Well I have been thinking about getting an extension. My bass is sort of on the heavier side so its is not as loud or powerful as some. It is not bad though and it does have a very nice tone. I am just worried that if I get the extension I may not be happy with the volume etc of the low C. Since I have a thicker top I do want good tension on my strings. Would an extension take tension of the top? Would I lose volume? My top is slab cut spruce. I currently have a solo string on tuned down to G- I actually get a good amount of sound out of that. Mabye the top is over stressed? How can I know?-it is a thick top. Anyway I just want to know if I might expirience a loss in volume when I get the extension. 
