Sound Waves - phase difference from time delay

[Arctangent]

For some reason I have trouble with questions like this. How would I get the phase difference if I were given the time delay of two loudspeakers side by side?

I'll use this question as an example:

"The speakers are now placed side by side. If the wire to speaker 1 is passed through a box that delays the signal by 1.56 ms, what is the new phase difference? "

The frequency is 392 Hz
The PD would be zero since they're beside each other
the speed is 340 m/s
the wavelengths are 0.86 m
and the time delay is 1.56 ms or 1.56e-3 s

I was able to find the period, 2.55e-3 s

But after this I kinda blank out. Any tips?

 

[Astronuc]

Think about what the time delay, 1.56 ms means in terms of the period, i.e. what fraction of the period, and how it relates to the wave length.

If one has a signal - A sin$\omega$t, and another signal of the same form but at a delayed time of t_d, one could write the delayed signal as A sin$\omega$(t - t_d).