Calculating Sound Power: I=P/A & Dependency on Area

[Mahathir]

Homework Statement

Is there any formula for calculating sound power? What does the A mean in I=P/A? Is the power of sound dependent on the area of its surrounding or something. I want to know if there's an equation for P like there's I=2π²a²f²ρv.

Relevant Equations

I=2π²a²f²ρv

Is there any formula for calculating sound power? What does the A mean in I=P/A? Is the power of sound dependent on the area of its surrounding or something. I want to know if there's an equation for P like there's I=2π²a²f²ρv.

 

[Master1022]

What does the A mean in I=P/A?

That looks like the intensity formula, where the A is cross-sectional area: $Intensity = Power/Area$

 

[haruspex]

Is there any formula for calculating sound power?

From what given variables?

 

[sound4haudio]

Can anyone tell me how to calculate the sound power of infrared rays and ultrasound rays and its unit is in db or dB

 

[haruspex]

Can anyone tell me how to calculate the sound power of infrared rays and ultrasound rays and its unit is in db or dB

Infrared is to do with light, not sound.
As I responded to Mahathir, you need some data from which to calculate the power. The method depends on which data you have.

There is no db, only dB. This can be used for relative power in any context, not just sound.

For sound specifically, see if https://www.noisehelp.com/decibel-scale.html helps.

 

[CWatters]

Sound power is the total energy radiated by a sound source in all directions.
Sound Intensity (I) is a measure of how "concentrated" the sound power is in a particular place.

Lets say you have an omnidirectional speaker that emits sound power P uniformly in all directions and the surroundings are "ideal" so there are no reflective surfaces etc. Then consider an imaginary sphere surrounding the speaker at some distance R. The sphere has area A = 4piR^2. Under ideal conditions all of the sound power would emerge uniformly through the surface of the sphere. The intensity at the surface of the sphere would be I = P/A or P/(4piR^2). So in this ideal example the intensity reduces in proportion to R^2.

If you have access to a sound chamber in which to set up such ideal conditions then you could use a sound meter to measure the intensity I at a point R and use the equation above to calculate the sound power P.

However such ideal conditions rarely exist. The sound source is unlikely to be omnidirectional and there may l be reflective surfaces (such as the ground) that changes with the way the sound propagates so that it's not proportional to R^2. This means it's not simple to measure sound intensity at a point and work back to calculate the sound power. Much more information is needed. Whole books and papers are written on this subject.