Variable directional microphone system

A variable directional microphone system comprising:

• (a) a casing having front and rear portions, said casing being arranged to allow sound waves from all directions to pass therethrough;
• (b) a first microphone unit of first order sound pressure gradient unidirectional type, said first microphone unit having a front and a rear, said first microphone unit disposed in said casing in such a direction that the front of said first microphone unit is oriented toward said front portion of said casing;
• (c) a second microphone unit of first order sound pressure gradient unidirectional type, said second microphone unit having a front and a rear, said second microphone unit disposed in said casing in such a direction that the front of said second microphone unit is oriented toward said rear portion of said casing, said second microphone unit being arranged in such a manner that the rear of said second microphone unit faces the rear of said first microphone unit;
• (d) a third microphone unit of first order sound pressure gradient unidirectional type, said third microphone unit having a front and a rear, said third microphone unit disposed in said casing in such a direction that the front of said third microphone unit is oriented toward said front portion, said first, second and third microphone units respectively having first, second and third axes which respectively pass through centers of the fronts and rears of said first, second and third microphone units, said first, second and third axes being aligned on a common axis;
• and
• (e) means for combining the output signals of said first, second and third microphone units at a variable ratio.

A second order sound pressure gradient unidirectional microphone system comprising:

• (a) a casing having front and rear portions, said casing being arranged to allow sound waves from all directions to pass therethrough;
• (b) a first microphone unit of first order sound pressure gradient unidirectional type, said first microphone unit having a front and a rear, said first microphone unit disposed in said casing in such a direction that the front of said first microphone unit is oriented toward said front portion of said casing;
• (c) a second microphone unit of first order sound pressure gradient unidirectional type, said second microphone unit having a front and a rear, said second microphone unit disposed in said casing in such a direction that the front of said second microphone unit is oriented toward said front portion of said casing, said second microphone unit being located in the rear of said first microphone unit;
• (d) means for combining the output signals of said first and second microphone units at a given ratio to produce an output signal;
• (e) first and second high pass filters respectively interposed between said first and second microphone units and said means for combining;
• and
• (f) an equalizer responsive to the output signal of said means for combining, said equalizer having a frequency characteristics so that the level of low frequency components of the combined signal is raised at a given rate per octave.

A second order sound pressure gradient unidirectional microphone system comprising:

• (a) a casing having front and rear portions, said casing being arranged to allow sound waves from all directions to pass therethrough;
• (b) a first microphone unit of first order sound pressure gradient unidirectional type, said first microphone unit having a front and a rear, said first microphone unit disposed in said casing in such a direction that the front of said first microphone unit is oriented toward said front portion of said casing;
• (c) a second microphone unit of first order sound pressure gradient unidirectional type, said second microphone unit having a front and a rear, said second microphone unit disposed in said casing in such a direction that the front of said second microphone unit is oriented toward said front portion of said casing, said second microphone unit being located in the rear of said first microphone unit;
• (d) means for combining the output signals of said first and second microphone units at a given ratio;
• and
• (e) an equalizer responsive to an output signal of said means for combining, said equalizer having a frequency characteristics so that the level of low frequency components of the combined signal is raised by a constant amount, and the level of middle frequency components of the combined signal is raised at a given rate per octave.