Showing papers in "Canadian Acoustics in 2001"

The effect of sound on the growth of plants

Abstract: This project is intended to show how the rate of growth of two different plant species was affected by sounds of varying frequencies. Two plant species, beans and impatiens, were selected because of their relatively fast growing rates. Ambient conditions were regulated by environmental chambers in which the plants were housed. One chamber was used as a control for the plants, and the plants in the other chambers were subjected to sounds of different frequencies at roughly the same sound intensity. Sounds of pure tones and random [wide band] noise were used. The changes in the growth of the plants were monitored every two days for twenty-eight days. Upon completion of the tests, it was observed that optimum plant growth occurred when the plant was exposed to pure tones in which the wavelength coincided with the average of major leaf dimensions. It is suggested that this was due to the "scrubbing" action of the traversing wave, causing air particle motion on the surface of the leaf; this movement removed the stagnant air layer adjacent to the leaf, thus increasing the transpiration of the plant. It was also noted that the plant growth was less when exposed to random noise.

Duration discrimination in younger and older adults

Abstract: Temporal modulation of the speech signal contributes to speech recognition in younger adults. Older listeners who have poor gap duration discrimination abilities show more trouble in understanding temporally degraded speech. Studies have shown that the contribution of age-related changes in temporal resolution to speech recognition are minimal. Age-related losses in detecting a gap may occur when the durations of the tones marking the gap are very short. Older adults have more difficulty in discriminating the signal durations than younger adults. The duration of stimuli has similar effects on younger and older adults duration ability of discrimination. The age effect is more at short standard tone durations, independent of audiometric threshold.

Sound transmission loss of insulating complex structures

Abstract: The Transfer Matrix Method (TMM) is extended to handle the transmission loss of finite stiffened and orthotropic structures lined by porous materials in a multi-layered configuration. The effects of curvature, stiffeners and heterogeneity are considered. The resulting model is easily adaptable to multi-layer configurations.

F2/F1 vowel quadrilateral area in young children with and without dysarthria

Abstract: A study was conducted to determine if use of a log n Hz scale would eliminate the effect of vocal tract size on vowel area across a broad age range of talkers and also be sensitive to potentially smaller vowel areas of dysarthric individuals. For this purpose, recordings produced by six 3 year-old children, six 5 year-old children and six young women, all with normal speech development, and six 5 year-old children with dysarthria were analyzed. It was found that vowel area, when measured in Hz 2 and log n Hz 2 , decreases in size as age increases, suggesting that a log n Hz scale does not normalize age differences in F2 and F1 vowel area.

Age-related changes in perception of tones within a stream of auditory stimuli: auditory attentional blink

Abstract: This research explored the immediate perceptual/cognitive consequences of an attended-to tonal stimulus within a stream of tonal stimuli. Previous results have suggested that processing information about a tone within a stream of tones presented at a rate of 11 tones/s can modify perception of subsequent tones. The results of the current study suggest that perception of subsequent tones is also a function of age.

ISO 1996 "Acoustics - Description and measurement of environmental noise" round robin testing

Abstract: The CSA 107.53 Working Group of the Industrial Noise Subcommittee of the Canadian Standards Association has been actively involved in the endorsement of ISO 1996 Standard "Acoustics-Description and Measurement of Environmental Noise" in Canada. Prior to endorsing methods to assess environmental noise and predict the potential annoyance response of a community to outdoor long term noise exposure, the working group conducted a round robin testing to determine if it could be applied consistently in the Canadian context. Each of the seven round robin participants was instructed to use the measurement equipment and techniques they would normally use in assessing environmental sound. Results were measured and reported in terms of the L LM (Logarithmic Mean Impulse Sound Level) and the Case 1 Rating Level.

A preview of the draft CSA guideline - Noise emission declarations for machinery

Abstract: To help reduce workplace and environmental noise, the Canadian Standards Association (CSA) is producing a guideline on noise emission declarations for machinery. This article provides excerpts from the draft CSA guideline to illustrate its use and to elicit further feedback from the acoustical community.

