When the sound waves have same wavelength, frequency and amplitude we just need the phase difference between them at a particular location to determine whether the waves are in constructive interference or destructive interference.
Interference is a phenomenon in which there is superposition of two coherent waves at a particular location in the medium of propagation.
When the waves are in constructive interference then we get a resultant wave of maximum amplitude and vice-versa in case of destructive interference.
For constructive interference the waves must have either no phase difference or a phase difference of nλ, where n is any natural number.
For destructive interference the waves must have a phase difference of n×0.5λ, where n is any odd number.