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Date: December 22, 2002 at 10:13:39
From: Doug, [wc02.mtnk.rnc.net.cable.rogers.com]
Subject: Re: Questions about mathmatical boxes....


Adrian is right in saying that the Qts of the driver will restrict the type of alignment we choose for a smoothest and flattest amplitude response. We can't just pick any alignment we want and apply it to any given driver, it depends on the Qts of the driver.

Many consider the B4 or 4th order Butterworth alignment ( desribed by A.N.Thiele )to be the ideal maximally flat design. It has a 24 dB per octive rolloff and a Q of .7 ( and this is important )it is "only" possible when the Qts of the driver is .4 (assuming a box leakage loss of QL 7) ie: box losses are close to QL 7 for box sizes up to approx 11 cu.ft. Above 11 cu.ft. box losses are around QL 5.

As Qts of the driver sinks below .4, the optimum vented alignment shifts toward a QB3 or quasi third-order Butterworth alignment. As Qts rises above .4, the optimum vented alignment shifts towards a C4 or 4th order Chebychev alignment.

Someone on this forum mentioned delay, well for those of you who don't completely understand the concept, think of it this way, the more you damp a speaker, the more you "hold" it back. It sounds better, but the problem is, frequencies around Fb (maximum damping) will sound behind the higher frequencies. That is why ported enclosures are sometimes called " phase inversion enclosures " At Fb, they can invert the phase by as much as 180 degrees. A disadvantage of ported boxes.

In pro audio they use digital delay to delay the higher frequencies in the system to bring them into alignment with the low end. Which reminds me, does anyone on the forum know of any delay units on the market for car audio at a decent price?

Hope this help's, DOUG
Moderated By: steele_b@spiceisle.com


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