Source: https://docs.jmrp.io/phonometry/devices/electroacoustics/headphones/
# Headphones and Earphones (IEC 60268-7)
A headphone is measured on an ear simulator, a coupler or a head and torso
simulator, never in a room, so the questions IEC 60268-7 asks are about the
transducer and the voltage that drives it: what impedance it presents, what
e.m.f. makes it produce 94 dB, how much it can take, how its response looks on
a coupler and to a panel of listeners. Several of those answers are given with
a noise that stands in for programme, the **simulated programme signal** of
IEC 60268-1. This guide builds that signal first, from its table and from the
filter the standard draws, and then walks a 32 Ω moving-coil headphone through
the characteristics of IEC 60268-7 that are computations: the code that names
it, its rated impedance, its voltages, powers and levels, its protective
device, its frequency responses, its distortion test signals and the probe
microphone that measures it in the ear canal.
## 1. The simulated programme signal (IEC 60268-1 Clause 7)
Clause 7 defines a stationary Gaussian noise whose power spectrum, read in
one-third-octave bands, follows **Table II**: 0 dB from 250 Hz to 800 Hz,
falling to −13.5 dB at 20 Hz and −21.6 dB at 20 kHz, with tolerances of
±0.5 dB in the middle widening to ±3 dB at the ends. The table is relative:
its 0 dB is the level of one band, and the Note under the clause states the
whole signal as "approximately 12.5 dB higher". It is the power sum of the 31
bands.
```python
import numpy as np
from phonometry import electroacoustics
from phonometry.filters import octave_filter
table = electroacoustics.SIMULATED_PROGRAMME_SPECTRUM
levels = np.array([band.relative_level_db for band in table.values()])
print(len(table), table[20.0].relative_level_db, table[20000.0].relative_level_db)
# 31 -13.5 -21.6
print(round(10 * np.log10(np.sum(10 ** (levels / 10))), 2)) # 12.56
```
"Such a signal may be obtained from a pink-noise source by means of the
filter circuit shown in Figure 2": a passive ladder of 430 Ω and 2.2 µF into
3.3 kΩ and 91 nF, then 330 Ω and 2.2 µF into 3.3 kΩ and 68 nF, then 0.47 µF
into 10 kΩ. `programme_signal_filter` is its exact transfer function, about
−4 dB in the passband. Pink noise through it lands inside every tolerance of
Table II, but closely: in ideal bands the smallest margin is 0.18 dB, at
400 Hz on one side and 5 kHz on the other, so a short record can fall outside.
`simulated_programme_signal` therefore offers two shapes. The default puts
every band on its printed level: a spectrum straight in decibels between the
band centres, with its nodes fitted so that each band, integrated in closed
form, is exactly the table. `spectrum="figure_2"` is the circuit.
`check_programme_signal` judges band levels against Table II. Since the table
is relative, it looks for the level that places every band inside its window
and passes when one exists; it reports the margin and the bands that bind.
```python
fs = 48000
x = electroacoustics.simulated_programme_signal(fs, 60.0, spectrum="figure_2", seed=2)
bands = octave_filter(x, fs, fraction=3, limits=[19.95, 19952.6])
check = electroacoustics.check_programme_signal(bands.frequencies, bands.levels)
print(check.passes, round(check.margin_db, 2), check.binding_bands_hz)
# True 0.12 (315.0, 5000.0)
y = electroacoustics.simulated_programme_signal(fs, 60.0, seed=2)
bands_y = octave_filter(y, fs, fraction=3, limits=[19.95, 19952.6])
check_y = electroacoustics.check_programme_signal(bands_y.frequencies, bands_y.levels)
print(check_y.passes, round(check_y.margin_db, 2)) # True 0.34
```
With the same seed, the table's own shape keeps 0.34 dB of margin and the
circuit 0.12 dB: the circuit has spent most of its margin before the record
adds its own fluctuation.
