2 Acoustics Quiz: Sound Absorption Principles

A number between 0 and 1 that quantifies how much sound energy is absorbed by a surface.

A surface that absorbs most of the sound energy that hits it.

A surface that reflects most of the sound energy that hits it.

The higher the absorption coefficient, the more sound is absorbed or transmitted, meaning less sound is reflected.

An open window has an absorption coefficient of 1.00, meaning it absorbs all sound energy and reflects none.

A perfect reflector, like a smooth, hard surface, has an absorption coefficient of 0.00, meaning it reflects all sound energy.

Materials like marble, with low absorption, reflect most of the sound, while materials like ceiling tiles, with high absorption, absorb most of the sound.

Different materials have varying absorption coefficients across different frequencies.

A material with unconnected pores is not effective at absorbing sound.

The efficiency of a porous material as a sound absorber can be tested by blowing air through it. If air travels freely, it's likely a good absorber.

Panel and resonant sound absorbers are effective in narrow frequency ranges, unlike porous absorbers which are better at absorbing a broader range of frequencies.

Panel and resonant absorbers can be adjusted to target specific frequencies by changing their mass, stiffness, or shape.

The total sound absorption in a room is determined by both the absorption coefficient of the surfaces and the total surface area.

A material's ability to absorb sound energy, usually expressed as a value between 0 and 1.

A numerical representation of how well a material absorbs sound. Higher values indicate greater absorption.

Materials with an absorption coefficient greater than 0.50 are considered good sound absorbers, effectively reducing sound energy in a space.

Materials with an absorption coefficient less than 0.20 reflect sound energy rather than absorbing it, contributing to a more reverberant space.

A type of sound absorber made from a network of interconnected pores, commonly found in materials like glass fiber, mineral fiber, and open celled foams.

The effectiveness of porous absorbers in reducing sound energy is determined by factors like thickness, fiber orientation, density, and the size of the pores.

At lower frequencies, porous absorbers convert sound energy into heat, effectively reducing noise levels.

At higher frequencies, the intricate network of pores in porous absorbers creates friction, which dissipates sound energy and reduces noise.

The average sound absorption coefficient of a room, calculated by considering the absorption coefficient of each surface and its area.

Changing the acoustic properties of a room by adding or removing sound-absorbing or sound-reflecting materials.

The situation where sound waves travel freely without reflections, typically in a large, open space.

The persistence of sound in a space after the source has stopped, caused by reflections.

The process of reducing reverberation and improving speech clarity by adding sound-absorbing materials.

The total sound absorption in a room, measured in sabins. It represents the sum of the sound absorption contributed by all surfaces in the room.

The sound absorption of a room is calculated by multiplying the absorption coefficient of each surface by its area and summing the results. This gives you the room's total sound absorption in sabins.

The average absorption coefficient of a room, which is calculated by weighting the absorption coefficients of each surface by their respective areas.

The area of a surface that is exposed to sound waves. It determines the amount of sound energy that the surface can potentially absorb.

Different materials have different absorption coefficients across different frequencies. This means that a material may absorb more sound at one frequency than at another.

A single-number rating that represents the average sound absorption of a material across four octave bands (250 Hz to 2000 Hz).

The higher the NRC value, the more sound energy is absorbed by the surface.

Averaging the absorption coefficients of the four octave bands (250 Hz, 500 Hz, 1000 Hz, and 2000 Hz) and rounding to the nearest 0.05.

A single-number average representing the absorption of a material across multiple frequencies. It simplifies the absorption information but loses detail.

NRC only considers middle frequencies, so it might not accurately represent a material's absorption at other frequencies.

A material with an NRC of 0.35 can be considered neither highly absorptive nor reflective.

Even though heavy carpet has an overall NRC of 0.35, its absorption coefficient at 125 Hz is very low, making it reflective at low frequencies.

Understanding a material's absorption coefficients across a range of frequencies provides a more complete understanding of its sound-absorbing properties.