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Helpful Resources | Acoustics

What is Acoustics?

Humans perceive sound through the sense of hearing. The scientific study of sound is called acoustics.



Sound insulation refers to the ability of a construction or building envelope to limit noise transmission through the building envelope.


Noise pollution is the excessive environmental noise that disrupts the activity or balance that a human hears.

 

Examples of noise

  • Noise entering the building from outside, eg industrial processes, traffic, trains, aircraft or animals
  • environmental noise emission from the building to surround areas
  • air conditioning or other plant noise within a unit
  • domestic applicance noise within a unit
  • room acoustic design for home entertainment systems
  • noise transfer within a unit

 

Recommended Types of Glass to dampen noise

To minimise unwanted noise that intrudes into our daily lives we need to evaluate all aspects of the building envelope

First you need to analyse the source of the unwanted noise and then take steps to choose the corect glass types to dampen the noise.

There are three types of glass that are used to help noise reduction:

  • Monolithic Glass (heat treated) - one piece of thick glass
  • Laminiated Glass - two pieces of glass with a middle layer of PVB fused together
  • Double Glazed Unit - two pieces of glass separated by an air space or some type of spacer or gas in a sealed unit
Monolithic Glass

Laminated Glass

Monolithic Glass

Cost effective method is thick mon olithic glass or laminated glass. Double glazing is normally more expensive.


Information on Speed & Sound


Speed or Velocity of Sound

Speed varies with the temperature of ambient air. Sound travels slower at higher altitudes or in cold environments.

Note: The difference between speed and velocity is that velocity usually includes the direction of travel.

The frequency of sound is the rate at which the waves pass a given point. It is also the rate at which a guitar string or a loud speaker vibrates. Frequency is also called the pitch of a sound. It is called the note in musical sounds.



Sound Waves

Sound is a wave which is created by vibrating objects (eg vocal chords) and transmitted through a medium (eg air) from one location to another. Through our ears (hearing sensory) we detect these sounds, whether it be someone talking, music or noise.

Sound Waves Travel

In other words, for sound to be generated and heard it must have a source, a medium through which to pass and a receiver.

As seen from the model below, sender (person talking) gets the message out to the other person through the channel/medium that carries the message but sometimes some type of interference, eg noise can cause distortion to the final message that can be unheard or misinterpreted.


Communication Model


Another definition of sound is vibrations or pressure changes in the air which are capable of being detected by the human ear.



Frequency

The number of times the wavelength occurs in one second. Measured in kilohertz (Khz) or cycles per second. The faster the sound source vibrates the higher the frequency.


Sound through vacuum

Sound is a mechanical wave which require a medium in order to transport their energy from one location to another.

Therefore sound waves cannot travel through a vacuum. An example, if a ringing bell was placed in a jar and the air was removed from the jar (no air) the sound of the ringing bell could no longer be heard. The reason is that there are no particles inside the jar to transport the disturbance through the vacuum.



What is a Decibel?

A decibel (dB) is the common measurement of sound level, ie loudness.

Threshold of hearing is assigned a sound level of 0 decibels (0dB). Example of sound pressure level measured in decibels.


Acoustic Sound Level

What is a STC?

SOUND TRANSMISSION CLASS (STC) OR WEIGHTED SOUND REDUCTION INDEX (Rw)

Sound Transmission Class (STC) and Weighted Sound Reduction Index (Rw) - measuring internal sound transmission (amount that will reduce noise) such as the human voice (high frequency). STC/Rw are made up of approximately 18 different frequencies and the ratings are determined from them.

Sound transmission through windows is governed by the same physical principles that affect walls, but practical noise measures are influenced by properties of glass and the characteristics of window assemblies. Increasing the glass thickness, for example, gives greater noise reduction at most frequencies, but the stiffness of glass limits the improvement, using multiple layers (secondary glazing) increases noise reduction at most frequencies, but this is dependent on the separation of the layers.

As with other building assemblies, transmission of sound through cracks may drastically reduce the effective noise reduction. Particularly for openable windows. Even windows with good weather sealing have reduced noise attenuation because of air leakage. To get optimum sound performance out of any product, eg internal or external wall, all gaps around joints and windows should be sealed.

Australian Building Code acoustics provisions are based on STC/Rw ratings

Glass & Noise

A 3mm single glazed window has a very low STC/Rw rating, and windows can let in considerable noise, open or closed. The potential sound reduction from a highly insulating wall can be substantially reduced by poor window design and installation.

Secondary glazing and laminated glass are both effective at reducing noise. The following table shows the percentage noise reduction compared to 3mm glass. Note that these percentage reductions are not the same as STC/Rw values



Noise Reduction Chart

Sound Transmission Control



For sound transmission control, the larger the air space, the better. If the air space between a double glazed unit is small (6 mm), the Sound Transmission Class (STC)/Weighted Sound Reduction Index (Rw) rating is the same (or can be lower) than that of a single pane of glass. This is because the air space acts as a spring, transferring vibrational energy efficiently from one layer of glass to the other.


In order to get a significant increase in STC/Rw, large air spaces between glazing units, from about 20 to 100 mm, is desirable.



For example,

  • double-glazing with two panes of 3mm glass with a l5mm air space has an STC rating of about 32;
  • with secondary glazing and a 50mm air space, the STC rating increases to 38;
  • and secondary glazing with a 100mm air space to 42.


Sound through a vacuum



For further information contact Trend Glass sales

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