DE1214272B - Directional pipe microphone - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

int. α .:

H04r

German KL: 21 a2- 14/01

Number: 1214 272

File number: S 92431 VIII a / 21 a ²

Filing date: August 1, 1964

Opening day: April 14, 1966

The invention relates to a directional pipe microphone, consisting of a microphone pointing towards the sound source Directional tube, which guides the sound to the front of the membrane, and any electro-acoustic Converter system, for example a capacitor capsule.

It is known to use shotgun microphones using acoustic pipes with side sound inlets to build. The sound inlets are covered with a resistance coating. It the aim is that the directional characteristic generated by the shotgun should be as independent of frequency as possible is. This is achieved in the previously known designs by changing the length of the directional tube for the lowest frequency at which a certain directional characteristic is required and the resistance coating staggered in such a way as a function of the tube length that the shotgun with acoustically shorter with increasing frequency. With these versions you either make the front, d. H. the part of the shotgun tube facing the sound source or the rear part of the shotgun tube ineffective for the high frequencies. Arrangements of this kind are described in the following publications: German Patent 955 247; U.S. Patent No. 2,856,022; Acoustic supplements, Acustica, Issue 1/1954, K. Tamm and G. Kurtze, "A new type of microphone with great directional selectivity"; Radio Mentor, issue 11/1965, Hans-Joachim Griese, "Das Telemikrofon"; Radio Mentor 1959, P. 090 to 093, Griese and Hoffmann, "A tele microphone with a frequency-independent directional characteristic".

Constructions of this type have the disadvantage that the shotguns are very long and that their Sensitivity is greatly weakened compared to the sensitivity of the transducer system itself.

In the Proceedings of the IRE, July 1939, pp. 438 to 455, H. F. Olson under the title "Line Microphones" describes a different principle. A tube bundle is used and the one entering at the front Sound given a transit time delay in the form of a hairpin-shaped bent piece of pipe, so that thereby the tube bundle appears elongated. Constructions of this type are by the The tube bundle itself and the hairpin-shaped transit time sections are very unwieldy. Besides, manufacturing is such bent pipes are very expensive. By merging the individual bundles in a hum pipe and ending in an acoustic sump incur significant losses, which the Reduce sensitivity very much.

Directional pipe microphone

Applicant:

Sennheiser electronic, Dr.-Ing. Fritz Sennheiser,

Wennebostel, Post Bissendorf (Hann.)

Named as inventor:

Otto Hoffmann, Hangelar on Siegburg

Claimed priority:

German industrial fair Hanover 1964,

Hanover, opening day April 26, 1964

It is the object of the invention to solve the above-described difficulties of the two different types To fix versions and to show a new principle, which makes it possible with a single very short shotguns produce the effect of long shotguns and also the sensitivity to increase compared to the previously known constructions.

This object is achieved in that the shotgun is an acoustic line that is used for frequencies, whose wavelength is greater than the mechanical length of the pipe, one that increases with decreasing frequency Has maturity.

An embodiment of the invention is characterized in that the aiming tube is open at the front and most of its length, measured from the sound inlet end, on its coat Sound inlets, for example, a longitudinal slot parallel to the pipe axis, or this approximately equivalent Individual openings, and that these inlets are occupied with acoustic resistances and that the acoustic resistance per unit length of the pipe is location-dependent.

Another embodiment of the invention is characterized in that the sound recording by the jacket inlets of the shotgun tube per unit length of the tube near the front opening Has a maximum, the amount of which is significantly greater, for example more than twice as large as the corresponding amount at the end of the pipe facing the transducer system.

Another embodiment of the invention is characterized in that the resistance lining of the Jacket inlets of the shotgun through a uniform

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union fabric covering is made and that the required location dependence of the resistance through the opening cross-section is established.

Another embodiment of the invention is characterized in that the resistance lining of the Jacket inlets of the shotgun tube is made by zones of different fabric layers, which different acoustic resistance, and that within each zone the required location dependence of the resistance due to the opening cross section of the jacket inlets is set.

Another addition to the invention is characterized in that the converter system has one more or has several inlets to the space behind the membrane, which are assigned to the low frequencies and the appropriate phase-shifting acoustic for these frequencies Elements provided skid.

Another embodiment of the invention is characterized in that electrical and / or ao acoustic elements are provided for influencing the low frequency response, if necessary adjustable or switchable.