Measurement of structural intensity on plate structures

Abstract: A scanning laser vibrometer and specially developed analysis software were used to systematically investigate the optimal point spacing, and the suitability of measurement quality indicators, such as the residual intensity index, for the two and four point methods. In addition, the sensitivity of the two-transducer to near fields close to sources and discontinuities was examined. The resulting data was analyzed.

Rating sound level - An overview of amendment 1 to Iso 1996-2

Abstract: An overview of the new method for description and measurement of environmental noise is presented. Although some issues related to the method implementation remain, as yet, unresolved, the method represents a significant improvement over the currently used assessment procedures. A new approach to the assessment of impulsive noise is the main advantage of the method.

Quantifying Receptor Annoyance From Low Frequency Industrial Noise In The Environment

Abstract: Two new measurement techniques using C-weighted along side the A-weighted scale was explored. The first technique was tested using two sets of comprehensive survey data. The first survey analyzed was from data collected at Residence "A" at a survey conducted on July 13-14, 1999. The second data was gathered on the night of June 15-16, 2000 at the Residence "B". An analysis using the second technique was performed for a survey conducted on the night of June 6-7, 2000 at Residence "C". Residence "D" was also assessed using the second technique. It was found that among the two techniques, the first one should be considered in the next review of the Noise Control Directive as a means of addressing low frequency noise.

Testing of ANR (Active Noise Reduction) headsets

Abstract: The Sensory Communications group at the University of Toronto is currently studying a method that uses an Acoustical Test Fixture (ATF or Artificial Head) and allows for the measurement of Insertion Loss (IL). In this paper, an overview is given on the repeatability from consecutive measurements on the same protector, between protectors of the same type, as well as comparison between protectors of different types and from different manufacturers.

Experimental study of propeller-aircraft run-up noise

Abstract: Measurements were made of the characteristics of the noise radiated by a Beechcraft 1900D twin-propeller aircraft during engine run-up. The objective was to determine the feasibility of controlling this noise using active noise control. Total noise levels varied with aircraft heading from 103 to 112 dB (100 to 109 dBA) at 73 m from the aircraft. Noise directivity plots were generated. Levels at the nearest community 3 km away varied from 74 to 77 dB (62 to 66 dBA). Near the aircraft the noise spectra comprised a series of equally-high peaks at the 112-Hz fundamental frequency and its multiples. In the community, the three lowest peaks dominated the A-weighted spectrum, with higher-frequency peaks being progressively attenuated. A coherence analysis was performed on the noises measured at 73 m and 98 m from the aircraft. The insertion loss of a blast fence near the run-up area was estimated from run-up noise measurements made on both sides of the fence. The insertion loss varied from 4 to 13 dB and was greatest at mid frequencies.

An interlaboratory evaluation of the vibration transmissibility of gloves following the ISO 10819 test method

Abstract: A study was carried out to deal with the difficulty associated with the application of the ISO 10819 test method for evaluating the vibration transmissibility of gloves at the palm of the hand. Four different gloves were tested in three different laboratories (two North American and one European). In these tests, some variations to the ISO 10819 test protocol were introduced by the laboratories, specifically by increasing the number of test subjects and test trials and by providing control for hand-held adapter orientation. Transmissibility values reported by the different laboratories were analyzed.

Design of antivibration gloves

Abstract: The hand-arm vibration (HAV) syndrome is associated with the destruction of the small blood vessels and with nerve damage in the fingers. It is caused by excessive vibration directed into the hands from vibrating hand tools and vibration-intensive work processes. To minimize the occurrence of HAV, it is important to reduce vibration energy into the hand and arm. One way to do this is to use protective clothing, in particular antivibration gloves. The factors to be considered in the design of an antivibration glove are discussed. Paying close attention to these factors increases the effectiveness of the glove in reducing vibration while making the glove comfortable to wear.

