SU77499A3 - Microphone - Google Patents

Description

The subject of the invention is a directional microphone for use with sound recording and the like installations where it is desirable to exclude the effect of interfering sounds on the microphone. The microphone provides directional characteristics that are independent of the frequency of the perceived sound.

The proposed microphone contains a large number of sound tubes of various lengths connected to a common channel, connected to one side of the sound to electric transducer, and loaded on its other side with acoustic impedance.

A feature of the proposed microphone is that the input ends of the sound tubes are arranged in steps. With this design, the distance between the longest and shortest tubes determines the directivity of the microphone.

The foregoing is explained in the drawings.

FIG. 1-14 show various modifications of a microphone made according to the invention; in fig. 15-17 are examples of the use in the proposed microphone of various transducers of acoustic oscillations into electric; in fig. 18 is a schematic diagram of a microphone in accordance with the invention; in fig. 19 and 20 - frequency characteristics of two versions of the proposed microphone; in fig. The 21-frequency characteristic of the microphone as shown in FIG. 18; in fig. 22 is a fully assembled microphone constructed in accordance with the present invention and mounted for operation as shown in FIG. 18.

The microphone contains several / -6 sound tubes with progressively varying length, connected to a common box 7 in which a tape 8 is mounted, which can vibrate in a magnetic field in a known manner. Tubes / -6 must be of such length as with 77499-2 -

Their free ends lie on the same straight line, preferably parallel, and so that sound waves can be directed to the front surface of the vibrating element or tape 8. The diameters of the I-6 tubes are preferably identical and small compared to the length of the tape 8. To the back of the box 7 is attached tube 9, filled with felt 10 or. similar material and acoustic resistance together with felt limited by tape S and having a value very close to the wave resistance of tubes 1-b / and greater compared to the resistance of the mass of tape 8. The total surface of the cross-sections of the tubes / -6 is chosen but the possibility of an equal surface of the cross tube section 9. This reduces the reflection in the box 7, especially if the acoustic resistance of the tape 8 is small compared to the resistance of the tube 9. If the resistance of the tape is comparable to the ripple If the tubes are i / 6, the vector sum of the resistance of the part of the device (tube 9 with felt 10 to tape 8) and the resistance of tape 8 itself must be equal to the wave resistance of the tubes.

The calculation of the magnitude of the pressure on the microphone generated by the received sound vibrations at different angles of incidence of the sound shows that by selecting the appropriate ratio of the length of the tubes to the wavelength it is almost possible to obtain any directional characteristic of the microphone.

In the microphone shown in FIG. 1, there may be some attenuation of sound in tubes / -6 at high frequencies. This loss can be compensated by attaching to the ends of the tubes 1-6 small consoles - horns.

The microphone shown in FIG. 2, has such prefixes, designated by numbers // - 16 and fixed on the free ends of tubes 1-6. The characteristic of each of the small horns // - 16 can be made such that the horns increase the pressure from any tube 1-6 at high frequencies and do not affect the sound at low frequencies. Increasing the pressure compensates for the loss of sound attenuation in each of the small tubes.

In some cases, it is inconvenient or undesirable due to losses in the tubes 1-b to attach the latter in the box 7 inside which the tape is placed. The microphone can therefore be made as shown in FIG. 3, where a tube section 17 is inserted between the tube 9 and the auxiliary box 18 to which the tubes / -5 are attached. Such a structure does not distort the characteristics at all. The cross-sectional area of the tube 17 is preferably made equal to the sum of the cross-sectional areas of the tubes 1-5, and the tape 8 can be set at the end of the acoustic impedance.

FIG. 4 shows a modification of the microphone, in which the tubes 2, 3, 4 and 5 are equipped with a double bend 2a, 3a, 4a, and 5a, respectively, contributing attenuation. The elbows 2a-5a progressively extend in accordance with the lengths of the tubes, parts of which they form, so that, for example, the very long tube 5 has the longest elbow 5a. As a result of the introduction of attenuation into the tubular elements by means of bends 2a-5a, a more pronounced characteristic of the directivity is obtained.

FIG. 5 shows the modification of the microphone, the action of which is based on the use of the difference of the resulting pressures of the two systems of tubes. One system comprises tubes 21-25, connected together in an element 26, to which is also connected a length of tube 19 filled with felt 20; another system consists of a series of tubes 31-35 connected to a common element 27, to which is also connected a tube 28

with felt 29 inside it. The difference between the lengths of both tube systems is characterized by the difference between the average length of the tubes 21-25 and the average length of the tubes 31-35 or, with the same changes in the length of the tubes in both systems, the difference in the lengths of the tube systems can be expressed by the difference in the length of any corresponding tubes, for example 2 and 32. The tube 28 in this form of the microphone is provided with a bend 30 having a length equal to the aforementioned difference between the lengths of both tube systems. Tape 5 is placed between the tubes 19 and 28 and is driven by the pressure difference in these tubes. The length of the knee 30, it is preferable to do so less than half the wavelength captured by the device, as far as possible practically. This creates significantly sharper characteristics.

FIG. 6 shows another variant of the microphone, similar to the microphone shown in FIG. 5, but with the direction of the individual tubes 21-25 of one system and the tubes 31-35 of the other system directly onto the tape 8 from its opposite sides, and not towards the boxes 26 and 27, as shown in FIG. 5, with tubes 31-34 having progressively changing elbows.

FIG. 7, a modification of the microphone is given, which is a combination of the embodiments of FIG. 4 and 5. The directional characteristic of this design is made narrower.

