Microphone circuit for linearizing the proximity effect in a dynamic directional microphone

Description

[0001] The invention relates to a microphone circuit for linearizing the proximity effect in a dynamic directional microphone according to the preamble of claim 1.

[0002] Dynamic directional microphones are commonly used in both studio recordings and live performances. These microphones have the ability to deliver different frequency responses depending on whether the sound source is in the near or far field. In the near field, higher sound pressure occurs at low frequencies, an effect known as the proximity effect. This proximity effect is often undesirable, as universal microphones, for example, are designed to be effective in both the near and far field.

[0003] Microphone circuits are used in the current state of the art for various purposes, such as suppressing handling or impact noise, or for other purposes of adjusting the recording signal. Typically, the aim is to influence the microphone signal as early as possible, ideally directly after the microphone capsule, in order to keep the overall energy in the system low. Possible microphone filter circuits are implemented as active, passive, or a combination of these networks in any configuration. Manual control via switches on the microphone is optionally available to the user.

[0004] US 2007079694 A1 shows a circuit for reducing acoustic feedback from a microphone. The signal emitted by the microphone is mirrored and calibrated via a resistor to such an extent that an offset to the base signal is created. The newly acquired signal is then combined (summed) with the base signal via a mixer. Assuming synchronization, a linearized output signal is obtained, which is said to exhibit more stable feedback behavior. Furthermore, the constant signal adjustment via a feedback loop is potentially error-prone, as this is only implemented after the actual microphone in the amplifier circuit. This introduces additional interfering factors into the signal to be corrected and distorts it. Such circuits are also unsuitable for low frequencies, where the proximity effect occurs.

[0005] US 20080019540 shows a circuit for an electret microphone in which a resistor is connected in parallel with a field-effect transistor (FET). In this way, the voltage between the drain and source of the FET is intended to be reduced in electret microphones, which are also active microphones. This amplifier circuit is arranged after the actual microphone capsule. The linearization of the sensitivity is mentioned as a positive effect of the parallel resistor, according to a derived formula and results based on it. The ratio of dVds / dVgs, which corresponds to the sensitivity of the electret microphone, can be reduced by linearizing the drain-source voltage through the resistor. This reduces the sensitivity, which in turn lowers the signal-to-noise ratio. This invention also provides no indication of possibilities for reducing the proximity effect.

[0006] US 9 813 791 B1 shows a microphone circuit in which the electrical recording signal is manipulated by switching on a classic high-pass filter between the two operating states "Voice Mode" and "Music Mode" in order to counteract the proximity effect.

[0007] Another known option from the state of the art is the mechanical damping of a microphone capsule, for example, using mesh or damping pads for the microphone diaphragm. Since the proximity effect occurs in a frequency range from 50 Hz to 300 Hz, this solution is fundamentally feasible. However, the disadvantage of this implementation is that, due to its purely mechanical nature, the behavior is rigid and offers no options for adaptation to the environment. Further complicating the situation is that the damping components alter the directional characteristics of the microphones, which is undesirable.

[0008] The aim and object of the invention is to solve this problem, i.e. to achieve an attenuation of dynamic directional microphones and a concomitant linearization of the proximity effect without mechanical components.

[0009] According to the invention, this is achieved by the features specified in the characterizing part of claim 1; in other words, by a microphone circuit for the directional microphone that has at least one impedance element with inductive properties. The impedance element can be any passive electronic component connected in parallel with the microphone capsule and having an effective and an inductive reactance. The value of the parallel-connected impedance is preferably between 20 and 1000 ohms, more preferably between 300 and 700 ohms.

[0010] In contrast to conventional filters, the impedance element connected in this invention disproportionately dampens the natural resonance or quality factor of the oscillating dynamic microphone system. The shape of the microphone's amplitude response returns to its original shape on both sides outside its effective range. The natural resonance damping of the oscillating dynamic system in the application described here occurs at the electrical level using components already present in the system. These components can, for example, correspond to a hum cancellation coil, noise suppression coil, or EMC components and thus perform a dual function in the system. The value of the parallel-connected impedance is also between 20 and 1000 ohms, whereby the effective resistance can be small. In this context, "small" means, for example, the ohmic resistance of a commercially available hum cancellation coil for dynamic microphones.

