1 accoustics

Architectural Acoustics

is the art and technique of designing spaces, structures and mechanical systems to meet hearing needs

Architectural Acoustics

The art and science of designing a room or building that insures both comfort and communications, and provide special features as to purpose and use of the building

1.To control echoes

2.To reduce sound

3.To isolate noise

three main objectives for acoustics in buildings

Sound

1. The oscillation in pressure of the atmosphere which is capable of being detected by the human ear.

2. Form of energy propagated in waves which continues to subsist until filtered through a material turning into heat by friction.

3. The sensation produced through the ear resulting from fluctuations in the pressure of the air.

1. Source of sound

2. Medium or Transmission Path

3. Receiver

The nature of sound, in order to be heard, requires the following elements

transducer

often used as a generic term for devices used in converting some form of energy into sound such as loudspeakers and microphones

Source of Sound

normally a vibrating body, which converts some other form of energy into vibration. The source can be made quieter.

Transmission Path

is any substance that allows the vibration to be transmitted in the form of a wave motion.

Airborne Sounds

sounds that are transmitted by air.

Structure borne Sounds

sounds that are transmitted through solid bodies

Receiver

pertains with the human ear.

1. Music – sounds organized to have melody, rhythm, harmony and dynamics.

2. Speech – to express with the voice. Music and Speech can be classified as ordered sounds since they are integrated.

3. Noise – sound, especially, of the loud and harsh kind. Noise is classified as disordered sound, as in a street noise.

Types of Sound

Sound waves

e longitudinal wave motion with which sound energy travels through a medium.

Cycle – full circuit by the particle.

2. Frequency – number of complete cycles per second measured in Hertz (Hz).

3. Amplitude – maximum displacement of a particle to either side of its normal position during vibration. 4. Period – the time required for one complete vibration, measured in seconds per cycle

Sound waves

Significance of Room Acoustics

-Direct Sound

-Reverberant Sound (reflections)

-Useful and harmful reflections

-Sound attenuation and absorption,

diffusion

Fanshape good for theatre

Echoes

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

Reverberation

is the persistence of sound in the enclosed space, after the source of sound has stopped

Prolonged Reverberation

due to large amounts of highly reflective surfaces and/or to large volume of space which will take considerable time for reflected sound to die out.

effect is blurring which is harmful to both speech and music.

reverberation time

The time during which the sound persists

Reverberation time is influenced by:

a.Volume of the room

b. Sound absorbing qualities of the room’s surfaces

c. Number of people and furniture in the room

Flutter Echoes

a rapid but repetitive succession of sounds caused by highly reflective parallel surfaces (wall to wall, or ceiling to floor). Flutter is often heard as a high frequency ringing or buzzing

Undue Focused Soun

caused by concave surfaces which causes sound to converge at certain points with resulting loss of energy in other parts of the room

angle of incidence

this applies when Sound wavelength is adequately smaller than the dimensions of the object causing the reflection The reflecting surface is even (not sound scattering) and hard (not sound absorbing

Resonance

the emphasis of sound energy at a particular frequency

External Noise

vehicles, traffic engines, factories, machines etc.

Raked seating

refers to seating which is positioned

on an upwards slope away from the stage, in order to

give those in the audience at the back a better view

than if the seats were all on the same level.

Why 60 dB?

decibel measurememt is based on a logarithmic scale

Noise

to unwanted, annoying, or discordant sounds as noise.

Noise from outside of a space can be controlled in the following ways:

Isolate the noise at its source.

• Locate noisy areas as far away as possible from quiet areas.

• Reduce the transmission of sound from one space to another.

Sound behaves within a space

Reflected, Transmitted, Absorbed

Noise reduction

refers to the perceived

difference in sound levels between two

enclosed spaces.

Noise reduction

depends on the following:

1.absorptive qualities of the receiving space

2. Transmission loss

3. The level of masking or background

   sound,

Transmission loss (TL)

measure of

the performance of a building material

or construction assembly in

preventing the transmission of

airborne sound.

NOISE REDUCTION

Background or ambient sound from

both exterior and interior sources is

normally present in an environment.

white noise

A type of background sound sometimes deliberately introduced into a

space to mask or obliterate unwanted

sound.

THE ABC’s of acoustic design

Absorb, Block, Cover