I have done and read some on the subject manner.
The following link was the information I found to most helpful in obtaining a well balance, flat frequency that closely matched the SPL of the main speakers and minimized frequency cancellations and bloom.
The sound is omni directional and it sounds as though it is being broadcasted from the main speakers and correctly positioned in the overall sound stage
This may be helpful to you
http://www.decware.com/paper01.htm
Brad
The following link was the information I found to most helpful in obtaining a well balance, flat frequency that closely matched the SPL of the main speakers and minimized frequency cancellations and bloom.
The sound is omni directional and it sounds as though it is being broadcasted from the main speakers and correctly positioned in the overall sound stage
This may be helpful to you
http://www.decware.com/paper01.htm
Brad