First it is important to understand how sound works.
A sound is generated by a vibrating object, for example vocal cords / drum skin or loud speaker cone. The sound leaves the object as a sound wave and travels away from the object.
Sound waves travel through air molecules and through objects, both air molecules and objects can affect the way sound waves travel.
Air can have a massive influence on sound waves: –
For example if play sound in a cold building or outside in the cold, the air molecules are able to move faster because the molecules are spread apart enable the sound wave to travel further. However if the room was hot or you were outside on a hot day, the air molecules are not able to move as fast as they have expanded limiting the distance in which the sound wave can travel.
This is one of the reasons why the sound can be heard further away and be bright and crisp when the air is cold and then change to muffled and quieter when the air is warm or hot.
Objects can also have a massive impact on sound waves: –
Just like sound waves can be slowed down by expanded air molecules, they can also be slowed do by objects. The denser the object the slower the sound wave can travel through that object.
There are many ways in which you can slow sound waves down, but we will discuss this more in acoustic advice.
Different Sound frequencies also act differently with air temperature and with objects: –
High frequencies require less energy to be produced, they are affected by air temperature and most objects because there sound waves are very short.
For example: – The higher the frequency the smaller the sound wave and the amount of energy required to produce the sound wave decreases. There is a considerable amount less energy to be absorbed by objects to have an effect on the sound wave. To the point were curtains can affect the way high frequency sound waves perform.
Lower frequencies require more energy to be produced, they are also less affected by air temperature and objects because there sound waves are much longer.
For example: – the lower the frequency the more energy they carry, the more energy will need to be absorbed to effect low frequencies. You will need a denser object to absorb a low frequency than you would for a high frequency.