A method is presented for the ultrasonic attenuation measurement as a function of frequency using a broad band transducer. The diffraction correction has been introduced in the expression such that an algorithm may be developed for evaluation of attenuation directly. This eliminates the introduction of the diffraction correction curve separately. Results are presented for various types of aluminium alloys. The method is suitable for samples placed a distance further than three times the near field and which have a size much larger than the transducer.