Method for obtaining a composite piece having a fibre volume greater than 58% in weight and with a porosity value lower than 2%, comprising the obtaining of a composite uncured laminate of n plies, (2.1,...,2.n), at least one ply having a fibre volume greater than 58% in weight, the method comprising the steps of: a. laying a first prepreg ply (2.1) over a working surface or a previously cured piece; b. performing ultrasound compaction over the first prepreg ply (2.1), the first prepreg ply (2.1) thus becoming the last compacted prepreg ply; c. laying a new prepreg ply (2.2,...,2.n) over the last compacted prepreg ply; d. performing ultrasound compaction over the new prepreg ply (2.2,...,2.n), the new prepreg ply (2.2,...,2.n) thus becoming the last compacted prepreg ply; e. repeating the steps c. and d. for n-2 additional times; and f. curing the composite uncured laminate of n plies; wherein n is a natural number equal or greater than 1, wherein at least one of the prepreg plies (2.1,...,2.n) has a fibre volume greater than 58% in weight, and wherein the steps b. and d. of performing ultrasound compaction over a prepreg ply (2.1,...,2.n) comprise at least applying an ultrasonic compactor over said prepreg ply (2.1,...2.n), the ultrasonic compactor comprising at least a probe, a probe housing, a booster and a horn and wherein the step b. is carried out using the following parameters: - the ultrasonic frequency being comprised between 20 and 80 kHz; - the ultrasonic waves amplitude being comprised between 70 and 100% of the amplitude of the movement of the ultrasonic compactor; - the ultrasonic compactor contact area being comprised between 50 and 200 mm 2., - the horn width being comprised between 5 and 30 mm; and - the probe housing angle respect the working surface, or the previously cured piece, being comprised between 15 and 65°, characterized by carrying out the step b. using the following parameters: - the booster ratio being comprised between 1:1.5 and 1:3; - the layup speed of the ultrasonic compactor being comprised between 50 and 180 mm/s; - the compaction pressure being comprised between 30 and 150 bar. a. laying a first prepreg ply (2.1) over a working surface or a previously cured piece; b. performing ultrasound compaction over the first prepreg ply (2.1), the first prepreg ply (2.1) thus becoming the last compacted prepreg ply; c. laying a new prepreg ply (2.2,...,2.n) over the last compacted prepreg ply; d. performing ultrasound compaction over the new prepreg ply (2.2,...,2.n), the new prepreg ply (2.2,...,2.n) thus becoming the last compacted prepreg ply; e. repeating the steps c. and d. for n-2 additional times; and f. curing the composite uncured laminate of n plies; - the ultrasonic frequency being comprised between 20 and 80 kHz; - the ultrasonic waves amplitude being comprised between 70 and 100% of the amplitude of the movement of the ultrasonic compactor; - the ultrasonic compactor contact area being comprised between 50 and 200 mm 2., - the horn width being comprised between 5 and 30 mm; and - the probe housing angle respect the working surface, or the previously cured piece, being comprised between 15 and 65°, characterized by carrying out the step b. using the following parameters: - the booster ratio being comprised between 1:1.5 and 1:3; - the layup speed of the ultrasonic compactor being comprised between 50 and 180 mm/s; - the compaction pressure being comprised between 30 and 150 bar.