IB Subwoofer question

[JasonB]

Why are multiple woofers often suggested when using an IB setup? I was under the impression that (and Unibox confirms) the maximum ouput for a driver in a sealed box at any chosen frequency is determined by it's X-max. In other words, a woofer will have the same maximum output at a given frequncey weather it's in a 2 cu ft box, or 2000 cu ft box.

So what am I missing?

Jason

[ThomasW]

Why are multiple woofers often suggested when using an IB setup?

Because I get a kickback for every driver sold....

So what am I missing?

The enclosure (for a small box) functions as an acoustic high-pass filter. That acts to protect the driver from over excursion at lower frequencies. Since an IB has no 'box', it doesn't have the benefit of protection from the acoustic filter. As a result it's low frequency output will continue until the suspension bottoms out.

Since bottoming has a rather negative impact on performance, the recommendation is for multiple drivers... :T

Another reason for recommending multiple drivers is as one might expect, the greater the number of drivers the lower distortion.

[GrahamT]

the maximum ouput for a driver in a sealed box at any chosen frequency is determined by it's X-max. In other words, a woofer will have the same maximum output at a given frequncey weather it's in a 2 cu ft box, or 2000 cu ft box.

So what am I missing?

Right, max output is the same at Xmax, but the power required for the same volume is MUCH less with and IB. And as Thomas mentioned the frequency response is also different.