Showing papers in "Canadian Acoustics in 1999"

Measurement of underwater sound intensity vector

Abstract: Localization of underwater sound sources and characterization of ambient noise fields can be achieved through measurement of the sound intensity vector. To evaluate this concept, a passive hydrophone array called SIRA (Sound Intensity Receiver Array) has been developed for measurement of underwater sound intensity in the frequency range 100 to 6000 Hz. The array is composed of three pairs of omni-directional hydrophones with the pairs aligned along orthogonal axes. The intensity is the time average of the product of instantaneous acoustic pressure and particle velocity. The instantaneous pressure is the average of the pressures measured by a hydrophone pair and the velocity is derived from the pressure gradient. Each hydrophone pair provides one of the components of the three dimensional intensity vector.

Canadian Standards Association activity in acoustics

Abstract: This article gives an overview of Canadian Standards activities in Canada, especially those of the Canadian Standards Association. They currently have 15 Acoustics Standards and two more with significant acoustics content. Two committees and a variety of subcommittees involving many Canadian acousticians and industry representatives write and review these standards for the Acoustics community. An overview is given of the main activities and future directions of these groups

Reverberation in gymnasia

Abstract: Gymnasia for public use are constructed and renovated on a regular basis, but the acoustical results are not always satisfactory or consistent. This paper examines this situation by presenting and discussing two case studies. In the first study, measurements of reverberation inside five public school gymnasia were carried out in the Mississauga area. The gymnasia were all geometrically alike, and had been constructed from typical building materials. Four of the gymnasia had been acoustically treated and were considered by the teaching staff of each to provide an adequate acoustical environment for typical activities. The remaining gymnasium was acoustically untreated, and its acoustic environment was considered by the staff to seriously impede its use. A brief literature review conducted to determine criteria specific to gymnasia revealed a notable lack of published information, both in terms of the traditional descriptor, the reverberation time (RT60), and in terms of more recently developed descriptors based on early/late arrival ratios. The measurement results and the subjective opinions expressed by each school's staff were used to determine reverberation criteria for a gymnasium, and to investigate the effectiveness of typical control measures. A second similar case study is presented. The results are discussed in terms of the relevance of various descriptors and potential building code implications

The current state of quantifying receptor annoyance related to low frequency noise in the environment

Abstract: Environmental noise from energy industry facilities in Alberta is regulated by the Alberta Energy and Utilities Board (EUB), as described in the Noise Control Directive, ID 99-8. ID 99-8 is the fourth edition of a comprehensive policy and guide, which has adopted A-weighted energy equivalent sound levels (L A eq) as the measurement system with sound pressure level criterion for a receptor location. With the receptor being some distance from the energy industry noise source, the high and mid-frequency components can dissipate or be absorbed by air and ground conditions, leaving mostly low frequency noise. Consequently, A-weighted measurements do not reflect the full annoyance potential of the remaining industrial noise. This paper examines the current state of research, begun by the EUB in 1995, to quantify potential receptor annoyance and meet the current noise control directive's technical approach.

Quelques propos sur le logarithme et le decibel

Abstract: It is very trite and classical to use decibels in acoustics, but when one looks in detail this definition may call us for several historical and methodological points, and more may render us puzzled. All of this because decibels are based upon logarithm function in order to define levels from adimensional ratios, and because there are many different ways in order to explain the presence of logarithm. The paper gives a short recall of logarithm properties and investigate the mean reasons, in mathematical and physical fields, in human and environmental sciences also. The conclusion is rather severe about the revelancy of Fechner law in Psychophysics, while very pregnant in decibels and levels definition.

Subjective evaluation of different error correction schemes for application with a 900 MHz frequency hopper communication system

Abstract: This paper presents an analysis of subjective tests conducted with a 900 MHz frequency hopper. The primary purpose of such a study is to evaluate the listeners' response to radio channel interference causing loss of speech data. The pre-testing phase determined the users' preference for a 32 kbits/s Adaptive Delta Pulse Code Modulation (ADPCM) system. The three main tests performed determined the parameters of the error correction schemes most preferred by the listeners. The purpose of the tests performed was three-fold: to determine the type of correction scheme preferred by the listeners, to subjectively evaluate the performance of the preferred correction scheme, and to determine the response of the listeners to different interference scenarios. Results from the subjective testing performed are presented and analyzed in this report.