GB2261950A

GB2261950A - Assessment of personal hearing protection

Info

Publication number: GB2261950A
Application number: GB9125295A
Authority: GB
Inventors: Richard Alan Graveling; Robin Middlemass Howie
Original assignee: INST OF OCCUPATIONAL MEDICINE
Current assignee: INST OF OCCUPATIONAL MEDICINE
Priority date: 1991-11-28
Filing date: 1991-11-28
Publication date: 1993-06-02
Also published as: GB9125295D0

Abstract

A method of and apparatus for assessing the attenuation capacity of a hearing protective device, the method including the steps of setting an initial unoccluded noise level just within the audible range of the subject and presenting a suitably amplified noise signal to the subject wearing a hearing protective device to determine an occluded noise level of audibility thereby to assess the efficacy of the device in attenuating the amplified noise.

Description

ASSESSMENT OF PERSONAL HEARING PROTECTION This invention concerns the assessment of personal hearing protection and in particular has reference to the assessment of the noise attenuation achievable by personal hearing protective devices employed or recommended for use in workplace environments.

It is recognised that excessive noise can temporarily impair or more seriously cause permanent damage to the hearing of individuals subjected to the relevant noise source. Although the optimum and indeed obvious solution is to reduce the noise to a safe level, such a course of action might not always be practicable, particularly in the short term, in view of the nature of the workplace environment. For example, in industrial workplaces the noise level of machinery cannot always simply be reduced or eliminated. Accordingly, a wide range of hearing protectors in the form of noise occlusive devices is available and are designed with the object of attenuating the sound entering the ear thereby reducing the risk of hearing damage. However, attenuation provided by such devices when worn in a noisy environment is often less than that predicted or expected from laboratory tests.The reasons for the apparently misleading predictions are varied and include such factors as the wearing of spectacles, the wearer's facial anthropometry not being compatible with the design of the protective device, the device being improperly worn, or displacement from the ear canal in the case of internally-worn protective devices.

Conventionally audiometers can be employed for assessing the effectiveness of personal hearing protective devices, but equipment of this kind is complex in character and requires a degree of expertise for its operation and is therefore unsuitable for user self-testing.

It is therefore an object of the present invention to provide an improved method of assessing the attenuation capacity of a hearing protective device.

A further object of the invention is to provide apparatus for carrying out the method.

According to a first aspect of the invention a method of assessing the attenuation capacity of a hearing protective device includes the steps of presenting a selected noise signal to a subject from a noise source, adjusting the source of noise to a level just within the audible range of the subject, applying a hearing protective device to the subject, amplifying the selected noise signal, presenting the amplified noise signal to the subject, and personally monitoring the audibility of the amplified signal thereby to assess the attenuation capacity of the device.

Conveniently, the noise signal is relevant to the noise to which the subject will be exposed and is amplified to the level of predicted or expected performance of the device, namely the level at which the device is predicted to be still effective at or within the limit of its range. The step of personally monitoring the amplified signal will thus determine the point at which the signal can be heard. In the event that the signal cannot be heard at that level, the occlusive efficacy of the device is better than expected. If the signal is as audible as when the subject is not wearing the hearing protective device, its performance is satisfactory in suppressing excessive noise levels before they reach the auditory senses. If the signal is more audible, then the device is not performing in a satisfactory manner and is not occluding sound to a sufficient degree.

In the alternative, the amplification of the noise signal may be effected until the subject assesses the audibility level of the signal to be the same as that experienced without the hearing protective device in place, the attenuation capacity thereby being established.

According to a second aspect of the invention there is provided apparatus for assessing the attenuation capacity of a hearing protective device applied to a subject, the apparatus including a noise source, an amplifier, a noise attenuator, and a noise transmitter adapted in operation of the apparatus to be directed to the subject.

Advantageously the noise transmitter is housed within an acoustic booth or hood in which in use the subject is to position his/her head. In order to ensure correct positioning of the head, an automatic sensing means may be provided. More than one transmitter may be provided in order to afford binaural as well as monaural assessment.

By way of example one method of and apparatus for assessing the attenuation capacity of a hearing protective device are described below with reference to the accompanying drawing which is a diagrammatic representation of the apparatus.

Referring to the drawing, the apparatus Comprises a noise source 1 which is adapted to emit a variety of sounds, such for example as a selectable frequency pure tone or a multi-tone sound such as 'pink noise'. Optionally, the noise source may include the capability of reproducing industrial sounds.

The sound produced by the source 1 is relayed to an amplifier and attenuation control 2 provided with two circuits and then to noise transmitters 3 which may be two in number for binaural as well as monaural assessment. The transmitters may conveniently be operable individually to test the monaural effectiveness of a hearing protective device. One of the attenuator circuits is provided with a selector switch (not shown) operable to select a predetermined type of protective device and its expected attenuation capacity.

