Shrishail Kamble Acoustics is usually very broadly defined as "the science of sound." Hall Acoustics The shaping and equipping of an enclosed space to obtain the best possible conditions for faithful hearing of wanted sound and the direction and the reduction of unwanted sound.

Shrishail Kamble 3 Fog Art Museum

Shrishail Kamble 4 The Fog Art Museum hall of Harvard University, USA when built was found to be so defective acoustically. The lectures given in it were not intelligible to audience.

Shrishail Kamble 5 In 1911 Prof. Wallace C. Sabine, Professor of Physics, Harvard University, first of all scientifically tackled the problem of satisfactory speech and music in a hall..

Shrishail Kamble 6 Basic Requirements of Acoustically Good Hall  There should be adequate loudness in every part of the room, especially in remote seats.  The total quality of the speech and music must be unchanged.  For the sake of clarity, successive syllables must be clear and distinct.

Shrishail Kamble 7 Basic Requirements of Acoustically Good Hall  The sound energy should be uniformly distributed within the room.  The boundaries should be sufficiently sound proof to exclude extraneous noise. no Echelon effect  There should be no Echelon effect. no resonance  There should be no resonance within the building.

Shrishail Kamble 8 Basic Requirements of Acoustically Good Hall  The hall must be full of audience. reverberation time  The reverberation time should be quite proper (optimum). 1 sec – 2 sec for music & 0.5 sec – 1 sec for speech.

Shrishail Kamble The persistence of sound in a room due to multiple reflections, even when the source stops, is known as reverberation. The time interval between reflections is usually so short that distinct echoes are not heard. Reverberation Reverberation is a basic acoustic property of a room.

Shrishail Kamble Parallel reflective surfaces generates unwanted reverberation

Shrishail Kamble It can enrich speech and music in all areas -- or it can generate higher noise levels throughout a room. The duration to which sound persists is called as Reverberation Time. The reverberation time for a room is the time required for the intensity to drop to one millionth (10 -6 ) of its initial value.

Shrishail Kamble The reverberation time for a room is the time required for the intensity to drop by 60 decibels. If the initial intensity is I i then, final intensity is I f = I i dB i = 10 log (I i / I) dB f = 10 log (I f / I) dB i – dB f = 10 log (I i / I f ) = 10 log 10 6 = 10 x 6 = 60 dB

Shrishail Kamble Room Acoustics Reverberation

Shrishail Kamble Absorption Coefficient The absorption coefficient ‘a’ of material is defined as the ratio of the sound energy absorbed by the surface to that of the total sound energy incident on the surface. Unit for absorption coefficient is Open Window Unit (OWU).

Shrishail Kamble 15 Sabines’ Formula Prof. Wallace C. Sabine studied reverberation time & concluded; The reverberation time is, 1.Directly proportional to the volume of auditorium. 2.Inversely proportional to the areas of sound absorbing surfaces. 3.Inversely proportional to the total absorption. 4.Depends on the frequency of sound waves. Since, absorption coefficient increase with frequency for most of the materials.

Shrishail Kamble 16 where, K is the proportionality constant K = 0.165, when the dimensions are in metric units.. where, A = ∑as = a 1 S 1 + a 2 S 2 + a 3 S 3 + ………+ a n S n where, a 1, a 2, a 3,…………….., a n are the absorption coefficients of the materials in the hall. where, S 1, S 2, S 3,…………….., S n are the surface areas of the absorbing materials in the hall. OR

Shrishail Kamble 17 Factors affecting Architectural Hall & their Remedies:

Shrishail Kamble The persistence of sound in a room due to multiple reflections, even when the source stops, is known as reverberation. (a)Reverberation The duration to which sound persists is called as Reverberation Time.

Shrishail Kamble 1.By providing windows & ventilators. 2.Decorating the walls & windows by pictures & maps. 3.Using heavy curtains with folds. 4.Having full capacity of audience. 5.By covering the floor with carpets. 6.By lining walls with absorbing materials Viz. felt, fiber board, glass wool. (a)Remedy for reverberation

Shrishail Kamble Sufficient loudness at every point in the hall is an important factor for satisfactory hearing. (b)Adequate loudness Remedy 1.Using large sounding boards behind the speaker & facing the audience. 2.Low ceilings to reflect sound energy. 3.Use of equipments like loudspeakers.

Shrishail Kamble Reflection

Shrishail Kamble If there are focusing surfaces on the walls or ceilings of the hall, they produce concentration of sound into particular region. (c)Focusing due to walls & ceilings Remedy 1.There should be no curved surfaces. If present, it should be covered with absorbent material. 2.Ceiling should be low. 3.A parabolic reflected surface arrangement with the speaker at the focus.

Shrishail Kamble Sound reflection

Shrishail Kamble An echo is heard when direct & reflected sound waves coming from the same source, reach the listener with the time interval of 1/10 th sec or more. (d)Echoes

Shrishail Kamble (d) Remedy for echoes 1.Echoes may be avoided by covering the long distance walls and high ceiling with absorbent material.

Shrishail Kamble (e) Echelon effect A set of railings or any regular spacing of reflected surfaces may produce a musical note due to the regular succession of echoes of the original sound to the listener. Remedy 1.This type of surfaces should be avoided or covered with proper sound absorbing material.

Shrishail Kamble (f) Resonance Some times the window-panes, sections of the window portions and walls lacking in rigidity are throw into forced vibrations and create other sounds. Remedy 1.Such resonant vibrations should be suitably damped

Shrishail Kamble (g) Noise Any unwanted sound is Noise. Three types of noises: 1.Air-borne noise 2.Structure borne noise 3.Inside noise

Shrishail Kamble 1.Air-borne noise The noise which commonly reaches the hall from outside through open windows, doors and ventilators, is known as air-borne noise.

Shrishail Kamble Remedy for air-borne noise 1.By allotting proper places for doors & windows. 2.Arrangement of perfectly shutting doors. 3.Use of heavy glass in windows & ventilators. 4.By avoiding opening for pipes & ventilators.

Shrishail Kamble Site Selection for Sound Control Orientation

Shrishail Kamble Acoustical Zoning

Shrishail Kamble 2.Structure borne noise The noises which are conveyed through the structure of the building are known as structural noises. E.g. footsteps, drilling operating machinery, moving of furniture, etc.

Shrishail Kamble Structure borne sound Steel Frame Plumbing Pipe

Shrishail Kamble Remedy for structure borne noise 1.Using double walls with air space between them. 2.Mechanical equipments viz. refrigerators, lifts, fans produce vibration in structure. These vibrations can be checked by insulating the equipment properly. 3.By insulating the machinery.

Shrishail Kamble Isolation Of Equipment Low-end RTUs (roof top units) are typically loud.

Shrishail Kamble Isolation of Equipment

Shrishail Kamble 3.Inside noise The noise which are produced inside the hall or room in big offices are called as inside noise. They are produced due to machinery like A.C., type writers, etc. in the hall.

Shrishail Kamble Remedy for inside noise 1.Noise free air conditioners are to be used. 2.The machinery like typewriters should be placed on the sound absorbing materials. 3.The floor should be covered with carpet. 4.Any engine should be fitted on the floor with a layer of wool or felt between them.

Shrishail Kamble 40 THANK YOU