GB2285552A - Sound amplification system for a hearing aid - Google Patents

Abstract

The system includes a casing (10) containing a microphone, a preamplifier and an amplifier, providing an output signal via a connecting cable (12) to an inductive loop system for use with conventional hearing aids. The microphone is positioned at the lower surface of the casing (10) facing downwards, and is spaced by feet (16) to be a predetermined distance from a supporting surface, typically a table top, which acts as a sound reflector. <IMAGE>

Description

"Sound Amplification System" This invention relates to a sound amplification system for use in conjunction with hearing aids.

It is known to use an inductive loop system in which a cable run as a loop around a given space provides a signal which can be picked up by a standard hearing aid in "T" position. Inductive loops are in common use in so-called "mini-loops" where the space is a domestic living room , an individual office, or the like.

One common application of a mini-loop system is to enable the hard of hearing to hear television sound without the television set volume being excessively high. This is commonly done by attaching a small lapel-type microphone to the loudspeaker grille of the television set by "Velcro" strips, with the microphone providing an input to an amplifier which drives the inductive loop.

While this arrangement is useful to the hard of hearing, it does have disadvantages. It is necessary for the user to have the hearing aid in "T" position and thus to hear only the signals transmitted on the inductive loop. However, owing to the position of the microphone, the loop signals contain only the television sound and thus the user cannot hear any other sounds such as conversation from other persons in the room, or sounds such as the ringing of telephones or door bells. Moreover, the user cannot hear the sound of his own voice and thus any utterance which he makes tends to be of excessive volume.

According to the present invention there is provided a sound amplification system comprising a microphone, amplifier means connected to the microphone to provide an amplified audio signal, and means for connecting the audio signal to an induction loop for communication with a hearing aid worn by a user in the vicinity of the loop, the microphone being mounted in microphone mounting means adapted to locate the microphone in a predetermined facing relationship with a surface capable of reflecting sound waves.

Preferably, the microphone mounting means comprises a casing having a lower surface provided with protruding feet whereby the casing may be placed on the feet on said surface to position the microphone a fixed distance therefrom.

The amplifier means is preferably contained within the casing, and may suitably comprise a preamplifier and a power amplifier.

In a preferred arrangement, the system includes power supply means contained in a separate housing which also carries the connecting means for the induction loop, a single multicore cable being used to interconnect the casing and the separate housing.

An embodiment of the invention will now be described, by way of example, with reference to the drawings, in which: Fig. 1 is a side elevation of an amplifier unit forming part of a system embodying the invention; Fig. 2 is a plan view of the unit of Fig. 1; Fig. 3 is an underneath view of the same unit; Fig. 4 is a plan view of a power unit forming part of the same system; Fig. 5 is a circuit diagram of the power unit circuit; and Figs. 6 and 7 are circuit diagrams of a preamplifier and amplifier, respectively, used in the system.

Referring to Figs. 1 to 3, an amplifier unit comprises a box-shaped casing 10 connected to the remainder of the system by a three-core cable 12 connected via a DIN socket 14. In use, the casing 10 is placed on a horizontal surface such as an occasional table (not shown). The casing 10 is spaced from the supporting surface by feet 16, the spacing suitably being in the range 2 to 10 mm.

The underneath of the casing 10 has an aperture within which is mounted a microphone 18, facing towards the supporting surface. The microphone 18 may suitably be an omnidirectional electret type microphone.

Referring to Figs. 4 and 5, the power unit is housed in a casing 20 which has a DIN socket 22 receiving the cable 12. The casing 20 also carries spring-loaded contacts 24 for connection to an inductive loop of the mini-loop type which may suitably consist of a loop of single-core stranded 0.2 mm cable around the room. As seen in Fig. 5, the power unit receives power from the domestic mains supply 26 which is reduced to the desired voltage via a transformer 28 with switchable secondary and rectified and smoothed by rectifier 30 and smoothing capacitors 32 and 34. The resulting dc is supplied to the amplifier unit via cable 12, the third conductor of which returns the amplified audio signal for connection to the loop.

The amplifier unit can therefore be readily positioned wherever convenient in the room, while the power unit is semi-permanently installed in a suitable position in relation to a power outlet and the ends of the induction loop, but is readily removable to another room.

Any suitable form of audio amplifier may be used.

Figs. 6 and 7 illustrate a suitable preamplifier with 325 mW output and power amplifier with 2.5 W output.

In this embodiment, the amplifier unit is 60 mm x 80 mm x 40 mm deep, and the power unit slightly larger.

The same amplifier unit may be used as a portable device, in conjunction with a portable power supply such as a rechargeable 9 V battery attached to the casing 10 and a portable induction loop. The portable induction loop (not shown) is suitably a coil measuring 25 cm by 25 cm by 1 cm contained in a cloth bag, which may be used on the lap or in a brief case or handbag.

As an alternative to a portable battery, the amplifier unit can be powered from an available low voltage source, such as a car battery via a cigar lighter socket.

It will be appreciated that in use the microphone faces towards a supporting surface. The results obtained are more satisfactory where the surface acts as a good reflector of sound waves, the surface preferably being hard, smooth and substantially flat. Acute curves forming a definite convex or concave shape are to be avoided, but some curvature and shaping of the surface may be tolerated before reflection of the sound waves becomes so adversely affected that not all sound can be picked up.

It will be understood that the arrangement described above ensures that the microphone is positioned at a predetermined distance from the reflecting surface.

The exact distance may vary depending on the specification of the microphone used and the surface to be utilised, but is generally in the range 1 to 15 mm, preferably 2 to 10 mm.

Locating the microphone to face a reflecting surface accentuate spick-up of high frequency sound. This is particularly advantageous since most people afflicted with hearing difficulties experience hearing loss for high frequency sound.

Where, however, a person has difficulties hearing sound in the low to middle range of audible frequencies, the amplifier unit may alternatively be placed on its side on the supporting surface, in which case non-reflected sound waves are also picked up by the microphone. In this position the treble output to the loop is reduced as a proportion of the overall signal.

Most conveniently, the surface used as a reflector is substantially horizontal and the amplifier unit is placed on that surface, facing downwards. for example, the amplifier unit may be placed on a table top or other item of furniture. It may, however, be attached to any suitable surface in any orientation; for example, attached to walls or ceiling or secured underneath tables or shelving.

It is also possible for the reflecting surface to be incorporated into the unit itself. Generally, a reflecting surface of 30 by 30 cm or larger gives adequate reflection to enable the device to function well.

Claims (7)

1. A sound amplification system comprising a microphone, amplifier means connected to the microphone to provide an amplified audio signal, and means for connecting the audio signal to an induction loop for communication with a hearing aid worn by a user in the vicinity of the loop, the microphone being mounted in microphone mounting means adapted to locate the microphone in a predetermined facing relationship with a surface capable of reflecting sound waves.

2. A system according to claim 1, in which the microphone mounting means comprises a casing having a lower surface provided with protruding feet whereby the casing may be placed on the feet on said surface to position the microphone a fixed distance therefrom.

3. A system according to claim 2, in which the amplifier means is contained within the casing.

4. A system according to claim 3, including power supply means contained in a separate housing connected to said casing by a cable.

5. A system according to claim 4, in which the connecting means for the induction loop are part of said separate housing, and the amplified audio signal is connected thereto by said cable.

6. A system according to any of claims 3 to 5, in which the amplifier means comprises a preamplifier and a power amplifier both contained within the casing.

7. A sound amplification system substantially as herein described with reference to and as illustrated in the drawings.