*Left, the filter of Figure 2: inside the tolerances, but riding the lower
edge on both shoulders of the curve. Right, the generator's spectrum clipped
for the limiting voltages of IEC 60268-7 (section 5), which still follows the
table: clipping at twice the RMS value spreads only a little power into the
weak upper bands.*
Show the code for this figure
```python
import matplotlib.pyplot as plt
clipped = electroacoustics.simulated_programme_signal(fs, 60.0, peak_to_rms=2.0, seed=2)
limiting = electroacoustics.check_limiting_test_signal(clipped, fs)
fig, (ax_figure_2, ax_limiting) = plt.subplots(1, 2, figsize=(13.5, 5.6))
check.plot(ax_figure_2)
limiting.plot(ax_limiting)
plt.show()
```
## 2. How the measurement goes (IEC 60268-7 Clause 7)
1. **The standard conditions** (7.2, 7.3). One earphone sits at its rated
application force on the coupler or ear simulator its standard names
(IEC 60318, IEC 60711, or the ear of the head and torso simulator of
IEC 60959, with the pinna simulator of Annex A where it applies), and the
type is stated with the results. The signal is a source e.m.f. applied
through the rated source impedance, 120 Ω for a headphone output by
IEC 61938, at the point an amplifier drives in use, and set for 94 dB at
the standard measuring frequency of 500 Hz; the manufacturer may set 1 mW
in the rated impedance instead. Volume controls sit at minimum attenuation.
2. **With the programme signal** (7.4, Figure 3). The same, with the
simulated programme signal of IEC 60268-1 from a generator and a power
amplifier whose voltmeter reads the e.m.f.; the simulator's output passes,
where a clause asks for it, through the A-weighting of IEC 61672-1 and a
filter with the inverse of the head and torso simulator's free-field
response, then a one-third-octave analyser. The NOTE under the figure
allows the same correction numerically, which is what section 5 does. A
noise reading wanders, so it is repeated and averaged (8.3.4.2 NOTE 2), and
for 8.3.5 the headphone is taken off and put back between 3 to 5 readings.
3. **With test persons** (7.5, 7.6). The comparison responses put a listener
in a free field, a progressive plane wave (7.5.2), or in a diffuse field
(7.5.3), and ask for equal loudness band by band; the ear canal responses
put a probe microphone that meets Annex B at least 4 mm inside the canal
and read levels instead. Annexes C to E give the practical details.
## 3. The code of a headphone (Clause 4)
IEC 60268-7 names a headphone by a code, `60268-7-IEC-XXXX-NNRN-N`: four
letters for the principle of the transducer, the type of earphone, the
acoustic coupling to the ear canal and the radiation to the outside, the
impedance in ohms in "mantissa and exponent" form, and the number of
channels. The clause gives three impedances, 8 Ω as `08R0`, 32 Ω as `32R0` and
600 Ω as `06R2`; the last one settles the choice the rule leaves open, between
`06R2` and `60R1`, in favour of giving every trailing zero to the exponent.
```python
code = electroacoustics.HeadphoneClassification("D", "C", "S", "C", 32.0, 2).code
print(code) # 60268-7-IEC-DCSC-32R0-2
print([electroacoustics.impedance_code(ohm) for ohm in (8, 32, 600, 150)])
# ['08R0', '32R0', '06R2', '15R1']
earbud = electroacoustics.parse_classification_code("60268-7 - IEC - DELO - 16R0 - 2")
print(earbud.description)
# electrodynamic (moving coil), intra-concha, acoustically open (controlled
# leakage), open-back
```
## 4. Impedance (8.2)
The rated impedance is a pure resistance the manufacturer states, "chosen so
that the lowest value of the modulus of the actual impedance within the rated
frequency range is not less than 80 % of the rated value"; a dip below that
anywhere up to 20 kHz should be stated, and the modulus is measured "at least
over the frequency range 20 Hz to 20 kHz". `verify_rated_impedance` judges the
first, lists the second and checks the third.
