M2 two way horn PA type speaker
4367 is a two way horn PA type speaker
Both the M2 and 4367 use studio-quality horns and drivers. Their basic configurations may appear similar to PA speakers at first glance, but they are not PA speakers.
Horns suffer from distortion due to non-linearity of air at the throat. This affects sound at high SPL and means distortion is high at elevated SPL - might not be noticed by your average wedding crowd who find DJ speakers acceptable but not exactly “end-game”
The non-linearity of air in the throat of a horn is of negligible consequence. It is not the source of the distortion you hear in the DJ's speakers at the wedding.
Earl Geddes on the subject:
"The air nonlinearity is indeed present, but it is very low order (inaudible) and low compared to the nonlinearities in the drivers." And with studio-quality prosound drivers, the "nonlinearities in the drivers" do not set in until much higher sound pressure levels than is the case for conventional home audio drivers because of their reduced excursion requirements for a given SPL.
That edgy distortion you hear in the DJ's horns, which becomes increasingly audible and objectionable as the SPL rises, is caused by diffraction and reflection within the horn itself. These are known as "Higher Order Modes", or HOMs, and are present in diffraction horns (which includes virtually all of the horns likely to be found in PA speakers, including your DJ's speakers) and in horns which have any sharp discontinuity (like around the lip on many horns).
Higher order modes are not non-linear; they are present in equal proportion independent of SPL. They are delayed in time and therefore create nonminimum-phase abberations, which are
linear, but our PERCEPTION of them is
non-linear. HOMs are typically unnoticeable at low SPLs, but become increasingly audible and objectionable as the SPL goes up. This leads many people to think the compression driver in a PA speaker is distorting non-linearly, but such is not the case: It is the ear which is having a non-linear
PERCEPTION of a
linear distortion.
Minimizing higher order modes is a high priority in a modern high-end horn, such as in the JBL M2 and 4367, hence their unorthodox horn geometries which combine minimizing higher order modes with an exceptionally wide and uniform coverage pattern. (Historically, such wide and uniform coverage patterns have been achieved by diffraction horns or horns with internal vanes, the latter also being a source of internal reflections.)