Quote Originally Posted by Dean H View Post
Jeff, I think I understand why, if the (double) woofers are near the floor, then crossing to the midrange at 350-400 Hz or so obviates the need for baffle step correction. Could you elaborate on how midrange baffle diffration loss affects the design of the midrange high pass filter? And what about a single woofer? Would the distance between woofer and midrange make near floor placement of the woofer problematic?
Baffle step or diffraction loss occurs when the wavelength of a particular frequency becomes significantly longer than the width of the baffle. The sound then "unloads" from a half-space environment into a full-space environment with a 6dB drop in forward radiated acoustic power. Of course, this occurs gradually over a 2-3 octave spread as this transition takes place. When a woofer is mounted near the floor, and the distance between the floor and the center of the woofer stays well within one wavelength of the frequencies being reproduced then this transition does not occur and the driver will continue to operate in a half-space environment over its entire range. This means there will not be a loss of 6dB in the forward radiation, and the half-space senstivity of the woofer will be maintained. As result, no baffle step compensation will be necessary for such an arrangement.

Now, at 350Hz the wavelength is about 39" long, so it is very easy to stay well within this distance between the woofer and the floor and the woofer and midrange on the other end. If the baffle is wide enough to keep the midrange loaded in half-space to about 500Hz or so (a 10" wide baffle could do this), then simply by custom tailoring the crossover between the two you can produce a design the maintains its full half-space senstivity and require no baffle step compensation at all. If you need a little in the midrange it is usuall not hard to shape the response a little for it anyway.

Since two woofers add 6dB in sensitivity; you need to be careful that two woofers mounted near the floor doesn't become too sensitive for the midrange and tweeter to balance right. The effect of the baffle step on the high pass for the midrange is simply that it can create the beginning of the roll-off and you can pick it up from there electrically to blend for a nice even slope. As for crossing between the woofer and midrange - if you keep the crossover in the frequency range I mentioned you will have no problem keeping the drivers close enough to work OK.

Jeff B.