```python
f = np.geomspace(10.0, 30000.0, 241)
z = 31.0 + 22.0 / (1.0 + ((f / 90.0 - 90.0 / f) / 0.9) ** 2) + 4.0 * (f / 20000.0)
impedance = electroacoustics.verify_rated_impedance(
f, z, rated_impedance_ohm=32.0, rated_frequency_range_hz=(15.0, 25000.0)
)
print(impedance.passes, round(impedance.minimum_ohm, 1), round(impedance.minimum_ratio, 3))
# True 31.3 0.979
```
*The coil's resistance sets the floor, the moving system's resonance the peak
and the coil's inductance the rise. The minimum, 31.3 Ω, is 98 % of the rated
32 Ω, well clear of the 80 % the clause allows.*
Show the code for this figure
```python
ax = impedance.plot()
plt.show()
```
## 5. Voltages, powers and levels (8.3 to 8.5)
Every input of IEC 60268-7 is a source e.m.f. applied through the rated source
impedance, 120 Ω for a headphone output by IEC 61938 (7.1 NOTE). The
**characteristic voltage** (8.3.3) is the 500 Hz sinusoidal e.m.f. that
produces 94 dB in the coupler or ear simulator; the headphone is linear there,
so one reading scales to it. Every voltage has a power counterpart (8.4), the
power it would dissipate in a resistance equal to the rated impedance through
the rated source impedance, $P = E^2 R/(R + R_\mathrm{s})^2$, and the
**working sound pressure level** (8.5.2) is the level at the e.m.f. that
dissipates 1 mW that way.
```python
characteristic = electroacoustics.characteristic_voltage(0.1, 100.0)
print(round(characteristic, 4)) # 0.0501 V
impedances = {"rated_impedance_ohm": 32.0, "rated_source_impedance_ohm": 120.0}
print(round(electroacoustics.headphone_source_emf(1e-3, **impedances), 3)) # 0.85 V
print(round(1e3 * electroacoustics.headphone_input_power(5.0, **impedances), 1))
# 34.6 mW from the 5 V rated source e.m.f. of 8.3.1 NOTE 2
print(round(20 * np.log10(5.0 / characteristic), 1)) # 40.0 dB above it
```
8.3.1 NOTE 3 draws attention to hearing damage and says the rated source
e.m.f. "should, preferably, not exceed the characteristic voltage (see 8.3.3)
by more than 10 dB to 15 dB". The 5 V of IEC 61938 on this headphone sits
40 dB above it. NOTE 3 states a preference over a range, so the number is
yours to read; the library gives no verdict on it.
The **simulated programme signal characteristic voltage** (8.3.4) is the same
94 dB with the programme signal, and 8.3.5 reads it after the A-weighting of
IEC 61672-1 and the inverse of the head and torso simulator's free-field
response. The NOTE under Figure 3 does without filters: the one-third-octave
band levels in the ear simulator are multiplied by the filters' coefficients
and power-summed,
$$
L = 10\lg \sum_k 10^{(L_k + A_k - F_k)/10},
$$
with $A_k$ the A-weighting at the exact centre of band $k$ and $F_k$ the
free-field response. 8.3.5 g) removes and refits the headphone between
readings and averages the e.m.f. of 3 to 5 fittings.
```python
centres = np.array(list(table))
in_range = (centres >= 100.0) & (centres <= 10000.0)
bands_hz = centres[in_range]
resonance = 9.0 / (1.0 + ((bands_hz / 3000.0 - 3000.0 / bands_hz) / 0.8) ** 2)
reading = 72.0 + levels[in_range] + resonance # dB re 20 µPa at 0.1 V
fittings = np.vstack([reading, reading + 0.6, reading - 0.4])
plain = electroacoustics.programme_characteristic_voltage(0.1, bands_hz, fittings)
weighted = electroacoustics.programme_characteristic_voltage(
0.1, bands_hz, fittings, a_weighted=True
)
print(round(plain.characteristic_voltage_v, 3), round(weighted.characteristic_voltage_v, 3))
# 0.241 0.253
print(weighted.fittings_conform) # True, three fittings
working = electroacoustics.working_sound_pressure_level(plain.levels_db[0], 0.1, **impedances)
print(round(working, 1)) # 104.9 dB at 1 mW
```
The `weighted` call stops at the A-weighting. 8.3.5 also compensates the
free-field response of the head and torso simulator of IEC 60959, which is
that manikin's own data and not a table the library holds; a real 8.3.5
reading passes it as `free_field_response_db`. The 0.253 V is therefore the
e.m.f. for 94 dB A-weighted only, not the corrected characteristic voltage of
8.3.5, and the figure says so in its title.
