[P1] BU - MODS 1-5

ACOUSTICS

is a branch of science that deals with the control and propagation of sound.

sound

- originates from a vibrating body. It is pressure have in an elastic medium. It is not restricted; it spreads outward from its source in all directions diminishing in intensity inversely as the square of the distance from the source increases

- these vibrations from the body come outward as compressions and rarefactions in the surrounding air

rarefaction

- the instantaneous, local reduction in density of a gas resulting from passage of a sound wave, or the region in which the density is reduced at some instant

- elongation of sound

- the vibration from a body are called frequencies

frequencies

- cycles per second (cps) or vibrations per second (vps) and the compressions and rarefactions are called sound waves

SOUND

- is a physical wave or simply a series of pressure vibrations

air

for airborne sound, the medium is _____

building materials

for structure borne sound, the medium is _____ such as concrete, steel, wood, glass or combinations of all these

20 to 20,000 Hz.

t is always assumed that the hearer has a pair of healthy young ears with the direction range

of _____

speed of velocity

1125 ft/sec at 20ºF, the velocity increases 1ft/sec for every 10º rise in temperature (in Fahrenheit)

frequency

- is the number of cycles of vibrations executed per second. Humans can hear sounds within the 40 vps to 16,000 vps range

molecular absorption

- a sound maybe covered up or absorbed by another sound. This phenomenon is called masking of sound and this is very useful in acoustics

- the sound masking is usually of lower frequency than the sound it masks

soporific effect

- that effect brought about by a low-steady sound

WAVELENGTH

distance between two crests of a sound wave

Longer wavelength

low frequency sounds have _____ than high frequency sounds.

WL

distance traveled by sound wave in one second/ the frequency of wave

reflected

when a sound wave in a room strikes a surface in a room, part of the energy is _____, part is absorbed by the surface and part is transmitted to the surface

reflects sound

A surface that is rigid, flat and smooth usually _____. The reflection of sound on a surface follows the behavior of reflected light, meaning that the angle of incidence is equal to the angle of reflection

diffraction of sound

One characteristic of sound is that, like light, it can bend around an obstruction known as "_____". Low frequency sounds are diffracted more easily than high frequency sounds

direct or original sound

- from the source and directly delivered to the hearer

reflected sound

- from all directions of the room

0.05

for a sound to be heard by a listener comfortably, the reflected sound must come to him not later than _____ of a second or in terms of distance, the direct sound and the path of the reflected sound should not exceed 57 ft

VELOCITY OF PROPAGATION

Sound travels at different velocities, depending upon the medium

344 m/sec or 1130 fps

On air, at sea level, sound velocity is _____, slow compared to light at 186,000 miles per second. Sound travels much faster in liquids and

solids than it does on air

SPEED OF SOUND

As sound travels much slower than the speed of light, the resulting defects in many rooms are echoes and reverberations

echoes

When the reflected sound, which reaches an observer, is delayed more than about 0.058 seconds relative to the direct sounds, they are distinguished as _____.

Reverberation

consist of successive reflections of sounds in a room, and since sound travels only about 1130 ft or 344 m/sec, these usually will be a rather long succession of these reflections before the sound dies away to inaudibility

architectural acoustics

Thus, the speed of sound plays a significant role in

RESONANCE

- Is what happen to a body when another vibrating body vibrates and initiates. The other body to vibrate in harmony with it

- Resonance can be useful to reinforce sounds at some specific frequencies

- This happens only however, if the resonating body or resonator has a dimension which is a multiple of the wavelength of the sound wave from the originating body

Low frequencies

_____ have more resonance than the high frequencies because low frequencies have longer wavelengths and therefore more multipliers to the dimensions of the room than high frequencies

100dB(A)

Unprotected exposure to soundpressure levels above _____ must be avoided where ever possible.

SOUND ABSORPTION

The sound phenomenon that happens to sound when it strikes a surface is that the sound is absorbed by the surface

heat energy

when sound wave strikes an absorbent surface, the sound waves through friction on the pores of the surface are transformed into _____

soft and porous surfaces

such as cork board, foam or styrofoam or any material which has this property like draperies on the walls and carpets on the floor

panel absorber

consisting of two layers of materials with an airspace between them. the outer layer being of porous type and the inner layer of solid background

cavity resonator

consisting of an enclosed body of air which is connected by a narrow passage with the space containing the sound waves.

sobius

this sounds absorption efficiency of a material is measured in terms of unit known as _____ in which one sabin means perfect absorption and 0 means no absorption

DECIBEL

measurement of the intensity of sound, abbreviated (db)

40db

limit for comfortable hearing

100-120db

can no longer be comfortable, that is painful to the ear

ECHO

reflected sound

REVERBERATION

is a series of echoes coming from the same source

REVERBERATION TIME

is the time in seconds that a reflected sound diminishes for the case by 60db after the original sound has stopped

TRANSIENT SOUND

is the term applied to the direct sound which if the originating body stops, vibrating also stops

DIFFUSION

when reflections are so large that the sound level becomes uniform throughout the room

SOUND FIELDS IN AN ENCLOSED SPACE

when a sound propagated in an enclosed space reaches a wall or other large (with respect to wavelength) obstruction, part is reflected and part is absorbed