JP2012119829A - Variable directional microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow directivity to be switched to either cardioid, super-cardioid and hyper-cardioid, by combination of existing microphone units.SOLUTION: The system includes a cardioid unit 20 with cardioid directivity and an omnidirectional unit 30 with omnidirectional directivity. Audio signal output of the omnidirectional unit 30 is adjusted in a level adjustment circuit to a prescribed level and subtracted from audio signal output of the cardioid unit 20 in an arithmetic circuit 21.

Description

  The present invention relates to a variable directional microphone capable of selecting directivity, and more specifically, a variable directional microphone capable of switching directivity to at least one of a cardioid, a super cardioid, or a hyper cardioid as required. It is about.

  In a microphone used in a live stage, a recording stage or the like, howling often occurs because the sound is amplified. In order to prevent this, microphone units with different directivities such as cardioid, hypercardioid or super cardioid are generally selected according to the situation. Since directivity can be selected using a single microphone, unit replacement can be saved.

  Among the variable directional microphones, models equipped with a condenser microphone unit in which diaphragms are arranged before and after the fixed pole, the unit is specially designed, and the capacitance between the diaphragm and the fixed pole is measured at the time of manufacture. In order to maintain the longitudinal symmetry of the tension, acoustic resistance, etc., fine setting is required.

  Separately, there are models that combine two microphone units with cardioid directivity in the 180-degree direction to adjust the output signal of each microphone unit. Since a geoid unit is required, the sorting operation is not easy.

  By the way, in a microphone used in a stage or the like, a non-directional and bi-directional microphone unit is rarely used. Therefore, a cardioid, a super cardioid, or a hyper cardioid may be selected.

  Therefore, the present applicant has proposed a variable directional microphone including two unidirectional condenser microphone units each having a diaphragm before and after the fixed pole in Patent Document 1.

  According to this microphone, directivity can be switched to one of cardioid, super cardioid, and hyper cardioid by selecting or mixing one of the outputs of the two microphone units. Since it cannot be used, a dedicated design is still necessary.

JP 2010-103637 A

  Accordingly, an object of the present invention is to produce a variable directional microphone that can switch directivity to at least one of cardioid, super cardioid, or hyper cardioid by a combination of existing microphone units.

  In order to solve the above problems, the present invention provides a first microphone unit having a cardioid directivity, a second microphone unit having a non-directivity directivity, and an audio signal output from the first microphone unit. An arithmetic circuit for subtracting the audio signal output of the unit, and a level adjusting circuit for adjusting the level of the audio signal output of the second microphone unit given to the arithmetic circuit, and obtaining a microphone output from the arithmetic circuit It is said.

  According to a preferred aspect of the present invention, an inverting amplifier or a non-inverting amplifier having a variable voltage gain is used for the level adjustment circuit.

  In addition, as the first and second microphone units, electrodynamic or electrostatic microphone units are used.

  The first and second microphone units are preferably arranged coaxially with the same sound collection axis.

  According to the present invention, the directivity can be switched to at least one of a cardioid, a super cardioid, and a hyper cardioid simply by adjusting the level of the audio signal output of the non-directional second microphone unit.

  In addition, the first microphone unit may be an existing cardioid unit and may be an existing omnidirectional unit even if it is a second microphone unit. There is no need for a special design.

The schematic diagram which shows the variable directivity microphone which concerns on embodiment of this invention. The circuit diagram which shows an example of a level adjustment circuit. The schematic diagram for demonstrating the directivity of a cardioid. The schematic diagram for demonstrating the basic effect | action of this invention. The schematic diagram of the directivity pattern selected in embodiment of this invention. The graph which shows the directional frequency response of a cardioid unit.

  Next, embodiments of the present invention will be described with reference to FIGS. 1 to 6, but the present invention is not limited thereto.

  As shown in FIG. 1, a variable directivity microphone 1 according to this embodiment is a dynamic microphone for vocals used in a stage or the like, and includes a metal microphone casing 10 as a grip portion formed in a cylindrical shape. I have.

