Why do standing waves need opposite directions, not different frequencies?

[lampshader]

Homework Statement

Am I right when i say, "Standing waves are produced by the superposition of two waves with the same amplitude and frequency, and opposite propagation directions".

If I am then why would it not be, the same amplitude and direction of propagation, but different frequencies??

Thanks for any help in advance.

Homework Equations

The Attempt at a Solution

 

[rl.bhat]

Stranding waves are formed by the reflection of the waves from a source. And the reflection does not change the frequency. A single source cannot produce two different frequencies. Two independent sources cannot produce standing waves.

 

[GreenLantern]

I just posted an in depth answer to your question in a related thread here: https://www.physicsforums.com/showthread.php?t=373374

(my) post #6

Hope you read it for clarification as it probably will answer your question more completely/thoroughly

-GL