JPH04122111A - Preamplifier for capacitor microphone - Google Patents
Preamplifier for capacitor microphoneInfo
- Publication number
- JPH04122111A JPH04122111A JP24312690A JP24312690A JPH04122111A JP H04122111 A JPH04122111 A JP H04122111A JP 24312690 A JP24312690 A JP 24312690A JP 24312690 A JP24312690 A JP 24312690A JP H04122111 A JPH04122111 A JP H04122111A
- Authority
- JP
- Japan
- Prior art keywords
- preamplifier
- filter
- magnetic field
- coils
- same
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000003990 capacitor Substances 0.000 title description 5
- 239000000696 magnetic material Substances 0.000 claims description 6
- 230000000694 effects Effects 0.000 abstract description 7
- 238000004804 winding Methods 0.000 abstract description 2
- 230000006698 induction Effects 0.000 abstract 1
- 239000000126 substance Substances 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/04—Circuits for transducers, loudspeakers or microphones for correcting frequency response
- H04R3/06—Circuits for transducers, loudspeakers or microphones for correcting frequency response of electrostatic transducers
Landscapes
- Circuit For Audible Band Transducer (AREA)
- Filters And Equalizers (AREA)
Abstract
Description
【発明の詳細な説明】
〔産業上の利用分野〕
この発明は、コンデンサマイクロホンのプリアンプに関
し、とりわけ、マイクロホンの周波数特性を平坦に補正
するフィルタを備えたコンデンサマイクロホンのプリア
ンプに関するものである。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a preamplifier for a capacitor microphone, and more particularly to a preamplifier for a capacitor microphone equipped with a filter that corrects the frequency characteristics of the microphone to be flat.
コンデンサマイクロホンにおいては、その周波数特性を
平坦化するために、振動膜と背極との間に音響抵抗を設
けている。然るに、この音響抵抗から発生する雑音のた
め、ごく低いレベルの音を受音し利用するには限界があ
る。In a condenser microphone, an acoustic resistance is provided between the diaphragm and the back electrode in order to flatten its frequency characteristics. However, due to the noise generated from this acoustic resistance, there is a limit to the ability to receive and utilize very low level sounds.
従来、超低雑音のコンデンサマイクロホンでは、振動膜
と背極間での音響抵抗を減じる工夫がされており、その
結果として、音場での周波数特性は、振動膜の共振周波
数に高いピークを生じる。そこで、マイクロホンの出力
を受けるプリアンプ内に、このマイクロホンの周波数特
性を平坦に補正するフィルタを設けていた。そうして、
このフィルタの特性は、第８図に示すように、減衰量が
制限されたノツチフィルタである。Conventionally, ultra-low noise condenser microphones have been designed to reduce the acoustic resistance between the diaphragm and the back electrode, and as a result, the frequency characteristics in the sound field have a high peak at the resonant frequency of the diaphragm. . Therefore, a filter is provided in the preamplifier that receives the output of the microphone to flatten the frequency characteristics of the microphone. Then,
The characteristics of this filter are that of a notch filter with limited attenuation, as shown in FIG.
第８図において、周波数ｆｏに、振動膜の周波数特性の
ピーク値Ｚがあられれる。In FIG. 8, the peak value Z of the frequency characteristic of the diaphragm is placed at the frequency fo.
また、プリアンプ内に設けられる上記フィルタとして、
抵抗とコンデンサと演真増幅器によるＲＣアクティブフ
ィルタが考えられるが、ＲＣアクティブフィルタは本来
の目的により、特に低雑音であることが要求され、演算
増幅器にも超低雑音のものが必要になる。さらに、演算
増幅器に供給する電源電圧により、最大人力レベルが制
限される。In addition, as the above-mentioned filter provided in the preamplifier,
An RC active filter using a resistor, a capacitor, and a net amplifier can be considered, but the RC active filter is required to have particularly low noise due to its original purpose, and the operational amplifier also needs to have ultra-low noise. Furthermore, the power supply voltage supplied to the operational amplifier limits the maximum human power level.
