Sound Power in Situ by Comparison (ISO 3747)

Some machines never travel to a test room: a compressor bolted to the floor of the plant, a press line, a packaging machine wired into the rest of the line. ISO 3747 determines their sound power where they stand, by comparison. A reference sound source (RSS) of calibrated band sound power is set beside the machine, the same three or four microphones listen to each source in turn from the reverberant part of the room, and because both sources see the same room the room cancels: the sound power of the source under test is the calibrated power of the reference source carried across by the difference of the two mean levels. The method reaches engineering grade 2 where the field is reverberant enough and the source not too directional, and survey grade 3 otherwise; an impulsive source gets a sound energy level instead of a sound power level by the same route. This guide covers the per-position background correction with its 6 dB and 15 dB rules, the one- and several-location forms, the single-event path, the Table 2 grade, the clause 9 uncertainty and the Annex C reference conditions. Which route fits which job is weighed in Sound Power.

1. The comparison in situ (ISO 3747)

The environment is the whole method, so the standard begins with it. The microphone positions must lie where the field is reverberant, which the standard measures as the excess of sound pressure level over the free field, $Δ L_{f} \geq 7$ dB (clause 4.1, Annex A): the level the reference source produces at a microphone must be at least 7 dB above what it would produce in a free field at that distance. Three or four positions are used, at least 2 m apart, none closer than 0,5 m to any boundary, distributed as evenly as possible round the machine and each with a line of sight to the same emitting areas (clause 7.4.1); the reference source stands alongside the machine, never closer than 0,5 m to its reference box, and where the machine is long it is run at several locations along the sides (clause 7.3). Both sources and the background are read at the same positions with the same microphone orientations, the reference source for 30 s (clause 7.5), and the whole determination is made in octave bands from 125 Hz to 8 kHz (clause 3.11); Table D.1 tabulates a 63 Hz row besides, for use only where the environment and the instrumentation are satisfactory there (footnote a), which is why the API accepts that band too.

The background is corrected position by position before anything is averaged (clause 8.1, Eq. 7):

K_{1 i} = - 10 lo g_{10} (1 - 1 0^{- 0.1 Δ L_{p i}}), Δ L_{p i} = L_{p i (ST)}^{'} - L_{p i (B)},

with three rules round it. A margin above 15 dB needs no correction at that position. A margin between 6 dB and 15 dB takes Eq. 7, which runs from 1,26 dB at 6 dB to 0,14 dB at 15 dB. A margin below 6 dB caps the correction at 1,3 dB and reduces the accuracy of the result: the level may still be reported, but as an upper bound, and the report must say that the background requirement was not met. sound_power_in_situ applies all three, returns the per-position $K_{1 i}$ it used, and flags every band where some margin fell below 6 dB in background_requirement_met, band by band, so the flag can travel into the report with the level it qualifies. The reference source is corrected the same way, with the same background reading unless it brought its own (clause 7.5 takes one reading for both), and the corrected levels are energy-averaged over the positions (Eq. 8, 9):

\overline{L_{p (ST)}} = 10 lo g_{10} [\frac{1}{n} i = 1 \sum n 1 0^{0.1 L_{p i (ST)}}], L_{p i (ST)} = L_{p i (ST)}^{'} - K_{1 i} .

The sound power level in each octave band is then the comparison itself (clause 8.3.1, Eq. 11):

L_{W} = L_{W (RSS)} - \overline{L_{p (RSS)}} + \overline{L_{p (ST)}} .

Where the reference source was run at $m$ locations, its calibrated powers and its per-location means are each energy-averaged over the locations first (clause 8.3.2, Eq. 12), so a location that samples the room better does not outvote one that samples it worse:

L_{W} = 10 lo g_{10} [\frac{1}{m} j = 1 \sum m 1 0^{0.1 L_{W j (RSS)}}] - 10 lo g_{10} [\frac{1}{m} j = 1 \sum m 1 0^{0.1 \overline{L_{p j (RSS)}}}] + \overline{L_{p (ST)}} .

Eq. 12 collapses to Eq. 11 when the locations are indistinguishable, and the background correction of the reference source is evaluated per location and per position, because the margin it comes from depends on both even though the standard prints $K_{1 i (RSS)}$ without the location index.

