NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here: www.cenelec.eu IEC 60268-3 - Sound system equipment - Part 3: Ampli
General safety requirements
Audiometers shall conform to IEC safety requirements (see IEC 60601-1) except where otherwise specified in this standard.
Acoustic safety requirements
As audiometers are capable of producing sound pressure levels that could cause hearing damage, a non-auditory warning indication to the operator is required for all settings above
Environmental conditions
The specifications must be adhered to for temperature combinations between 15°C and 35°C, relative humidity levels ranging from 30% to 90%, and ambient pressure maintained between 98 kPa and 104 kPa.
The actual values of the environmental parameters at the time of calibration shall be stated
Reference equivalent threshold sound pressure levels can vary greatly with ambient pressures outside the specified range Consequently, recalibration should be performed at the nominal ambient pressure of the user's location when the calibration site and user site have differing ambient conditions.
Warm-up time
The performance requirements must be fulfilled following the specified warm-up period and any necessary adjustments as per the manufacturer's guidelines The manufacturer will indicate the minimum warm-up time, which should not exceed 10 minutes if the audiometer has been maintained at the ambient temperature of the testing environment.
Power supply variation
Interruption of power supply
If any interruption of the power supply occurs for up to 5 s, the audiometer shall revert to a condition that will neither endanger the subject’s hearing, nor yield invalid results.
Mains operation
The specifications require that any long-term deviation in mains supply voltage or frequency must remain within the limits of ± 10% for voltage and ± 5% for frequency to ensure optimal performance.
Battery operation
The manufacturer must define the acceptable battery voltage range to ensure compliance with specifications An appropriate indicator will be included to verify that the battery voltage remains within these limits The audiometer's specifications must be fulfilled across all battery voltages within the defined range.
Other power supplies
The manufacturer must specify the type of power supply for the audiometer if it is not powered by mains or battery, including its characteristics and the tolerances required to meet the audiometer's specifications.
Electromagnetic compatibility
During EMC immunity testing in accordance with IEC 60601-1-2, the unwanted sound produced by any air conduction transducer must not exceed a hearing level of 80 dB Subclause 13.3 outlines the methods for demonstrating compliance with this requirement.
Unwanted sound
General
Objective acoustical measurements may not be feasible for detecting unwanted sound from the audiometer Therefore, subjective tests must be conducted with at least two otologically normal subjects, whose hearing thresholds do not exceed 10 dB for frequencies ranging from 250 Hz to 8 kHz The test room must comply with the specifications outlined in Table 4 of ISO 8253-1:2010 For EHF audiometers, these tests should include frequencies up to the maximum available.
NOTE For the frequency range above 8 kHz test rooms according to ISO 8253-1:2010 have shown in practice to provide sufficiently low ambient noise levels.
Unwanted sound from an earphone
Unwanted sound in earphones can result from electrical signals produced within the audiometer when the tone switch is turned off This phenomenon, known as breakthrough or cross talk, may also affect the non-test earphone when the test tone is active Section 13.4.1 outlines specific requirements and methods for indirectly measuring and subjectively verifying performance.
An unwanted tone may also occur in the earphone due to the tone switch not being completely effective Requirements for the tone switch are described in 8.6.
Unwanted sound from a bone vibrator
The manufacturer must specify the test frequencies at which the bone vibrator may emit sound that could affect the accuracy of bone conduction measurements by reaching the test ear through the unoccluded ear canal Additionally, the manufacturer should indicate the potential degree of this impairment A method for demonstrating compliance with this requirement is outlined in section 13.4.2.
Unwanted sound radiated by an audiometer
Audiometers must operate quietly to ensure accurate hearing tests, with any sound from the device or associated computer systems remaining inaudible at hearing levels up to 50 dB Compliance with this standard can be demonstrated as outlined in section 13.4.3.
The restriction on noise from controls is designed to prevent any sounds that could provide the patient with hints that may affect test outcomes This limitation does not extend to mechanisms like output selection switches or frequency switch detents that may produce noise when the subject is not undergoing testing.
Testing of automatic-recording audiometers
Automatic-recording audiometers shall be provided with means to adequately control the signals for the purpose of measuring the characteristics of the audiometer.
