DE1162415B - Sound receiver with preferably one-sided, optionally adjustable directional characteristic, containing one or more transducer systems working according to the electrostatic principle - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: H 04 w

German class: 21 a2 -3

Number: 1 162 415

File number: A 39536 VIII a / 21 a2

Filing date: February 22, 1962

Opening day: February 6, 1964

The unilateral directional effect of a microphone is known to be achieved in that the moving element of the transducer, so the membrane, is acted upon by sound from both sides, with one side of the The membrane (front) is directly exposed to the sound, while the other side (rear) is exposed to a phase-rotating acoustic network is connected to the sound field. Through this arrangement the phase of the driving sound pressure is rotated by as much as the running time of the Front corresponds to the back of the membrane. It is easy to see that as a result the Sound waves reaching the microphone on the back are compensated in their effect on the membrane so that the membrane remains at rest (backward damping).

The same effect can also be achieved by using a pressure receiver with a spherical (all-round) directional characteristic electrically with a pressure gradient receiver with figure eight (two-sided) directional characteristic combined.

A microphone constructed in this way produces the optimum effect in the flat sound field, i.e. H. in one relatively large distance from the sound source. If you approach it mostly as punctiform assumed sound source, its sound field can no longer be regarded as flat, but than spherical.

In the spherical sound field, however, the value of the pressure gradient increases when the sound source is approached with decreasing frequency increases strongly, whereas the pressure difference in the plane sound field between two points lying in the direction of propagation of the sound waves approximately linearly up to that frequency increases, at which half the wavelength becomes equal to the distance between the two points.

It is therefore understandable that a microphone adapted to pick up plane sound waves, the has the pressure gradient as the driving force, in the spherical sound field (i.e. when speaking at close range) the reproduces low frequencies in preference to medium and high frequencies.

Another consequence, as theoretical and practical studies have shown, is a very great one severe degradation in reverse attenuation (cancellation) for these frequencies, i.e. a degradation the one-sided directional characteristic. Associated with this is an increase in the recorded Sound energy, which is known to be around a quarter smaller in transducers with a cardioid characteristic than with an omnidirectional converter.

To reduce the above-described sound receiver with preferably one-sided,
optionally adjustable directional characteristic,
containing one or more transducer systems working according to the electrostatic principle

Applicant:

Acoustic and cinema equipment company m. B. H., Vienna

Representative:

Dipl.-Ing. W. Scherrmann, patent attorney,

Eßlingen / Neckar, Fabrikstr. 9

Named as inventor:

Dipl.-Ing. Bernhard Weingartner, Vienna

Claimed priority:

Austria of June 19, 1961 (No. A 4749/61)

Disadvantages have already been proposed, the increase in the low frequencies when talking at close range Activation of appropriately dimensioned, possibly also controllable acoustic or electrical Balance attenuators, with the regulation affecting the frequency response of the output voltage the converter system, which can also consist of several individual systems, is limited. It is Obviously, this improves the frequency response, but by no means improves it the backward attenuation can be achieved, because for this the influencing of the frequency response remains the combined output voltage of all transducer systems of the sound receiver used without effect.

In contrast, it is the aim of the invention to provide measures that allow both the effect of the pressure as well as the pressure gradient at any frequency and at any distance from the To make the sound source approximately the same and so not only the O ° frequency response as a function of the To make distance selectable adjustable, but also, independently or coupled with this setting

409 507/304

3 4

ment, the extinction for rearward sound incidence can be seen at the output of the pressure gradient receiver 2 for each meeting (sound) distance opti- and the input of the amplifier 4 a frequency times to design. dependent electrical attenuator which, as in

This goal is achieved with a sound receiver shown in Fig. 1, as a switchable .RC member can be formed with preferably one-sided, possibly one-sided. This attenuator consists of an adjustable directional characteristic, which contains one or more of the source impedance of the transducer 2 with the wall capacitance C ₀ operating on the electrostatic principle and the angelersystems via the capacitance C, in that to compensate for the switched three resistors R ₁ , R . ,, R ... of which the influence of a sound system from each different one can be switched on at least one of the built-in io capacitorsC by means of the switch U on the Able distances. In a tube amplifier, the counter-transducer systems variable, frequency-dependent, attenuators can be associated with equal electrical and / or acoustic attenuators as grid leakage resistors of the amplifier tube, which are assigned via setting elements that also serve.

