Soundproofing & Acoustics of Audiometry / Audiology Rooms

There are a number of acoustic factors that need to be considered when planning and designing a new audiometric test room facility. Routine clinical assessments of hearing are normally carried out under strict and controlled conditions, in a specifically designed facility.

Puretone and Sound Field (free field) audiometric practices are often used when assessing the hearing/ hearing loss of a patient. Once a hearing loss has been identified in a patient, clinical investigations begin.

Commonly there are 2 types of hearing test, unaided and aided.

Unaided measurements are undertaken using an audiometer, usually with a form of head-set or ear inserts for increased accuracy. Children are often assessed using a free field speaker system and set up within the testing room/ space. In aided assessments, the aim is to assess the functional gain of the patients’ hearing aid.

For either type of test, a controlled acoustic environment should be provided to give the most accurate results. Audiological testing is usually carried out in accordance with the international standard ISO 8253. This design standard has 3 elements and is often defined and specified as follows:

ISO 8253-1 Pure-tone and Narrow Band Test Signals. The primary purpose of the standard is in determining hearing threshold levels, primarily in the 125Hz to 8000Hz frequency range. Head-sets or ear inserts are generally used when carrying out adult assessment and testing.

ISO 8253-2 Sound Field (free field) Audiometry. This part of the standard is focused on Paediatric assessment and additionally how to best assess the value/ functional gain achieved following the fitting of a hearing aid.

ISO 8253-3 Speech Audiometry – This section is often referred to when considering audiological rehabilitation and evaluation of hearing disability.

The overall specification of the test room environment can vary depending on the space available, location, external noise factors and the types of test being carried out.

The following are all considerations and can act as a guide when designing an audiometric test room.

Ideally an audiometric test room should have a minimum internal space of 8m2 for clinical testing and assessment. This size is often increased, often up to as much as 24m2 (space permitting) for paediatric assessment and free field audiology. The size of the room can also play a part in optimising the acoustics. The larger the room, the smaller the impact of furniture, equipment and people will have on the free-field environment.

Although the ISO guidance states that ambient sound pressure levels should not exceed specific levels at certain frequencies when testing down to 250Hz and 0dB HL. In practice, this is sometimes not always possible, especially within existing builds and in this instance, due consideration should be given, however in a newly designed room of the appropriate construction, these figures should be the benchmark to achieve.

The reverberation times inside an audiology room should be no greater than 0.25 seconds. Although relatively low, this can usually be achieved through the use of absorption within the walls and ceiling in an existing room. For newly constructed facilities, then walls can be built using absorptive surfaces for a better aesthetic.

Furniture and equipment should be considered and ideally placed in fixed positions to ensure acoustic measurements are not affected, resulting in consistent testing results. This does not need to be done at the design phase, but will need to be finalised for the purpose of having a test environment commissioned and certified for use.

If loudspeakers are being installed as a part of a turnkey package, then these should be positioned at head height for the seated listener and angled directly at the reference point. Speakers need to be at least 1m from the reference point in order to minimise the effects of the inverse square law.

Sound attenuating doors, windows and ventilation systems are essential and are often prove to be the key factor in how well the acoustic environment performs for testing purposes. Acoustic doors and acoustic glazing and attenuating airways should be considered at the very early stages of the design and room locations.

Once all of the above have been considered, the physical construction of the space can begin. Depending on the available budget and specification required, common building materials may be used for the structure or specifically-designed acoustic panels. A combination of the two is often used, especially in refurbishing existing rooms currently used for different purposes.

New rooms are generally designed and constructed as rooms within rooms, so as to structurally isolate the test room space from the host room or building, as much as possible. Single or double walls can be installed depending on the level of acoustic isolation required. A single acoustic wall is usually capable of achieving 40dB – 45dB sound reduction. Double walls can achieve up to 70dB – 75dB reduction.

The location of an audiology room or department can have a huge impact on the required levels of acoustic isolation required. Busy corridors, adjacent roads, traffic noise and mechanical plant are some of the most difficult sounds to reduce. Locating an audiometric test room as far away as possible from any of these noise sources would be ideal, but often not possible given the constraints of available space and accommodation.

The audiometry room shall have a sound absorption coefficient based on laboratory tests in accordance with ASTM C423-77 as shown in the table below.

Given the sensitive tests required, ensuring a facility performs adequately from an acoustic perspective is equally as important as creating a welcoming and comfortable environment for patients and clinicians. A well-designed facility should make the patient feel comfortable and at ease, especially if their condition makes them feel disorientated. Consideration of colours, lighting and fixtures & fittings should all be considered at the design stage. Acoustic environments can often feel claustrophobic due to the lack of background noise and anything to compensate for this will aid in reducing patient anxiety.

Another and very important consideration is ventilation as mentioned within 6 above. Acoustically treated rooms provide a high level of thermal isolation and are generally tightly sealed. This can have a negative impact on the availability of fresh air and temperature control. Acoustic test room design should as a minimum, have an acoustically treated ventilation system provided to ensure that a minimum number of air changes per hour are achieved for room occupants. Full and complete acoustically engineered air conditioning is often preferred, giving complete and adjustable temperature and  humidity control within the test room.

The design of new audiology testing facilities is often a complex and difficult process, often involving a number of building constraints and factors. Key stakeholders, the room users, acoustic engineers, and often an architect and builder all will have an input and some influence . Understanding the key design elements by all parties and how they fit with one another, is essential when designing and budgeting for appropriate audiometric testing facilities.

Aural Exchange does not provide modular audiology booths, but we are able to assist with a range of acoustic products to sound treat conventionally built rooms for hearing aid fitting and speech therapy. Available products / services include:

• High performance Nankarrow Isogate acoustic doors complete with frames
• Observation windows with optional one-way viewing
• Secondary glazing for room windows
• Acoustic ceilings
• Nankarrow sound absorptive foam wall panels
• Floating floors and isolation mats for structural isolation
• Silent air conditioning and ventilation systems