Temporally jittered speech produces PI-PB rollover in young normal-hearing listeners

Abstract: The question of whether or not temporal jitter simulates neural asynchrony in young, normal hearing listeners was addressed by temporally jittering word discrimination lists and presenting them to young adults with normal hearing to see if they will show performance-intensity phonetically balanced (PI-PB) rollover. Speech discrimination scores were measured for each of the 16 participants using intact NU6, jittered NU6 and jittered W22 word lists presented at four levels, 40, 55, 65, and (UCL-5) dB HL, denoted respectively as Level 1, Level 2, Level 3, and Level 4. The results are analyzed in detail.

A look at throat singing

Abstract: Throat singing enables a singer to sing simultaneous with two,three and four voices. The main sound is generated by the vocal cords and other flexible structures like false cords, arytenoid cartilages, aryepiglottic folds and epiglottic root are vibrated to cause throat singing. The spectral analysis of the three samples of throat singing depicts peaks and valleys at the same frequencies with some large differences in the sound level at same frequency. Among the three distinct peaks observed, the first peak is due to the vibration of the vocal cords, corresponding to the fundamental frequency. The second peak is the harmonic of the first whereas the third peak represents the independant vibrations of the structures other than vocal cords.

Repetitive impacts from manual hammering: Physiologic effects on the hand-arm system

Abstract: Vibration mapping was determined from individual trials on subjects performing a standardized hammering task A set of four uni-axial accelerometers were placed perpendicular to the longitudinal axis of, and bisected the lengths of the distal, middle, and proximal phalanges, and the metacarpal of a particular finger Conventional commercial hammers were used to provide single impact force mapping As was expected, vibrations were observed to be higher in the distal phalanges when compared to the metacarpals The peak acceleration values on the metacarpals were greater than the proximal phalanxes

Techniques for using ray tracing for complicated spaces

Abstract: During the last decade, the ray tracing method has contributed considerably to improve the prediction accuracy of acoustic room modelling. Ray tracing methods allow the analysis of complicated sound field for any room. However, the use of these methods and their validation are not always trivial. Even so, right and useful modelling is obtained only when each construction stage of the model is well done. The objective of this paper is to present, through a complicated example (a hydroelectric power station), some original techniques of modelling and validation. The identification of noise sources and the determination of their acoustic power, the representation of a non-single point source, the validation and some modelling techniques meant to reduce time computation will be presented. Furthermore, an efficient method for the evaluation of noise reduction provided by the various treatments will also be shown. This method, based on an evaluation of transfer functions between noise sources and different computation points in the room, can be used to choose the best acoustic treatment for a given noise reduction objective. All techniques presented in this paper have been applied and validated on an industrial case.

Acoustic attenuation performance of double expansion chamber silencers with interconnecting tube

Abstract: A three-dimensional substructure boundary element technique was employed to predict the acoustic attenuation performance of double expansion chamber silencer with inter-connecting tube. The effect of the lengths of inter-connecting tube and expansion chambers, as well as the extensions of inlet and outlet tubes was studied. Overall, significant results were obtained.

Structure and correlation in the detection of melodic sequences

Abstract: The detection performance of randomly generated signals of varying degrees of structural content was measured Fractal melodies were used and the degree of self-correlation (structural content) was changed in a continuous manner Overall, significant results were obtained

Comparative investigation of muffler models

Abstract: The feasibility of using simplified theoretical modeling equations was studied as a preliminary step in the design process for exhaust muffler systems. In particular, the results were compared to the results of a computer model. Furthermore, the results of a relatively simple computer model were then compared to the results of a very complex computer simulation model of a muffler system complete with a modeled internal combustion engine as the source. As a result, the merits of using the fundamental equations for preliminary design considerations for muffler systems were demonstrated.

The vibro-acoustics of a plate-backed cavity with non-homogeneous porous materials

Abstract: The effects of air pocket or elastic patches in a homogeneous porous domain were studied. The different domains were modeled by using accurate finite element methods. It was found that the addition of air pocket does not deteriorate the acoustic performance, but leads to a reduction of the weight of the configuration. On the other hand, an increase of the acoustic performance was obtained by insertion of elastic patches, but not without any increase of the configuration weight.