*The band levels at the e.m.f. that gives 94 dB A-weighted: their power sum
is 94 dB, carried mostly by the four bands around the ear simulator's canal
resonance near 3 kHz. With the free-field compensation of a head and torso
simulator as well, the same call gives the corrected characteristic voltage
of 8.3.5.*
Show the code for this figure
```python
ax = weighted.plot()
plt.show()
```
The method of 8.5.3 c) sets the 1 mW e.m.f. another way, so that the voltage
across the headphone's own input connector is the one that would put 1 mW
into the rated impedance. The two agree only when the headphone presents its
rated impedance at 500 Hz. Given the measured impedance,
`working_sound_pressure_level` gives the method's reading as well; for a
32 Ω headphone that is 40 Ω at 500 Hz it is 1.49 dB lower, and the errata
register records the disagreement.
```python
by_definition = electroacoustics.working_sound_pressure_level(100.0, 0.5, **impedances)
by_method = electroacoustics.working_sound_pressure_level(
100.0, 0.5, **impedances, headphone_impedance_ohm=40.0
)
print(round(by_definition, 2), round(by_method, 2)) # 104.61 103.11
```
The **limiting voltages** of 8.3.2 are the e.m.f.s a headphone survives, for
ten minutes of one-minute bursts or for 100 h, of the programme signal "with
additional clipping": its spectrum still that of IEC 60268-1, its
peak-to-RMS ratio "between 1,8 and 2,2". That window is IEC 60268-7's own:
IEC 60268-1 asks for noise "without amplitude limiting" and specifies no crest
factor, whatever NOTE 1 of 8.3.4.2 says. `peak_to_rms` clips the generator to
exactly that ratio, and `check_limiting_test_signal` judges a record on both
counts.
```python
print(round(limiting.peak_to_rms, 2), limiting.passes) # 2.0 True
unclipped = electroacoustics.check_limiting_test_signal(y, fs)
print(round(unclipped.peak_to_rms, 2), unclipped.passes) # 4.92 False
```
## 6. The protective device (8.3.6)
A protective device "causes a change of at least 1 dB in the sensitivity" at
its protection voltage, and the impedance and level are then measured 1 dB
below and 1 dB above it. `protection_voltage` takes a sweep of e.m.f. and
level, reads the sensitivity at each step against the first, and interpolates
where the change reaches 1 dB.
```python
emf = np.array([0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 3.0, 5.0])
shortfall = np.array([0.0, 0.0, 0.05, 0.2, 0.7, 1.6, 3.5, 7.0])
protection = electroacoustics.protection_voltage(
emf, 94.0 + 20 * np.log10(emf / 0.1) - shortfall
)
print(round(protection.protection_voltage_v, 2)) # 1.65 V
print([round(v, 2) for v in protection.measurement_voltages_v]) # [1.47, 1.85]
```
## 7. Frequency responses (8.6) and crosstalk (8.12)
The **coupler or ear simulator frequency response** (8.6.2) is the level
against frequency at the rated e.m.f., over at least the rated frequency
range, and its graph is drawn with "the same length representing 50 dB as
represents one decade of frequency". The **crosstalk attenuation** (8.12) is
the difference between the level in a channel's coupler driven by that channel
and by another.
```python
fr = np.geomspace(20.0, 20000.0, 241)
level = (
104.0
- 10.0 * np.log10(1.0 + (60.0 / fr) ** 4)
+ 6.0 / (1.0 + ((fr / 3200.0 - 3200.0 / fr) / 0.6) ** 2)
- 10.0 * np.log10(1.0 + (fr / 12000.0) ** 6)
)
response = electroacoustics.coupler_frequency_response(
fr, level, rated_frequency_range_hz=(20.0, 20000.0)
)
crosstalk = electroacoustics.crosstalk_attenuation(
bands_hz, np.full(bands_hz.size, 100.0), 52.0 - 12.0 * np.log10(bands_hz / 1000.0) ** 2
)
print(response.covers_rated_range, round(crosstalk.minimum_db, 1)) # True 48.0
```
None of these responses has a tolerance: "It is not at present possible to set
limits for the frequency range based on deviations from a flat, or defined,
frequency response" (8.6.6 NOTE 2). The rated frequency range is the
manufacturer's statement, with the criteria its limits were chosen by, and
enters here only as the range a measurement has to cover.