Interface connections
No unintentional change of the audiometer’s calibration shall be possible via any interface
Pure tones
Frequency range and hearing level range
Fixed frequency audiometers must include test frequencies with specified minimum hearing level values for supra-aural earphones and bone vibrators, as outlined in Table 2 For Type 1 audiometers utilizing circumaural or insert earphones, the maximum hearing levels can be 10 dB lower than the values listed for frequencies between 500 Hz and 8 kHz Additional frequencies up to 8 kHz may be employed if RETSPL values are provided in the ISO 389 series.
Table 2 – Minimum number of frequencies to be provided and the minimum range of values of hearing level for fixed frequency audiometers
Frequency in Hz Type 1 Type 2 Type 3 Type 4
Air Bone Air Bone Air Bone Air
8 000 100 – 90 – 80 – – a Maximum hearing level to be at least equal to the tabulated values Minimum hearing level to be –10 dB or lower
EHF test signals must be within the frequency range of 8,000 Hz to 16,000 Hz, specifically adhering to the one-sixth-octave frequencies outlined in ISO 266 The mandatory EHF test signal frequencies include 8,000 Hz, 10,000 Hz, 12,500 Hz, and 16,000 Hz, along with their corresponding hearing level ranges as detailed in Table 3.
NOTE Some EHF instruments have the capability of going up to 20 kHz, but at present no standardized reference threshold data are available
Table 3 – Minimum range of values of hearing level for EHF audiometers
* 16 000 60 a Minimum hearing levels to be -10 dB or lower for all frequencies
6.1.1.3 Test signal level range for earphones
The minimum hearing level shall be -10 dB or lower
NOTE 1 Due to the large spread of hearing threshold levels in normal hearing subjects at the highest frequencies a minimum hearing level of -10 dB is not sufficient to reach threshold in many subjects Consequently, a minimum hearing level of less than -10 dB is recommended
NOTE 2 No requirement is given for the range of output for loudspeakers and bone vibrators
For sweep frequency audiometers, the range of frequencies and hearing levels shall be at least equal to those given in Table 2 for fixed frequency audiometers.
Frequency accuracy
For fixed frequency audiometers, the frequencies shall be equal to the stated values within the following tolerances:
For continuous sweep frequency audiometers, the frequency of the test tone shall agree with the value indicated on the audiogram within ± 5,5 %.
Total harmonic distortion
The maximum total harmonic distortion shall not exceed the values given in Table 4
Table 4 – Maximum permissible acoustic total harmonic distortion, for supra-aural, circumaural, insert earphonesand bone vibrators
Frequency range in Hz 125 to 200 250 to 400 500 to 8 000 250 to 400 500 to 800 1 000 to
Total harmonic distortion (THD) is measured in percentages, with values of 3% and 6% noted The maximum output level of the audiometer should not exceed these percentages For circumaural and insert earphones, the hearing level must be set 10 dB lower than the specified levels in the table.
Rate of frequency change
Automatic recording facilities must feature a continuous sweep frequency, with at least one frequency change rate of one octave per minute, allowing for a variation of ± 25% Additionally, if an automatic recording audiometer uses fixed frequencies, it is essential to allow a minimum duration of 30 seconds at each frequency.
Frequency modulation
If frequency modulated tones are provided they shall have the following characteristics: a) Carrier frequency
The carrier frequency shall be chosen from the audiometric test frequencies specified in Table 2 with a tolerance of ± 3,5 % of the stated value b) Waveform of modulating signal
The waveform of the modulating signal shall be either sinusoidal or triangular with symmetrical rising and falling portions on a linear or on a logarithmic frequency scale
If the modulating waveform is sinusoidal, its total harmonic distortion shall not exceed
For a triangular waveform, the ramps must maintain a linear form, deviating no more than 5% from their amplitude Additionally, the duration of the rising and falling segments should not vary by more than 10% It is also important to consider the repetition rate of the modulating signal.
The repetition rate of the modulating signal shall be within the range of 4 Hz to 20 Hz with a tolerance of ± 15 % of its stated value d) Frequency deviation
The frequency deviation shall be in the range from ± 2,5 % to ± 12,5 % of the carrier frequency with a tolerance of ± 15 % of its stated value
The manufacturer shall state the characteristics and tolerances of the signals provided.
