BUILDING UTILITIES 3 (ACOUSTICS MIDTERM)

ACOUSTICAL DEFECTS

1. Formation of Echoes 2. Reverberation 3. Sound foci 4. Dead Spots 5. Insufficient loudness 6. External noise 7. Sound Shadow 8. Resonance 9. Loudness 10.Noise

TYPES OF SOUND ABSORBERS

Acoustical foam panels White paintable acoustical wall panels Fabric wrapped panels Acoustical wall coverings Ceiling tiles Baffles and banners for ceiling Fiber glass blankets and roll

DESIGN STARTEGIES

Characteristic of Good Acoustics Factors affecting acoustics of a building Auditorium acoustic design considerations Acoustic Materials Acoustics For Different Types Of buildings

DEAD SPOTS

Dead Spots • This defect is an outcome of the formation of sound focii. • Because of high concentration of reflected sounds at sound foci, there is deficiency of reflected sounds at some other points. • These points are dead points where sound intensity is so low that it is insufficient for hearing.

FORMATION OF ECHOES

Echoes mainly produced due to the reflection of sound waves (mainly from the surface of walls, roofs, ceilings etc.) coming from some sources, reaches to the ear, just when direct sound wave is already heard and thus there is a repetition that is nothing but echoes. 1. Normally the formation of echoes (happens when the time lag between the two voices or sounds is about 1/17 of a second. And the reflecting surfaces are situated at a distance more than 15 meter. 2. If the reflected surface is curved with smooth surface this problem usually occurs. To minimizes this problem, select ion of proper geometry of auditorium and surface and also use the rough and porous material for the interior surface. Not all sound that hits matter is absorbed. Some of it is reflected. That means sound bounces off the solid matter the way a tennis ball bounces off a wall. Sound reflected back to its source is an echo. • An echo is produced when the reflected sound wave reaches the ear just when the original sound from the same source has been already heard. • Thus, there is repetition of sound. • The sensation of sound persists for 1/10th of a second after the source has ceased. • Thus, an echo must reach after 1/10th second of the direct sound • Multiple echoes may be heard when a sound is reflected from a number of reflecting surfaces placed suitably. • This defect can be removed by selecting proper shape of the hall. • And by providing rough and porous interior surfaces to disperse the energy of echoes. REMEDIES • This defect is avoided by selecting proper shape for the auditorium. Use of splayed side walls instead of parallel walls greatly reduces the problem and enhance the acoustical quality of the hall. • Echoes may be avoided by covering the opposite walls and high ceiling with absorptive material.

EXTERNAL NOISE

External noises from vehicles, traffic engines, factories, machines etc. may enter the hall either through the openings or even through walls and other structural elements having improper sound insulation.

Characteristic of Good Acoustics

Good distribution of sound to all the seats, which depends on proper shaping and finishes of all interior surfaces. Natural sound diffusion and envelopment. A sense of intimacy for the audience and a sense of ensemble for both performers and audience Proper reverberation times throughout all frequencies, which depend on room's volume and the total sound absorption of all materials. Freedom for the acoustical faults of echoes, flutter, and focus.

INTERNAL NOISE

Internal noise is the noise produced in the hall or office etc. They are produced by air conditioners, movement of people etc. REMEDIES Provided with enough sound absorbing materials. The gadgets or machinery should be placed on sound absorbent material. SOURCES OF INDOOR AND OUTDOOR NOISES . .

NOISE

Noise is unwanted sound which masks the satisfactory hearing of speech and music. There are mainly three types of noises that are to be minimized. They are i) air-borne noise, (ii) structure-borne noise and (iii) internal noise.

AIR BORNE NOISE (REMEDIES)

REMEDIES The building may be located on quite sites away from heavy traffic, marketplaces, railway stations, airports etc. They may be shaded from noise by interposing a buffer zone of trees, gardens etc.

STRUCTURE BORNE NOISE (REMEDIES)

REMEDIES The problem due to machinery and domestic appliances can be overcome by placing vibration isolators between machines and their supports. Cavity walls, compound walls may be used to increase the noise

RESONANCE (REMEDIES)

REMEDIES • The resonance may be avoided by fixing the window panels properly. any other vibrating object which may

EXTERNAL NOISE (REMEDIES)

REMEDIES • This defect can be removed by proper planning of the hall with respect to its surroundings and by proper sound insulation of external walls.

SOUND FOCI (REMEDIES)

REMEDIES • This defect can be removed by suitably placing diffusers and reflectors. • Right proportions of internal spaces. • Geometrical shape of roof helps in proper distribution of sound

FORMATION OF ECHOES (REMEDIES)

REMEDIES • This defect is avoided by selecting proper shape for the auditorium. Use of splayed side walls instead of parallel walls greatly reduces the problem and enhance the acoustical quality of the hall. • Echoes may be avoided by covering the opposite walls and high ceiling with absorptive material.

