The speaker has to be linear, with a minimum of crossover points. Harmonic distortion should be less than 2%. The directivity of the speaker should be constant and be extended as low as possible. It would be nice if the speaker were fairly efficient, upper 90's would be nice. The bass should extend to below 20 HZ, and be non resonant to an octave above the 16,000 Hz. 110 db is all I need, which would be about 120 db at 1 meter. The speaker should keep signal off the floor and ceilings above 300 HZ. I don't mind a fairly large foot print as long as it is shallow. 20" or less. The HF should be emitted at ear height unless you use a line array. See if you can approve on a JBL M2 as a start.