Acoustics Flashcards
What is the definition of sound
Vibrations that travel through the air or another medium and can be heard when they reach the ear
Definition of Noise
Sound that is unwanted by the recipient
How is sound created
Sound is a pressure wave that is created by a vibrating object. The vibrations set particles in the surrounding medium in vibrational motion, thus transporting energy through the medium
How do sound waves travel
In a longitudinal wave
What are the 2 parts of a longitudinal wave
Compressions - Air particles are compressed together, creating regions of high air pressure
Rarefactions - Air particles are spread apart, creating regions of low air pressure
What are the physical properties of sound
Frequency - Vibration rate (Hertz, Hz)
Sound Pressure - Vibration Amplitude (decibels, dB)
What levels of frequencies can be tolerated at greater sound pressure levels
Low-frequency noise can be tolerated at greater sound pressure levels than high-frequency noise
What are the main factors of room acoustics
- Volume, Shape, Surfaces & their size
-Position of noise barriers & absorbers
-Positioning of sound sources - Arrangement of audience
- Materials and their location
What are the ways that Sound can be received
- Direct Sound (no reflections)
- Reflective Sound (reverberation)
What is background noise
The total of all sounds within the room when the room is unoccupied
What is the signal to noise ratio
The signal level minus the background noise level
What is reverberation time
The time taken for sound to drop by 60dB after the sound has stopped
How is reverberation time affected by room size
Reverberation time increases with room size
Does the location of your seat in a classroom affect the sound that arrives at your ear?
The sound pressure level decreases 6dB for each time the distance from the source is doubled
What are the approaches that can be applied in noise control
- Control Noise at Source (e.g. use quieter equipment)
- Control noise along transmission path (e.g. use sound barriers)
- Control noise at receiver (e.g. use ear defenders)
What are the two types of sound transmission
- Airborne (sound generated in the air)
-Impact (sound generated in the structure)
What are reflection/absorption and transmission of sound all dependant on
The frequency of sound and the physical properties of wall
What makes a wall better at absorbing sound
The greater the mass of the wall, the better the sound absorption
What is the a lightweight panel in sound transmission
A lightweight panel is easily moved by the sound wave from the left: it can then easily move the air on the right hand side
What is a heavyweight panel in sound transmission
A heavyweight panel is harder to be moved by the sound: air on the right hand side does not move as much as the lightweight panel
What is the absorption coefficient of sound absorption coefficient
The proportion of sound absorbed by the surface compared to that which is reflected back into the room
Why do materials absorb different amounts of sounds at each frequency
Due to the natural vibration frequency of their fibres and the method of their construction
What way do stiff, dense materials absorb sound
Molecular Vibration
How are porous materials able to allow sound wave to quickly penetrate the material thickness
They have air ways