[0011] The invention is explained in more detail below with reference to the drawing, which shows: the Fig. 1 a standard design of a dynamic microphone circuit with hum compensation coil, which Fig. 2 another standard design of a dynamic microphone circuit with hum compensation coil, which Fig. 3 an inventive microphone circuit with a microphone capsule and a parallel impedance, the Fig. 4 another microphone circuit according to the invention with a microphone capsule and a hum compensation coil or noise suppression coil that can be connected in series or in parallel, which Fig. 5 a variant of a circuit of a dynamic microphone according to the invention according to Fig. 3 and amplifiers that Fig. 6 a variant of a circuit of a dynamic microphone according to the invention with switchable hum compensation coil according to Fig. 4 and amplifiers that Fig. 7the differences in the amplitude response of an output signal achievable according to the invention, normalized at 1 kHz.

[0012] In accordance with technical jargon, the term "impedance element" is often used below and in the claims simply as "impedance".

[0013] The Fig. 1 shows a standard design of a dynamic microphone 1 circuit, as known from the prior art, with a hum-cancelling coil 2 connected in series with a moving coil 3. The microphone 1 does not have an integrated amplifier.

[0014] The Fig. 2 shows another prior art standard design of a dynamic microphone circuit 1 with a hum compensation coil 2 connected in series with a moving coil 3. The microphone 1 does not have an integrated amplifier.

[0015] The Fig. 3shows an example of a circuit according to the invention of a microphone 1, in which a microphone capsule 4 of an inductive impedance 5 can be connected in parallel via a switch S1. For the signal appearing at the signal output 6 and the differences resulting from the circuit states, reference is made to the Fig. 7 The illustration shown with open switch S1 corresponds to an undamped behavior.

[0016] The Fig. 4shows an example of a circuit according to the invention for a microphone 7, which comprises a microphone capsule 4 and an inductive impedance 5, which can be, for example, a hum compensation coil, a noise suppression coil, or more generally a mechanically oscillating system that dampens mechanical noise (handling noise, impact noise, etc.). This also consists of a membrane / coil system without sound ingress. In the position shown, the impedance 5 and the microphone capsule 4 are connected in series. This position corresponds to the undamped behavior at the signal output 6. Fig. 7 If switch S2 is closed, impedance 3 and microphone capsule 2 are connected in parallel, which corresponds to the damped behavior at signal output 4. Fig. 7 corresponds.

[0017] The Fig. 5shows an exemplary embodiment of a circuit of a dynamic microphone 1 according to the invention with serial hum compensation coil 2 and downstream inductive impedance element 5 according to Fig. 3 This can be switched on and off as needed using switch S1. An amplifier 8 is connected downstream of the actual microphone capsule 4 as part of the dynamic microphone. The microphone is divided into an electronic part 9, which contains the amplifier 8 and the parallel impedance 5, and a purely passive mechanical-acoustic part 10, which contains the microphone capsule 4 with the separate hum compensation coil 2.

[0018] The Fig. 6 shows an exemplary embodiment of a circuit of a dynamic microphone 7 according to the invention with a hum compensation coil as a switchable parallel impedance 5 according to Fig. 4The switch S2 makes it possible to switch from the standard series connection of the hum cancellation coil as a parallel impedance 5 and moving coil 3 to a parallel connection. An amplifier 8 is shown connected downstream as part of the dynamic microphone. The microphone is divided into an electronic part 9, which contains the amplifier 8, and a purely passive mechanical-acoustic part 10, which contains the microphone capsule 4 with the hum cancellation coil 2 built into it and the switchable parallel impedance 5.