これに対し、第９図に示すようなＬＣフィルタ（受動フ
ィルタ）では、演算増幅器を使用する必要がない点で、
ノイズに対して有利であり、加えて、最大入力レベルが
電源電圧の制約を受けない上、部品点数が少なくて済む
。On the other hand, an LC filter (passive filter) as shown in Fig. 9 does not require the use of an operational amplifier.
This is advantageous against noise, and in addition, the maximum input level is not restricted by the power supply voltage, and the number of parts can be reduced.
さらに、可変コイルを使えば、共振周波数の微調整が容
易である等、ＲＣアクティブフィルタよりも優っている
。Furthermore, if a variable coil is used, the resonant frequency can be easily finely adjusted, which is superior to an RC active filter.
このＬＣフィルタを設けたプリアンプの出力特性は、第
１０図に示すように、磁界の周波数ｆｔｇにおいて、プ
リアンプ自身の雑音レベルよりも約３０ｄＢのピークが
みられる。As shown in FIG. 10, the output characteristics of the preamplifier provided with this LC filter have a peak of about 30 dB higher than the noise level of the preamplifier itself at the frequency ftg of the magnetic field.
以上のような従来のコンデンサマイクロホンのプリアン
プでは、プリアンプのケースはその加工の容易さから、
非磁性体である黄銅などの材料からなっており、その場
合、プリアンプがさらされている磁界の変化に伴い、内
部のコイルに信号が発生して雑音となる。In the conventional condenser microphone preamplifiers mentioned above, the preamplifier case is easy to process.
It is made of a non-magnetic material such as brass, and in that case, as the magnetic field to which the preamplifier is exposed changes, a signal is generated in the internal coil, resulting in noise.
なお、プリアンプのケースに磁性体を使い磁気シールド
してこの問題を解決することも考えられるが、顕著な磁
気シールド効果は実際には得られない。それは磁力線が
全て磁器シールド材の中を透過する訳ではないことと、
また、加工の容易な磁性体の入手が困難な上、コストも
高く、加工性がよくない材質が多いため加工のコストが
嵩む。It is possible to solve this problem by using a magnetic material in the case of the preamplifier to provide magnetic shielding, but a significant magnetic shielding effect cannot actually be obtained. This is because not all lines of magnetic force pass through the magnetic shielding material,
In addition, it is difficult to obtain a magnetic material that is easy to process, and the cost is high, and there are many materials that do not have good processability, which increases the cost of processing.
この発明はかかる課題を解決しようとするもので、プリ
アンプ内部に設けられるフィルタを、コイルとコンデン
サによる受動フィルタとした場合に、周囲の磁界の変化
がコイルに作用して信号として出力されることを防止す
ることができるコンデンサマイクロホンのプリアンプ
的とする。This invention aims to solve this problem, and when the filter provided inside the preamplifier is a passive filter consisting of a coil and a capacitor, changes in the surrounding magnetic field act on the coil and are output as a signal. This can be prevented by using a preamplifier for condenser microphones.
この発明に係るコンデンサマイクロホンのプリアンプは
、コイルを等価に２つに分けて直列または並列に接続し
たＬＣフィルタが非磁性体ケースのプリアンプ内に設け
られている。In the preamplifier for a condenser microphone according to the present invention, an LC filter in which a coil is divided into two parts and connected in series or in parallel is provided in the preamplifier in a non-magnetic case.
この発明においては、２つのコイルが互いに磁界の影響
を打消し合う。In this invention, two coils mutually cancel out the effects of magnetic fields.
第１図〜第４図はこの発明の一実施例を示し、第１図、
第２図においてプリアンプ（３）に付設されるＬＣフィ
ルタのコイルは、し、とＬ２の直列２分割構成とし、Ｌ
ｌとＬ２は互いに同一寸法、同一形状、同一インピーダ
ンスおよび同一巻方向とし、外部磁界Ｍと逆方向に互い
に等しい誘導電流■，４１、ＩＮｚがそれぞれ発生する
ように配置する。したがって、外部磁界Ｍによるフィル
タ終端における電流Ｉ ＮＴは、Ｉ ＮＴ＝Ｉ ＭＩ
Ｉ Ｎｚ＝ｏ・・・（１）となる。1 to 4 show an embodiment of the present invention, and FIG.
