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This report explains the development of a sound measuring system for continuous monitoring of sound levels. Dedicated telephone lines are used for data transmission so that sound level data can be monitored at installations far from the area of concern. This allows the sound sensing equipment to be left unattended and thereby greatly reduces the manpower costs of operation. That predetermined data conditions can be detected when they occur and corrective action can be taken immediately at the data receiving installation further justifies the method used. Background information and general need for such a system are discussed. Growing public concern with noise is creating a demand for more and better sound measurement devices and for more control of unnecessary noises. For description, the system is divided into functional sections. The sections are described and design considerations are given in order of data flow starting with the sound sensing devise, or microphone, and ending with the warning system which alerts the operator when a predetermined signal level has been exceeded. Circuits to detect selected conditional of excess sound and to control the alarm to these conditions are included.

This thesis represents the development and evaluation of a theory for sound transmission analysis by sound intensimetry. In the context of this study sound transmission analysis is understood to embrace the following: (1) The measurement of sound reduction indices. (2) Diagnostic analysis of sound transmission through panels and structures. The sound intensity method is examined against the theoretical background of the classic two-room method which forms the basis of currently used international standards. The flanking problem, which is one of the principle limiting factors in the use of the classic method, is analyzed. The standard formulation of the intensity method is expanded to account for leakage error, boundary interference effects and calibration mismatch. It is shown that the commonly observed low-frequency discrepancy between intensity and classic method results is resolved by application of the Waterhouse correction. Sound absorption by the test object on the receiving side is shown to cause an error which increases with the flanking factor and with the fraction of the receiving room absorption located on the surface of the test object. Guidelines are developed for the assessment and control of absorption error in practical situations. Using the common mode rejection index as a performance rating for sound intensity meters, the measurement of sound transmission in reactive fields is investigated. Derivation of a formula for the reactivity near the surface of a transmitting panel surrounded by a flanking structure in a reverberant field, leads to the development of a theoretical framework and criteria for the planning and evaluation of test arrangements for sound transmission analysis. Guidelines are given for the calculation of minimum receiving room absorption and the microphone spacing required in practical situations. A study of the characteristic properties of sound intensity fields in diffuse and non-diffuse environments is used as a basis in formulating a new method of measuring directional diffusivity. Based on the relationship between reactivity and the degree of directional balance in a sound intensity field, this method involves spatial averaging of the pressure level and determination of the magnitude of the total intensity vector at the point under consideration. A direct-reading diffusivity meter has been developed and employed in assessing diffusivity in practical situations. The effect of a lack of directional diffusivity on the accuracy of sound transmission analysis in reactive fields is examined. Criteria for calculating minimum diffusivity requirements in the source and receiving room are developed and evaluated experimentally. / Thesis (Ph.D.)-University of Natal, 1985.

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The absolute measurement of acoustic particle velocity using Laser Doppler Anemometry (LDA) provides the basis for a method of microphone calibration. In this thesis, after the current standardized calibration method (called reciprocity) is explained, the application of LDA to the determination of sound pressure acting on a microphone is discussed. From a measurement of the output voltage for a given sound pressure, the sensitivity of the microphone can be calculated. In LDA, there are two different techniques for detecting and analysing the Doppler signal generated by acoustic particle motion: continuous detection followed by frequency or time domain analysis, and photon correlation. After a brief discussion of the theory of both methods, their application to measurements within a standing-wave tube is investigated. Velocity measurements extracted from Doppler signals are used to derive values of sound pressure, which are compared with probe microphone measurements. The continuous detection and photon correlation LDA systems are used to measure particle velocity amplitude in a standing wave for frequencies between 660 Hz and 4kHz and velocities between 1 mms⁻¹ and 18 mms⁻¹. LDA is applied to the measurement of microphone sensitivity. The frequency response of the probe microphone is characterized relative to the response of a reference microphone. From the frequency response information, the output voltage of the probe microphone, and the LDA derived sound pressure in a standing wave the sensitivity of the reference microphone is established. Using the continuous detection system, the microphone sensitivity is measured to within ±0.1 dB of the sensitivity obtained by reciprocity calibration for frequencies between 660 Hz and 2 kHz. Using the photon correlation system, the sensitivity is measured to within ±0.2 dB for the same frequency range. Initial measurements were performed in a free field environment, using the photon correlation system, to demonstrate the potential for further development of the LDA calibration technique.

