Room Certifications for audiometry in South Africa
Yes, it’s true, you can and may perform hearing tests without a sound booth. To do this you need to ensure that your audiometer headset attenuates, or reduces sound, as effectively as, or better than a sound booth. Additionally you must ensure that the test environment is quiet enough for audiometric testing. This can be achieved with the KUDUwave™ audiometer, utilising Ambi-Dome™ technology. Ambi-Dome attenuates ambient noise at most frequencies better than a mini sound booth. At the same time the KUDUwave monitors the ambient noise levels in real-time. This allows you to perform tests in the same room where you would typically place and certify a sound booth.
Out of date suppliers and calibrators of audiometric equipment, still recommend that you not use boothless audiometers for occupational health care. This recommendation is only correct if using traditional audiometers with supra-aural and some circumaural headsets. With the KUDUwave™, similar attenuation to that of a 1m x 1m sound booth is achieved, thus the KUDUwave digital portable audiometer can be used outside of a sound-treated booth.
SANS 10083 stipulates that a hearing test can be conducted inside a booth, a room or a mobile unit. Nowhere in the standard does it say you have to test inside a sound booth. If an inspector or “trusted” audiometric supplier tells you that a sound booth is needed for the KUDUwave™, share the below paragraph from SANS 10083.
SANS 10083:2013 Edition 5.2
Standards for assessing and measuring acoustic environments for audiometric testing
SANS 10182 is the reference standard in terms of measurement and assessment of acoustic environments for audiometric tests. It is critical to have a clear understanding of this standard, or you may adopt incorrect practices that could cost you that sought-after contract.
SANS 10182 requires that the environment for testing must be quiet enough, but the standard does not stop here. It also mentions two other important points to consider to ensure the environment is quite enough:
- The minimum threshold for testing to ensure Percentage Level of Hearing (PLH) is calculated correctly.
- The headset used, as each type of headset has different sound attenuating capabilities.
The minimum threshold to test to
SANS 10083 states that the minimum PLH is 1.1, and can be calculated from the tables and formulas as stipulated in Annex E of the standard. Whether you test to a minimum of -10dBHL, 0 dBHL or 15dBHL, the PLH calculation will stay the same. To test each patient to a minimum of 0 dBHL takes a lot of extra time, and will not influence the PLH. Hearing below 15 dBHL is classified as normal by Clark and the World Health Organisation.
SANS 10182 lists the Maximum Permissible Ambient Sound Pressure Levels (MPASPLs) (also known as MPANLs) for a supra-aural headset (headset that rests on the ear) if testing is conducted to a minimum of 0 dBHL. See column 2 below.
Column 3 indicates MPASPL for supra-aural headset if the minimum level for testing is 15dBHL for PLH calculation. You will see that the environment can be a lot noisier compared to testing to 0dBHL. Unfortunately, the ambient noise in a standard office is around 45dBSPL, and this is too noisy for compliant testing with supra-aural headsets. That is why a sound booth is required when using supra-aural headsets because the sound booth adds the additional required attenuation. This is unlike the KUDUwave audiometer that utilises Ambi-Dome technology to significantly attenuate sound within the actual headset.
SANS 10182 does not have MPASPL values for headsets like the KUDUwave™, but it specifies a method for manufacturers of headsets other than supra-aural headsets to determine the MPASPLs for that specific headset. The KUDUwave MPANL was determined using the stipulated method.
Column 4 lists the MPASPL for testing down to 0 dBHL with the KUDUwave. The lowest MPASPL is 55.3dBSPL at 2000 Hz, 10dB above the 45dBSPL office noise level, thus allowing for testing inside an office, room or outside a booth to a minimum of 0 dBHL. By selecting to test to a minimum threshold of 15dBHL instead of 0dBHL, it is possible to test in noisier areas, for instance where people are talking and in environments that are as noisy as 65dBSPL. The KUDUwave (with Ambi-Dome) can still test PLH correctly.
Electro-acoustic room certifications
MPASPL can be defined as the permitted ambient noise level in an audiometric test environment in order to test down to a certain intensity level without ambient noise masking the presented pure tones. In order to comply with stipulated MPASPL, electro-acoustic room certifications have to be conducted.
Various standards recommend the measurement of ambient noise levels in an audiometric room or booth annually with a type 1 sound level meter. An important point is that the sound pressure levels (SPL) measurement is performed during the noisiest time of day and not at 7 AM, for instance, before all the machinery in a factory has started up. You will need evidence that the measurement was done at the noisiest time of the day. It is concerning to note that a lot of clinics, which usually house soundproof booths, are situated in high traffic and noisy areas of an industrial plant or mine etc. Whilst the administrative areas with boardrooms and other meeting areas are usually in considerably quieter areas. These areas could quite easily facilitate audiometric testing utilising KUDUwaves. Once the SPLs in the room or booth are measured and determined, the SPL octave frequency results are then compared with the MPASPLs (as tabulated above and in SANS 10182). The room or booth is certified as valid for audiometric measurements if the measured SPLs are softer than the MPASPLs for testing down to a specific intensity.
It is critical to note that this is not a calibration certificate, as it is impossible to calibrate a booth, room or mobile unit for noise attenuation. This is simply a noise survey certificate, to verify that the noise levels of the environment are quiet enough for testing, depending on the headset that is to be used, and to which minimum threshold the testing will be conducted. If you use non-eMoyo room certification services, then please make sure the person issuing the room certificate knows about the MPASPLs of the KUDUwave, as tabulated earlier. They cannot just use the levels in the standard, as the levels in the standard are there for supra-aural headsets and not for the KUDUwave™ with Ambi-Dome™.
Psycho-acoustic room certifications
SANS 10183 references ISO 8253. This standard states that if an SPL meter is not available, a psycho-acoustic verification test can be done. It is a simple procedure to collect this evidence. An audiometrist must test the hearing of two people, with normal hearing, to establish if they both have a PLH of 1.1. The first two employees with a PLH of 1.1 will serve as evidence. If however 40% of the employees at a factory tested to have PLHs of 1.1, then there is more than enough proof that the environmental noise level is at an acceptable level for hearing tests to be performed. The problem with the electroacoustic MPASPL room certification is that it does not take into account new additional noise sources, such as new machinery, for example, that could have been installed since the last MPASPL survey, rendering the test results inaccurate. The benefit of the psychoacoustic certification is that it compensates for this dilemma where the environmental noise could have changed since the electro-acoustic certification.
ISO 8253-1:2010(E) page 16
This article by Dr Anita Edwards (CSIR) describes Psycho-acoustic Room Certifications and Sound Level Meter Room Certification in more detail.
You can test outside a sound booth provided the headset attenuates, or blocks, sound better than or equivalent to a sound booth.
The KUDUwave headset can test in the same environment as that of a traditional audiometric-sound booth setting.
Electro-acoustic room certifications are the golden standard. If you do not, however, have access to the equipment you can conduct a psycho-acoustic room certification as indicated in this article.
- Acoustics — Audiometric test methods — Part 1: Pure-tone air and bone conduction audiometry. Geneva: ISO 8253; 2010.
- The measurement and assessment of acoustic environments for audiometric tests. SANS 10182; 2006.
- Edwards AL. Evaluation of the Kuduwave 5000 audiometer for compliance with standards for hearing conservation purposes. Telemedicine Journal & E-Health. 2010;16(5):557-63.