In Fig. 2, the coil of the LC filter attached to the preamplifier (3) has a series two-part configuration with L and L2.
1 and L2 have the same dimensions, the same shape, the same impedance, and the same winding direction, and are arranged so that mutually equal induced currents 1, 41, and INz are generated in directions opposite to the external magnetic field M, respectively. Therefore, the current I NT at the end of the filter due to the external magnetic field M is I NT=I MI
I Nz=o...(1).
第３図は、この実施例の配置構成を示し、非磁性体でな
るケース（１）に、コンデンサマイクロホン（２）およ
びプリアンプ（３）が収納され、プリアンプ（３）の基
板（４）にコイルし，、Ｌ２が配置されている。Figure 3 shows the arrangement of this embodiment, in which a condenser microphone (2) and a preamplifier (3) are housed in a case (1) made of non-magnetic material, and a coil is mounted on the board (4) of the preamplifier (3). , L2 are arranged.
第４図はプリアンプ出力の特性を示し、磁界Ｍの周波数
ｆｍにおいて、プリアンプの事故雑音レベルよりも約１
５ｄＢのピークがみられ、第１０図に比較して雑音の抑
制効果が顕著に表れている。Figure 4 shows the characteristics of the preamplifier output, and at the frequency fm of the magnetic field M, it is approximately 1
A peak of 5 dB is seen, and the noise suppression effect is more pronounced than in FIG. 10.
以上のように、コイルＬ＋１Ｌｚは外部の磁界の変化に
対して互いに逆相の信号を発生するため、外部磁界の影
響は、フィルタ内部で吸収され、外部磁界の影響は外部
に表われない。また、フィルタの構成要素としてみると
、双方のコイルのインピーダンスは各々の和としてフィ
ルタ動作に寄与し、その定数さえ適正の値に設定するこ
とで、所望の特性とすることができる。As described above, since the coil L+1Lz generates signals having opposite phases to each other in response to changes in the external magnetic field, the influence of the external magnetic field is absorbed inside the filter, and the influence of the external magnetic field does not appear outside. Furthermore, when viewed as constituent elements of a filter, the impedances of both coils contribute to the filter operation as a sum of their respective impedances, and by setting their constants to appropriate values, desired characteristics can be obtained.
第５図〜第７図はそれぞれ他の実施例を示し、同一の磁
界による起電力の方向が、逆になるようにし，とＬ２を
直列ないし並列に接続したもの、第６図は互いに同一巻
方向のし，とＬ２を並列接続したもの、第７図は互いに
逆巻きのＬ＋とＬ２を並列接続したものである。Figures 5 to 7 show other embodiments, in which the and L2 are connected in series or parallel so that the direction of the electromotive force due to the same magnetic field is reversed, and Figure 6 shows an example in which the electromotive force due to the same magnetic field is connected in series or in parallel. Figure 7 shows a configuration in which L+ and L2, which are wound in opposite directions, are connected in parallel.
いずれも（１）式が適合し、同一の効果を奏する。In either case, formula (1) is applicable and the same effect is achieved.
