rear firing tweeters

[cinema bob]

so I've looked around for info on designing speakers with rear firing tweeters for added ambiance and haven't found anything. I know that Jon has done a design or two with them and would like some info.
are they worth the time and effort to add or do they add so little that they are not worth it? is the quality of the rear tweeter as important as the front or can something like a tang band be used? and lastly I have noticed that most company's use different types of tweeters for front and rear (metal, soft dome, etc) is this to offer up different types of sound or is it some other reason?


thanks a lot.

[JonMarsh]

Actually, I haven't noticed companies using different types of materials for front and rear, but then I may not be looking at the same companies (Wilson Audio) as you are.

The general rationale for using a rear firing tweeter it to raise the overall HF reverberent sound field, without increasing the on axis HF response. A lot depends on the type of room, speaker setup, etc, as to whether that will be actually "beneficial". (I'd call it more of a "grace note" after you've got everything else really working well, not a primary design consideration).

The only speakers I've ever built using augmented HF dispersion are a couple of sets of AR LST klones I did back in the early 70's, and the Wilson X1 SLAMM clones. The former used four identical tweeters; the latter used titanium dome based tweeters, but not the same ones- the rear firing were active only above ~8-10 kHz; they were Audax Titanium types, as used in the Wilson X1. The front firing tweeters were Focal TC120dx2, as close as you can buy on the open market to the Focal tweeter used by Wilson.

Other folks do things like vertically firing tweeters with waveguides or deflectors. Being an old luddite, I'm a little more concerned about the basic driver choices and implementation than some features that may actually make room placement and performance more tricky. (i.e, rear wave combining with front wave after reflection from nearby rear wall). (we call that comb filtering out here in CA.).

~Jon