that of the long enclosures without branches or with one branch.     

Down-mixing of multi-channel audio for sound field reproduction based on spatial covariance

This article describes a method for automatic down-mixing multi-channel audio content on the basis of spatial covariance. Such a down-mixing method should be able to convert the signal of the original multi-channel audio system into that for an alternative system with the lesser number of channels, while maintaining the spatial impression of sound. Moreover, it should take into account the listener’s position and transfer function. Wave surface control and convolving the head related transfer function are techniques used in sound field control or reproduction. We consider that the spatial impressions of a sound field, which we perceive through our ears, are reproduced by preserving the relative relationship between observation points even if the wave surface is not completely controlled. Takahashi et al. proposed a new sound field reproduction method that we named “SOund field Reproduction based on sPAtial Covariance” (SORPAC). SORPAC can control the point-to-point covariance in a sound field. We expect that this sound field reproduction method based on spatial covariance can be applied to down-mixing of multi-channel content because SORPAC does not require the listener’s position or transfer function. This article describes SORPAC and its characteristics. We used SORPAC for down-mixing audio content. We confirmed that SORPAC-based down-mixing could accurately reproduce the interaural cross correlation (IACC) in relation to the listener’s position.     

Study of vertical sound image control with parametric loudspeakers

A parametric loudspeaker utilizes nonlinearity of a medium and is known as a super-directive loudspeaker. In this paper, the sound localization in the vertical direction using the upper and lower parametric loudspeakers is confirmed by listening tests and physical measurements. The differences in levels between the upper and lower parametric loudspeakers are varied as a parameter. The direction of sound localization in the vertical plane can be controlled not only when the acoustical axis is set to the right ear but also when it is set to at 5 deg to the right of the right ear. The effect of the level difference between the upper and lower loudspeakers is weaker than the differences observed when using ordinary loudspeakers. We obtained interesting characteristics of the left-right sound localization in the horizontal plane with the upper and lower parametric loudspeakers in the vertical plane. It is found that by setting the parametric loudspeaker at the right ear (that is, the horizontal angle of a listener to it is only 3 deg to the right), the direction of sound localization in the horizontal plane moved approximately 10 deg to the right. Moreover, by setting the parametric loudspeaker 5 deg to the right, the direction of sound localization moves approximately 20 deg to the right. The ILD (Interaural Level Difference) using a dummy head is calculated from the measured left and right sound signals. It is determined that ILDs of the parametric loudspeaker are larger than those of the ordinary loudspeaker. A simple geometrical acoustic model is introduced and analyzed. The analysis helps to explain the measured characteristics.     

A theoretical model for the evaluation of measurement uncertainty of a sound level meter calibration by comparison method in an anechoic room

A theoretical model for the evaluation of measurement uncertainty of a sound level meter (hereafter as `SLM') calibration by comparison method in an anechoic room was developed. Through this model, the uncertainties in the semi-automatic calibration and that in the full-automatic calibration were estimated for the recently developed SLM calibration system. In order to estimate the standard uncertainty against the SLM positioning, which is a significant uncertainty component, the sound field curve-fitting formulae were adopted. The validity of the curve-fitting method was proven by the similarity of the spatial distributions of radiation sound field produced by the plane circular piston source and that by the cone shape source. A linear equation was used to fit the measurements of the sound field distribution along the radiation axis. A quadratic equation was used to fit the measurements along the radial axis normal to the radiation axis. The fitting parameters gave us the sensitivity coefficients of the propagation of the uncertainty. In addition, one of the quadratic fitting parameters was found to be a positional uncertainty itself. Using this model, the expanded uncertainties were evaluated for the semi-automatic and full-automatic calibration of SLM.     

Changes in laryngeal airway resistance in young adult men and women as a function of vocal sound pressure level and syllable context

A noninvasive pressure-flow technique was used to assess laryngeal airway resistance (R_law) in eight young adult women and seven men. Syllable structures used were consonant-vowel (/pi/) and consonant-vowel-consonant (/bip/). The data were obtained from oscillographic records of intraoral air pressure and transglottal airflow over 2 consecutive days. Repetitions of each syllable context were produced at each subject's 25th, 50th, and 75th percentiles of vocal sound pressure level. No significant differences in R_law were found across days for the two groups. Women had significantly greater R_law than did men for the /pi/ and /bip/ contexts. Men showed a significantly greater average airflow rate than did women for both syllable contexts. Airflow, air pressure, and the ratio R_law increased as the sound pressure level of voice increased. The technique appears to be useful for characterizing certain features of laryngeal airway resistance for men and women.     

Influence of structural variability upon sound perception: Usefulness of fractional factorial designs

The present paper introduces an efficient and time-saving approach for the evaluation of the consequences of structural uncertainties on sound perception. Its aim is to validate the use of fractional factorial designs for perceptual assessment of a model system. A test bench was used, which allowed to accurately control the variability of several structural design parameters. Sounds emitted by the bench were recorded with a dummy head and submitted to listeners during two experiments, in which they had to evaluate the dissimilarity of each sound to a reference, representing the nominal state of the device. In the first experiment, six factors, assumed to be independent, were used to define a fractional factorial design. As an analysis of variance showed that two interactions between factors should have been taken into account, a second experimental design was developed to quantify these interactions. These two experiments allowed to define an accurate model of sound perception, describing the effect of each factor on the perceived dissimilarity. Thus, it was possible to relate the variability of the structure to the perception of the sound emitted with few experimental effort.     

Calculation of sound radiant efficiency and sound radiant modes of arbitrary shape structures by BEM and general eigenvalue decomposition

In this paper, a numerical method is presented to calculate sound radiant efficiency and radiant modes of arbitrary shape structures. Some methods have been proposed to compute sound radiant efficiencies and sound radiant modes of plates and beams. However, there is not a valid method to calculate for arbitrary shape structures except for measurement at the present time. The method proposed can predicate the sound radiant efficiencies and the sound radiant modes for arbitrary shape structures by boundary element method (BEM) and general eigenvalue decomposition. The validity of this method is demonstrated by two numerical examples of pulsating sphere and radiation cube.     

Experimental study on sound absorption performance of microperforated panel with membrane cell

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, a composite MPP sound absorber with membrane cells (MPPM) is introduced. Sound absorption properties of the MPPM are studied by the impedance tube experiment. Results show that the membranes have a significant influence on the sound impedance. The sound absorption performance of MPPM gradually increases with the increase of the membrane area. The single-layer MPP with some small area membrane cells may have the same effect and single large area membranes. By adjusting the size of the membrane cells, one can implement a sound absorber with a wider absorption bandwidth and higher absorption peaks than the single-layer MPP.     

Estimation of directivity and sound power levels emitted by aircrafts during taxiing, for outdoor noise prediction purpose

Integrated noise model (INM) is the most internationally used software to calculate noise levels near airports. Take off, landing or pass by operations can be modeled by INM, but it does not consider aircrafts taxiing, which, in some cases, can be important to accurately evaluate and reduce airports’ noise assessment.Aircraft taxiing noise emission can be predicted using other prediction tools based on standards that describe sound attenuation during propagation outdoors. But these tools require data inputs that are not known: directivity and sound power levels emitted by aircraft during taxiing.This paper describes methods used to calculate directivity indexes and sound power levels, based on field measurements made in Madrid-Barajas Airport (Spain). Obtained results can be used as inputs for general purpose outdoor sound prediction software, which will be able to evaluate noise at airports vicinity as industrial noise.Directivity and sound power levels have been estimated in octave and third octave band terms, for several aircraft families.