[0019] The Fig. 7 shows an amplitude response, standardized at 1 kHz, for an undamped (state-of-the-art) and a damped output signal achievable according to the invention for the frequency range of 20 Hz - 20,000 Hz. The amplitude difference between the damped and undamped states for the frequency range of 50 Hz - 300 Hz is clearly visible.

[0020] If, due to the general conditions, a higher output signal is required in the relevant frequency range, the impedance 5 can be adjusted either via the Fig. 3 or Fig. 5 and Fig. 4 or Fig. 6 deactivate the switches S1 and S2 shown, or amplify them by means of an amplifier 8 connected downstream of the output signal.

[0021] The Fig. 3 and Fig. 4 shown embodiments of the invention as well as their more detailed representations Fig. 5 and Fig. 6 are to be understood as examples. Although it is advantageous in most cases if the designs have the switches S1 and S2 shown in the figures, for cases where this is not desired for certain reasons, a microphone circuit is also possible that does not require the switches S1 and S2. This design then corresponds analogously to Fig. 3 and Fig. 4 permanently closed switches.

[0022] As an inductive impedance element 5, hum compensation coils (as in Fig. 6 shown) but also noise suppression coils or EMC components. The advantage lies in the fact that these components are often already included in the microphones, but are connected in series. With a simple circuit, these existing components, such as in Fig. 6 As shown, they can be connected in parallel and used to dampen the microphone's natural resonance. Damping the natural resonance thus leads to a simple and efficient linearization of the proximity effect.

[0023] Measured examples of the ratio of effective resistance to reactance of the impedance are: Example 1: 600 Ohm active resistance and 16 Ohm reactance, measured at 1kHz Example 2: 260 Ohm effective resistance and 12 Ohm reactance, measured at 1 kHz Example 3: 360 Ohm effective resistance and 7 Ohm reactance, measured at 1 kHz

[0024] However, the explanations are not limited to the examples given; in principle, any ratio of reactive impedance to effective impedance can be assumed, provided that subsequent measurements show it to be effective for reducing the proximity effect in a dynamic directional microphone. The impedance range is preferably between 20 and 1000 ohms, and even more preferably between 300 and 700 ohms.

[0025] A parallel circuit is the connection of several reactive and / or active resistors that have the same voltage direction in the steady state (see Deimel et al., "Fundamentals of Electrical Engineering 1," 2000, R. Oldenbourg Verlag, Vienna, pp. 82ff and Deimel et al., "Fundamentals of Electrical Engineering 2," 2001, R. Oldenbourg Verlag, Vienna, pp. 86ff). In contrast, structures with an opposing element are referred to as negative or feedback loops (see Lutz & Wendt, "Handbook of Control Engineering," 2010, Wissenschaftlicher Verlag Harri Deutsch, Frankfurt am Main, pp. 34ff).

[0026] The features and variants specified in the individual embodiments and examples can be freely combined with those of the other examples and embodiments and can be used in particular to characterize the invention in the claims without necessarily including the other details of the respective embodiment or example. List of reference symbols:

[0027] 1Microphone circuit 2Hum compensation coil 3Moving coil 4Microphone capsule 5Parallel impedance element 6Signal output 7Microphone circuit 8Amplifier 9Electronic part of the microphone circuit 10Mechano-acoustic part of the microphone circuit S1Switch S2Switch

Claims

1. Microphone circuit (1, 7) for linearising the proximity effect in a dynamic directional microphone, characterised in that the microphone circuit has at least one inductive impedance element (5) which can be connected in parallel with the microphone capsule (4).

2. Microphone circuit (1, 7) according to claim 1, characterised in that the impedance element (5) arranged in parallel can be connected via a switch (S1, S2).

3. Microphone circuit (1, 7) according to claim 1 or 2, characterised in that the impedance element (5) is a hum compensation coil or noise suppression coil which, in the non-damping state, is connected in series with the microphone capsule (4) of the directional microphone.

4. Microphone circuit (1, 7) according to any one of claims 1 to 3, characterised in that the impedance of the impedance element (5) is between 20 and 1000 ohms.