# Amplitude in plane x=y from two speakers placed on x and y axes.

#### Saraphim

1. The problem statement, all variables and given/known data
Two speakers at (x,y,z)=-L,0,0 and (x,y,z)=(0,-L,0)

Find the amplitude at all positions in the plane x=y

2. Relevant equations
The waves are given by:

$$\tilde{f}_x(\overline{r},t)=\frac{A}{r_x} e^{i(kr_x-\omega t)}$$

$$\tilde{f}_y(\overline{r},t)=\frac{A}{r_y} e^{i(kr_y-\omega t+\delta)}$$

And the amplitude A is real.

3. The attempt at a solution
I'm unsure how to proceed here, at least with finding the amplitude in the plane itself. I'm thinking that the amplitude for all points must be given by the real part of

$$\tilde{f}(\overline{r},t)=\tilde{f}_x+\tilde{f}_y=Ae^{-i \omega t}\left( \frac{1}{r_x} e^{i kr_x} + \frac{1}{r_y} e^{i(kr_y+\delta)}\right)$$

But how do I go from here and to only the x=y plane? Do I just set $$r_x=r_y$$? How does this carry any information about z? I think I just need a nudge in the right direction.

#### Saraphim

To elaborate a bit, what is stumping me is that both functions completely discard any information about z, and if I take, for instance, $$\tilde{f}_x((x,y,z),t)$$ for any set values of (x,y), then the result doesn't depend at all of z! This would make the wave propagate as a cylinder with infinite z-length. Am I going insane?

#### Saraphim

Wow, okay, that was utter nonsense. I've now managed to confuse myself to the point where I don't know what I'm doing.

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving