The Rebirth of the Coaxial Horn: Rent Com Inc: Audio Visual, Video, Projection, Presentation Rental AV Equipment

The Rebirth of the Coaxial Horn

Obviously part of the definition of a coaxial is that two loudspeakers share the same axis. But, if they do share the same axis, do they have the same acoustic origin? And what about the acoustic centers? For a coaxial device to work properly, all of these questions must be resolved.

The concept of placing one horn inside another has been attempted in past decades, most notably by Blattner in the 1930's, Community (FRC, For Real Coaxial) in 1972, and Frazier in 1975.

Unfortunately, since both horns are radiating from a unique point in space, the resulting pressure wave was severely distorted in the region of crossover due to phase cancellation. The horn within a horn was doomed until crossover and delay technology advanced to the point where the needed corrections in time and bandpass could be realized and implemented.

In 1987, consultant Jim Young of Ruston, Louisiana approached Dr. Eugene Patronis, a physics professor at the Georgia Institute of Technology. He needed assistance in reducing the size of an array he was designing for a church. Dr. Patronis suggested the concept of a horn within a horn, utilizing the components Mr. Young had hoped to use in the array.

The M4 with pattern control horn was the midrange device of choice. It's high acoustic output and low distortion made it ideal for the installation. Dr. Patronis added an EV HP640 horn with an EV DH1A driver inside the Community horn to convert it to a coaxial unit. Next, a 24dB/octave crossover was added, and the optimum corner frequency was determined to be 1250 Hz. This solved the bandpass problems, but the offset acoustic origins remained. A Klark-Teknik 20-microsecond/step delay reconciled the origins, and provided a true mid/hi range device with excellent pattern control and smooth response. The rebirth of the horn within a horn was complete, and many companies rushed to develop similar products.