SOUND PROPAGATION IN LISTENING PLACES- OUTDOORS AND INDOORS

The Propagation of sound Sound is a sequence of waves of pressure which propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). During their propagation, waves can be reflected, refracted, or attentuated by the medium. The purpose of this experiment is to examine what effect the characteristics of the medium have on sound.

All media have three properties which affect the behavior of sound propagation: 1. A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium. 2. The motion of the medium itself, e.g., wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported. 3. The viscosity of the medium. This determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible. What happens when sound is propagating through a medium which does not have constant properties? For example, when sound speed increases with height? Sound waves are refracted. They can be focused or dispersed, thus increasing or decreasing sound levels, precisely as an optical lens increases or decreases light intensity. One way that the propagation of sound can be represented is by the motion of wavefronts-- lines of constant pressure that move with time. Another way is to hypothetically mark a point on a wavefront and follow the trajectory of that point over time. This latter approach is called ray-tracing and shows most clearly how sound is refracted

Outdoor Sound Propagation Introduction Outdoor sound propagation or atmospheric sound propagation is of special interest in environmental acoustics which is concerned with the control of sound and vibrations in an outdoor environment. Outdoor sound propagation is affected by spreading, absorption, ground configuration, terrain profile, obstacles, pressure, wind, turbulence, temperature, humidity, etc. The subjects covered in this page are speed of sound in air, decibel scales, spreading losses, attenuation by atmospheric absorption, attenuation over the ground, refraction, diffraction and sound reduction examples.

Outdoor Sound Propagation The transmission of sound in a free –space environment involves the fall-off of sound to 25% of its intensity ,for every doubling of distance. A further decrease in sound energy is evident in an outdoor facility because of the sound absorption by the audience as sound travels directly over people’s heads. The well-known Greek and Roman outdoor theaters countered this problem by arranging the audience in steeply tiered fashion and by arranging them as close to the performance as possible, reducing the distance sound was required to travel and ensuring direct line-of-sight transmission from the performers to all members of the audience without much audience absorption.

Greek and Roman outdoor theaters

AMPHITHEATER DESIGN A good deal of listening occurs outdoors with no sound – containing enclosure surrounding the audience. Except in the most small-scale and intimate of settings, electronic sound reinforcement is used to supplement the live sound. The audience ma number in tens of thousands, it may be seated on flat or gently sloped lawns ,and ambient noise from traffic and other sources may be present. Such condition call for a concert enclosure for symphony orchestras , and an audience-coverage sound system.

Propagation of Sound Indoors Sound and noise in a room will reach the receiver as direct and reverberant sound.

Commentaire de Concert & opera halls : how they sound : The music is only as good as the hall you play or hear it in -- this book tells you why, for both music afficionados and acoustical design professionals. In the opening chapters, Beranek presents a fascinating look at the ways in which the acoustics of concert halls affect composers, musicians, and listeners. From interviews with musicians and music critics he places many of the world's renowned halls into categories of acoustical excellence. Chapter six, more than half the book (348 pages), is devoted to descriptions, photographs, and drawings of 66 concert halls and 10 opera houses. In the remaining chapters the shape, size, surface arrangements, materials, balconies, boxes, seats, and suspended ceilings in those halls are related to the categorizations by the experts, thus offering new direction to architectural and acoustical design. Leo Beranek has consulted on the acoustical design of many concert halls around the world and at present is the acoustical design consultant for the Tokyo Opera City/New National Theatre. `No one has done more to unlock for musicians the scientific mysteries of acoustics and for acousticians an appreciation of the aesthetic experience of musicians and listeners.' Philip Gossett, Professor of Music, University of Chicago. `It deserves to be in every school of music, architecture and science, with every musician and music lover.' Chrisopher Jaffe, Acoustical Consultant. `... essential reading for the musicians who perform in these halls, for music lovers, music critics, architects, impresarios, and for building committees.' Russell Johnson, Acoustical and Theatre Consultant. FEATURES : Author is an award-winning, internationally renowned acoustics consultant and author - he has also consulted on the acoustical design of many halls. 76 halls presented with 203 architectural drawings and 152 photos. Appendices provide modern acoustical data on 80 concert and opera halls READERSHIP : Musicians and concert-goers, concert hall managers, recording and audio engineers, acousticians.

opera halls

opera halls

REVERBERATION Reverberation is the persistence of sound in a particular space after the original sound is removed.[1] A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air.[2] This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. The length of this sound decay, or reverberation time, receives special consideration in the architectural design of large chambers, which need to have specific reverberation times to achieve optimum performance for their intended activity.[3] In comparison to a distinct echo that is 50 to 100 ms after the initial sound, reverberation is many thousands of echoes that arrive in very quick succession (.01 – 1 ms between echoes). As time passes, the volume of the many echoes is reduced until the echoes cannot be heard at all.

DON BY : RUWAYA SULIEMAN ALI AL SARKHI ID: 15134807 submitted to Dr DON BY : RUWAYA SULIEMAN ALI AL SARKHI ID: 15134807 submitted to Dr . NOOR HANITA