Monitor 5 is heavier than Monitor 7?

ANWKLO

Although the size of M7 is bigger than M5, but M5 is heavier than M7. Can you tell me the reason?

http://www.polkaudio.com/homeaudio/specs/monitor5/
Total Shipping Weight 48.00 lbs. (21.77kgs)

http://www.polkaudio.com/homeaudio/specs/monitor7/
Total Shipping Weight 33.00 lbs. (14.97kgs)

ND13

5s were shipped in pairs and 7s were shipped in seperate boxes, iirc.