SOUND FOCI

Reflecting concave surfaces causes concentration of reflected sound waves at certain spot creating a sound of large intensity. These spots are called sound foci. • This defect can be removed: • Geometrical designed shapes of the interior faces, including ceilings. • Providing highly absorbent materials on focusing areas This defect is the outcome of formation of sound foci. • Because of high concentration of reflected sound at sound foci, there is deficiency of related sound at some other points. • These spots are known as dead spots where sound intensity is so low that it is insufficient for hearing.

RESONANCE

Resonance occurs due to the matching of frequency. if the window panels and sections of wooden portions have not been tightly fitted, they may start vibrating, thereby creating an extra sound in addition to the sound produced in the hall or room.

REVERBERATION

Reverberation means the prolonged reflection of sound from wall floor or roof of a hall: 1. When the sound is reflected back (some part of the sound is absorbed) resulting in formation of echoes, but sometimes this reflection of sound does not stop even the sound is died out. 2. The sound reflected back and forth against the walls, ceilings and floors for several times This is mainly when sound in closed spaces successively reflected by .

Factors affecting acoustics of a building

Reverberation time • When the reverberation time is too high, the sound produced by the speaker will persist for a long period of time. • Similarly, when the reverberation time is low, sound dies quickly and becomes inaudible in a short amount of time. • In order to improve the sound, reverberation time of a hall should be increased to an optimum value. Loudness • Reverberation time of a hall is directly proportional to loudness. • Low loudness results in existence of sound for a shorter period while high loudness results in existence of sound for a longer period. • Therefore, sound produced by the speaker should be within audible range. Echelon effect • Unwanted sounds are produced when people walk on staircase or floors or hard paved paths due to poor finishing of the floor surface, structural effects, etc. • The above-mentioned unwanted sound is termed as 'echelon effect'. Structure Borne sound • Sound waves generated inside a hall are known as structure-borne sound. • They are produced due to apparent motion of benches & footsteps & propagated through walls Ald floors. Echo • If the time interval between direct sound and reflected sound is less than 1/15 of a second, the reflected sound is helpful in increasing loudness. But if the time interval is less than that, then the sound arrives later and will cause confusion. Focusing due to Walls and Ceilings • Sound produced by speaker undergoes multiple reflections at ceilings and walls. • Reflected sounds from ceilings and walls should not be focused on particular point, rather it should be distributed throughout a hall. Generally, a plane surface reflects sound uniformly, but a curved surface does not. So, reflection of sound from a curved surface produces a harmful.

AIR BORNE NOISE

The noise that comes into building through air from distant sources is called air-borne noise. A part of it directly enters the hall through the open windows, doors or other openings while another part enters by transmission through walls and floors.

STRUCTURE BORNE NOISE

The noise which comes from impact sources on the structural extents of the building is known- as the structure-borne noise. It is directly transmitted to the building by vibrations in the structure. The common sources of this type of noise are footsteps, moving of furniture, operating machinery etc.

LOUDNESS

The uniform distribution of loudness in a hall or a room is an important factor for satisfactory hearing. sometimes, the loudness may get reduced due to excess of sound- absorbing materials in a hall or a room.

Sound Absorbers

These sound absorbing acoustical panels and soundproofing materials are used to eliminate sound reflections to improve speech intelligibility, reduce standing waves and prevent comb filtering. A wide variety of materials can be applied to walls and ceilings depending on your application and environment. These materials vary in thickness and in shape to achieve different absorption ratings depending on the specific sound requirements.

NOISE CONTROL

This involves the following activities: The control of air-borne noise through the insulation of sound or the shutting-out of unwanted sounds from the outside. This requires a study of the sound insulating values of walls, partitions, doors and windows and a study of the ventilating systems to provide a basis for the reduction of the transfer of unwanted sound from one room to another. The control of structure-borne noises through the isolation of machines from the rooms or the building's structure.

SOUND SHADOW

• An acoustic shadow or sound shadow is an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers.

LOUDNESS (REMEDIES)

• If the loudness of sound is not adequate, the loudness can be increased by adopting the following methods • by using suitable absorbent at place where noise is high, as a result, the distribution of loud by constructing low ceiling for the reflection of sound towards the listener. • by using large sounding boards behind the speaker and facing the audience. • by using may become uniform. • by using public address system like loudspeakers.

INSUFFICIENT LOUDNESS

•the sound waves should be properly reflected, and uniform ally spread all over the interior part of the auditorium. • But due to the lack of sound reflecting flat surfaces near the sound source or stage and excessive absorption of sound in the hall resulting the defect of insufficient loudness. This defect can be minimized by providing hard surface near the stage and absorbent material should be provided as per the requirements. Also, the location of the loudspeakers should be adjusted. So that there is no dead spots and sound foci. Also, use of adequate no of windows or door openings