  A guard net 11 made of, for example, a wire mesh is provided on the front side (left side in FIG. 1) of the microphone housing 10, and an output connector is provided on the rear side (right side in FIG. 1) of the microphone housing 10. 12 is mounted.

  Inside the microphone casing 10, a middle cylinder 14 is coaxially supported via a shock mount (buffer member) 13 made of an elastic material. The middle cylinder 14 provides a predetermined volume of the back air chamber to the dynamic microphone unit.

  In the guard net 11, a dynamic microphone unit is provided on the front side of the middle cylinder 14. In the present invention, two microphone units of the first microphone unit 20 and the second microphone unit 30 are used as the microphone unit. .

  In this embodiment, of the two microphone units, the first microphone unit 20 has a cardioid directivity, and the second microphone unit 30 has a non-directional directivity. Therefore, in the following description, the first microphone unit may be referred to as “cardioid unit 20”, and the second microphone unit may be referred to as “omnidirectional unit 30”.

  The variable directivity microphone 1 includes an arithmetic circuit 21 and a level adjustment circuit 31 as an electrical circuit configuration for making the directivity variable.

  The audio signal output of the cardioid unit 20 is preferably amplified by the amplifier 22 and given to the arithmetic circuit 21, whereas the audio signal output of the omnidirectional unit 30 is supplied via the level adjustment circuit 31. It is given to the arithmetic circuit 21.

  Then, the arithmetic circuit 21 subtracts the level-adjusted audio signal output of the omnidirectional unit 30 from the audio signal output of the cardioid unit 20, and the subtracted audio signal output is subtracted from the variable directional microphone 1. It is output from the output terminal 23 as a microphone output.

  In this embodiment, since the inverting amplifier circuit 31a shown in FIG. 2 is used for the level adjustment circuit 31, the arithmetic circuit 21 is the adder circuit 21a.

  That is, in the adder circuit 21a, the audio signal output of the omnidirectional unit 30 whose level is adjusted by the inverting amplifier circuit 31a and whose polarity is inverted to negative from the audio signal output of the cardioid unit 20 is added ( Substantial subtraction process).

  Note that a non-inverting amplifier circuit (not shown) may be used for the level adjustment circuit 31, and in that case, a subtraction circuit is used for the arithmetic circuit 21. The output terminal 23 may be included in the output connector 12.

  In FIG. 1, the omnidirectional unit 30 is arranged so as to overlap the cardioid unit 20, but this arrangement may be reversed. In any case, the units 20 and 30 are preferably arranged coaxially with the same sound collection axis (the X axis in the 0 ° direction with respect to a sound source (not shown)).

  As schematically shown in FIG. 3, the cardioid directivity is obtained by synthesizing the bi-directional component and the omni-directional component. Here, for ease of explanation, assuming that the sensitivity of the bi-directional component in the 0 ° direction is “1” and the sensitivity of the omnidirectional component in all directions is also “1”, the synthesis results in 0 ° in the cardioid. The sensitivity in the direction is “2”, and the sensitivity in the 90 ° direction is “1”.

  In the present invention, directivity is subtracted from the audio signal output of the cardioid unit 20 by subtracting the audio signal output of the omnidirectional unit 30 whose level is adjusted to a predetermined level by the level adjustment circuit 31 (inverting amplifier circuit 31a). Can be switched from the cardioid shown in FIG. 5 (a) to the super cardioid shown in FIG. 5 (b) and the hypercardioid shown in FIG. 5 (c).

  In FIG. 4, the audio signal output level of the omnidirectional unit 30 is adjusted to 0.2 by the level adjustment circuit 31 (inverting amplifier circuit 31a) from the audio signal output of the cardioid unit 20 described in FIG. An example in which the directivity is super cardioid will be shown.

  In this super cardioid, the sensitivity in the 0 ° direction is “2.0” → “1.8”, the sensitivity in the 90 ° direction is “1.0” → “0.8”, and the sensitivity in the 180 ° direction is “0”. .2 "sensitivity.