FIG. 8 illustrates the modification of the microphone shown in FIG. 7. The microphone is similar in shape to the microphone shown in FIG. 6, in that the sound tubes are directed directly to the tape 8.

In the embodiment of the microphone shown in FIG. 9, tubes 21 and 31, 22 and 52, and so on, are pairwise connected, and tubes 31-35 for doing retardation are provided with elbows 31a-35a. The branches of the tubes 21-25 are connected by tubes 216-256 to one side of the tape 8, and the branches of the tubes 31-35 are connected by tubes 316-556 to the opposite side of the tape 8. Each tube system reaches acoustic resistances 19-20 and 28-29 as described above. This modification contains two tube systems, which are designed so that the output pressure characteristic is cosine.

In some cases, it is desirable to limit the low frequency portion of the microphone range. FIG. 10 shows how this can be done. If the tube 9, which reaches the rear side of the box 7 with the tape 8, is very long and is filled with sound damping material 10, then the impedance of the tube to the tape 8 is practically active resistance for all wavelengths. If tube 9 is less than a quarter of the wavelength, it acts as a capacitance. This means that the impedance increases as the tube length decreases. Thus, the impedance of the tubes becomes larger and the speed of the tape moving decreases. The effect of using a long tube 9, which represents the resistance, compared to using a short tube, is explained by the frequency response shown in FIG. 19. A microphone with a short tube 9, ending at the tape 8, as shown in FIG. 10, limits the low frequency.

For microphones of the type in question, the tubes have attenuation which is proportional to the frequency and inversely proportional to the diameters of the tubes.

FIG. 11 shows a microphone with tubes of 36-40 different diameters. The tube 40 has the smallest diameter and the smallest pressure at high frequencies. But at low frequencies, it will produce the same pressure as a short tube of the same diameter. This is a phenomenon

- 3 - № 77499

No. 77499 4 -

provides a method for producing such a system of tubes, which becomes shorter with increasing frequency and makes it possible to obtain a characteristic of uniform directivity. If the parameters are chosen so that the length is inversely proportional to the frequency, then the directivity will be independent of frequency.

FIG. 12 shows another way of shortening the effective length of the tubing system. The free or sound absorbing ends of the tubes 41-45 are provided with elements 41a-45a, which are obtained by narrowing the free ends of the tubes, preferably progressively and in accordance with the lengths of the tubes 41-45.

In such a design, the pressure on the belt 8 is weaker at high frequencies and the magnitude of the attenuation increases as it narrows. A suitable choice of parameters for the length of the system can be made inversely proportional to the frequency. Therefore, the ordinates of the directivity characteristics will be inversely proportional to the frequency.

In the microphone shown in FIG. 13, another method of shortening the effective length with frequency is used. Here, the tubes (-5) are provided with expanded sections or volumes (46-50) for receiving acoustic capacities, and these volumes progressively increase in the direction from the shortest tube / to the longest tube 5. Thus, it is possible to reduce the pressure created by any tube when high frequencies. A suitable choice of parameters for the length of the system can be made inversely proportional to the frequency.

In the microphone shown in FIG. 14, a reduction in the high frequency amplitudes of the entire system is achieved. In this form of implementation, a narrowing 9a is made. As noted above, the constriction impedance increases with frequency. Narrowing 9a will reduce the speed of the tape 8 at high frequencies. The relative effect of the constriction is shown by the frequency characteristics in FIG. 20.

In all the microphones described, the tape 8 serves as electroacoustic transducers for converting sound vibrations into corresponding electrical oscillations. For this purpose, as shown in FIG. 15, the magnet 51 creates a magnetic flux in the air gap in which the tape 8 is placed with the possibility of its oscillation between the pole pieces 52. In FIG. 16 shows a microphone design using an electrodynamic system consisting of a magnet 53 and a membrane 54 with a voice coil, which is known in a known manner in the air gap between the poles of the magnet 53.

FIG. 17 shows the construction of a microphone with a capacitor transducer 55 acoustic oscillations into electrical. This design has certain advantages, since the acoustic impedance of the condenser microphone is large and does not change the impedance of the connection of the sound tubes to the large tube.

FIG. 18 shows a diagram of a fully assembled microphone with four separate tube systems 56, 57, 58 and 59. These tube systems can be formed in accordance with any form of the invention described above and commensurate to overlap from 50 to 10,000 Hz, for example, so that each system of tubes covered a given portion of the range and so that the characteristics were uniformly directed over the entire range. In practice, the low-frequency system of tubes 56 can have a length of about 3 m, the system of tubes 57 of an average low frequency is about 1 m, the system of tubes 58 of an average increased frequency is about 300 mm, and the high-frequency system of tubes 59 is about 100 mm. Appropriate electrical connections can be connected to these tube systems, respectively.

filters 56a-59a for frequency separation at the output. The frequency characteristics of the individual tube systems along with the filter system may be as shown in FIG. 21. Such a complex system makes it possible to obtain a characteristic of almost uniform directivity.

FIG. 22 shows a fully assembled microphone mounted for operation. The microphone includes tube systems 56-58 mounted inside a perforated box 64, open at the sound pickup end, and pivotally supported by a bracket 60 on a stand 61. The latter consists of two pivoting telescopically extending sections 62 and 63; With the help of them and the hinge bracket, the microphone can be directed in any direction.

Subject invention

A directional microphone, characterized in that the input ends of the sound tubes, each of which has a length that is different from the length of the others, are arranged in steps.

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