Gross volume vs. Net volume

I read the datasheet of Braun LS200, or ADS L1590/2, speakers. It states two values of cabinet volume: Gross and Net volumes, as depicted in the red circle.

Translated from German, the one with 125 liters is Gross volume, while the other with 94 liters is Net volume. The enclosure of these speakers is sealed type.

What is the difference between these two values?
 

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Gross volume has usually been the internal volume of the cabinet with nothing in it. Net is after the bracing, damping, sub enclosures, and driver displacement (frame, cone, and magnet volume) are subtracted. Some spec sheets have displacement listed for ease of calculation. Don’t forget to subtract the port area as well!