Why amplitude doesn't affect speed of sound?

  • #1
If amplitude is the measure of energy in a sound wave -
On increasing amplitude, the medium particles should hit each other in lesser time because they have more force(which increases their speed) and this cycle should repeat and repeat. Eventually, the speed of sound should increase. But that's not what happens.
So what's wrong in this cycle?
 

Answers and Replies

  • #2
davenn
Science Advisor
Gold Member
2019 Award
9,347
8,025
ahhhh but the the energy of the sound wave attenuates with distance through a medium
because energy is absorbed by the medium
 
  • #3
314
18
Sound is a pressure wave. The amplitude of sound pressure is much less than ambient athmospheric pressure (see the table). When they become comparable it's called shock wave.
 
  • #4
rcgldr
Homework Helper
8,715
539
  • #5
2,257
7
If amplitude is the measure of energy in a sound wave -
On increasing amplitude, the medium particles should hit each other in lesser time because they have more force(which increases their speed) and this cycle should repeat and repeat. Eventually, the speed of sound should increase. But that's not what happens.
So what's wrong in this cycle?

individual particles of air are being accelerated fater and are moving faster but the speed of the wave itself is the same
 
  • #6
grandpa
Can you elaborate please. Thanks.
 
  • #7
sophiecentaur
Science Advisor
Gold Member
25,214
4,835
The range of speeds (Kinetic Energy) of air molecules is immense. The speed of sound in a gas is dominated by the average time taken for each molecule to travel across the space between, to the next molecule. (simple model for the purpose of making the point). So the speed depends, essentially, on the gas temperature. Any effect in which the 'forward travelling' molecules from the source (pushed forward by the loudspeaker cone) would, somehow, push the downstream molecules away faster would be counterbalanced by the fact that there would be an equal and opposite effect in the other direction on the other half of the sound cycle. The mean addition to velocity would be zero.- certainly in the 'far field' situation.

The only thing that would increase this speed would be the injection of a lot of energy (in total) to increase the temperature. A 'normal' level of sound, from a loudspeaker or even a Jet engine (not the exhaust gases, of course) would not constitute a significant amount of energy and doesn't affect the temperature so I can't see how the speed of sound would be level dependent. Has anyone ever detected an increase in temperature right in front of a high-power loudspeaker, that could be attributed to the flux of sound energy? It would be interesting to know.
 

Related Threads on Why amplitude doesn't affect speed of sound?

Replies
12
Views
21K
Replies
3
Views
6K
Replies
2
Views
1K
  • Last Post
Replies
3
Views
4K
Replies
3
Views
2K
Replies
15
Views
8K
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
6
Views
19K
  • Last Post
Replies
5
Views
6K
Top