以上の説明から明らかなように、この発明は、プリアン
プのケースが非磁性体でなる場合において、比較的安価
なコイルを２個用いたＬＣフィルタを設けたことにより
、周囲磁界の変化の影響を排除しうる効果がある。As is clear from the above description, in the case where the preamplifier case is made of a non-magnetic material, the present invention eliminates the influence of changes in the surrounding magnetic field by providing an LC filter using two relatively inexpensive coils. It has the effect of eliminating
第１図〜第４図はこの発明の一実施例を示し、第１図は
プリアンプの結線図、第２図はコイルの結線図、第３図
はプリアンプの側面図、第４図はプリアンプの出力特性
線図である。
第５図〜第７図はそれぞれ他の実施例のコイルの結線図
である。
第８図〜第１０図は従来のコンデンサマイクロホンのプ
リアンプを示し、第８図はフィルタの周波数特性線図、
第９図はフィルタの結線図、第１Ｏ図はプリアンプの出
力特性線図である。
（１）・・・プリアンプ（３）のケース、（２）・・・
コンデンサマイクロホン。
←ＩＮ２
−ＩＮ２
霧
＋−ｒｒＩ
→チ
第４
閣
第７
閣
←ＩＮ２
セーＩＮ２
館８ａｌｌ
第９
閣
輻
ｍ−うチ
第１０１１Figures 1 to 4 show an embodiment of the present invention, Figure 1 is a wiring diagram of the preamplifier, Figure 2 is a wiring diagram of the coil, Figure 3 is a side view of the preamplifier, and Figure 4 is a wiring diagram of the preamplifier. It is an output characteristic diagram. 5 to 7 are wiring diagrams of coils of other embodiments, respectively. Figures 8 to 10 show a conventional condenser microphone preamplifier, and Figure 8 is a frequency characteristic diagram of a filter.
FIG. 9 is a connection diagram of the filter, and FIG. 1O is an output characteristic diagram of the preamplifier. (1)... Preamplifier (3) case, (2)...
condenser microphone. ←IN2 -IN2 Fog+-rrI →chi 4th cabinet 7th cabinet ←IN2 SeIN2 Hall 8all 9th cabinet convergence m-uch 1011
Claims (1)
等価の２つのコイルが、それぞれの前記誘起電流が互い
に打消し合うように接続されているＬＣフイルタと、 を備えてなるコンデンサマイクロホンのプリアンプ。[Claims] A preamplifier case made of a non-magnetic material and two mutually equivalent coils in which induced currents in directions opposite to the direction of an external magnetic field are induced are connected so that the respective induced currents cancel each other out. A condenser microphone preamplifier equipped with an LC filter and a
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24312690A JPH04122111A (en) | 1990-09-13 | 1990-09-13 | Preamplifier for capacitor microphone |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24312690A JPH04122111A (en) | 1990-09-13 | 1990-09-13 | Preamplifier for capacitor microphone |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH04122111A true JPH04122111A (en) | 1992-04-22 |
Family
ID=17099191
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP24312690A Pending JPH04122111A (en) | 1990-09-13 | 1990-09-13 | Preamplifier for capacitor microphone |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04122111A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2303990A (en) * | 1995-07-31 | 1997-03-05 | Sony Uk Ltd | Microphone amplifier |
| GB2344252A (en) * | 1998-11-26 | 2000-05-31 | Nec Corp | Compact microphone for a portable telephone with a coil for cutting out high-frequency interference |
| JP2005341118A (en) * | 2004-05-26 | 2005-12-08 | Hitachi Communication Technologies Ltd | Filter circuit, logic ic, multichip module, filter mount type connector, transmitting device, and transmission system |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5337012A (en) * | 1976-09-16 | 1978-04-05 | Sharp Corp | Flame retardant speaker |
| JPS5514719B2 (en) * | 1976-04-05 | 1980-04-18 |
-
1990
- 1990-09-13 JP JP24312690A patent/JPH04122111A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5514719B2 (en) * | 1976-04-05 | 1980-04-18 | ||
| JPS5337012A (en) * | 1976-09-16 | 1978-04-05 | Sharp Corp | Flame retardant speaker |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2303990A (en) * | 1995-07-31 | 1997-03-05 | Sony Uk Ltd | Microphone amplifier |
| GB2303990B (en) * | 1995-07-31 | 1999-05-05 | Sony Uk Ltd | Microphone amplifier |
| GB2344252A (en) * | 1998-11-26 | 2000-05-31 | Nec Corp | Compact microphone for a portable telephone with a coil for cutting out high-frequency interference |
| JP2005341118A (en) * | 2004-05-26 | 2005-12-08 | Hitachi Communication Technologies Ltd | Filter circuit, logic ic, multichip module, filter mount type connector, transmitting device, and transmission system |
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