*At 50 dB to the decade a coupler response looks as flat as the ear hears it:
the 6 dB peak near 3 kHz, which a stretched axis turns into a mountain, is a
modest bump.*
Show the code for this figure
```python
fig, (ax_response, ax_crosstalk) = plt.subplots(1, 2, figsize=(13.5, 5.2))
response.plot(ax_response)
crosstalk.plot(ax_crosstalk)
plt.show()
```
The other responses are measured with **test persons**. In the comparison
methods (8.6.3, 8.6.4) each person adjusts the e.m.f. until the headphone is
as loud as a free or diffuse reference field in each one-third-octave band of
pink noise; the response is the field's sound pressure over that e.m.f.,
"expressed in decibels referred to the value at the standard reference
frequency", averaged over at least eight persons with the standard deviation
in each band, and a headphone measured on at least 16 may serve as the
reference of the substitution method. The ear canal method (8.6.5) puts a
probe microphone in the ear canal instead of asking for a judgement, and
reads Formula (1),
$$
L_\mathrm{f} = L_\mathrm{e} - L_\mathrm{s} - (L_\mathrm{e} - L_\mathrm{s})_{500},
$$
after averaging two fittings of the headphone and two readings of the sound
field, with the procedure repeated when the fittings differ by more than
2.5 dB in any band and the 500 Hz band matched to the field's within 3 dB;
16 persons calibrate the headphone that replaces the sound field of the
indirect method (8.6.5.3).
The two use different reference bands. Formula (1) prints its own, 500 Hz,
the standard measuring frequency of 7.2 b). "The standard reference
frequency" of the comparison responses is a term IEC 60268-7 never defines;
IEC 60268-1 Clause 3, which it cites, sets it at 1 000 Hz "in the absence of
a clear reason to the contrary", the band 8.6.3.2 c) begins and ends the test
sequence on, so `field_comparison_response` refers to 1 kHz unless it is
given `reference_frequency_hz`.
```python
rng = np.random.default_rng(7)
shape_db = 3.0 / (1.0 + ((bands_hz / 2500.0 - 2500.0 / bands_hz) / 0.7) ** 2)
equal_loudness_emf = 0.05 * 10.0 ** (
-(shape_db + rng.normal(0.0, 1.2, (8, bands_hz.size))) / 20.0
)
comparison = electroacoustics.field_comparison_response(
bands_hz, 70.0, equal_loudness_emf, field="free"
)
field = 70.0 + rng.normal(0.0, 0.4, (8, 2, bands_hz.size))
earphone = field + shape_db + rng.normal(0.0, 0.6, (8, 2, bands_hz.size))
ear_canal = electroacoustics.ear_canal_frequency_response(bands_hz, earphone, field)
band = list(bands_hz).index(2500.0)
print(comparison.meets_panel_size, round(comparison.mean_db[band], 1)) # True 2.8
print(round(ear_canal.mean_db[band], 1), ear_canal.fittings_consistent.all()) # 3.2 True
print(comparison.reference_frequency_hz, ear_canal.reference_frequency_hz) # 1000.0 500.0
```
*The same headphone through two panels, at the 50 dB to the decade the part
prefers, where a 3 dB rise is the modest bump it is. The loudness judgements
scatter by 0.7 dB to 1.6 dB in every band but the reference; the probe
microphone, which needs no judgement, scatters by 0.2 dB to 0.8 dB and shows
the same 3 dB rise at 2.5 kHz.*
Show the code for this figure
```python
fig, (ax_comparison, ax_ear) = plt.subplots(2, 1, figsize=(10, 9.6))
comparison.plot(ax_comparison)
ear_canal.plot(ax_ear)
plt.show()
```
## 8. The distortion test signals (8.7)
The distortions of a headphone are the ones of IEC 60268-2, read with
`harmonic_distortion`, `modulation_distortion` and
`difference_frequency_distortion` and expressed as $20\lg$ of the ratio. What
IEC 60268-7 adds are the signals. For modulation distortion, 70 Hz and 600 Hz
in the amplitude ratio 4:1 with the peak of the rated input voltage, "−1,9 dB
at 70 Hz and −14,0 dB at 600 Hz" (NOTE 1 of 8.7.3.3); for difference-frequency
distortion, two tones 80 Hz apart, each at half the rated input voltage. Both
generators start every tone at its crest, so the sum reaches the rated peak.
Below, a drive with a little square law in it puts the second-order product
of the two tones at 80 Hz, 35.1 dB under them.
