Sound collecting device

Abstract

A sound accumulation device in which a microphone is mounted at the focus of parabola for movement along the longitudinal axis to receive audio information reflected from the sidewalls of the parabola at different focuses and further incorporating a sound penetrable shield mounted over the open face of the parabola which functions as a wind shield to attenuate wind generated noises.

Parent Case Text

This is a continuation of application Ser. No. 265,052, filed June 21, 1972 .

Description

In the receipt of audio information it has been known that parabola surfaces can be use in conjunction with microphones and the like to accumulate sounds so that the amount of audio energy is increased at the microphone. Such devices have often been used to read audio information from distant locales and to create a higher signal to noise ratio input for audio information emanating from a closer position for higher fidelity recording applications. Such applications for example, are most noted in motion picture recording applications where microphones cannot be placed in the immediate proximity of the actors or other sound emanating subjects.

In the past, some microphones have been known to have been placed along the longitudinal axis by the midsection of the parabola so that a sound complement would normally strike the inside wall of the parabola for several reflective bounces prior to reaching the microphone. In such structures it was necessary to provide mounting devices extending from the sidewalls of the parabola to hold the microphone at the longitudinal axis. Such devices had the disadvantage of forming an obstruction to sound that would normally enter the parabola and of also tending to shift the direction or angle at which the sound would strike the parabola wall, thus affecting both the intensity and the linearity of the sound. In addition, the microphone was subject to wind noise disturbances.

In the present invention the microphone is located at approximately the focus of the parabola. This, in the conventional parabola, is several inches from the inside of the parabola bowl and on the axis. In such a position each sound wave would normally strike the inside of the parabola wall once and thereafter be deflected to the focus. Sound waves of different frequencies have a tendency to be deflected at slightly different angles and also the exact location of the focus sometimes varies in accordance with the position of the sound emanating source in relation to the directional axis of the sound collecting device. In this respect the microphone is mounted for movement along the axis of the parabola through the focus so that it can extend towards the opening of the parabola beyond the focus and inwardly towards the base of the parabola inside of the focus. It has been found that the specific position of the microphone causes attenuation or extenuation of sound waves of different frequencies depending upon the specific placement of the microphone with reference to the longitudinal positioning of the microphone with reference to the focus.

By this control selected frequencies can be either attenuated or extenuated while other selected frequencies are similarly attentuated or extenuated. Thus providing not only an optimization of extenuation of sound but a control of attenuation and extenuation of selected frequencies.

As a further object of this invention there is provided a sound penetrable shield over the open mouth of the parabola which has the effect of spacing the shield a substantial distance from the active face of the microphone. It has been found that the shield mounted over the open face of the parabola attenuates the noises that are often encountered with sound reflecting devices. As a practical matter it has been found that the sound shield in combination with a microphone being mounted at the focus along the device to be operated in severe wind conditions where other parabola listening or sound collecting devices would be totally unacceptable due to the high noise level created by the wind.

Referring now to the drawings:

FIG. 1 is an elevational view showing the sound collecting device of this invention in cross section;

FIG. 2 is a perspective view of the sound collecting device with the sound penetrable membrane installed;

FIG. 3 is an enlarged view showing the microphone movement along the axis of the parabola to various positions with respect to the focus; and

FIG. 4 is a front elevation of the sound collecting device with the sound penetrable membrane removed.

In FIG. 1 a parabola 15 is formed with an aperture 16 mounted at the base. A microphone 18 having a microphone head 19 in which a sound transducer is mounted is formed with a shaft 20 extending rearwardly of the transducer. Shaft 20 is formed of a constant diameter and is arranaged to project through aperture 16 on the base end of the parabola. A bearing mount 22 is mounted on the outer face of the parabola forming a bearing surface concentric with aperture 16 and forming a slideable bearing to rigidly mount shaft 20 of the microphone. By this means the transducer 19 can be slid to and fro into a variety of positions within the inside area of the parabola. Bearing 22 is aligned with the bearing surface in longitudinal alignment with the axis of the parabola so that the microphone's reciprocal movement will be along the axis of the parabola.