Distance information bearing scales, markings, of the known arrangements in which a

Symbols or the like interact, are adjustable. 15 pressure receivers with spherical characteristics

According to a further feature of the invention with a pressure gradient receiver with eight

are used in a sound receiver that has both a moderate characteristic in a common housing

Pressure receiver as well as a pressure gradient is housed and their outputs at the entrance

receiver contains, the latter are the frequency-dependent, a common amplifier, so that one

adjustable electrical and / or acoustic 20 one-sided, preferably cardioid-shaped directional character

Attenuators assigned, so that the increase teristics results, the invention differs

of the gradient at the low frequencies in the spherical circuit arrangement in that for each

sound field (close-up discussion) are compensated for, a separate amplifier is provided and a converter is provided

can. the frequency-dependent electrical attenuator

In the case of a sound receiver that has only one transducer 25 not in the common amplifier output, but rather

system with a unidirectional directivity, in the transmission path of the pressure gradient receiver,

that with a phase-rotating, acoustic RC- so preferably between microphone output and

Element is equipped, is switched on according to a further memory amplifier input. This will

times the invention of the acoustic capacitance an acu in the invention in contrast to the known

static frictional resistance connected in parallel or an arrangement that only corrects the fre-

with this capacitance in a series connection causes a sequential response, for each frequency and for each

arranges. Meeting distance the same sensitivity and

In addition to this measure, the same backward attenuation of the converter combination can be

tric transmission path of this transducer system achieves a nation in the sound receiver,

controllable, frequency-dependent electrical damper 35 It also differs accordingly from one

Fungelement, preferably an IC element, switched on already proposed measure, in such

be. Combination converters frequency-dependent electrical

The invention is now to approximate links in the transmission path of a single system with reference to the drawings explained. assign. These limbs were the only ones to have

Fig. 1 shows the electrical circuit diagram of an additional task, the frequency response in a flat sound field

to correct interconnection of a pressure receiver with and at those high frequencies, at

Pressure gradient receiver, in which only one elec- tric half the wavelength is equal to the sound

tric control is provided, in detour and where therefore the gradient microphone

Fig. 2 is the cross section through a pressure - a very strong undesirable phase response on-

gradient receiver arranged according to the invention.

Neten acoustic attenuators schematically Of course, the resistances of the in

shown; Steps of the switchable ÄC element must be dimensioned in such a way that

Fig. 3 shows the corresponding equivalent circuit diagram that within certain limits for each discussion

to this, at a distance of the pressure gradient

Fig. 4 is another embodiment of the invention 50 caused increase of the low frequencies compensate

to which is being sated. In this way, the reception

F i g. 5 is the corresponding equivalent circuit diagram, and the sensitivity of each of the two individual converters is always

FIG. 6 shows the external view of the same size according to the invention, and also the set one-sided directional view Sound receiver. Characteristic remains independent of the meeting

As already obtained in the description above.

Introduction was carried out, the goal of the With the arrangement according to the invention according to FIG. 1

Finding either purely electrically or it is also possible, optionally with the sound receiver

with purely acoustic means or a combination of either a spherical or a figure-of-eight pattern

nation of both measures. to give, depending on which converter of the system

In Fig. 1, an electrical circuit diagram 60 is first used alone. Switching can be done by

a sound receiver with two individual systems - a simple switch, since only elec-

provided, of which one of the receivers is to be connected to a pressure-tric circuit. In the position

is receiver 1 with spherical characteristics. "Figure eight characteristic" is also characterized by the

This works on an amplifier stage 3, so that it uses the device according to the invention in all

a uniform frequency response from the pressure gradient receiver 2 completely 65 meeting cases

is decoupled. The latter works on the amplifier 4, achieved.

its output together with that of the amplifier 3 Another embodiment of the invention,

is switched on. According to the invention, there is now between which a frequency-dependent acoustic damping

is used is shown in FIG. It is a directional microphone with a one-sided directional characteristic, which is achieved by an acoustic phase-rotating element. With such a microphone it is difficult to achieve selective attenuation of the figure eight. Theoretical considerations on a phase-rotating element formed from an RC element, as is usually used in condenser microphones, have shown that the deterioration of the backward attenuation and thus the increase in the recorded sound energy can be countered by very simple measures. For this purpose, according to the invention, the capacitance (restoring force) of the phase-rotating element causing the unilateral directional characteristic is connected in parallel with an acoustic frictional resistance, which can optionally be replaced by an equivalent series resistance. ao The value of the parallel acoustic

