The two speakers at S₁ and S₂ are adjusted so that the observer at O hears an intensity of 4 W/m² when either S₁ or S₂ is sounded alone. They are driven in phase (at the speakers) with various frequencies of sound. Assume that the speed of sound is m/s.

a) Find the three lowest frequencies, f₁ < f₂ < f₃, for which the observer at O will hear an intensity of 16 W/m² when both speakers are on.

f₁ = Hz   

f₂ = Hz   

f₃ = Hz

b) Find the three lowest frequencies, f₁ < f₂ < f₃ , for which the observer at O will hear no sound when both speakers are on.

f₁ = Hz    

f₂ = Hz   

f₃ = Hz

c) Find the lowest frequency for which the observer at O will hear 8 W/m² when both speakers are on.

f = Hz

d) Find the lowest frequency for which the observer at O will hear 4 W/m² when both speakers are on.

f = Hz