A. Airborne Sound

• Airborne sound is sound which travels through the air before reaching a partition.

• Sound which has been produce as wave in the air by a vibrating object such as a voices, loud speaker, radios, a musical instrument, traffic and aircraft noise.

• Sound waves which are produced in the air move out from the source can be spread around.

• When the sound energy arrives at the floor, ceiling or wall it might be reflected or absorbs. A sound wave may sometime experience multiple reflection or echoes in an enclosure before it is finally absorb.

• Once a sound had been absorbed by a structure it may be transmitted into a material.

• It is important to realize that a material which is good sound absorber may not necessarily be a good sound insulates.

The sound energy generated can be transferred in a number of ways as describe below:

1. Holes, cracks and openings

• Partition made from porous material have low sound reduction factors as sound energy travel very easy through the holes, cracks and openings.

• Therefore to prevent surface transmission, surface should be preferably sealed. Example, a brick partition may be sealed by painting to improve insulating properties.

• Door should not be ill fitted as it will allow the penetration of sound through cracks.

2. Vibrating partitions

• Another way of sound energy can be transmitted from one room to another room is when incident sound wave set entire partition vibrating like a drum.

• The intensity of the sound on the other side of the partition is reducing compare to the incident intensity.

• The amount of sound energy transmitted in this ways depends on 2 factors:

i. Mass per unit area of the wall

In general as the mass per unit area of the wall increase so does it insulating properties. This is because increasing in amount of energy would be needed to maintain the vibration of the wall.

ii. Continuity

A discontinuous partition which has gap between the two partition surfaces will have improved insulating properties.

The amount sound energy transmitted is reduced because it is more difficult to get to the surface of a far side of the partition to vibrate them.

c. Flanking Transmission

Paths for Sound Transmission between Adjacent Rooms

• Sound moves in variety paths, sometime indirectly. Example, through a corridor and window. The transmission of sound in the indirect path is called Flanking Transmission.

B. Structure Borne Sound

• Impact sound is sound which is generated on a partition.

• It occurs when a structural unit is vibrating due to impact such as by footstep, noisy pipes and vibrating machinery.

• A continuous vibration can be considered as a series of impact and impact sound is also termed structure-borne sound.

• The sound thus generated is transmitted through the structure of the building.

• The sound transmitted through the structure of the building its nuisance because it can be carry for a long distant in many directions.

• The best way to reduce structure borne sound:

1. Reduce the force of impact, hence reduce resulting vibration. This can be achieved by using thick resilient material on surface likely to suffer impact. Example floor can be carpeted.

2. Shock absorbing material can be place at the point of contact between the machine and the building.

3. The structure can also be made discontinuous to reduce the distance travel by the vibration.