The transmitters 3 in this example are housed within a booth or an acoustic hood 4 such as a telephone hood, thus affording a relatively controlled environment for the presentation of noise at the correct level and exclusion of unwanted extraneous noises.

In operation of the apparatus, a subject (not shown) places his/her head into the hood 4 with the hearing unoccluded. A noise is selected at the noise source 1 and is presented to the subject who adjusts the sound level by means of the amplifier and attenuation control 2 until the sound is just within audible range against the prevailing background noise. The subject then dons the desired protective device (not shown) and uses the selector switch on the relevant attenuation circuit to choose that device to give an expected attenuation capacity therefor. The noise is then presented to the subject who assesses the attenuation capacity of the protective device.

Thus, if the noise is inaudible to the subject or is less audible than the level set unocoluded, the attenuation capacity of the device is better than expected. If the noise presents the same level of audibility as when unoccluded, the device meets its performance prediction, but if the noise level exceeds that level of unoccluded audibility, the protection afforded by the device is unsatisfactory.

In an alternative method of operation, the initial occluded threshold is set in the same way, but once the hearing protective device is in situ the subject varies the noise level, now occluded, until it reaches the same audible level as with the initial unoccluded setting. The difference between the two thresholds is thus the attenuation capacity of the device.

The apparatus of the present invention can be located at appropriate entry points to the workplace so that the attenuation capacity of the hearing protective device can be assessed in situ. AlternativelyS the apparatus may be employed where hearing protection is provided as part of the process of checking on the suitability of a particular proprietary brand for any individual and/or teaching purposes such as for demonstrating the importance of correct fitting.

In alternative forms, the apparatus may be automated to minimise training of the users. For example, the subject would select the type of noise signal required and would indicate the type of protective device to be assessed. The subject would as with the manual control place his/her head into the hood with the ears unoccluded and the apparatus would automatically increase the level of the noise signal until it reached the just audible range which the subject would select. This step would be repeated a number of times to secure accuracy and then the subject would don the hearing protective device and carry out the same steps as previously described.

Once the assessment had been completed, the apparatus would automatically compare the occluded and the unoccluded hearing levels to determine the attenuation capacity achieved and to compare the result with the minimum acceptable for the relevant protective device. The apparatus would then provide to the subject an indication of the performance of the device in relation to the acceptable minimum.

An optional feature of the apparatus is shown at 5 in the drawing and comprises a noise detector, in this example a microphone, suitably mounted for adjustment within the hood 4 such that in use it can be disposed adjacent the subject's ear. Additional circuitry is provided into which is linked the microphone 5 to provide automatic control of the sound level rather than relying on prior calibration. Two microphones may be provided to give binaural control.

A further optional feature (not shown) of the apparatus is a microprocessor or some other suitable mechanism for control and data storage and retrieval. Such a feature would have several advantages in terms of monitoring the operation of the apparatus to ensure its correct usage, and ,by comparison of serial unoccluded attenuation levels, to serve as a rough monitor of individual hearing ability.

Claims

1. A method of assessing the attenuation capacity of a hearing protective device including the steps of presenting a selected noise signal to a subject from a noise source, presetting the source of noise to a level just within the audible range of the subject, applying a hearing protective device to the subject, amplifying the selected noise signal, presenting the amplified noise signal to the subject, and personally monitoring the audibility of the amplified signal thereby to assess the attenuation capacity of the device.

2. A method according to claim 1 in which the noise signal is amplified to the level of predicted or expected performance of the device.

3. A method according to claim 1 in which the progressive amplification of the noise signal is effected until the subject assesses the audibility level of the signal to be the same as that experienced without the hearing protective device in place, the attenuation capacity thereby being established.

4. A method according to any one of the preceding claims in which presentation of the noise to the subject is automatically progressive until the subject in an unoccluded condition presets the level of the noise signal within the audible range.

5. A method according to claim 4 in which progressive amplification of the noise signal is effected with the subject in the occluded condition with a hearing protective device in place, the subject monitors the noise level and indicates the occluded noise threshold, and the attenuation capacity is automatically computed therefrom.

6. A method according to any one of the preceding claims in which a microprocessor is provided to control the steps and to effect storage of the information generated therefrom.

7. A method of assessing the attenuation capacity of a hearing protective device substantially as hereinbefore described with reference to the accompanying drawing.

8. Apparatus for assessing the attenuation capacity of a hearing protective device applied to a subject, the apparatus including a noise source, an amplifier, a noise attenuator, and a noise transmitter adapted in operation of the apparatus to be directed to the subject.

9. Apparatus according to claim 8 in which the noise transmitter is housed within an acoustic booth in which in use the subject is to position his/her head.

10. Apparatus according to claim 8 or 9 in which an automatic sensing means is provided to ensure correct positioning of the subject's head.

11. Apparatus according to any of claims 8 to 10 in which more than one transmitter is provided.

12. Apparatus substantially as hereinbefore described with reference to the accompanying drawing.