Sound volume and distance & decibels

[Jennifer Murphy]

Does the volume of a sound decrease as the square of the distance? That is, if I move twice as far from the sound source, will the volume be 1/4? One website says it does, but another says that the pressure varies directly with distance.

Are these two statements both true? If so, how is sound pressure related to volume?

Another website says that doubling the distance from the source will reduce the sound by 6 dB. I know that the decibel scale is logarithmic, so this would seem to support the first statement that volume decreqases as th3 square of the distance. Is decibels not a measure of volume?

I'd appreciate any help understanding these concepts.

Thanls

 

[James R]

Does the volume of a sound decrease as the square of the distance? That is, if I move twice as far from the sound source, will the volume be 1/4? One website says it does, but another says that the pressure varies directly with distance.

The sound intensity (in Watts per square metre) certainly decreases as the inverse square of the distance.

The perceived volume is a different matter, because human hearing doesn't have a linear response to sound intensity. This is one reason why we have the decibel scale of sound level, which is logarithmic.

I'd have to look up the relationship between pressure and intensity. I'd guess that, probably, intensity goes as the square of the pressure, or something like that (but that's just a guess).

Another website says that doubling the distance from the source will reduce the sound by 6 dB. I know that the decibel scale is logarithmic, so this would seem to support the first statement that volume decreqases as th3 square of the distance. Is decibels not a measure of volume?

Volume is not a precisely defined concept, as far as I am aware. Human perception of volume depends on a few different things. Sound intensity is one, but there's also a frequency dependence - we don't hear equally well at all frequencies we can perceive.

 

[gmilam]

Human perception of volume depends on a few different things. Sound intensity is one, but there's also a frequency dependence - we don't hear equally well at all frequencies we can perceive.

For more info, Google "Fletcher Munson equal loudness contour".