External signal source
Signals
Audiometers can utilize speech signals or complex signals alongside pure tones The IEC 60645-2 standard outlines the equipment necessary for speech audiometry, while ISO 8253-3 details the techniques involved However, these standards do not define the specific parameters needed for conducting speech audiometry or for employing complex signals.
Frequency response
When a constant voltage is applied to the external input socket, the output sound pressure level produced by the earphone must not vary by more than ± 4 dB from the average sound pressure level of all test signals within the frequency range of 250 Hz to 4 kHz, as measured using the same ear simulator utilized for audiometer calibration.
250 Hz the tolerance is + − 11 4 dB and above 4 kHz the tolerance is − + 6 4 dB
For the bone vibrator output, the manufacturer shall specify the frequency response and tolerances in the frequency range from 250 Hz to 4 kHz.
Electrical sensitivity
The manufacturer must define the electrical sensitivity of the external input by indicating the voltage of a specified input signal needed to achieve a designated output sound pressure level, with the signal indicator positioned at its reference point.
Reference level for external signal source
The external signal shall be capable of being monitored by a signal indicator (see 8.2) The reference level shall be stated when the signal indicator is at its reference position.
Operator to subject speech communication
A facility must enable clear speech communication between the operator and the test subject during standard testing conditions It is essential to regulate the speech signal level to ensure the reliability of the test results is not compromised.
Subject to operator speech communication
A facility shall allow speech communication from the test subject to the operator under normal test conditions.
Masking sound
General
When using audiometers that deliver masking sound, it is essential to conduct all masking sound measurements in the same ear simulator or mechanical coupler utilized for pure-tone measurements.
The standard primarily addresses requirements for pure tones, indicating that narrow-band noise is the suitable masking noise Additionally, IEC 60645-2 outlines the specifications for masking noise related to speech signals when integrated into a pure-tone audiometer.
Narrow-band noise
Narrow-band masking requires the noise band to be geometrically centered around the test frequencies, with specific band limits outlined in Table 5 Beyond these limits, the sound pressure spectrum density level of the noise must decrease by at least 12 dB per octave for a minimum of three octaves and remain at least 35 dB below the level at the center frequency Measurements should be conducted within the frequency range of 31.5 Hz.
10 kHz for instruments limited to 8 kHz For EHF instruments measurements are required up to 20 kHz
Due to the limitations of transducers, ear simulators, and mechanical couplers, measurements of bandwidth at frequencies of 4 kHz and higher may not accurately reflect the spectrum of masking noise Consequently, for center frequencies exceeding 3.15 kHz, measurements should be conducted electrically across the transducer terminals.
Table 5 presents the upper and lower cut-off frequencies for narrow-band masking noise, specifically at a sound pressure spectrum density level of -3 dB, referenced to the level at the center frequency of the band.
Lower cut-off frequency in Hz Upper cut-off frequency in Hz
NOTE 1 The bands of noise correspond to one-third octaves as a minimum and one-half octaves as a maximum
At center frequencies of 400 Hz and higher, the bands are broader than the critical bands needed for effective masking, necessitating an overall sound pressure level that is approximately 3 dB greater than the critical bands (refer to ISO 389-4) Utilizing wider bands helps reduce the perceived tonality of masking noise.
NOTE 2 The minimum and maximum lower and upper cut-off frequencies, f l (min.), f l (max.), f u (min.) and f u (max.), are given by the following formulae (see IEC 61260): f l (min.) = f m /2 1/4 f l (max.) = f m /2 1/6 f u (min.) = f m × 2 1/6 f u (max.) = f m × 2 1/4 where f m is the centre frequency
NOTE 3 The given values are rounded to the first three significant digits.
Other masking sound
If other types of masking sound are provided the manufacturer shall specify the frequency spectrum and use
Type of transducers
The types of transducers used in pure-tone audiometry consist of different types of earphone (supra-aural, circumaural and insert), bone vibrators and loudspeakers.