  In this case, the audio signal output level of the omnidirectional unit 30 can be adjusted to a predetermined level by changing the resistance value of the feedback resistor Rf of the inverting amplifier circuit 31a shown in FIG. 2 as a variable resistor. Alternatively, the feedback resistor Rf may be selected as a plurality of resistance elements having different resistance values, and any of them may be selected as the feedback resistor Rf.

  In addition, when the audio signal output level of the omnidirectional unit 30 and the level of the omnidirectional component (90 ° direction component) of the cardioid unit 20 are the same, the bidirectionality is obtained.

  Next, referring to the graph of the directed frequency response of the cardioid unit 20 shown in FIG. 6, the level difference between 0 ° and 90 ° of the cardioid unit is usually 6 dB. The 90 ° level is the omnidirectional component of the cardioid unit.

  In the present invention, as described above, the audio signal level from the omnidirectional unit 30 is adjusted so as to reduce the omnidirectional component of the cardioid unit 20 and subtracted from the audio signal output of the cardioid unit 20. However, along with this, the sensitivity in the 0 ° direction also decreases. Therefore, it is verified how much the sensitivity in the 0 ° direction changes.

  For example, if the level difference between 0 ° and 90 ° is 6 dB → 7.5 dB (Δ−1.5 dB) and the directivity is super cardioid, the omnidirectional component of the cardioid unit is 0.84. Thus, the audio signal level from the omnidirectional unit is adjusted.

  Along with this, the sensitivity (level) in the 0 ° direction becomes 1 + 0.84 = 1.84. Here, since 20 log 1.84 = 5.296 dB, the sensitivity in the 0 ° direction is reduced by about 0.70 dB from 6-5.296≈0.70.

  Next, if the level difference between 0 ° and 90 ° is changed from 6 dB to 9.5 dB (Δ−3.5 dB) and the directivity is set to hypercardioid, the omnidirectional component of the cardioid unit is set to 0.67. The audio signal level from the omnidirectional unit is adjusted so that

  Accordingly, the sensitivity (level) in the 0 ° direction is 1 + 0.67 = 1.67. Here, since 20 log 1.67 = 4.454 dB, the sensitivity in the 0 ° direction is reduced by about 1.5 dB from 6-4.454≈1.5.

  According to the present invention, it is possible to continuously or stepwise change the directivity from cardioid → supercardioid → hypercardioid while suppressing the decrease in sensitivity in the 0 ° direction to this extent. In the case of a cardioid, for example, an on / off switch or the like may be provided in the output system of the omnidirectional unit 30 so that the output of the omnidirectional unit 30 is zero.

  In the above embodiment, the cardioid unit 20 and the omnidirectional unit 30 are dynamic units, but both of them may be capacitor units. Further, although a vocal microphone used on a stage or the like is taken as an example, a microphone for other purposes may be used.

DESCRIPTION OF SYMBOLS 1 Variable directional microphone 10 Microphone housing | casing 11 Guard net 12 Output connector 20 Cardioid unit (1st microphone unit)
21 arithmetic circuit 21a adder circuit 22 amplifier 23 output terminal 30 omnidirectional unit (second microphone unit)
31 level adjustment circuit 31a inverting amplifier

Claims (4)

  A first microphone unit with cardioid directivity, a second microphone unit with non-directional directivity, and an arithmetic circuit for subtracting the audio signal output of the second microphone unit from the audio signal output of the first microphone unit; And a level adjustment circuit for adjusting a level of an audio signal output of the second microphone unit supplied to the arithmetic circuit, and obtaining a microphone output from the arithmetic circuit.   The variable directional microphone according to claim 1, wherein the level adjustment circuit includes an inverting amplifier or a non-inverting amplifier having a variable voltage gain.   The variable directional microphone according to claim 1 or 2, wherein both the first and second microphone units are electrodynamic or electrostatic microphone units.   The variable directional microphone according to any one of claims 1 to 3, wherein the first and second microphone units are coaxially arranged with the same sound collection axis.

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