Week 5 Flashcards
How is transport defined wrt noise?
Transport - source of noise which impacts life, health, and land value (externalities)
How is the Environmental Noise Directive (END) (Directive 2002/49/EC) enforced through the Environmental Noise (England) Regulations?
Defra is required to produce maps showing people’s exposure to the environmental noise every 5 years
Noise mapping informs action plans
The aim is to preserve environmental noise quality where it’s good
The public is informed on environmental noise and it’s effects
Define sound
A pressure wave which travels through air and is detected by ear
Surface vibration creates air pressure changes leading to pressure waves
Perceived sound consists of many pressure waves of varying characteristics (ie wavelength) and depends on human ear sensitivity
Define noise
A sound which is unpleasant, loud, and disturbs
What is amplitude ?
The magnitude of the change in pressure due to the sound wave
What is frequency?
Rate of vibrations per unit time (Hz)
Range of perception for young person 20-20,000 Hz
What is an octave ?
Interval between one frequency and double that frequency
Characterised by central frequency = 10002^n
Lower freq = f1=fc/sqrt(2)
Upper freq= f2=fcsqrt(2)
How is pressure defined ?
F/A [Pa]
What range of pressures does human hearing cover ?
2x10-5 Pa to 200 Pa
What is sound intensity ?
I [W/m2]
Rate energy is transferred by sound wave p unit area
I= (pressure)^2 / (density * speed of sound)
What is sound intensity level?
Sound intensity relative to hearing threshold
I0 = 1*10^-12 (Wm-2)
SIL (dB) = 10log10(I/I0)
What is sound pressure level?
Sound pressure relative to threshold of hearing
SIL(dB) = SPL(dB) (approx)
SPL(dB)= 10log10((p^2)/(p0^2))
P0= 2*10^-5 (N/m2)
How are SILs added ?
Solve for I for both sound intensities
Ie log10(x)=2 -> x= 10^2
Sum the intensities (sum I)
Solve for SIL with summer intensities
How do humans identify source of sound ?
Through having two ears which enables stereo hearing
What does perception of sound rely on?
The frequency of the source
Perception of sound not same as sound intensity/pressure level
How does weighting change the SIL and SPL?
Approximates sensitivity of human hearing
De-emphasises low and very high frequencies which risk hearing
Units dB(A)
Gain (positive or neg) in dB(A) added to SIL or SPL
If SPL or SIL is increased by 10dB and the frequency remains the same how does loudness change ?
It doubles
When SPL/SIL is increased by 10dB how does this affect loudness if frequency doesn’t change ?
Loudness doubles
What is the loudness ratio?
2^ (SPL/10)
How is p/p0 related to SPL?
P/p0 = 10 ^ (SPL/20)
How is I/I0 related to SPL?
I/I0 = 10^ (SPL/10)
What are the noise metrics in terms of distribution?
Lmax - max SPL in set time
L10 - SPL exceeded less than 10% in monitoring period
LAeq,T - A-weighted energy intensity averaged SIL over time. Assessed by taking average intensity and converted back to SIL
What are the noise metrics in terms of time periods ?
Lday - LAeq from 0700 to 1900
Levening - LAeq from 1900-2300
Lnight - LAeq from 2300-0700
Lden- LAeq from 0000-2400 with evening values weighted by +5dB and night by +10dB
What is the pyramid of effects for noise ?
Direct pathway: causes hearing loss, leads to stress
Indirect pathway: creates annoyance, leading to stress
Increase in risk factors: blood pressure, cardiac output, blood lipids etc
Increase leads to cardiovascular diseases: hypertension, heart disease,
Who regulates noise?
The International Civil Aviation Organisation ICAO
