Two identical sounds S1 and S2 reach at a point P in phase. The resultant loudness at point P is n dB higher than the loudness of S1. The value of n is:

Let a be the amplitude due to S1 and S2 individually.Loudness due to S1 = I1 = Ka2Loudness due to S1 + S2 = I = K(2a)2 = 4I∴ n = 10 log10(4l1l1)          = 10 log10(4) = 6