isobaric box

i saw in a magazine a single 12" woofer mounted isobarically, you know magnet on the outside, cone facing in. how would you calculate what size the box has to be that the sub is firing into? do they have to be sealed, or ported. any help would be greatly appreciated. thanx

That's called Inverted mounting. An Isobarric mount requires 2 subs. For Inverted mounts you would use the Net Internal Volume (does not have the subs displacement factored in already) recommended by the manufacture. This is actually the volume that most manufacturer's will give, and you usually have to add the sub displacement to that before calculating the total required volume for a Normal mount. As far as going sealed or ported, I'd use the manufacturer's recommendation as well. Since the sub is inverted, I believe you have to switch the phase of the amp as well (look for a switch called "Phase" that usually has 2 settings: 0 degrees and 180 degrees). For an Inverted mount you would use the 180 degree phase setting. A normal mount uses the 0 degrees setting.Squirrel

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I have two Kicker XPL 15"s and one of them is inverted.  I experienced better sq and better spl this way.  I recommend giving it a shot to see if you like the results.--Adam

thanx ghs, i only want to use one sub, in the middle poking out between my seats, i have a reg. cab truck, and deep boxes behind the seat are a pain in the a$$.  i can utilize the width and cut down on the depth. by the way are yours ported? and sorry about the slow response.

I have ran many isobaric (equal pressure) boxes, the advantage is the box size is about half (2 subs) of what one sub takes. Isobaricly mounting 2 subs is not the best for SPL as you dont get db coupling like you do with your subs facing the same direction.