Frictional resistance should be approximately - ^ - times

of the frictional resistance of the i? C element, if r denotes the distance between the microphone and the sound source and Δ denotes the detour of the sound from the front to the rear of the membrane. In order to be able to adapt to the different meeting intervals, the frictional resistance must be changeable. Above all, it maintains the backward attenuation at low frequencies depending on the distance to the meeting, whereas the increase in sensitivity with 0 ° exposure can be compensated for by a selective attenuator in the course of the transmission path. The control of the backward attenuation as well as the output level can either be carried out separately from one another or else be carried out simultaneously by means of a single setting element.

In the case of the one shown in FIG. 2 shown schematically in section a unidirectional condenser microphone vibrates the diaphragm 5 relative to the highly perforate counter electrode 6. The charge for the formation of the single-sided directivity phase rotating RC element is formed by the represented by a cavity capacitance C and the acoustic frictional resistance R. Via the channel 7 and the narrow adjustable gap R 'there is a connection to the room C ", the acoustic impedance of which is much smaller than the frictional resistance R' formed by the narrow gap, so that the effect of this resistance far outweighs and if the Dimensioning according to the invention causes the desired effect.

In the equivalent circuit diagram F i g. 3 Z _{0 is} the acoustic impedance of the membrane 5, p ₀ and ρ _ϋ + Ά / ρ are the driving forces in two different points of the sound field. The other designations correspond to the identically named elements of the circuit diagram in FIG. 2.

It has already been mentioned that the additional controllable or adjustable acoustic frictional resistance can also be placed in series with the capacitance of the phase-rotating element generating the unilateral directivity. F i g. 4 shows schematically in cross section such an arrangement, to which FIG. 5 represents the corresponding equivalent circuit diagram. With 5 and 6 membrane and counter electrode are again referred to. The counter electrode 6 is designed here as a frictional resistance which, together with the annular space C, results in the phase-rotating member. According to the invention is now the lower chamber "corresponds to the g the parallel resistor R 'in F i. 2, connected to the capacitance C. The frictional resistance R" behind the diaphragm 5 via an acoustic friction resistance R is here also through a narrow, adjustable slit or Gap formed.

Finally, FIG. 1 shows how the proposal according to the invention can be implemented in practice. 6. The designed as a cylindrical, rod-shaped body has a sound-permeable sound receiver Part 7 and a housing part 10. On this housing part are, for example, annular Adjusting elements 8,9, which cooperate with scales with distance information, so that for each meeting distance both the backward attenuation and the output level to optimal transmission ratios can be adjusted. As already mentioned, the adjusting members can also be coupled or from a common organ be operated.

Finally, it should be pointed out that such a converter has a phase-rotating element for setting different directional characteristics in a manner known per se, also symmetrically with two membranes can be built up.

Claims (4)

Patent claims: 1. Sound receiver with one-sided, optionally adjustable directional characteristic, with a or several converter systems working according to the electrostatic principle, thereby characterized in that to compensate for the influence of a sound from each different Distances of at least one of the built-in converter systems changeable, frequency-dependent, electrical and / or acoustic attenuators are assigned, which via adjusting elements, the scales, markings, symbols or the like bearing distance information interact, are adjustable. 2. Sound receiver according to claim 1, characterized in that it has two electrostatic Contains transducer systems, one as a pressure receiver, the other as a pressure gradient receiver is formed and both systems are electrically interconnected, the frequency-dependent electrical and / or acoustic attenuators are assigned to the pressure gradient receiver, so that at this converter, the increase in the gradient at the low frequencies in the spherical sound field (near sound field) is compensable. 3. Sound receiver according to claim 1, characterized in that the sound receiver only contains a single transducer system with one-sided directional characteristic, which is equipped with a phase-rotating, acoustic i? C-GMed is equipped, the acoustic capacity of which is changeable acoustical frictional resistance is associated, either in series with or parallel to the named capacity. 4. Sound receiver according to claims 1 and 3, characterized in that in the electrical transmission path of the converter system in addition, an adjustable, frequency-dependent electrical attenuator, preferably one ÄC member is inserted. Considered publications: German Patent Nos. 927 037, 924 807, 821,920 311; German interpretative document No. 1044 170. For this purpose, 1 sheet of drawings 409 507/304 1.64 © Bundesdruckerei Berlin