Reassurance for Physics Coursework (Sound)

In summary, the distance is proportional to the inverse square of sound intensity, meaning as the distance increases, the intensity decreases significantly. However, in terms of amplitude, the sound power is still the same but spread out over a larger surface area. As for the second question, it is not clear enough to answer accurately. If adding a wall or frame around an open-frame speaker does not significantly change the volume, the main change occurs when an enclosure is added at the back.
  • #1
Life|Time
Hello :rolleyes:

I just wanted to make sure I have these ideas right before I right them up in my physics coursework! I recently did some tests and got these relationships out, but didn't really have enough time to double-check them.

Ok. I took a simple test involving sound and distance. Is the distance proportional to the inverse square of sound intensity? So, as the distance increases a bit the intensity decreases by a lot?

Also, if I had a case around a speaker (say made from cardboard), but it still had the speaker exposed, would it increase the volume as opposed to no case? (I got this shown in my results - I think the case was called a "baffle" by my teacher)

I'm not too good around this area of physics as you may be able to tell!

Thanks!
 
Physics news on Phys.org
  • #2
"Is the distance proportional to the inverse square of sound intensity? So, as the distance increases a bit the intensity decreases by a lot?"

You mixed up your words a bit in there. The sound power is proportional the the inverse square of the distance. Basically think of concentric spheres centered on an isotropic sound source (like a firecracker). As the sound waves radiate out from the source at the center, the same power is going to go through each concentric sphere. But the surface area of each sphere is bigger and bigger, going as r^2, right? So the same sound power is going through a bigger surface area, so the sound intensity (something like power/area ?) will fall off as 1/r^2.

Your second question is not worded well enough to answer, IMO. You would need an accurate diagram of what you are trying to ask. If the "speaker" is already enclosed and you put a 5-sided box around the back of it, nothing will happen. If by "speaker" you mean an open-frame speaker cone assembly, then putting an enclosure behind it can definitely increase the volume that you get out in front of the speaker.
 
  • #3
berkeman said:
"Is the distance proportional to the inverse square of sound intensity? So, as the distance increases a bit the intensity decreases by a lot?"

You mixed up your words a bit in there. The sound power is proportional the the inverse square of the distance. Basically think of concentric spheres centered on an isotropic sound source (like a firecracker). As the sound waves radiate out from the source at the center, the same power is going to go through each concentric sphere. But the surface area of each sphere is bigger and bigger, going as r^2, right? So the same sound power is going through a bigger surface area, so the sound intensity (something like power/area ?) will fall off as 1/r^2.

Your second question is not worded well enough to answer, IMO. You would need an accurate diagram of what you are trying to ask. If the "speaker" is already enclosed and you put a 5-sided box around the back of it, nothing will happen. If by "speaker" you mean an open-frame speaker cone assembly, then putting an enclosure behind it can definitely increase the volume that you get out in front of the speaker.


Thanks for the reply! When I just re-read what I wrote I noticed I was using the wrong word, I meant amplitude rather than intensity. I think :smile:

Ok. I did word the second question completely uselessly and I didn't even mean a box. lol. I'm in a bit of a rush you see! :rolleyes:

I mean like a speaker with a card square around it, with no depth (except for the thickness of the cardboard). Like a fram with a picture, except a large piece of card then a cut out piece for the speaker to fit in.

Thanks!
 
  • #4
So if the 2nd question is really whether adding a wall where the cone frame mounting points are changes the volume in front of the speaker cone, then I would guess the answer is no. If you have an open-frame speaker, with the metal frame around it and the magnet and coil to the rear, the putting a wall or frame on it shouldn't do much of anything. The sound waves being pushed out the front still go out the front, and the sound waves being pushed out the back (through the big openings in the metal frame) still go out the back.

The main change happens if you put an enclosure of some kind in the back. That can change the amount and character of sound that you get out the front.
 

FAQ: Reassurance for Physics Coursework (Sound)

How does sound travel through different mediums?

Sound travels through different mediums by creating a series of compressions and rarefactions in the molecules of the medium. These vibrations are then transmitted from molecule to molecule, allowing the sound to travel through solids, liquids, and gases.

What factors affect the speed of sound?

The speed of sound is affected by the density, elasticity, and temperature of the medium it is traveling through. In general, sound travels faster in denser and more elastic mediums, and slower in colder temperatures.

How is the loudness of sound measured?

The loudness of sound is measured in decibels (dB). This is a logarithmic scale that compares the intensity of a sound to the threshold of human hearing. A sound that is 10 dB louder is perceived as being twice as loud.

What is the difference between pitch and frequency?

Pitch is the subjective perception of how high or low a sound is, while frequency is the objective measurement of how many cycles of a sound wave occur per second. Pitch and frequency are directly related, with a higher frequency resulting in a higher pitch sound.

How does the Doppler effect apply to sound?

The Doppler effect is the perceived change in frequency of a sound wave when the source of the sound is moving relative to the observer. As the source moves closer, the frequency increases and the sound is perceived as higher pitched. As the source moves away, the frequency decreases and the sound is perceived as lower pitched.

Similar threads

Back
Top