Acceptable party wall sound insulation criteria

Abstract: Results of aggregate response data from a field survey of the sound insulation walls separating multiple unit housing in 3 Canadian cities were analyzed. Only the apparent STC ratings of the walls were considered. Data were aggregated into 8 groups by apparent STC rating. Based on the analysis, it is proposed that an effective STC of 55 is a realistic goal and STC 60 is a more ideal goal for party wall sound insulation.

Song memory: Are text and tune asymmetrically related in recognition memory?

Abstract: The relationship between the texts and tunes of songs in recognition memory was studied. Thirty native English speakers from the Queen's psychology subject pool took part in the study. Six pools of 20 songs were created and calibrated for the experiment. The results confirm the asymmetrical integration effect. In particular, the study showed a clear asymmetry in the relationship between text and tune in recognition memory.

Sound transmission through gypsum board walls - Effect of shear membranes and framing details

Abstract: An overview is given on trends observed in the sound transmission results from a research project that studied both sound and fire resistance of wall assemblies intended for multi-family residential buildings. Focus is on factors controlling airborne transmission and structure-related aspects.

Aeolian tones in wind tunnels

Abstract: Two mechanisms that produce strong noise levels within the circuit and thereby increase the test section noise levels are illustrated with examples from a climatic wind tunnel and an aero-acoustic wind tunnel. Both of the example wind tunnels have been provided with extensive acoustic treatment to reduce background noise levels. These two mechanisms for the production of Aeolian tones can be important for any wind tunnel.

A comparison of acoustic effects of two stopper and crown systems in the modern flute

Abstract: A new stopper and crown system developed by flute maker Robert Bigio is reported to produce a louder, harmonically richer and faster response in the orchestra flute. Using spectral analysis software, the author compared the two systems (Standard and Bigio) in a test flute to find any significant differences in relative loudness and amplitude of recorded test note harmonics. A homemade impedance head mounted on the flute's embouchure plate was used to measure the pressure response of the flute sound wave produced in response to signal excitation (Schroeder chirp, 500 to 5000 Hz). Results showed that the Bigio unit was associated with stronger levels of amplitude and total power, higher amplitude in harmonics, and a slightly higher pressure response. The Bigio unit may be important for improving the timbre of the flute, but more work must be done to ensure that harmonic changes are more consistent, and to decide whether pressure differences make for an easier or harder blowing flute.

The relation of vocal emotions and gender to convey urgency of verbal auditory warnings

Abstract: An on-going study was designed to examine methods for improving aircrew reaction time to verbal auditory warnings. The "attention getting" of verbal auditory warnings that differed in both vocal style and gender was measured, while subjects were performing a visual tracking task. Overall, initial results are encouraging.

In-situ sound insulation measurement when a room is very absorptive

Abstract: The sensitivity of the ASTM E336 to absorption in either the source or receiving room and its effect on the number of microphones needed to sample the resulting field was studied. Nine microphone positions satisfying the ASTM E336 location requirements sampled the SPL. The apparent transmission loss (ATL) was measured in both directions between the three possible room pairs: horizontally separated by a partition wall, vertically separated by a floor, and diagonally where there was no common element. The results indicate that measurements in rooms having absorption typical of furnished multifamily dwellings are possible if the room volumes are adequately sampled.

Uncommon noise signatures in a wind tunnel

Abstract: An on-site investigation was undertaken to correct a resonant tone that was eventually traced to the main fan support structure. It was found that the trailing edge flow leaving the stator blades and impinging on the flat support vanes was the main cause of the tonal noise problem. The fan manufacturer was apprised of these findings and the support vanes were modified with additional ribs to change their natural frequencies. The intensity of the tonal noise reduced substantially and the control noise levels are within the allowable tolerance of 60 dBA at all speeds.