Headband
A headband must be supplied to secure supra-aural or circumaural earphones or bone vibrators, adhering to the nominal static force outlined in the ISO 389 series for the specific transducer model If a different static force is necessary, the manufacturer must specify this requirement, and a suitable headband will be provided accordingly.
Loudspeaker
Sound-field audiometry can be conducted in various environments that differ significantly from free-field conditions ISO 8253-2 outlines the characteristics of free-field, diffuse-field, and quasi-free-field conditions, along with the procedures for sound-field audiometry It is essential for manufacturers to specify the test conditions relevant to measuring the performance of loudspeaker outputs.
Marking
The signal level control shall be identified by the designation “Hearing Level” (HL) or an equivalent national designation
The zero marking on the hearing level control must align with the output from the transducers, corresponding to the reference equivalent threshold values specified in the applicable sections of ISO 389.
Signal indicator
To ensure proper operation, manufacturers must define a reference reading for the signal indicator, which allows monitoring of the external input signal level (refer to Table 1) Additionally, this indicator can be utilized to track internally generated signals.
The manufacturer must specify the signal indicator's characteristics, including time weighting, dynamic range, and rectifier features Additionally, if the indicator is designed for speech signals, it must comply with the IEC 60645-2 standards.
The indicator must be installed at a location in the circuit prior to the hearing level control Additionally, the amplifier should include provisions for gain adjustments to support a variety of settings.
20 dB in the overall level of the signal presented
The manufacturer must specify the output level measured on the ear simulator, with the hearing level control adjusted to a designated value This measurement is taken when the input is activated by a specified signal at a stated level, ensuring the monitor indicator reaches its reference indication.
Accuracy of sound pressure level and vibratory force level
When a single signal channel is connected to the earphone, the sound pressure level generated must not vary by more than ± 3.7 dB from the indicated value at any setting of the hearing level dial across specified frequencies.
125 Hz to 4 kHz and by not more than ± 6,2 dB at frequencies up to and including 8 kHz At higher frequencies this difference shall be within ± 6,5 dB
Similarly the force level produced by the bone vibrator minus the reference equivalent threshold force level shall not differ by more than ± 5,5 dB in the frequency range 250 Hz to
4 kHz and by ± 7,0 dB at higher frequencies
When multiple channels for signal or noise are connected to a single transducer, the output level must not vary by more than ± 1.7 dB compared to when only one channel is connected, applicable for frequencies between 125 Hz and 4 kHz For frequencies ranging from 5 kHz to 8 kHz, a tolerance of ± 3.2 dB is acceptable, while frequencies above 8 kHz up to 16 kHz require a tolerance of ± 3.5 dB These specifications are relevant for hearing levels up to 20 dB below the maximum output level.
Sweep frequency audiometers shall meet the requirements above at all appropriate one-third- octave frequencies; the output level shall vary smoothly between these frequencies.
Hearing level control
Manual audiometers
A hearing level control must feature a single scale and a unified reference zero point applicable across all frequencies The indicator readings for hearing levels should be clearly marked at consistent intervals.
5 dB or less, with the 0 dB setting at each frequency corresponding to the reference equivalent threshold level.
Automatic-recording audiometers
All automatic-recording audiometers must have a change rate of 2.5 dB/s, with optional additional rates of 1.25 dB/s and/or 5 dB/s The tolerance for these rates is set at ± 25%.
The smallest increment of the hearing level control shall be stated by the manufacturer.
Accuracy of control
The difference (in decibels) between the measured difference and the indicated difference between two successive hearing level settings shall be less than or equal to the smaller of:
• three-tenths of the indicated difference in decibels or
• 1,5 dB for settings of -10 dB HL to 0 dB HL
• 1,4 dB for settings of 0 dB HL to 45 dB HL
• 1,2 dB for settings of 45 dB HL or greater
Masking level control
General
The masking level control shall have only one reference zero point that is common for all frequencies The masking level shall be adjustable in steps of 5 dB or less.
