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Discussion Starter #1
I can't seem to find a definitive answer about what parameters to look for when choosing a subwoofer for an IB system. So far this is forum has the most info I've ever seen on the subject.

While expect the results to far from ideal, I would like to try and build an IB system in my car using the trunk as the box.
 

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The Exodus Audio link on this board brings you to the DIYCable site, which itself seems to be stale. There is still a notice about Holiday hours on its front page. Anybody know what's happening?
 

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Thanks, for the replies folks. Hi Kevin. I'm doing a little research into the IB sub thing and being in Canada I would prefer purchasing here if I can. I noticed over at Cult of the Infinitely Baffled that the FiAudio units are very popular. Can you folks point me to some example IB builds using the Exodus drivers?
 

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Discussion Starter #14
I found the answer I was looking for on this page: http://www.caraudiomag.com/specialfeatures/0507cae_speaker_box/index.html

"When purchasing IB speakers, keep in mind the following parameters to assure that the speaker is right for the application. The first is the Qts (the total resistance of the driver at its resonance). Speakers with a Qts greater than 0.6 typically work well in an IB environment. The second is the Vas (the volume of air having the same compliance as the driver's suspension). The Vas should be smaller than the total volume of the environment the speaker(s) are being placed in."

The page also states that a IB setup is only about 50% efficient. Is this true?
 

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Very nice, Darren. I like the fact that you rounded over the edges of the manifold, even though it can only be seen in the attic. I imagine it was much nicer to handle while wrestling it into place on the supports.
 

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To answer the original question, think of an IB as a "boxless" loudspeaker. The "enclosure" basically is nothing more than something to hold the driver in place, and block immediate sound waves from the rear of the driver so they don't cancel with the front. For this reason, the bigger the box (or baffle), the better.

To determine the best parameters for an IB speaker, it's helpful to look at what a sealed box does for / against the response. Putting an enclosure on a driver raises the Q of the system. The smaller the box, the higher the Q. This has the effect of raising the output response at F3 (a good thing) but raising it and causing a steeper rolloff below that (a bad thing). An ideal speaker response will have a Q of around 0.707 (butterworth response). Since the enclosure raises the Q, and hopefully approaches 0.707, the closer to that Q you can get with the driver alone, the better for an IB system.

Also, since the idea is to get deep bass, a low Fc is helpful. The most efficient way to get that is to have a large Vas (equivalent volume); that means a soft suspension. Since it will have to move a LOT to get deep bass, a long Xmax is needed, as is a large Sd (diameter), or multiple drivers (or both). Unfortunately, a long Xmax and a large Vas is a recipe for voice coil rub, so it's difficult to find that combination. Go for a large Vas (and correspondingly low Fc), and large piston over large Xmax.

Oddly, these parameters are the same as a sealed box driver, except for the Q. The motor will reduce the Q, so a strong motor is antiproductive for a good response in an IB system, where it is a boon in a sealed box system; so yes, it pays to get drivers made specifically for IB systems. They are rare, so will cost a pretty penny. Good luck!
 

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Oddly, these parameters are the same as a sealed box driver, except for the Q. The motor will reduce the Q, so a strong motor is antiproductive for a good response in an IB system, where it is a boon in a sealed box system; so yes, it pays to get drivers made specifically for IB systems. They are rare, so will cost a pretty penny. Good luck!
Not necessarily. The AE IB15, has a .7Qts with an fs of 16hz and a VAS in the mid 400L's, however an xmax of 18mm I think. Real nice option and is 125/ea if you buy 4.
 
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