Question about SPL

First a little background:

I have a 12" Brahma II, it's going into a 3 cubic foot ported box tuned to 20Hz.

It will be powered by a 1250 watt rms amp at 4 ohms.

Using a calculation  I found during my research [SPL=(10*(A)) + B] where A is max input power and B is the 1w/1m rating of the subwoofer

On the Brahma,  the 1w/1m rating at 4 ohms is 87.4. Now, using that calculation I get something like 118.37 max SPL.

That calculation does not include the box in any way though, so I guess my question is:

What effect on SPL can I expect from the box?

Judson

generally speaking, spl ratings are on an assumed enclosure that is optimized for the driver.  having your speaker sitting in the free air condition with that much power on it would probably rattle it to pieces.   just a note, that speaker seems somewhat inefficient having an spl at 87.4.  i'm not saying it's a bad speaker necessarily, just - well, very inefficient if 118db is the max you're going to get out of it with that many watts being used.  it would have to be painfully clean sounding for me to justify that kind of waste of power.

Efficiency is more a function of the enclosure rather than the driver.  Power is cheap, so Adire decided to make it a little less efficient to allow a smaller enclosure requirement and still obtain a decent low frequency extention.  But this sub is one of the cleanest subs on the market.  It has a motor topology that offers less distortion than the more common topologies used by the competition. 

SPl is somewhat useless as a parameter.  For one thing, it's small signal and actually changes when the cone moves.  In fact the SPL on the Brahma is somewhat misleading because it's BL curve is so flat.  Every other sub's efficiency decreases as it moves due to BL dropping off, while the Brahma's stays the same.  So at decent excursions it can actually be more efficient than the competition.

Now I do want to say that 3 cubes is a little large for that sub.  So be careful with the gain and volume knob with that kind of power.  I know you will enjoy that setup.  Just go out and install it and experience it for yourself.

Thanks for all the info, but if anyone has an equation or a difinitive answer as to what a given box will do with a given sub, I would be elated.

Also I noticed that my equation was lacking one very important factor, the correct equation should be:

[SPL=(10*(log A))+B]      A = Max Input Power,  B = 1W/1m rating

forgetting that log is a bad idea ;)

Jud

yea just to agree with what they said, many things go into what the final SPL will be. if its a car suv truck, how big the box is the frequency type of box etc, etc. Also your not going to need anywhere near that much power to push the brahma when i had my brahma i had a JBL BP 1200.1 (with the gain way way down) hooked to it with 1.5 cubic ft box and it didnt last a year! so definatly watch the gain in a box that big and dont push it too far too much, because when you destroy it like i did you lose a great SQ speaker!

Allen