In the principal embodiment of this invention the shaft 20 of the microphone is mounted in a sleeve 28 of a microphone stand 29. The stand of conventional design is simply formed of a base 30 having an upwardly extending standard 31. A rotating fitting 33 is mounted on the top of the standard having a pivotal connector 34 which is connected to support bearing 28. By this device bearing 28 can be rotated to point the microphone 18 and parabola 15 in the vertical axis while fitting 33 can be rotated to rotate the microphone and parabola in the horizontal axis. The outer edge of the parabola is formed with a recess 39 into which a sound penetrable membrane 40 is supportably fitted and there held in position by a cylindrical clamp 42. Clamp 42 is removable to allow membrane 40 to be removed so that the devices can be conveniently used either with or without membrane 40. Furthermore, membranes of different sound penetrability can be substituted for one another.

Parabola 15 is formed to have a focus located at about .F as shown in FIGS. 1 and 3. The focus in this embodiment is located approximately six or seven inches from the base of the parabola and along the longitudinal axis thereof. The transducer of microphone 18 is by the sliding mount afforded by the engagement of bearing 22 with shaft 20 capable of moving towards diaphragm 40 or rearwardly towards bearing 22 so that the transducer can be positioned forward of, at, or rearwardly of the focus. It has been found that under certain conditions the sound amplification of certain frequencies can either be attenuated or enhanced when the microphone is moved either forwardly or rearwardly of the focus. Thus, by the longitudinal movement of the microphone with respect to the focus a great deal of specific sound control can be attained and regulated.

In operation, parabolas so formed that specific sound waves or elements such as indicated in FIG. 1 by arrowed lines 50, 51, 52 and 53 are arranged to strike the parabola wall and are thereby reflected therefrom to the focus. It is noted as illustrated in the drawings, that each sound element strikes the parabola wall by a single reflection enroute to the focus. This is important in maintaining clarity and fidelity of the received signals. Multiple reflections of sound waves contributes to distortions and lack of clarity of the received signal. Thus by locating the microphone at the approximate focus of the parabola each sound wave is allowed to directly hit the microphone only after but one reflection. It is noted that other devices that have been used for this purpose rely on multiple reflection to the microphone.

It is also noted that by moving the microphone 19 as shown in FIG. 3 to a forward position as indicated at 60 or that the transducer 19 will position the microphone forward of the focus. By moving the microphone to position 61 the transducer will be located at the focus and by moving the microphone to rearwardly position 62 the microphone will be positioned rearwardly of the focus. It is apparent that the slideable mount through bearing 22 is along any intermediate position desired between 60 and 62. It is also noted that other forms of mounting other than using the cylindrical shaft 20 formed integrally with the microphone assembly in a complementary bearing 22 can also be used. The essence of the device is that the microphone be formed on a mount which is slideably mounted through an aperture for movement along the axis of the parabola through the focus.

In further operation, the wind shield 40 can be formed of a highly porous plastic, cloth, or other sound penetrable material. The function of wind shield 40 is to prevent the spurious sounds normally encountered from wind flow across the open face of the parabola. It has been found that the wind shield has immense efficiency in reducing the spurious sounds generated by the aforesaid wind flow, thus allowing the device with the wind shield to be used in high wind conditions due either to ambient wind or caused by the device being mounted on a moving vehicle during sound collecting operations.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the invention, as limited only by the scope of the appended claims.

Claims

I claim:

1. A sound collecting device for accumulating sound at a focus while substantially eliminating wind noise having an elongate parabola with an open mouth having side walls coaxial with the axis of the parabola and a closed base, said parabola formed with a focus located near the base of the parabola along its longitudinal axis and distant from the open mouth of the parabola, a microphone including a sound entry face adjacent the focus of the parabola so that the sound entry face of the microphone is distant from the open mouth of the parabola, said sound entry face oriented towards said open mouth for the direct reception of sound from its source, and a membrane of sound permeable material mounted at said mouth overlying the entire opening to the interior of said parabola, the combination of the closed base of the parabola and the membrane substantially preventing air currents from reaching the sound entry face of the microphone to substantially eliminate wind generated noises.

2. A sound collecting device according to claim 1 and wherein said mounting means is slideably mounted relative to the base of said parabola for longitudinal movement of said microphone to various positions to position said microphone ahead of and behind said focus.