# Resonance ans normal modes in an open pipe

## Main Question or Discussion Point

Hello,

I have a question about standing sound waves in an open pipe caused by a speaker, I know that normal mode frequencies are given by

$$f_n = n\frac{v}{4L}, \quad n=1,2,3,...$$

if we put a microphone into the pipe, and if the frequency of the speaker is a normal mode frequency, we see nodes and antinodes.

but I dont understand what happen when the speaker frequency isn't a normal mode frequency.. I think that we see always nodes and antinodes but they have lower amplitude, I'm not sure at all.

If someone can help me, it would be nice.

Thanks.