Lecture 2-Sound Power/Intensity Flashcards
What is energy radiation measured in?
Joules
rate of radiation of energy= power output (joules/sec or watts)
A nearfield loudspeaker in a recording studio may have a power rating of 60W and a Farfield loudspeaker in a small PA system may have a power rating of 1000W: why does it have to have a higher sound output than the other?
Distance of the listener from the sound source. In the free field, where sound encounters no boundaries or obstacles, sound from a point source spreads spherically and as sound travels further away from the source the area of the sphere over which it propagates increases.
The same sound intensity must spread over an increasing area suffering a loss of intensity when arriving at a listener positioned further away from the source.
What is the inverse square law?
The area of a sphere is 4pie r^2, the area of the sphere increases by four (2^2) when the distance between source and listener is doubled. Sound intensity at position L2 is reduced to 1/4. At L3 the distance between source and listener is tripled, the sphere has increased its area by 3^2. Sound intensity at position L3 is reduced to 1/9. In a free field the intensity of sound drops by 6 dB for each doubling of distance from the source.
What is the calculation for the inverse square law?
I (watts per metre square)=w / 4pie r^2
For every doubling of distance what’s is the drop in intensity?
6dB
What is the maximum intensity humans can endure/threshold of pain?
10 watt/m^2
What is the minimum intensity detectable by human ear?
10^-12 watt/m^2 or 1 picowatt
Why do you need to use a logarithmic scale instead of a linear scale when measuring loudness?
Equal jumps in perceived loudness do not correspond to equal jumps in intensity. Logarithmic scales don’t involve equal step sizes along the axis.
What is the threshold of hearing?
What is the threshold of discomfort/pain?
What is the reference level and calculation for loudness?
Threshold of hearing: 10^-12W/m^2
Threshold of discomfort/pain: 10W/m^2
Reference level 10^-12
Log10(10^-12/10^-12)=0
How is the BEL scale derived?
Log10(intensity measured/reference intensity)
Sound of whisper: Log10(10^-10/10^-12)=2
What is the decibel threshold of hearing and the threshold of pain?
Multiply by 10 range 0-130
threshold of hearing 0>
Threshold of pain 130>
How is the decibel scale derived?
10*Log10(intensity measured/ reference intensity)
E.g. 10log(10^-12/10^-12=10log(1)=0dB
An increase of how much is perceived as a doubling of loudness?
6-10dB
What is the Just Noticeable Difference (JND) of change in level of sound?
Around 1dB
In dubbing theatres what are loudspeaker systems calibrated to?
85dB(SPL)
