Rear-Firing Midrange to Help with Beaming?

[goody75]

Let's say you are designing/building a 2-way system that uses a 10-15" woofer that can extend over 2kHz with no problem except for the beaming issue. Would adding a rear-firing midrange speaker that overlaps with the woofer somewhere around 1kHz up to the point where the tweeter comes in help with beaming? Let's assume that I'll have biamping ability and an active crossover to help figure out volume levels and the frequency that the mid comes in and goes out.

[AllenB]

Radiation will go from all around, through just forward, and to a narrow angle. This question depends on which pattern you wish to maintain. For example some want an omnidirectional speaker, and some will accept the 'baffle step' transition.

[dewardh]

There are, somewhat generaly speaking, three frequency response curves that matter . . . and we don't directly measure, and often don't even much consider, any of them. The forward "on axis" curve that we generally design to is just a small part of what defines how a loudspeaker sounds, although it typically comes close (if one ignores diffraction) to describing direct radiation into the listening area. Note "listening area" as opposed to "sweet spot" or "test point".

After that comes frequency response at the angle which provides first reflection into the listening area (which our ear typically treats as part of the "direct" sound). What angle that is depends on placement and toe-in, and how it sounds is heavily influenced by "treatment" at the reflection points. The room has become a part of the loudspeaker.

Third there's the overall power response (which is what you are asking about here). For most listening positions this multiply reflected sound is the major contributor to the sound we hear, and establishes our sense of overall frequency response. If it differs considerably from the direct sound we unconsciously attribute the difference to the room, although if we are familiar with the room we may recognize, and correctly identify, the speaker's contribution. That's one of the primary indicators that lets us tell "real" from "reproduced" (and judge the overall quality of a loudspeaker). But once again the room, or more accurately the room's absorbtion response, becomes a part of the loudspeaker. Two "general" rules: a smoothly falling (with frequency) power response makes the room sound "bigger", and an irregular power response screams "loudspeaker".

Whether auxiliary speakers can effectively "fill in" the flawed power response of loudspeakers of uneven directivity without themselves being perceived is one of those questions so complex, so dependent on other considerations, and so dependent on specific circumstance as to be almost unanswerable. It's a big "maybe". Better, probably, to simply forego the speaker with irregular "beamy" directivity and try something else.