Compare the BL 10 to the SSD 10 and the ssd has the same xmax so wouldn't it move the same air therefore being the same.

and on the website it say the bl has 18 mm xmax and the ssd has 21mm so wouldnt the ssd be louder then?

Cant compare just one measurement between two subs.

I don't think those are current. Might want to check their sight again for their current specs.

from the pics you posted you put a 15 and a 10

there is allot more than xmax that determines the way a sub functions. you are missing on what actually makes the two different, such as the difference in motor force, qts, power handling, sensitivity, ect. just because they have the same xmax doesn't mean they are the same.

That is like saying that the Mustang GT, Boss, and V6 are the same as they are on the same chassis. Depending on your needs though, it may not be better. IE, why buy the boss if you drive like a complete wimp and really never want to go or accelerate fast.

I don't think those are current. Might want to check their sight again for their current specs.

Just from the pictures, neither of those are current models (considering the SSD isn't even in production right now)

Xmax alone will not tell you anything. If that were the case, manufacturers would only list Xmax. Do some more research on Thiele/Small parameters and then decide which woofer best suits your goals.

Then wouldn't a BTL without the HiXmax coil not be as good as those because it is only 18mm.. Kind of strange that a company would make there most expensive subs the worst one they produce? Xmax determines next to nothing, look at the other parameters.

Analogy:

You do not use a chrome plated socket for something that you are going to smack with an air impact wrench, even though they are the same sized bolts..odds are you are going to snap the chrome plated socket.

You use an impact socket for impact tools.

ie:

You use a BL for the purpose that the BL is made for (read the blub about the product line on the website), and you use the SSD for what it is intended for.