Line array theory has been around since the 1930’s. In the 50’s and 60’s basic line arrays were very popular in the form of the column loudspeaker commonly used for PA. These days we are used to seeing massive line array speaker systems flown above the stage at festivals and concerts.
On the other hand the line array microphone is a rare breed and the few that are around, such as the impressive Microtech Gefell KEM970, tend to be expensive. The KEM970 is around £10,000.
In common with the shotgun microphone, the line array is a phase-reactive device. Unlike the shotgun where the on-axis position is down the length of the interference tube, with the line array the on-axis position is side-on at 90 degrees to the vertical column. Sound arriving at 90 degrees will be in phase at all of the capsules. The electrical output from each capsule will be identical and therefore additive. Sound arriving off-axis will suffer varying degrees of phase cancellation, depending on the frequency and the angle of incidence.
The polar pattern of a line array microphone is therefore wide in the horizontal plane and narrow in the vertical, getting narrower with rising frequency. This enables the mic to pick up over longer distances whilst rejecting mid and high frequency sound arriving off axis ( ie below and above.)
N.B.The longer the array (ie the more elements in the line) the lower the frequency at which it starts to be effective.
Below about 400Hz my 4 element model becomes increasingly omni-directional. In this respect it is once again similar to a shotgun.
Over the next few months I am planning a number of experiments to explore how this array will behave and to see what practical applications I can find for it! I’ll report back…………..