```python
modulation = electroacoustics.headphone_modulation_signal(fs, 1.0, rated_source_emf_v=1.0)
products = electroacoustics.modulation_distortion(modulation, fs, f_low=70.0, f_high=600.0)
print(round(float(np.max(np.abs(modulation))), 4)) # 1.4142, the peak of 1 V RMS
print(products.sideband_frequencies) # [460. 530. 670. 740.]
difference = electroacoustics.headphone_difference_frequency_signal(
fs, 1.0, upper_frequency_hz=1000.0, rated_source_emf_v=1.0
)
driven = difference + 0.05 * difference**2 # a drive with 5 % of square law
second = electroacoustics.difference_frequency_distortion(driven, fs, f1=920.0, f2=1000.0)
print(round(20 * np.log10(second), 1)) # -35.1 dB, the product at 80 Hz
```
The third-order products are at 460 Hz and 740 Hz, as item b) of 8.7.3.3
says. Formula (3) under it prints $U_{470}$, and Formula (5) of the
difference-frequency distortion closes a parenthesis it never opened; the
[errata register](https://docs.jmrp.io/phonometry/reference/errata/) records both, with the
cross-references of 8.6.3 to 8.6.5 and of Table 1 that name the wrong
subclause, the NOTE under Figure 3 that cites the head and torso simulator as
IEC 60969, the NOTE of 8.3.4.2 that credits IEC 60268-1 with a crest factor,
and the two settings of the 1 mW e.m.f. in 8.5.2 b) and 8.5.3 c).
## 9. The probe microphone (Annex B)
The microphone in the ear canal of 8.6.5 is specified by the normative Annex
B: a cross-sectional area of 5 mm² or less in the concha and the first 4 mm of
the canal, less than 0.6 of the canal's area beyond (an adult's averages
45 mm²), a volume under 130 mm³, responses to neighbouring one-third-octave
bands of pink noise within 3 dB of each other, and an output at least 15 dB
lower with the entrance sealed. `verify_ear_canal_microphone` judges all five.
```python
microphone = electroacoustics.verify_ear_canal_microphone(
entrance_area_mm2=3.8,
canal_section_area_mm2=19.0,
volume_mm3=95.0,
pink_noise_band_levels_db=[61.0, 62.2, 63.1, 62.5, 61.4],
open_levels_db=[62.0, 63.0, 62.5],
sealed_levels_db=[41.0, 44.0, 45.5],
)
print(microphone.passes, round(microphone.area_ratio, 3)) # True 0.422
```
*Left, a limiter that cuts in gently: the sensitivity has lost 1 dB at
1.65 V, where 8.3.6.2 b) reads the protection voltage. Right, the probe
microphone of Annex B: four upper limits met with room to spare, and the
sealed entrance 17 dB down against the 15 dB required.*
Show the code for this figure
```python
fig, (ax_protection, ax_microphone) = plt.subplots(1, 2, figsize=(13.5, 5.4))
protection.plot(ax_protection)
microphone.plot(ax_microphone)
plt.show()
```
## What this guide covers
**Covered.** IEC 60268-1:1985 Clause 7 with its two amendments of 1988: Table II and its
Note, the filter of Figure 2 as an exact transfer function, a generator of the
programme signal with the table's band levels or through the filter, optionally
clipped to a peak-to-RMS ratio, and the verdict on a one-third-octave spectrum.
IEC 60268-7:2010: the classification code of Clause 4; the rated impedance and
the measured range of 8.2; the characteristic voltage (8.3.3), the
programme signal characteristic voltages of 8.3.4 and 8.3.5 by the power
summation of the NOTE under Figure 3 with the averaging of 3 to 5 fittings,
the clipped programme signal of the limiting voltages (8.3.2.2 b) and the
protection voltage (8.3.6.2 b); the powers of 8.4 and the working sound
pressure levels of 8.5.2, by the definition or by the method of 8.5.3 c); the
coupler or ear simulator response (8.6.2), the free-field and diffuse-field
comparison responses with their panel sizes, referred to the standard
reference frequency of IEC 60268-1 Clause 3 (8.6.3, 8.6.4), the ear canal
response by Formula (1) with its fitting and level checks and the 16 persons
of a reference (8.6.5); the distortion test signals of 8.7.3 and 8.7.4; the
sound attenuation of 8.11, which is ISO 4869-1 and is computed by
`hearing.real_ear_attenuation`, with `hearing.anr_total_attenuation` of
ISO 4869-6 for a headphone with active noise compensation; the crosstalk
attenuation (8.12); and the probe microphone of Annex B, items a) to e).
