Jus thought I update this thread, originally I installed these as a rush job but had a little bit more time today to take them out and re do them.
Originally I had just screwed them down into the enclosure and did not block up the connector block (left if open). i spent over a week adjusting my settings on my amp (jl xd 400/4) and they just did not sound right, it did not hit the low notes like my Logic 7 subs and was wondering why other people where givng them great reviews.
Attempt number 2 - I took out the sub and sound proofed the enclosure, used the spacer provided kindly by Afsar. I used silicone sealent to seal all the way around and the connector block and re fitted. did the same on the other side and re tuned my amp and wow it is totally different, huge improvement over the L7 subs and being able to hit the lower notes that previously were not heard.
Just got the grill to refit now as I ran out of time but I have ended up using 6mm thickness maybe if I can get away with 12mm but will report back.
On another note do these eartquake subs are suited closly matched to amp that provides 150w rms or can they handle a bit more?
At the moment I am ony powering these at 75w rms each but will add a 2nd amp for the subs only