A source of emitting sound of 616hz is bloked on block 'A' which is attached to the free end of string. The detector fixed on block 'B' attached to free end of spring Sb detects the sound .The blocks A and B are simultaneously displaced towards each other through distance of 1m and then left to vibrate. Find maximum and minimum frequencies of sound detected by the detector, if vibration frequency of each block is 3.5Hz.(sound velocity is 330m/s).