In this instance power refers to electrical power measured in watts and spl and loudness are acoustic power measured in decibels. Watts and decibels are not comparable scales of measurement and do not scale up linearly to each other
Try this article, give it a read and let me know if you have further questions
https://jlaudio.zendesk.com/hc/en-us/articles/217201737-Doubling-Power-vs-Doubling-Output
Josh Evans, Professional Live Sound Engineer, High End Commercial AV Install Technician