Masking level
For narrow-band noise, the masking level control must be calibrated in decibels of effective masking according to ISO 389-4 If the exact bandwidth of the masking noise is unknown, the mean values from columns 1 and 2 in Table 1 of ISO 389-4:1994 should be utilized For other sound types, the calibration of the masking level control should be based on sound pressure level, measured with the earphone on the same ear simulator used for pure tone calibration The manufacturer is required to specify both the overall sound pressure level and the sound pressure level in one-third-octave bands across the specified frequency range of the masking noise.
For EHF instruments, the masking level can be obtained from Table 1 in ISO 389-4:1994, which provides data for one-third-octave bandwidth A useful approximation is to raise the reference equivalent threshold sound pressure levels by 5 dB.
Accuracy of masking levels
The level of the masking sound produced by an earphone shall not differ from the indicated value by more than − + 4 6 dB
The measured difference in output between any two indications of masking level shall meet the requirements of 8.4.3 for pure tones
Due to the dynamic characteristics of the narrow-band masking signal, it is often more practical to direct a pure-tone test signal through the masking attenuator, when available, for accurate measurement.
Masking level range
The masking sound must be provided at levels adequate to effectively mask pure tones in the same ear, specifically at a hearing level of 60 dB at 250 Hz, 75 dB at 500 Hz, and 80 dB from 1 kHz onward.
4 kHz The level of the masking sound shall be adjustable over a range from 0 dB hearing level to these levels.
Tone switching
Tone switch for manual audiometers
Manual audiometers must include a tone switch that allows for the presentation and interruption of the test tone This switch and its circuitry should ensure that the subject responds to the test tone itself, rather than being distracted by mechanical noise or signal switching transients.
NOTE An audiometer may be equipped with an automatic gating function for controlling the duration and/or repetition rate of a tone pulse.
On/off ratio for manual audiometers
When the switch is in the "OFF" position and the hearing level control is set to 60 dB or lower, the output must be at least 10 dB below the reference equivalent threshold level Additionally, for hearing level settings above 60 dB, the output should not increase by more than 10 dB for every 10 dB rise in the hearing level setting while the switch remains in the "OFF" position.
Rise/fall times for manual audiometers
When the tone switch is moved to the "ON" position the rise time requirements shall be as follows (see Figure 1):
– AC rise time shall not exceed 200 ms;
– BC rise time shall be at least 20 ms;
– between B and C the sound pressure level shall rise in a progressive manner without discontinuities
When the tone switch is moved to the "OFF" position, the fall time requirements shall be as follows (see Figure 1):
– DH fall time shall not exceed 200 ms;
– EG fall time shall be at least 20 ms;
– between E and G the sound pressure level shall fall in a progressive manner without discontinuities
The sound pressure level generated by the earphone must not exceed 1 dB above its steady state level while the tone is rising or falling in the "ON" position.
NOTE The measurement of AC and DH may require special consideration due to the uncertainty involved.
Automatic pulsed presentation
Where automatic pulsed presentation is made available, the pulse sequence generated shall meet the following requirements (see Figure 1):
– rise time: BC shall be at least 20 ms and shall not exceed 50 ms;
– fall time: EG shall be at least 20 ms and shall not exceed 50 ms;
– rise/fall rates: between B and C and between E and G the sound pressure level shall vary smoothly and without discontinuities;
– "ON" phase: CE shall be at least 150 ms;
– "ON"/"OFF" times: FJ and JK shall each have values of (225 ± 40) ms;
– “ON”/”OFF” ratio: between G and I the output shall remain at least 20 dB below the maximum reached in the “ON” phase CE
Instant of switch operation (ON)
Instant of switch operation (OFF)
Figure 1 – Rise/fall envelope of test tones
Subject’s response time for automated test procedures
The time available for a subject to respond to a test stimulus shall be specified by the manufacturer who shall state the algorithm for the test procedure.
Subject’s response system
The subject’s response system is a means by which the tester is made aware that the subject has responded to the signal
The response system typically consists of a hand-held switch that activates a visual indicator on the audiometer For automatic-recording audiometers, the subject's switch is used to manage a specific function, usually adjusting the level of the test signal.
The switch must be designed for easy and reliable one-handed operation while ensuring it operates silently to prevent any errors in hearing threshold level measurements.
