acoustics

Acoustics ( Science of Sound)

acoustics treatments can be defined in to four categeories

1. Absorbers
2. Free Standing Devices
3. Diffusers
4. Resonators

THUMB RULES

1. 20 dB = one order of magnitude – 20 Log10 (10)
2. 10 dB = half an order of magnitude – 20 Log (3.16)
3. 6 dB = doubling of pressure – 20 Log10 (2)
4. 94 dB = 1 Pa.

SPEED OF SOUND

The speed of sound in air is around 768 mi/hr (1,125 ft/sec, 343m/sec), or about 5 seconds per mile, or 3 seconds per kilometer.
 In water the speed is 1,433 m/s. speed of sound at sea level is 340.29 m / s.
The speed of sound in any medium is dependent upon the coefficient of stiffness


SOLIDS:-

1. Aluminum, rolled - 6420 m/s
2. Gold, hard - 3240 m/s
3. Iron - 5960 m/s
4. Steel - 5960 m/s
5. Glass, heavy silicate flint - 3980 m/s
6. Rubber - 1600 m/s

HUMAN BODY:-

Soft Tissues - 1540 m/s
Brain - 1541 m/s
Liver - 1549 m/s
Kidney - 1561 m/s 
Blood - 1570 m/s
Muscle - 1585 m/s
Lens of Eye - 1620 m/s
Skull Bone - 4080 m/s
Water - 1540 m/s

difference between echo & reverbaration:-

ECHO:-

it will be defined in terms of mechanical waves.it wiil be applied to radio,ultrasound &mechnanical waves.when the sound bounce back or reflected from any
hard surface it ia known as echo. The echo can create a secondary echo by bouncing off another wall.
The echo can be used to determine the distance of a reflecting object such as a large building or a mountain, if the reflecting object is far away the echo can not be
defined properly.

REVERBERATION:-

it is similar to echo.it will be produced by overlapping mulitiple echos.Reverberation is usually experienced in closed spaces with multiple reflecting objects.

STC AND NRC & SAC:-

The Noise Reduction Coefficient (NRC) is a scalar representation of the amount of sound energy absorbed upon striking a particular surface.
 An NRC of 0 indicates perfect reflection; an NRC of 1 indicates perfect absorption. Acoustical materials manufacturers often report NRC values higher than 1.0 due to the way the number is calculated in a laboratory. 
A test material's area does not include the sides of the panel (which are exposed to the test chamber) which vary due to its thickness. A certain percentage of the sound will be absorbed by the side of the panel due to diffraction effects. 
Sound Transmission Class (STC) is an integer rating of how well a building partition attenuates airborne sound.it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations
The sound absorption coefficient indicates how much of the sound is absorbed in the actual material.

Noise absorption is one of those words/phrases that take on many levels and meanings. Noise absorption does typically refer to the absorbent type materials that one uses on ceilings, walls and floors to reduce the noise reverberation (which is sound bouncing off surfaces). 
However the technical term to compare apples to apples and STC to STC is actually referred to as NRC. NRC = Noise Reduction Coefficient.NRC is representation of the amount of sound energy which is absorbed while striking a particular surface or material. 
For example NRC of 0 means ideal reflection. NRC of 1 indicates perfect absorption.You’ll note the NRC variable on a frequency chart which typically is 250 Hz, 500 Hz, 1000 Hz and 2000 Hz which general encompass fundamental frequencies of typical human speech. 
NRC essentially simplifies the quantification of how a surface will absorb human speech. The best materials for improving speech intelligibility and absorbing these sounds are, noise absorption products (bringing us in full circle to how the term is often used as a less technical reference to NRC – Noise Reduction Coefficient.
As to which is more important to people…that is a question that requires information about the acoustic problem trying to be corrected. In general speech / human voice are important for application such as churches, office settings, corporate, retail, telemarketing scenarios. 
You’re trying to improve things like worker productivity and customer experience through improving acoustics – speech intelligibility, reduction of reverberation, echo and other such problems. This is where NRC is most likely a priority.
STC is a priority in industrial settings where you’re attempting to block a noise sound source (equipment in plants, noisy facilities, manufacturing, warehousing etc). Most people looking for this are preventing sound from transmitting from the source and/or preventing the sound from travelling into neighboring spaces, office / work areas etc.
 STC is also synonymous with OSHA regulations and the Health and Safety of workers and constant exposure to particular decibel levels can create health problems.
All Noise Control – Noise Control & Soundproofing Specialists.
 useful WEB SITE:- www.AllNoiseControl.com

sound absorption of different materials:-

1. Acoustic tiles                   0.4 - 0.8
2. Brickwork, painted                   0.01 - 0.02
3. Brickwork, unpainted                   0.02 - 0.05
4. Cork sheet, 6 mm                   0.1 - 0.2
5. Fiberboard on battens,                          0.3 - 0.4
         12 mm -
6. Hardwood -                   0.3
7. Mineral wool, 100 mm -                   0.65
8. Persons, each -                   2.0 - 5.0
9. Snow -                   0.75
10. Plywood panel, 3 mm -                   0.01 - 0.02
11. Plaster walls -                   0.01 - 0.03
12. Rubber sheet, 6 mm porous -    0.1 - 0.2
13. Wood wool cement on                            0.6 - 0.07
         battens, 25 mm


Posted by:  
Swaroop Bapat
(Founder)
The Interior Master