Sound pressure gradient microphone

1. A sound pressure gradient microphone, comprising:

a first non-directional microphone;

a second non-directional microphone;

a first high-pass filter that receives an output of the first non-directional microphone;

a second high-pass filter that receives an output of the second non-directional microphone;

a delay device that receives an output of the second high-pass filter; and

a subtractor that receives an output of the first high-pass filter and an output of the delay device, and outputs a difference between the output of the first high-pass filter and the output of the delay device,

wherein the first high-pass filter includes a first capacitor, which is disposed between the first non-directional microphone and the subtractor, and is connected in series to the first non-directional microphone and the subtractor,

the second high-pass filter includes a second capacitor, which is disposed between the second non-directional microphone and the delay device, and is connected in series to the second non-directional microphone and the delay device, and

a capacitance value of the first capacitor is smaller than a capacitance value of the second capacitor so as to achieve a state where a phase of a signal output from the first high-pass filter is ahead of a phase of a signal output from the second high-pass filter.

2. The sound pressure gradient microphone according to claim 1 ,

wherein the first high-pass filter further includes a first resistor having a grounded first end and a second end connected to a line between the first non-directional microphone and the subtractor, and

the second high-pass filter further includes a second resistor having a grounded first end and a second end connected to a line between the second non-directional microphone and the delay device.

3. The sound pressure gradient microphone according to claim 1 ,

wherein at least one of the first capacitor and the second capacitor is a variable capacitor.

4. A sound pressure gradient microphone, comprising:

a first non-directional microphone;

a second non-directional microphone;

a first high-pass filter that receives an output of the first non-directional microphone;

a second high-pass filter that receives an output of the second non-directional microphone;

a delay device that receives an output of the second high-pass filter; and

a subtractor that receives an output of the first high-pass filter and an output of the delay device, and outputs a difference between the output of the first high-pass filter and the output of the delay device,

wherein the first high-pass filter includes a first capacitor and a first resistor, the first capacitor is disposed between the first non-directional microphone and the subtractor and is connected in series to the first non-directional microphone and the subtractor, and the first resistor has a grounded first end and a second end connected to a line between the first non-directional microphone and the subtractor,

the second high-pass filter includes a second capacitor and a second resistor, the second capacitor is disposed between the second non-directional microphone and the delay device and is connected in series to the second non-directional microphone and the delay device, and the second resistor has a grounded first end and a second end connected to a line between the second non-directional microphone and the delay device, and

a resistance value of the first resister is smaller than a resistance value of the second resistor so as to achieve the state where a phase of a signal output from the first high-pass filter is ahead of a phase of a signal output from the second high-pass filter.

5. The sound pressure gradient microphone according to claim 4 ,

wherein at least one of the first resistor and the second resistor is a variable resister.