Hello Ezio Marchetti,
Thank you for writing in and appreciate your purchase .
Regarding to the item you buy,there are some informations for your reference.
Impedance: 4Ω
Sensitivity: 87dB
Rated Power: 25W
Diagonal Pitch: 83mm
Speaker Height: 55mm
Magnet Diameter: 65mm
Hole Diameter: 71mm
Equivalent Volume: 2.2L
Effective Frequency Range: 90Hz-5KHz
Hope this can help you.
Best regards.