General
The requirements of Clause 9 apply where means are provided for the alternate or simultaneous presentation of a reference tone and a test tone of the same or different frequency
The operator must effectively present tones at appropriate durations and intervals Alongside the primary hearing level control for adjusting the sound pressure level of the test tone, an additional control, known as the reference tone level control, is necessary for setting the level of the reference tone The standards for frequency accuracy, distortion, stability, and the rise and fall of the reference tone are outlined in other relevant sections of this standard.
Frequencies
As a minimum, the one-octave frequencies provided in the range 250 Hz to 4 kHz and additionally 6 kHz shall be available as reference tones for air conduction tests.
General
To demonstrate conformance to the standard, measurement results must fall within the specified tolerances, taking into account the expanded uncertainty of the testing laboratory If measurements are unsuitable, alternative methods such as visual inspection or review of supporting documentation can be used to establish compliance.
Environmental conditions and power supply variation
To demonstrate conformity with the specifications outlined in section 5.3, one sample of each type of earphone provided with the audiometer must be tested This involves measuring frequency, distortion, and sound pressure level at an indicated frequency of 1 kHz, at a hearing level of 100 dB or the maximum hearing level setting, whichever is lower Distortion measurements should follow the guidelines specified in section 6.1.3.
Environmental tests according to 5.3 shall be performed at the following three combinations of temperature and relative humidity, the ambient pressure being within the range specified in 5.3:
– and one additional combination from within the range specified in 5.3
Under specified temperature and relative humidity conditions, testing must also be conducted at pressures of 98 kPa (± 1 kPa) and 104 kPa (± 1 kPa), unless there is clear evidence indicating that ambient pressure does not significantly impact the results.
To demonstrate conformity with specifications 5.4 and 5.5, one sample of the earphone provided with the audiometer, capable of delivering the highest sound pressure level, must be tested This involves measuring frequency, distortion, and sound pressure level at an indicated frequency of 1 kHz, at a hearing level of 100 dB or the maximum hearing level setting, whichever is lower Distortion measurements should follow the guidelines outlined in section 6.1.3.
Electromagnetic compatibility
During EMC tests, the audiometer must be equipped with all manufacturer-specified accessories and units Additionally, various positions of the audiometer in relation to the radiating antenna should be thoroughly tested.
The ambient acoustic noise in the EMC testing space must be below 55 dB when measured with a one-third-octave filter at 1 kHz The audiometer's hearing level control should be set to its minimum, with the frequency control at 1 kHz and the tone switch activated for the right-hand earphone, if applicable EMC tests are to be conducted across a frequency range of 80 MHz to 2.5 GHz in 1% increments, with appropriate dwell time for each frequency based on the instrument under test It is essential to adhere to the requirements outlined in section 5.6, even when testing at a limited number of frequencies.
Unwanted sound
Unwanted sound from an earphone
Unwanted sound can produce extremely low acoustic levels that are challenging to measure directly To assess this unwanted sound indirectly, equivalent electrical measurements can be utilized One effective method involves measuring the root mean square (r.m.s.) voltage across a suitable dummy load, which replaces the test earphone, using a sound level meter with time-weighted F, as specified in IEC 61672.
To ensure accurate testing, a resistance matching the earphone's nominal impedance should be used at each test frequency At a hearing level control setting of 60 dB with the tone "OFF," the electrical signal across frequencies from 125 Hz to 8 kHz must remain at least 10 dB below the reference equivalent threshold level for the corresponding one-third-octave band center frequency Additionally, when the tone is "ON," any unwanted signal in the non-test earphone or a substitute dummy load must be at least 70 dB below the test tone, with the hearing level control set to 70 dB or higher.
In subjective measurements of unwanted sound from the non-stimulus earphone, test subjects should not detect any sound within the frequency range of 250 Hz to 6 kHz, regardless of the masking or hearing level controls, even at a maximum setting of 70 dB Additionally, for frequencies between 125 Hz and 8 kHz, subjects should only hear the test sound up to a setting of 50 dB The testing will be performed with the tone switch in both the "ON" and "OFF" positions.
