Topic Five - Amplitude, Power, Intensity, Pressure and Decibels Flashcards
What is the difference between power and intensity?*
Describe the inverse square law*
The inverse square law describes how sound intensity decreases as a sound wave spreads outward from its source.
Specifically, intensity is inversely proportional to the square of the distance from the source.
For example, as the distance from the source doubles, the intensity is reduced by 1/4.
The formula is:
intensity = power/4π²
or
intensity = 1/distance²???
Describe the relationship between pressure and intensity*
Intensity is proportional to the square of pressure
Intensity and pressure can be calculated through the following equations:
Intensity = pressure²/characteristic impedance
Pressure = √ intensity??????
List the different ways we can measure amplitude and when they may be used*
- Peak measurement (p)
- This is the value taken from the midline (0) to the top/peak of the wave
- Useful to describe sine waves - Peak-to-peak (pp)
- This is the value of the highest peak and the lowest peak
- Useful to describe sine waves - Root Mean Squared (RMS)
- We can not take an overall average of a wave as the numbers will cancel out and equal zero, RMS is a way to calculate the power of a wave
- Not strongly affected by a single unusual point
- Good for complex waves
- Negative values don’t cancel positive values as they are squared.
What reference does dB SPL use?*
20 Micro Pascals
What is power?
It is the rate at which work is done, or energy is transferred.
It is the expression of acoustic energy emanating from a source.
It is measured in watts, where 1 watt = 1 joule per seconcd
Does power vary depending on where you measure it?
No
What is intensity?
Intensity is the combination of power and the distance from the source.
Intensity is the power per unit area (W/m²)
Does intensity vary depending from where you measure it?
Yes, the further away from the source, the lower the intensity.
What is pressure?
Pressure is the force per unit area
Pressure = force/area
How can you use the inverse square law to calculate pressure?
Pressure is inversely proportional to the distance from the source
Pressure ∝1/r
How do you calculate the root mean squared?
- Multiple the wave form by itself (squaring). This is called rectification.
- Take the mean of all the positive values
- Take the square root of this mean.
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