High Efficiency Speaker Asylum

Posted by tomservo (M) on August 28, 2007 at 06:11:43

In Reply to: RE: How does much different is the equalization required using waveguide-CD vs exponential horn-CD ? posted by Artesmio on August 27, 2007 at 13:20:59

How different?
I don’t think there is one answer as each horn and driver type is different.
In general one can say a few things that are always true though.
The on axis response of a horn is set by the driver’s raw acoustic power response, modified by the horns directivity.
For a true CD horn, one has the same frequency response shape one has when you measure the driver on a plane wave tube, you see the drivers true power response.
For an exponential or curved wall horn, one has the same thing, the raw power response BUT the curved wall horn becomes more directional as the frequency increases.
This acts to confine the radiation pattern to a progressively narrower angle, which acts to raise the level at least on axis.

In the olden days, exponential (curved wall) horns and drivers were matched (as well as possible) so that on axis, they would have flat response without EQ.
While this seems like a good idea at least for those on axis, it makes the region where one has the full range a narrow angle in front.

Also, since your reverberant field is more closely related to the power spectrum, these systems tended to sound dark and murky if you’re not in the radiation pattern.
It was found (by F Toole and others) that having the power response and direct field more closely matched was preferred by listeners, especially outside the sweet spot.
For a crowd or larger audience, Constant Directivity was more desirable, originally this was through sectorial and then multi-cell horns and finally true CD horns.
The down side is with a CD horn, you need to compensate for the drivers mass and then inductive hf roll off.
The up side is that this is a minimum phase thing and eq generally fixes both amplitude AND phase.
Hope that helps,

Tom Danley