Acoustic Flashcards
What are the two main types of sound waves?
Longitudinal waves: Particles vibrate parallel to wave propagation.
Transverse waves: Particles vibrate perpendicular to wave propagation (common in solids)
What is sound intensity, and how is it measured?
Sound intensity is the power per unit area carried by a sound wave, measured in W/m2
What is the relationship between sound intensity and distance in free fields?
Sound intensity decreases proportionally to the square of the distance from the source (1/r2) in a free field
Define the decibel (dB) scale.
The decibel scale is a logarithmic measure of sound intensity relative to a reference intensity (𝐼0=10 ^−12W/m 2) I=W/A
What is the formula for sound pressure level (SPL)?
What is a free field in acoustics?
A free field is an environment without obstructions, where sound propagates spherically from the source
Define directivity factor (Q) and directivity index (DI).
Directivity factor (
𝑄
Q): The ratio of the intensity of a source in a specific direction to the intensity in all directions.
Directivity index (DI): DI=10log 10(Q)
How is sound pressure level (SPL) affected by distance doubling in a free field?
SPL decreases by 6 dB for every doubling of distance from the sound source
What is the difference between sound power level and sound pressure level?
Sound power level: The total acoustic energy emitted by a source, measured in dB.
Sound pressure level: The pressure variation caused by sound at a specific location, also in dB
What is the typical range of frequencies audible to humans?
Humans can hear frequencies ranging from 20 Hz to 20 kHz
What are the units of sound energy density or sound density?
Sound energy density is measured in J/m3
What is a decibel scale’s reference intensity?
The reference intensity is 𝐼0=10 ^−12 W/m2, corresponding to the threshold of human hearing
What are the three main acoustic parameters for evaluating sound fields?
Sound intensity.
Sound pressure level (SPL).
Reverberation time
What is the formula for sound intensity?
I= P/A, where I is the intensity (𝑊/𝑚2), P is the power (W), and A is the area (𝑚2)
What is the relationship between frequency (𝑓), wavelength (𝜆), and the speed of sound (𝑣)?
λ= v/f, where 𝜆 is the wavelength, v is the speed of sound, and f is the frequency
What is the formula for sound power level (𝐿𝑤)?
L w=10log 10(W/W0), where 𝑊 is the sound power, and 𝑊0=10^−12𝑊, is the reference
How is the sound pressure level (𝐿𝑝) related to sound power level (𝐿𝑤) in free fields?
What is the formula for sound intensity level (𝐿𝐼)?
What is the relationship between sound pressure (𝑝) and sound intensity (𝐼)?
How do you calculate the total sound pressure level for multiple sources?
How do you calculate the sound energy density (w)?
What is reverberation time (T 60)?
Reverberation time is the time required for sound pressure to decay by 60 dB after the sound source stops
What is Sabine’s formula for reverberation time?
Define porous materials in acoustics.
Porous materials absorb sound by converting acoustic energy into heat through friction and viscous losses in their pores
What is a Helmholtz resonator, and how does it work?
A Helmholtz resonator absorbs sound at specific frequencies using a cavity and neck. Sound energy vibrates the air mass in the neck, converting it into heat
What is the formula for the resonance frequency of a Helmholtz resonator?
What is the role of vibrating panels in sound absorption?
Vibrating panels absorb sound by converting acoustic energy into vibrational energy, which is then dissipated as heat
What is the formula for the resonance frequency of a vibrating panel?
What is the sound reduction index (R)?
What is the mass law in sound insulation?
The mass law states that sound insulation increases by 6 dB each time the mass of a wall or barrier is doubled
What is the apparent sound reduction index (R′)?
includes the influence of flanking transmissions, representing the actual sound insulation performance in a real setting
What is the formula for the total absorption area (A) of a room?
How does temperature affect sound absorption in air?
Higher temperatures increase air absorption due to enhanced molecular activity, especially at higher frequencies
What is the formula for the sound energy density (w) in a diffuse field?
What is critical distance in a room?
The critical distance is the point where the direct sound level equals the reverberant sound level
What is the formula for early-to-late arriving sound energy ratio (C 50)?
