Sound and air movement: do they affect each other?

  • Context: Undergrad 
  • Thread starter Thread starter fisico30
  • Start date Start date
  • Tags Tags
    Air Movement Sound
Click For Summary

Discussion Overview

The discussion revolves around the interaction between sound and air movement, specifically addressing how sound propagates in different scenarios, such as when a speaker is not facing the listener and the effects of compressed air on sound transmission. The scope includes theoretical considerations of sound propagation and practical implications of air movement on sound detection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether sound diffracts enough to be heard from behind a speaker, suggesting that sound primarily moves forward from the mouth as an aperture.
  • Another participant notes that sound can be carried by air movement, citing personal experience of hearing speech on windy days, and questions the sufficiency of diffraction alone to explain sound heard from behind a speaker.
  • A different participant mentions that the acoustic radiation pattern of certain sources can exhibit a 'doublet pattern', indicating that sound may not be uniformly distributed in all directions.
  • Concerns are raised about the effect of compressed air on sound detection, with one participant proposing that flowing air could disrupt the behavior of air molecules and potentially obscure the sound from a speaker.
  • There is a reiteration of the idea that sound spreads spherically from a point source, which may include sound reaching areas behind the speaker.

Areas of Agreement / Disagreement

Participants express differing views on how sound propagates in relation to air movement and the effects of obstacles. There is no consensus on the mechanisms by which sound is heard from behind a speaker or the impact of compressed air on sound transmission.

Contextual Notes

Participants discuss various assumptions about sound propagation, including the role of reflections and the nature of sound sources. The discussion does not resolve the complexities of these interactions.

fisico30
Messages
362
Reaction score
0
Hello Forum.

I have two basic sound questions:

I know sound (large wavelength) diffracts a lot when it exits an aperture. But if someone is speaking and he/she is not facing us we still hear them, even if we are in an empty field.
Does sound diffract so much that it ends up even behind us?

2. If we created a flow of compressed air in front of a speaker playing some music, would the receiving microphone simply detect the noise from the compressed air or would the compressed air disrupt the air molecule behavior (sound coming out of the speakers) and change it?
After all, sound is simply compressions and rarefactions of air density, i.e. molecules that bump into each other...
If we push some air in front of the microphone we should be able to randomize the air molecules motion and not here the music...

thanks,
fisico30
 
Physics news on Phys.org
Sound can get carried by air movement.

You can hear this on a windy day if you walk around someone speaking.

I'm not sure that all the sound you hear behind someone speaking in still air is the result of diffraction alone. The human voice is not a single point source.

If we created a flow of compressed air in front of a speaker playing some music

Flowing air has a lower pressure than still air. So if you blow air at or across the speaker it will experience a lower pressure than if you didn't.
 
Well, when someone speaks the aperture is his/her mouth. It would seem that sound would move forward, in a hemispherical region of space...but not be present in region behind the the person speaking...
Reflections have an effect, but if we are in the middle of a football field we still hear a person's voice even if they are not facing us...How do air molecules get to vibrate behind the person speaking?
 
If you look at the acoustic radiation pattern of many chamber type sources you will see the characteristic 'doublet pattern' (figure of eight).

Don't forget that the back of the head/throat/chest is not a very good acoustic barrier.
 
fisico30 said:
Well, when someone speaks the aperture is his/her mouth. It would seem that sound would move forward, in a hemispherical region of space...but not be present in region behind the the person speaking...
Reflections have an effect, but if we are in the middle of a football field we still hear a person's voice even if they are not facing us...How do air molecules get to vibrate behind the person speaking?

Sound emitted by a point source (not exactly someone's mouth, but similar) the sound energy spreads shperically...that is, in all directions.
 

Similar threads

Undergrad Why do sound waves not bounce off of each other?
  • · Replies 20 ·
Replies
20
Views
6K
Graduate How does a Western free reed work? (musical instruments)
  • · Replies 12 ·
Replies
12
Views
4K
Undergrad Reading Russell's ABC of Relativity, stuck in chapter 3 (about speed of sound)
  • · Replies 6 ·
Replies
6
Views
2K
High School How Do Different Sounds and Heat Relate to Object Interaction and Air Movement?
  • · Replies 4 ·
Replies
4
Views
3K
Modern Digital Audio: Understanding Dither and Oversampling in Hi-Res Age
  • · Replies 17 ·
Replies
17
Views
6K
Solaculture: A novel biological approach for low cost energy?
  • · Replies 3 ·
Replies
3
Views
4K
Exhaust and engine accoustics for asthetics and performance
  • · Replies 2 ·
Replies
2
Views
8K
Graduate Cherenkov Radiation for lighting
  • · Replies 1 ·
Replies
1
Views
6K
Graduate Interesting paper, require feedback
  • · Replies 3 ·
Replies
3
Views
3K
Time: What is it? How do We Know it?
  • · Replies 3 ·
Replies
3
Views
4K