Loudspeakers, nodes and antinodes question help please

[ppy]

Homework Statement

two loudpeakers emit sound waves along the x axis. The sound has maximum intensity when the loudspeakers are 20cm apart. The sound intensity decreases as the distance between the speakers is increased reaching zero intensity at 60cm apart.


What is the wavelength of the sound??
If the distance between the speakers continues to increase at what separation will the intensity be a maximum again??

I thought that the distance between a maximum and zero intensity is equal to the distance between an antinode and a node which is equal to 1/4 of a wavelength. so the wavelength= 4x(60-20)=160cm and the next maximum would be at 20cm+160cm=180cm.


The book says the wavelength is 80cm i do not undestand this i thought this is the distanc between a maximum and a minimum of the wave which is only half the wavelength.

Help appreciated

 

[TSny]

I don't think this question involves standing waves. So, there are not any nodes or antinodes. My interpretation is that you just have two waves traveling along the x-axis in the same direction that are initially in phase. Then the separation between the speakers is changed to put the waves out of phase.