Noise pollution

The sound waves we hear is the quickly changing pressure of the air in our ear.
In audible sound and noise we look at 20 and 20,000 times per second (i.e. at a frequency between 20Hz and 20kHz).
The sound wave moves trough the air with a speed of about 350m/sec or 1200km/h.


Measuring noise pollution
The human perception of the noise pollution is dependent of frequency and
the human perception of the noise pollution is logarithmic. This means that when we hear double the loudness the sound is about six times stronger.


Noise pollution in our home
I our home we can split the sound problems in two groups.


1: External intruding sound and noise pollution  
When the sound wave comes across a non compressible material a part of the wave will reflect, and a part will move the object and start a sound wave on the other site of the object.
Each type of material has a flexibility (spring effect), weight and internal moving resistance.
When the internal resistance is low, the weight and flexibility is high the material start to swing in a fixed frequency like a violin string, this frequency is the resonance of the object.
-trough the glass
A glass pane has a resonance frequency. From a sound outside the house we will hear a certain frequency very strong. This can be solved by using double glass with different thickness. (different resonance)
-trough the wall
The solution here is a heavy and soft real sound insulation on the wall site of the receiver or an isolation of the source of sound.
-trough a tiny hole of the wall
A sound damping material has to be heavy and soft for absorbing the energy of the sound. A tiny hole in the barrier will destroy your efforts.

2: Internal reflecting sound and noise pollution
A smooth wall acts like a mirror. A heavy and unequal wall does not reflect smoothly the sound wave, the sound is reflected on a different moment, in a different direction.