GB2027318A - Sound detectors - Google Patents

Abstract

The present invention relates to a directional sound detector comprising a substantially parabolic sound reflector, a transducer located substantially at the focal point of the reflector for converting incident sound waves reflected from the reflector into electrical signals and means for shielding the transducer from extaneous sound.

Description

SPECIFICATION Sound detectors The present invention relates to sound detectors.

The present invention provides a directional sound detector comprising a substantially parabolic sound reflector, a transducer located substantially at the focal point of said reflector for converting incident sound waves reflected from the reflector into electrical signals, and means for shielding the transducer from extraneous sound.

In a preferred embodiment according to the present invention said means comprises a housing for the transducer. The housing opens along the axis of and towards the reflector and the position of the housing is adjustable relative to the transducer and axially of the reflector.

The transducer is conveniently spaced from the plane in which the rim of the reflector lies by a distance of substantially half the diameter of the reflector rim.

Advantageously the plane in which the rim of the reflector lies intersects the axis of the reflector at a location between the focal point of the reflector and the centre of the reflector.

Preferably the position of the transducer relative to the reflector is adjustable.

In a further preferred embodiment according to the present invention the edge region of the reflector is angled inwardly of the reflector and is substantially frustoconical.

Conveniently the means for shielding the transducer is made from sound absorbing material and the space between the means for shielding the reflector and the reflector is filled with sound absorbing material.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of a preferred form of sound detector, partially broken away for clarity; and Figure 2 is a partiai section through the detector of Fig. 1.

The drawings show a preferred form of hand held directional sound detector 10 which, although primarily intended as a toy also fins use in other spheres, such as birdwatching for recording bird sounds. Superficial modifications may be made to the detector depending upon its intended use, for example a more robust packaging for outdoor use, but the details of the preferred embodiment need not be altered.

The illustrated sound detector 10 comprises a casing 12 which mounts a grip 14 having an on/off trigger switch 1 6 and a stock 1 8 which conveniently serves either as a second hand grip or a shoulder butt. The stock 1 8 conveniently telescopes into the casing 1 2 and is illustrated in its retracted position. At the opposite end of the carriage to the stock 1 8 the casing mounts a parabolic reflector 20 whose principal axis is preferably parallel with or aligned with the casing axis.

The reflector 20 in turn mounts a shield 22 conveniently on legs 24 integral therewith or secured thereto, although any suitable mounting may be used, in which shield 22 is housed an acousto-electric transducer 26. The latter is conveniently a microphone although again any suitable transducer may be used.

The legs 24 or other mounting means should not be so bulky that they attenuate to any noticeable extent sound reflected from the reflector 20 to the microphone 26.

The interior surface of the shield 22 and conveniently the legs 24 are preferably covered with a natural or synthetic sound absorbing material 28 to inhibit the reflection of sound from the surface and thus improve the selectivity of of the detector. The material is conveniently of a plastics foam such as polyeurethane foam or a fibrous material such as cotton wool. Alternatively or additionally the shield and legs may be made from a sound absorbing material suitably strengthened, if necessary, to support the microphone. The latter may be directly supported on the legs 24.

The microphone 26 is located at the focal point of the reflector 20 and, in the preferred embodiment, because the reflector 20 is of relatively small size the edge of the reflector lies between the focal point and the centre of the reflector. Preferably the microphone is spaced from the plane in which the reflector rim 30 lies by a distance of approximately half the diameter of the reflector rim 30. The positioning of the microphone aids the directionally of the detector 1 0. As can be seen from Fig. 2 sound waves 32 travelling parallel to the principal axis of the reflector 20 are reflected to the microphone 26 but unwanted waves such as wave 34 are either shielded from the microphone 26 or pass by the microphone to be absorbed by the material 28.

The shield 22 may be of any suitable shape such as conical, frusto-conical or cylindrical.

Its position relative to the microphone 26 is preferably adjustable to enable the screening of the microphone 26 and thus the selectivity to be varied. This may be accomplished by attaching the shield 22 to the legs 24 or the legs 24 to the reflector 20 or preferably the casing 1 2 by means of screw threads so that rotation of the shield 22 adjusts its position along the reflectors principal axis. Alternatively the legs 24 are telescopic.

The periphery 36 of the reflector 20 is preferably deformed as shown to provide additional rejection of unwanted sounds.

The microphone 26 is electrically coupled to an amplifier (not shown in the drawings) in the casing 12. The amplifier has a volume control 38 and drives a loudspeaker 40 also located in the casing. The maximum amplification of the amplifier is preset to prevent acoustic feedback or microphony sending the amplifier into oscillation.

An accoustic headset 42 is connected to an acoustic line 44, conveniently a flexible tube, which may be plugged into an opening 46 in the casing adjacent the loudspeaker. In the absence of an acoustic headset the speaker may be located behind a grill (not shown in the drawings). Alternatively, electrically coupled headphones may be used.

The detector is powered by one or more batteries and is energised by depressing the on/off trigger switch 1 6.

The detector may be made of any suitable materials and items such as the casing 12, reflector 20, shield 22, legs 24, grip 14 and stock 1 8 are conveniently moulded from plastics material. The inner surface of the reflector 20 preferably has a smooth surface for best results.

The reflector is detachably mounted on the casing 1 2 conveniently by means of a bayonet fitting.

The detector may conveniently mount a telescope with, if necessary, a hole in the reflector in the sight path of the telescope.

The hole may conveniently be covered with a transparent material such as a plastics material so as not to reduce the reflector efficiency.

Alternatively, the reflector may be made of a rigid transparent material.

Claims (11)

1. A directional sound detector comprising a substantially parabolic sound reflector, a transducer located substantially at the focal point of the reflector for converting incident sound waves reflected from the reflector into electrical signals and means for shielding the transducer from extraneous sound.

2. A directional sound detector as claimed in claim 1 wherein said means comprises a housing for the transducer which housing opens along the axis of and towards the reflector.

3. A directional sound detector as claimed in claim 2 wherein the position of the housing is adjustable relative to the transducer and axially of the reflector.

4. A directional sound detector as claimed in any of claims 1 to 3 wherein the transducer is spaced from the plane in which the rim of the reflector lies by a distance of substantially half the diameter of the reflector rim.

5. A directional sound detector as claimed in any of the preceding claims wherein the plane in which the rim of the reflector lies intersects the axis of the reflector at a location between the focal point of the reflector and the centre of the reflector.

6. A directional sound detector as claimed in any of the preceding claims wherein the position of the transducer relative to the reflector is adjustable.

7. A directional sound detector as claimed in any of the preceding claims wherein the edge region of the reflector is angled inwardly of the reflector.

8. A directional sound detector as claimed in claim 7 wherein said edge region is substantially frusto-conical.

9. A sound detector as claimed in any of the preceding claims wherein the means for shielding the transducer is made from sound absorbing material.

1 0. A directional sound detector as claimed in any of claims 1 to 9 wherein the space between the means for shielding the reflector and the reflector is filled with sound absorbing material.

11. A directional sound detector as claimed in any of the preceding claims wherein the means for shielding the reflector is supported from the reflector on struts which are spaced from one another a distance such that they do not substantially inhibit the passage of sound waves from the reflector to the transducer.

1 2. A directional sound detector substantially as hereinbefore described with reference to the accompanying drawings.