A compressor is to be used $30m$ away from a house and a long, $2m$ high barrier is to be erected $5m$ from the compressor to reduce the noise. The ground between the compressor and the house is hard, flat and level. The centre of the compressor is $0\mathrm{.}5m$ above the ground. Calculate the noise reduction produced by the barrier at a height of $1\mathrm{.}5m$ above the ground at the house. The velocity of sound is $330\frac{m}{s}.($Octave band, Hz; $125,250,500,1000,2000,4000).$