**Not covered.** The rated conditions (7.1, 8.6.6, 8.8, 8.13, 8.14) are stated by the
manufacturer, the frequency responses carry no tolerance to judge (8.6.6
NOTE 2), and the endurance runs of 8.3.2 are a test schedule, not a
computation. The preference of 8.3.1 NOTE 3, a rated source e.m.f. no more
than 10 dB to 15 dB above the characteristic voltage, is a range, so it gets a
number and no verdict. The external field (8.9) and the unwanted sound
radiation (8.10) are readings. The free-field response of the head and torso
simulator of IEC 60959 is an input, not a table the library holds. Annex A is the geometry of a pinna simulator, and
Annexes C to E are informative practical conditions; the sound pressure level
limit of 85 dB and the 10 dB signal-to-noise ratio of 8.6.5.2 b) need
calibrated readings the response function is not given.
## See also
- [Electroacoustics](https://docs.jmrp.io/phonometry/devices/electroacoustics/electroacoustics/):
the IEC 60268-3 harmonic, modulation and difference-frequency distortions
that read the test signals of section 8.
- [Loudspeaker Characterisation (IEC 60268-5)](https://docs.jmrp.io/phonometry/devices/electroacoustics/loudspeakers/):
the transducer of the same family that radiates into a room instead of a
coupler.
- [Microphone Characterisation (IEC 60268-4)](https://docs.jmrp.io/phonometry/devices/electroacoustics/microphones/):
the measuring microphone behind every coupler reading.
- [Filter Banks](https://docs.jmrp.io/phonometry/signals/filters/filter-banks/):
the one-third-octave analysis that reads Table II.
- [Hearing Protectors (ISO 4869-1, -2, -3 and -6)](https://docs.jmrp.io/phonometry/perception/hearing/hearing-protectors/):
the sound attenuation of 8.11, measured by ISO 4869-1 on test subjects, and
the active noise reduction of ISO 4869-6.
- [Test signals and sample-rate tools](https://docs.jmrp.io/phonometry/signals/spectra/test-signals/):
the tone bursts of IEC 60268-1 Annex A, the other part of that standard the
library implements.
- API reference: [`electroacoustics.programme_signal`](https://docs.jmrp.io/phonometry/reference/api/electroacoustics/programme-signal/)
and [`electroacoustics.headphones`](https://docs.jmrp.io/phonometry/reference/api/electroacoustics/headphones/).
## Standards
IEC 60268-7:2010, *Sound system equipment – Part 7: Headphones and earphones*. Edition 3.0. The classification code (Clause 4), the standard conditions and the measurement with the simulated programme signal (7.2, 7.4, Figure 3 and its NOTE), the impedance (8.2), the voltages (8.3: the limiting values with the clipped programme signal, the characteristic voltage, the programme signal characteristic voltages and the protective devices), the powers (8.4), the sound pressure levels (8.5), the frequency responses (8.6: coupler, free-field and diffuse-field comparison, ear canal Formula (1)), the distortion test signals (8.7), the sound attenuation (8.11, by ISO 4869-1), the crosstalk attenuation (8.12) and the probe microphone of Annex B.
IEC 60268-1:1985, *Sound system equipment – Part 1: General*. With Amendment 1 (1988-01) and Amendment 2 (1988-06), neither of which touches Clause 7. The standard reference frequency of Clause 3, and the simulated programme signal: Clause 7 with its Note, Table II (the power spectrum and its tolerances) and Figure 2 (the filter for a pink-noise source).
IEC 60268-3:2013, *Sound system equipment – Part 3: Amplifiers*. The difference-frequency distortion of 14.12.8.1 b), the reading Formula (5) of IEC 60268-7 needs where its brackets are unbalanced.
IEC 61672-1:2013, *Electroacoustics – Sound level meters – Part 1: Specifications*. The A-weighting whose band coefficients the NOTE under Figure 3 of IEC 60268-7 sums with, Table 3.
