Coupling Member for a Capacitive Microphone

The present invention relates in general to microphones and in particular to a new and useful coupling member for capacative microphones.

Rod or generally cylindrically shaped microphone assemblies incorporate a capacitive michrophone and a preamplifier. A coupling member is detachably connected between the capacitive microphone and preamplifier by a screw thread connection, a plugging connection or the like.

Such coupling members are known per se and, in general, are intended for connecting microphone capsules of various types to a respective suitable microphone preamplifier. The problem underlying the present invention, however, is different. The coupling member is to be of a design which prevents sound which is transmitted through solids, from passing from the housing of the preamplifier to the microphone capsule, without substantially increasing the volume of the microphone.

To prevent solid-borne noise caused by movements of a cable connected to the housing or by vibrations of the microphone casing, which pass to the transducer diaphragm where they produce electrical, disturbing, low-frequency oscillations, it is known to suspend the capacitive transducer in a resiliently damping manner within the microphone housing. A resilient mounting of this kind is described in German AS No. 14 37 433, for example. such a resilient mounting substantially comprises elastic, vibration-absorbing rings enclosing the electroacoustic transducer and fitted by their outer circumference into the microphone housing. Such a mounting has the disadvantage of considerably enlarging the volume of the housing and making it impossible to design the microphone housing in the shape of a slender cylindrical rod to be accommodated as inconspicuously as possible, for example during transmissions of theater productions, etc.

The present invention is directed to a rod-shaped capacitive microphone that is substantially cylindrical throughout and which is to a large extent insensible to sound that is transmitted through solids. To this end, it is provided, in accordance with the invention, that the above-mentioned coupling member has components which are made of elastic electrically conductive material.

Accordingly, an object of the invention is provide a coupling member for coupling a microphone capsule to a preamplifier which comprises a shaped body of vibration-absorbing elastic electrically conducting material for forming a first conductive connection between the capsule and the preamplifier, a contact pin including at least a portion made of vibration absorbing elastic electrically conducting material, extending axially in the shaped body for forming a second conductive connection between the capsule and the preamplifier, and connection means for connecting one end of the shaped body to the capsule and an opposite end of the shaped body the preamplifier.

The invention is based on the idea of providing the absorbing elastic mounting means outside the microphone housing, which results in a very simple construction in no way affecting the design of the housing as a slender, rod-shaped body, and ensuring the desired attenuation of structure-borne sound at the same time. Since the material of the shaped body is electrically conducting, this property is utilized for establishing an electrical connection between the microphone capsule and the preamplifier. Another electrical connection is then established through a contact pin which is located within the coupling member in central axial position and comprises a portion which again is made of a vibration-absorbing, elastic and electrically conducting material, so that no solid-borne sound can pass through the pin either. This contact pin may be a loose component part of the coupling member, or it may be mounted within the coupling member through a plate or diaphragm of a non-conducting material. This latter design has the advantage that the contact pin cannot get lost, while the design with a loose contact pin is simple and thus less expensive.

The coupling member designed as a resilient connecting piece performs the function of a mechanical filter, dissipating to the largest extent, the prevailing noise energy, so that hardly any low-frequency noise oscillations are transmitted to the diaphragm of the capacitive microphone accommodated in the capsule. Advantageously, the sound-absorbing connecting piece may be designed for conveying to the diaphragm, over the entire transmission range of 20 Hz to 20kHz of the capacitive microphone, as little nois energy as possible. This is obtained, in accordance with the invention, by providing that the elastic material for absorbing vibrations and used for the connecting part exhibits an internal mechanical friction which is frequency dependent and decreases with increasing frequency. The oscillatory system formed by the mass of the microphone capsule and the elastic coupling member has its natural frequency in the lower transmission range of the capacitive microphone and requires a strong attenuation within this range if a solid-borne sound transmission is to be avoided. It is well known that above the .sqroot.2-fold resonance frequency, a strongly damped oscillatory system for noise energies is more responsive to excitation than an oscillatory system which is damped only slightly or not at all. Therefore, with a frequency-dependent damping decreasing with the frequency increase, the noise energy is suppressed most effectively.

As already mentioned, it is further intended to make the coupling member of an electrically conducting material and thus to simplify the construction by omitting other electrically connecting parts. The invention therefore provides for the use of butyl rubber, bromobutyl rubber or nitrile rubber as the electricity conducting material for the coupling member.

A further object of the invention is to provide a coupling member for substantially rod-shaped microphone assemblies which is simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.

In the drawings:

FIG. 1 is a side elevational view of a rod-shaped capacitive microphone including the inventive coupling member; and

FIG. 2 is a sectional view of the coupling member.

Referring to the drawings, in particular, FIG. 1 shows a coupling member 2 which is provided between a microphone capsule or transducer 1 and the housing of a preamplifier 3, which causes only a slight, not disturbing, extension of the microphone. Coupling member 2 may even be used as a transition compensating piece for differences in diameter between the microphone capsule 1 and the preamplifier housing 3, as illustrated in FIG. 1.

The coupling member itself is shown in FIG. 2 in a partly sectional view. In the shown embodiment, it is assumed that the microphone capsule is connected to the coupling member by a screw thread and that the coupling member is connected to the preamplifier housing in the same way. However, a plug connection or a bayonet joint, or even a magnetic connection may be provided as well. In the shown example according to FIG. 2, the coupling member comprises an upper threaded ring 4 and a lower threaded ring 5. These rings are connected to each other by a shaped body 6 made of a vibration-absorbing, elastic, and electrically conducting material. Threaded rings 4,5 may be vulcanized to body 6, but they also may be connected thereto by an electrically conducting adhesive. A centrally located and axially extending contact pin 10 is supported by a plate 7 which is peripherally anchored in body 6. Plate 7 must be made of an insulating material, otherwise the two conductive paths from the microphone would be shorted. Advantageously, the ground connection will be provided in the in the externally extending body 6, and contact pin 10, which is connected to a contact button 8 through an elastic and electrically conducting cylinder 9, will be used as the live connection.

It is assumed in this design, that the electroacoustic transducer 1 comprises a downwardly projecting contact pin (not shown), so that pin 10 terminates within coupling member 2 in a contact button 8. To prevent the contact pin from axial displacement, a spring washer 11 is provided cooperating with plate 7 and securing the pin. Button 8 also has a recess in the top thereof for a contact pin of transducer 1.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.