Originally Posted by LTD02
"it takes twice the swept area in an IB as one would otherwise need in a small sealed."
i'm wondering what you are thinking there as it would seem to go against the physics by which the two systems operate.
Not really, let me explain. It's what I call the IB powering conundrum.
LTD, much of this is review for you, but I'll cover this for everyone. IBs and small sealed are just so different. Clearly, the manner in which the box affects the driver's operation, via acoustic back pressure/air spring, is the primary mechanism of action differentiating them. The small sealed box acts like an acoustic high-pass filter, and this fundamentally changes the manner in which the driver's limits are encountered.
The small sealed box exhibits a vari-limiter characteristic ... protects the driver from excessive excursion as the frequencies go lower. The deeper the freq, the more back pressure up against the cone at peak travel. Thus, with a small sealed, you can have large amounts of power on tap both above and below the "knee" of the response curve
, ... a very efficient use of the driver's limitations.
While a small sealed is thermally limited, an IB excursion limited. A theoretically superb approach, but it could use more amp power for complex material, .. but you need to power it according to it's limits at say 10hz. Now different driver bottoming characteristics may allow you to examine the powering a bit different. Fi's Xmax and Xmech are relatively close.
A proper IB isn't impacted by the box, thus it's very "bass efficient". An IB driver can often reach full excursion with a fraction of the power needed in a sealed system. The IB possesses other superiorities as well, but that's another discussion entirely. The Fi IB3-18s I have can handle about 300w@10hz, much more and they'll bottom. So I power them accordingly.
So, fundamentally the difference the way the power is utilized up against the driver limits. Now if the IB owner runs without a high pass filter, then the limit is above the knee. My 18" Fi's encounter their excursion limits about 300 watts or so @10hz. So wide open with no hi-pass, you're limited to a modest amount of power. Now, they'll play much louder with tons of impact with an hi-pass and much more power. However, that negates the wonderful, natural extension of an IB in the first place.
This is why there's more drivers needed with an IB system as compared to a typical small sealed ....