For higher settings, an external electrical attenuator must be added to the stimulus earphone connection Compliance tests at these elevated settings should be conducted with the external attenuator adjusted to a level that is the number of decibels above the audiometer hearing level settings, minus 70 dB or 50 dB, as applicable During testing, the opposite earphone should be disconnected, and the audiometer output terminals should be connected to a suitable dummy load.
In the EHF range, test subjects should not perceive any unwanted sounds from the transducer during the presentation of the test tone, even when the hearing level control is set to maximum.
Many test subjects exhibit minimal hearing ability at frequencies of 14 kHz and 16 kHz, yet they demonstrate strong hearing capabilities at lower frequencies This important observation is overlooked in section 5.7 of the standard.
Unwanted sound from a bone vibrator
The impact of sound radiation from the bone vibrator on audiometric test results is assessed by first determining the bone conduction threshold at 2 kHz and higher frequencies, following ISO 8253-1:2010, with the test ear occluded by an earplug that attenuates sound by at least 20 dB, as per ISO 4869-1 This process is then repeated without the earplug Finally, the mean hearing thresholds for each frequency are calculated from the results of both tests.
The influence is considered insignificant when the average hearing threshold levels of 16 ears comply with the criteria outlined in section 5.7.1, provided that the difference between any two mean values does not exceed 3 dB.
NOTE The maximum permissible total harmonic distortion given in Table 4 may lead to false bone conduction thresholds due to the perception of harmonics of lower test frequencies.
Unwanted sound radiated by an audiometer
The test for the requirements in 5.7.4 shall be made on at least two test subjects meeting the requirements of 5.7.1, wearing a pair of disconnected earphones and located at a distance of
The audiometer should be positioned 1 meter away, and its electrical output must be absorbed by a resistive load that matches the earphone's impedance at 1 kHz If a bone conduction facility is available, the test should be conducted again with the ears unoccluded.
Total harmonic distortion of test signals
Conformity with the specification in section 6.1.3 is assessed at the hearing levels indicated in Table 2 or at the maximum audiometer setting, whichever is lower, following the IEC 60268-3 procedure, excluding harmonics above 16 kHz For air conduction, distortion is measured acoustically using an ear simulator designed for equivalent reference threshold levels, while for bone conduction, it is measured on a mechanical coupler.
Due to the inability to define maximum allowable harmonic distortion that guarantees precise bone conduction results across all hearing loss types, manufacturers must specify the frequencies and hearing levels at which the non-linearity of the bone vibrator may affect the accuracy of bone conduction measurements.
NOTE Due to the limitations of ear simulators and mechanical couplers, measurements of harmonics may not accurately describe the non-linear properties of the system.
Signal accuracy
Accuracy of sound pressure level and vibratory force level
To demonstrate conformity with the specifications in section 8.3, each earphone must have its output measured at a hearing level setting of 70 dB or the maximum, whichever is lower, across all available frequencies using a specified ear simulator For bone vibrators, the hearing level setting should be 30 dB or the maximum, whichever is lower, and the measurements should be taken on a mechanical coupler as outlined in IEC 60318-6.
Accuracy of hearing level control
The hearing level control accuracy must be tested at a minimum frequency of 1 kHz, with an additional test at 8 kHz if an EHF option is available Measurements for compliance with the requirements in section 8.4.3 should ideally be conducted acoustically If electrical measurements are necessary, they should be taken at the input to the transducer connected to an ear simulator, or a dummy electrical load may be used to simulate the transducer at the test frequency.
Masking sound
Narrow-band noise
To demonstrate conformity with section 6.4.2, the spectrum of the masking noise must be measured acoustically up to 3.15 kHz using the same ear simulator employed for pure tone measurements For frequencies above 3.15 kHz, the measurement should be conducted electrically across the transducer terminals while positioned on the same ear simulator.
Masking level
Conformity with the specification in 8.5.3 shall be demonstrated using a sound level meter that conforms to the class 1 requirements of IEC 61672-1, by measuring the S time-weighted,
Z frequency-weighted sound level at a hearing level setting of 70 dB at all available frequencies and with the same ear simulator as used for the measurement of pure tones.
Headbands
General
To meet the requirements outlined in section 7.2, the headband static force must adhere to the specifications of the ISO 389 series or the manufacturer's specifications for the specific transducer model This compliance is valid when the stated tolerances are adjusted to account for the maximum permitted measurement uncertainties listed in Table 8.
