Interfence with reflected sound

  • Thread starter Thread starter sanado
  • Start date Start date
  • Tags Tags
    Sound
Click For Summary

Homework Help Overview

The discussion revolves around the phenomenon of sound interference, specifically focusing on the creation of standing waves when sound waves emitted from a speaker reflect off a wall. Participants are exploring the locations of nodes and antinodes in this context, as well as the implications of wave direction and path differences on these locations.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to identify the positions of nodes and antinodes based on the phase relationship of the waves. Questions are raised about how the direction of wave travel affects these positions, particularly when considering reflections from a wall. There is also a discussion about the definition of soft spots and how they relate to nodes in the standing wave pattern.

Discussion Status

The discussion is active, with participants providing insights and questioning each other's reasoning. There is a recognition of the complexity involved in determining the locations of nodes and the number of soft spots, with some guidance offered regarding the relationship between wave properties and their interference patterns.

Contextual Notes

Participants are working under the constraints of a specific problem involving a loudspeaker and a concrete wall, including given values for the speed of sound and wavelength. There is uncertainty regarding the interpretation of nodes and the conditions under which soft spots are formed.

sanado
Messages
55
Reaction score
0
Hey guys, was hoping you could help me with a sound question. When sound is emitted from a speaker and it strikes a wall, it rebounds. Since both waves are in phase, a standing wave is created. Are nodes located at wavelength/2, 3wavelength/4? If not, where is there location?
 
Physics news on Phys.org


Well please attempt this question, I'll give you some pointers. Both waves have the same wavelength, and you said they are in phase.

So if they were traveling the same direction then the antinodes would become 2A and the antinodes would stay as 0A right? Where A is standard amplitude, and the x nodal positions would not change. ie. nodes at 0 and wavelength/2
Does traveling in opposite direction change this?
 


Rake-MC said:
ie. nodes at 0 and wavelength/2
Does traveling in opposite direction change this?

Well if that's the case for them traveling in the same direction, they should change shouldn't they? Does this mean that anti-nodes are now located at 0 and wavelength/2?
 


Well that depends on if you are measuring your 0 as from the start of a wave from the original pattern or a distance from the wall on which they are reflected.

If you keep it as the start of the original wave, then it should be identical.
Nodes at 0, wavelength/2
 


Perhaps it may be easier if i post the question that has sparked my confusion:

A science student connects a dynamic loudspeaker to a low voltage AC power pack in an Australian school. The loudspeaker sends sound waves directly towards a concrete wall 3.0 metres away. Take 340 ms-1 as the speed of sound. Wavelength = 6.8m

How many softspots are there located between the wall and speaker? Explain.

Okay, a soft spot is formed due to the presence of a node. When sound is emitted from the speaker it is reflected from the wall and intefers with the wave emitted from the speaker. This produces a standing wave.

That is as far as i can get, i do not understand how to find how many nodes there would be. My understand of a node is when the path difference of two sound waves in phase is wavelength/2, 3wavelength/2, etc. If that's the case then the first soft spot should occur 3.4m from the wall, therefor no soft spots formed. However the answer states that there should be 1 soft spot?
 

Similar threads

Sound Wave Interference and Finding the Path Differences with Diagrams
  • · Replies 20 ·
Replies
20
Views
5K
Reflection of sound wave in an open organ pipe
  • · Replies 4 ·
Replies
4
Views
2K
The hot chocolate effect to investigate the effects on speed of sound
  • · Replies 4 ·
Replies
4
Views
2K
What is the Maximum Wavelength for Constructive Interference of Sound Waves?
  • · Replies 3 ·
Replies
3
Views
3K
Contradiction in Phase of reflected sound
  • · Replies 1 ·
Replies
1
Views
1K
Acoustics type question on reflection....
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Are 1D Longitudinal Waves Reflected at an Open End?
  • · Replies 11 ·
Replies
11
Views
2K
Sound Interference Problem -- Observer moving between two speakers
  • · Replies 3 ·
Replies
3
Views
4K
Finding Nodes in a Standing Wave at 800 Hz
  • · Replies 4 ·
Replies
4
Views
5K
Resonance box with tuning fork, standing wave
  • · Replies 4 ·
Replies
4
Views
3K