How Do You Calculate Decibel Intensity at a Distance in Spherical Waves?

In summary, the problem involves finding the decibel intensity 100m away from a spherical wave source with an initial intensity of 8.0 W/m^2 at 1.0 m. The equations used are β=10ln(I1/I0) and β=(10dB)ln(8.0/10^-12), but the latter may be confusing due to the use of dB as a unit for both relative and absolute intensities. The reference level for the absolute intensity should be specified, such as dBm or dBmW.
  • #1
PCPanos
2
1

Homework Statement


The intensity of a certain spherical wave is 8.0 W/m^2 at a distance of 1.0 m from the source. If the medium is isotropic and nonabsorbing, calculate the decibel intensity 100m from the source.

Homework Equations


β=10ln(I1/I0)

The Attempt at a Solution


I know how to use these equations... And to find the original dB level i use
β=(10dB)ln(8.0/10^-12)

Im just not sure what to do to find intensity 100m away?
 
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  • #2
What do you mean with "original dB level"?

How does intensity depend on distance for spherical waves without absorption?
 
  • #3
"Decibel" is very confusing because the term is used both for relative and absolute intensities. As far as I am aware, the unit dB always denotes (or should always denote) a relative intensity. If an absolute intensity is intended then it should be qualified to indicate the reference level, like dBm or dBmW.
Where does your 10-12 come from?
 

Related to How Do You Calculate Decibel Intensity at a Distance in Spherical Waves?

1. What is intensity and how is it measured?

Intensity refers to the amount of energy carried by sound waves, and it can be measured in different ways depending on the context. In acoustics, intensity is commonly measured in watts per square meter (W/m²). In audiology, it is measured in decibels (dB). Intensity can also be measured in terms of pressure or amplitude, but these are less commonly used units.

2. What is the difference between sound intensity and loudness?

Sound intensity and loudness are closely related but different concepts. Intensity is a physical measure of the energy carried by sound waves, while loudness is a subjective perception of how loud a sound is. Loudness depends on factors such as the sensitivity of our ears, the frequency of the sound, and the distance from the sound source, whereas intensity is solely based on the physical properties of the sound wave.

3. What is the decibel (dB) scale and how is it related to sound intensity?

The decibel (dB) scale is a logarithmic scale used to express the loudness or intensity of a sound. It is based on the ratio between two sound intensities, with 0 dB representing the threshold of human hearing and 120 dB representing the threshold of pain. This means that a sound with an intensity of 10 times that of a reference sound will be 10 dB louder or more intense.

4. How does distance affect sound intensity and dB level?

As sound waves travel through space, their intensity decreases due to the spreading out of the energy. This means that at a greater distance from the source, the sound will be quieter and have a lower dB level. The decrease in intensity follows an inverse square law, meaning that doubling the distance from the source will result in a 6 dB decrease in intensity.

5. What are some common examples of intensity and their corresponding dB levels?

Common examples of sound intensity and their corresponding dB levels include a whisper (30 dB), normal conversation (60 dB), a lawnmower (90 dB), a rock concert (110 dB), and a jet engine (140 dB). It's important to note that prolonged exposure to sounds above 85 dB can cause hearing damage, and sounds above 120 dB can cause immediate hearing loss.

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