Zaph|Audio

Common Enclosures in 2.5-Way systems

Jan 22, 2006 - Initial Publication

Question: What are the effects of placing the lower baffle step compensation woofer into the same enclosure as the primary woofer?

Hookup number one (top) has the drivers paralleled with baffle step applied to both drivers. The transfer function is identical for both drivers. The baffle step circuit consists of an inductor paralleled with a resistor, both of which are in series with the paralleled woofers. Hookup number two (bottom) has one driver run full range and the other with a large baffle step compensation inductor in series between the woofer terminal and the input. The component values in each case have been adjusted so the final response is close. Variation is not more than a couple of decibels.

The close mic location is required so that I can greatly raise the gating without a whole lot of room response showing up. This is a 20ms window, which should allow a lot of detail in the 200-1000Hz range.

Note that this driver arrangement is far from optimum, as is the close mic location. The enclosure is way too small, which results in severe harmonic distortion below 100Hz. The mic location is placed between the drivers, a few inches away from the baffle. This shows the top end greatly rolled off. How the drivers are used is not important at all in this test. The difference between the results is what we are looking for.

What do we see? There isn't much difference in either case. I half expected to see a little response ripple through the 300-1000 range, but each case was minor enough that the delta response was more likely caused by simple value differences in the components used. A mild dip in 3rd order HD at 250hz on the .5-way hookup is somewhat unexplained. I would expect more distortion in that area. In summary, while there are minor differences in linear and non-linear distortion, it's nothing substantial.

These results are far from definitive, but what I see so far points to seperate enclosures not being a necessity. All commercial 2.5-way speakers have lower woofers that share volumes with upper woofers, but I had always assumed that was a cost saving measure. It could be that it's simply not required and does not negatively affect the design.

Page done by John "Zaph" Krutke © 2005
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