The A b b. 1 to 3 are intended to explain the invention. In Fig. 1, the short shotgun is shown schematically as an embodiment. For example, it is 40 cm long. It is denoted by 1, the transducer system by 2. The membrane 3 is indicated by dashed lines. The tube is open at its end 1.0 facing the sound source. In this example, a longitudinal slot 11 and a longitudinal slot 12 are shown as the jacket inlet on its jacket surface. The cross section of the slot 11 increases a little towards the pipe end 1.0 when viewed from the transducer element. The increase in cross section of the slot 12 increases significantly more in the same direction. The slot 11 is covered over most of its length with the fabric covering 11.1, for example made of silk or synthetic fibers, which per unit area, for example, has the acoustic resistance 2.0 - this number is an arbitrarily chosen number. On the remaining part, a fabric material is used whose resistance per unit area is less, for example 1.7. This material is designated 11.2. It also covers part of the slot 12. The remaining part of the slot 12 is then covered with a fabric whose resistance per unit area is even smaller, for example 1.3. In this example there are three zones of different resistance material. The zones are labeled 11.1, 11.2 and 12.1. The Ab b. 2 shows the sensitivity E of such a directional tube, based on a unit length of the tube at different frequencies. The slot length is measured in the direction of the pipe length. The curve shows that through the front opening, the large cross section of the slot, the fabric layer 12.1 and the air mass in the front part of the tube near the end 1.0 of the tube, there is a maximum of sensitivity at low frequencies. The sensitivity then falls sharply due to the above-mentioned points and due to the type of occupancy, and then finally remains approximately constant over the largest part of the pipe. In this example, the housing of the transducer system 2 also has an opening 4 which is used for sound entry to the rear of the membrane 3. A pipe dimensioned in this way shows, as an acoustic line, a special behavior which is used according to the invention. The sound entering at the very front receives an increased phase shift due to the air plug at the front end of the pipe (1.0 in A b b. 1) and the illustrated resistance assignment of the jacket inlets, especially at the low frequencies.

It causes a delay in running time without mechanical extension of the tube, so that the shotgun acoustically acts as if it were mechanically much longer. Fig. 3 shows these relationships for the frequencies 0.2, 0.5, 1.0, 3 kHz. For a 40 cm long shotgun is for the frequencies 1 and 3 kHz the relative phase response - = const.

At 0.5 and 0.2 kHz, the illustration shows that there are also very strong phase rotations, which is synonymous is a propagation delay.

Fig. 4 shows an example of the location dependency the resistance assignment of the slots.

Claims (7)

Patent claims: 1. Directional pipe microphone, consisting of a directional pipe pointing to the sound source, which conducts the sound to the front of the membrane, and any electroacoustic transducer system, for example a condenser capsule, characterized in that The shotgun is an acoustic line that is used for frequencies whose wavelength is greater than that mechanical length of the pipe, has a running time that increases with decreasing frequency. 2. directional tube microphone according to claim 1, characterized in that the directional tube at the front , is open and it is open over most of its length, measured from the sound inlet end its jacket has sound inlets, for example a longitudinal slot parallel to the pipe axis or This approximately equivalent individual openings that these inlets with acoustic resistances are proven and that the acoustic resistance per unit length of the pipe is location-dependent. 3. Directional pipe microphone according to claim 2, characterized in that the sound recording at low frequencies through the jacket inlets of the shotgun per length unit of the shotgun in the vicinity of the front opening has a maximum, the amount of which is significantly greater, for example is more than twice as large as the corresponding amount at the end of the pipe, which facing the converter system. 4. Directional pipe microphone according to claim 2, characterized in that the resistance coating the jacket inlets of the shotgun tube is made by a uniform fabric covering and that the required location dependence of the resistance due to the opening cross-section of the jacket inlets will be produced. 5. Directional pipe microphone according to claim 2, characterized in that the resistance coating the jacket inlets of the shotgun is made by zones of different fabric layers, the has different acoustic resistance, and that within each zone the required location dependence of the resistances through the opening cross-section the jacket inlets is made. 6. Directional pipe microphone according to one or more of the preceding claims, characterized in that indicates that the transducer system has one or more inlets to the space behind the Membrane possesses, which are assigned to the low frequencies, and possibly for this Frequencies are provided with corresponding phase-shifting acoustic elements. 7. Directional pipe microphone according to one or more of the preceding claims, characterized in that that it contains electrical and / or acoustic elements to influence the low frequency response, which can optionally be set or switched on. 1 sheet of drawings