The hospital sound environment is complex. Emergency Departments (EDs), in particular, have proven to be hectic work environments populated with diverse sound sources. Medical equipment, alarms, and communication events generate noise that can interfere with staff concentration and communication. In this study, sound measurements and analyses were conducted in six hospitals total: three civilian hospitals in Atlanta, Georgia and Dublin, Ohio, as well as three Washington, DC-area hospitals in the Military Health System (MHS). The equivalent, minimum, and maximum sound pressure levels were recorded over twenty-four hours in several locations in each ED, with shorter 15-30 minute measurements performed in other areas. Acoustic descriptors, such as spectral content, level distributions, and speech intelligibility were examined. The perception of these acoustic qualities by hospital staff was also evaluated through subjective surveys. It was found that noise levels in both work areas and patient rooms were excessive. Additionally, speech intelligibility measurements and survey results show that background noise presents a significant obstacle in effective communication between staff members and patients. Compared to previous studies, this study looks at a wider range of acoustic metrics and the corresponding perceptions of staff in order to form a more precise and accurate depiction of the ED sound environment.

Studier har visat att höga bullernivåer kan vara skadliga för såväl röst, hörsel och språkliginlärning som andra kognitiva förmågor. Höga ljudnivåer kan bidra till ett hyperfunktionelltröstbeteende som kan ge kroniska besvär. Barns röstorgan kan vara särskilt sårbara då de ännuinte är fullt utvecklade. På många förskolor är bullernivån hög och ogynnsam för både barn ochpersonal och därmed utgör de båda en riskgrupp för att utveckla röstbesvär och hörselskador.Föreliggande studie består av ljudnivåmätningar av två förskolors lokaler samtfokusgruppsintervjuer av 16 femåriga barn. Syftet var att kartlägga hur barnen upplever bulleroch kommunikation på förskola samt relatera det till uppmätta ljudnivåer. Studien ingår i ettstörre nordiskt projekt.Resultatet visar att barnen förefaller ha viss kunskap om bullrets påverkan på hörseln men intealls på rösten. Barnens utsagor speglar att de har viss kunskap om att buller försvårarkommunikation och att de föredrar lägre ljudnivåer. Barnen uttrycker även egna erfarenheter avatt det ibland är svårt att kommunicera på förskolorna. Resultatet av bullermätningarna indikerarockså detta. Utifrån föreliggande studies intervjuer framkommer följande tre teman och sexunderkategorier; egna upplevelser (kroppsliga, emotionella), miljöfaktorer (rumsliga, buller)samt strategier (röst, hörsel). Bullervärden mättes i samtliga rum både med och utan barn ochpersonal närvarande. Ljudnivåer förekom från 60 till 93 dB(A) med barn och personal i rummen.Bullernivåerna låg ofta över 70 dB(A) och det högsta uppmätta värdet var 93 dB(A) i lekrummetvid en gemensam fri lek. / Studies have shown that high levels of background noise are damaging on voice, hearing andlanguage learning skills but also affects other cognitive skills. High sound pressure can lead to ahyperfunctional and faulty voice use. This can cause chronic voice disorders. The voice organs inchildren may be particularly vulnerable since they are not yet fully developed. The noise level ishigh in many preschools and therefore both children and teachers are at risk for developing voicedisorders and hearing impairment.The study consists of sound pressure level measurements and focus group interviews of 16 fiveyear-old children in two different preschools. The purpose was to find out how five-year-oldchildren experience noise and communication in preschools and relate their opinions to themeasured sound pressure levels. The study is included in a bigger Nordic project.The result showed that the children seem to have some knowledge of the effects of noise onhearing but not at all of the effects on voice. The statements reflect that they seem to have someknowledge about negative effects of noise on communication. The children also express that theyprefer lower levels of background noise rather than high. The children expressed that they hadexperiences of occasionally having difficulties to communicate in their preschool due to highbackground noise. These statements are supported by the high levels of background noisemeasured in the study. Three themes and six categories were identified from the interviews, theywere: Own Experiences (Physical, Emotional), Environmental Factors (Spatial, Noise) andStrategies (Voice, Hearing).Sound pressure levels were measured in all rooms with and without the children and teacher’sattendance. With children and teachers present noise levels were ranging from 60 to 93 dB(A).The noise levels were frequently over 70 dB(A) and the highest noise value was 93 dB(A) in the playing room when free play occurred. / “How does it Work? Voice, Speech and Communication”