Sound


Sound is a form of energy that causes vibrations of the air which the ear detects. Sound energy can be transferred through the air or through a solid object: 

  • Airborne sound travels through the air (eg: singing)
  • Impact sound travels through a structure (eg: Knocking on a door)
Sound Insulation
Sound or acoustic insulation is the reduction of sound energy transmitted into an adjoining air space. Sound insulation is important in buildings where large numbers of people live and/or work in close proximity, for example apartment buildings or hotels. In home design it is unusual to consider sound insulation as a requirement for ordinary houses. the only requirement for sound insulation stated in the current building regulations relates to the prevention of noise through the party wall of a semi-detached or terraced house through the floor of a dwelling where the space below is part of another dwelling.

The following minimum levels of sound insulation should be achieved:  
  • Walls - airborne sound - 45dB min. sound insulation value
  • Floors - airborne sound - 45dB min. sound insulation value. Impact sound - 62dB min. sound insulation value.
Sound Insulation Principles
1. Heaviness heavyweight structures (eg. concrete) with high mass transmit less sound energy than lightweight structures.
2. Completeness - Airtightness - airborne sound will travel through any gaps in the structure.
- Uniformity - sound will take the "path of least resistance". A small poorly insulated area can significantly reduce the performance of the whole structure (eg. when a window is slightly ajar the sound insulation of the whole wall drips dramatically.)
3. Flexibility - flexible materials (eg. quilted insulation) tend to absorb sound energy. The level of insulation provided by a structure (eg. plasterboard stud partition) can be affected by resonance and coincidence.
  • Resonance - if the natural frequency of the material from which the partition is constructed is the same as the frequency of the sound matches, the insulation performance of the partition drops.
  • Coincidence - if the frequency of the sound matches the frequency of the bending in the material, the insulation performance of the partition drops.
4. Isolation - Discontinues construction (eg. double/triple glazing) is effective in reducing sound transmission. Sound energy is lost when it travels from one medium to another. (eg. glass to air)

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