I noticed in Hoosier's pictures of his HT2-TLs that the RAAL tweeter is offset to one side (I've noticed this in some other models as well). What is the purpose of this?
It is to control diffraction artifacts. That is also why the edges of the cabinets around the drivers are rounded over.
When sound leaves a driver, it tends to travel in all directions. Very high-frequencies have such short wavelengths, however, they don't make it to the edge of the cabinet. Instead, they bounce off the front baffle and are reflected toward the listening position. (That is why you don't hear high treble when standing behind a speaker.)
As frequencies get lower and the wavelengths increase, the signals move toward the edges of the cabinets. And as they go even lower, they pass completely around the cabinets.
But at a certain frequency, the wavelength is just right and the signal hits the cabinet edge. The result is turbulence. The sharper the edge, the more turbulence is created and you can see it in the FR measurements. That is why you see the edges of cabinets rounded over. Rounded edges help mitigate some of this effect and are better than the sharp edges you often see on less expensive speakers (cabinets are less costly to build with 90-degree corners).
By off-setting the tweeters, you essentially have two distances to the cabinet edges rather than one. So the diffraction artifacts appear at two frequencies rather than one. But each is half the amplitude. So while the artifacts are still there, their impact is cut in half.
The goal here is to minimize the impact of diffraction artifacts as sound hits the edges of the cabinets. You can't completely eliminate it (unless you have no baffle or a baffle of infinite size), but you can minimize it by rounding over the edges, creating a smoother transition and by spreading its effect over multiple frequencies with less resulting impact at any given frequency.
I hope that made sense.
- Jim