Supra-aural and circumaural earphone headband
To ensure conformity, the earphones must be positioned 145 mm apart horizontally, while the headband height should be adjusted to create a vertical distance of 129 mm from the top center of the headband to a line connecting the centers of the earphones The acceptable tolerance for these dimensions is ± 5 mm.
Bone vibrator headband
To ensure compliance, the distance between the bone vibrator and the opposite end of the headband must adhere to the specifications outlined in section 13.8.2 However, for forehead placement, this distance should be set at 190 mm, allowing for a tolerance of ± 5 mm.
14 Maximum permitted expanded uncertainty of measurements U max
The table outlines the maximum allowed expanded uncertainty for a coverage factor of k = 2, related to the measurements specified in this standard It provides a single set of values for U max applicable to both basic type approval measurements and periodic verification.
The maximum permitted expanded uncertainties of measurement, as outlined in Table 8, are essential for demonstrating compliance with this standard If a test laboratory or maintenance service's actual expanded uncertainty surpasses the values specified in Table 8, that measurement cannot be utilized to prove adherence to the standard's requirements.
Table 8 – Values of U max for basic measurements
Measured quantity Relevant subclause number Basic
Sound pressure level 125 Hz to 4 000 Hz 8.3, 9.3.4 0,7 dB
Sound pressure level 5 000 Hz to 8 000 Hz 8.3, 9.3.4 1,2 dB
Sound pressure level 9 000 Hz to 16 000 Hz 8.3, 9.3.4 1,5 dB
Narrow-band masking noise cut-off frequencies 6.4.2 1 %
Masking level 125 Hz to 4 000 Hz 8.5.3 1,0 dB
Force level 250 Hz to 4 000 Hz 8.3 1,5 dB
Force level greater than 4 000 Hz 8.3 2,0 dB
Rate of change in level (%) 8.4.2 5 %
Linearity of hearing level control -10 to 0 dB
Linearity of hearing level control 5 dB to
Linearity of hearing level control above
Rise and fall time 8.6.3, 8.6.4 5 ms
Marking
The audiometer must display the manufacturer's name, model, type, and serial number, as outlined in Table 1 Additionally, each test signal transducer should have its own unique instrument identification marked on it.
The left and right earphones shall be readily identifiable If the earphones are colour coded the left earphone shall be coded blue and the right earphone red.
Instruction manual
An instruction manual for the audiometer must include essential information such as the instrument type and compliance details, permissible power supply variations, and environmental conditions It should describe the correct installation method to minimize unwanted sound radiation and identify transducers along with their reference equivalent threshold levels, including calibration origins and static force The manual must also detail frequency response characteristics, masking effects, warm-up time, sensitivities, nominal impedances of input and output facilities, and pin assignments for external connections Additionally, it should specify the mode of operation, sound pressure level changes for automatic-recording audiometers, and characteristics of frequency-modulated signals.
– the frequency of the modulating signal;
– the modulation waveform, i.e sine wave or triangular;
The modulation range of the test frequency is expressed as a percentage, while the sound attenuation characteristics of the earphones are measured according to ISO 4869-1 Maximum hearing level settings at each test frequency must be provided, including any limitations due to harmonic distortion It is essential to consider the effects of airborne sound radiation from the bone vibrator to ensure accurate test results Additionally, information regarding the time window for a subject's response during automated test procedures is outlined in section 8.6.5 For battery-operated instruments, details about the battery type, checking methods, replacement procedures, and expected battery life are crucial Maintenance and calibration procedures, along with schedules, are specified in ISO 8253-1:2010 Lastly, an EMC warning should be issued regarding the potential impact of radiated electromagnetic fields, especially from high-powered medical devices, on audiometer performance.
IEC 61260, Electroacoustics – Octave-band and fractional-octave-band filters
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3:Guide to the expression of uncertainty in measurement (GUM:1995)
ISO 389-9, Acoustics – Reference zero for the calibration of audiometric equipment – Part 9: Preferred test conditions for the determination of reference hearing threshold levels