US2032389A - Sound pick-up device - Google Patents

Description

March 1936. L. J. ANDERSON SOUND PICK-UP DEVICE Filed Feb. 18, 1935 INVENTOR ATTORNEY Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE SOUND PICK-UP DEVICE Delaware Application February 18, 1935, Serial No. 7,008

3 Claims.

This invention relates to sound pick-up devices such as that disclosed in United States Reissue Patent 19,115 of Harry F. Olson and Julius Weinberger, and has for its principal object the provision of an improved arrangement of the acoustic labyrinth of the pressure responsive element of such. devices.

As pointed out in the aforesaid patent, a sound pick-up device or microphone of the ribbon type may be operated in response both to the pressure of a sound wave and the pressuregradient of a sound wave by terminating a part of the ribbon diaphragm in a pipe or tube containing damping material. Such a microphone has the advantage that its response is substantially uniform throughout a comparatively wide angle. The terminating tube or labyrinth as heretofore constructed, has resulted in increasing the bulk of the microphone and milita'ting somewhat against its appearance and portability. In accordance with this invention, this disadvantage is avoided by incorporating the labyrinth or acoustic resistance tube in microphone. The invention will be better understood from the following description when considered in connection with the accompanying draw and its scope will be pointed out in the appended claims.

Referring to the drawing:

Fig. 1 is a perspective view of the improved microphone, and

Fig. 2 is a sectional view. of the acoustic labyrinth arranged to cooperate with the pressure gradient responsive section of the microphone ribbon.

The microphone in Fig. 1 includes a corrugated ribbon diaphragm or conductor which is loosely suspended in an intense magnetic field produced between the pole pieces H and I2 of a magnet I3 mounted on a casing 14 which may contain suitable amplifying equipment having its input circuit connected through leads 15 to the opposite ends of the loosely suspended ribbon l0. Mounted at the back of the ribbon I0 is a tubular member IS, the mouth of which covers the lower section of this ribbon and communicates through tube 11 with the acoustic labyrinth contained within the casing l8. Through lead IS the microphone amplifier is connected to suitable amplifying or other associated apparatus.

Fig. 2 shows the arrangement of the casing I8 and its relation to a microphone stand provided with a base 2|. It will be observed that the casing I8 is readily adjusted within the stand 20 by means of a thumb screw 22 and a collar 23 and that a tube 24 communicating with the tube ll extends into the adjustable casing I 8.

As explained in the aforementioned patent, the exposed or upper section of the ribbon l0 operates in response to the pressure gradient of the sound waves applied to it and the lower section of the ribbon, which is adjacent the opening of the tubular member 16, operates in response to the pressure, of the sound wave. The phase relation of the voltages generated in these sections is such that the directional response characteristic of the microphone is approximately a cardiac of revolution.

The pressure operated portion of the microphone should theoretically be terminated in a tube of infinite length but is in practice terminated in a relatively long tube packed with damping material such as Ozite. The path of the damping cavity extends from the lower section of the ribbon I0 downwardly through tubes I1 and 24 and upwardly through tube I8 in the annular space surrounding the tube 24. In a satisfactory microphone construction in accordance with this invention, the length of this path is 90 inches.

This arrangement of the acoustic resistance or damping path has the advantage that it is better balanced mechanically, has a neater appearance, is more readily moved from one position to another and presents no difiiculty in the adjustment of the microphone height. In cases where additional damping space is desired the path may obviously be extended to include the microphone base.

Having thus described my invention, I claim:

1. The combination of a microphone mounted upon a support and provided with a diaphragm one section of which is responsive to the pressure gradient of a sound wave, and means extending into said support for rendering another section of said diaphragm responsive to the pressure of said wave.

2. The combination of a microphone mounted upon a support and provided with a diaphragm one section of which is responsive to the pressure gradient of a sound wave, means extending into said support for rendering another section of said diaphragm responsive to the pressure of said wave, and means for adjusting the height of said microphone.

3. The combination of a pick-up device ineluding a hollow support and a diaphragm, an

acoustic labyrinth extending into said support for rendering a part of said diaphragm responsive to the pressure of a sound wave and for supporting said diaphragm, and means for adjusting the position of said labyrinth within said support.

LESLIE J. ANDERSON.

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