Table 1 of the standard is worth reading before placing anything, though it is guidance and not arithmetic. It sorts the microphone positions by line of sight: a position that sees the source under test but not the reference source strongly overestimates the machine, one that sees the reference source but not the machine strongly underestimates it, and where both are in sight the sign of the error follows which of the two is nearer, vanishing when the two measurement distances agree within 10 %. The positions to choose are the ones in that last zone. The library evaluates none of this: it takes the levels it is given and assumes the positions were chosen well.

import numpy as np
from phonometry import emission

# A floor-standing screw compressor, 2.2 m x 1.4 m x 1.8 m, that cannot
# leave the plant: four microphone positions 1.5 m from its reference box,
# one reference sound source location alongside, octave bands 125 Hz - 8 kHz.
freqs = np.array([125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0])
lw_rss = np.array([84.5, 88.0, 91.0, 92.5, 92.0, 90.5, 87.0])  # calibrated
st = np.array([  # L'pi(ST): one row per microphone position, dB
    [82.4, 84.9, 86.1, 85.3, 82.6, 78.4, 72.1],
    [80.9, 84.1, 85.4, 84.7, 81.8, 77.5, 71.3],
    [83.1, 85.6, 86.8, 85.9, 83.2, 79.0, 72.8],
    [81.7, 84.5, 85.8, 85.0, 82.3, 78.0, 71.7],
])
rss = np.array([  # L'pi(RSS): the reference source at the same positions
    [78.2, 81.8, 84.6, 86.0, 85.6, 84.1, 80.4],
    [77.5, 81.1, 84.0, 85.4, 85.0, 83.4, 79.8],
    [78.9, 82.4, 85.1, 86.5, 86.1, 84.6, 80.9],
    [78.0, 81.6, 84.4, 85.8, 85.4, 83.9, 80.2],
])
background = np.array([  # Lpi(B): the factory floor, loud at the low end
    [75.0, 74.0, 72.0, 70.0, 67.0, 62.0, 57.0],
    [76.5, 75.0, 73.0, 71.0, 68.0, 63.0, 58.0],
    [74.5, 73.5, 71.5, 69.5, 66.5, 61.5, 56.5],
    [75.5, 74.5, 72.5, 70.5, 67.5, 62.5, 57.5],
])

res = emission.sound_power_in_situ(
    st, rss, lw_rss, freqs, background_levels=background,
    conditions=emission.GradeConditions(
        excess_levels=[8.2, 7.6, 8.9, 8.0],   # dLfA at each position (Annex A)
        directivity_range=4.0,                # +/-4 dB round the machine (7.2)
    ),
    sigma_omc=0.5,                        # a steady source (9.2 NOTE)
)
print(np.round(res.sound_power_level, 1))   # [88.8 91.5 92.6 91.8 88.9 84.7 78.6]
print(round(res.sound_power_level_a, 1))    # 96.1 dB(A)
print(res.background_requirement_met)       # [False  True  True  True  True  True  True]
print(np.round(res.background_correction[1], 2))  # position 2: [1.3 0.57 0.26 0.19 0.18 0.16 0.21]
print(res.grade, res.sigma_r0, round(res.expanded_uncertainty, 1))  # engineering 1.5 3.2

The 125 Hz band is the one to read twice. At one of the four positions the margin over the floor is below 6 dB for the machine, and it is below 6 dB at every position for the quieter reference source, so $K_{1}$ takes its 1,3 dB cap there and the 88,8 dB the band reports is an upper bound, which is what the False says. Every other band clears 6 dB everywhere, 250 Hz with corrections of half a decibel that Eq. 7 evaluates rather than ignores, and from 1 kHz up the margin passes 15 dB at two or three of the four positions, where the correction is zero; the correction the others still take stays below 0,25 dB.

Two panels over the seven octave bands from 125 Hz to 8 kHz. The upper panel plots the sound pressure levels at the four microphone positions: the corrected levels of the source under test as filled blue circles with their energy mean as a blue line, the corrected levels of the reference source as green squares with their mean as a green line, the measured levels before the background correction as hollow circles joined to the corrected ones wherever the correction moved them, and the background at each position as grey crosses. A boxed note at 125 Hz says the margin is below 6 dB at that position and at every position for the reference source, K1 is capped at 1.3 dB and the band is an upper bound. The lower panel draws the resulting sound power level of the source under test as blue bars, the 125 Hz bar hatched as an upper bound, with the calibrated sound power level of the reference source as a red dashed line with diamonds, and states in its title an A-weighted level of 96.1 dB(A), grade 2, and an expanded uncertainty of 3.2 dB with k = 2 and a 0.5 dB operating-condition deviation

The comparison position by position. Above, both sources at the four microphones after the Eq. 7 correction, with the hollow markers showing where each level was before it; the reference source sits below the machine at the low end and above it from 1 kHz up, which is what the shape of the calibrated curve below does to the result. Below, Eq. 11 band by band, with the calibrated $L_{W (RSS)}$ beside it and the 125 Hz upper bound hatched.

Show the code for this figure

import matplotlib.pyplot as plt

# res is the InSituSoundPowerResult computed above. One line:
res.plot()   # LW bars, LWA in the title, the upper-bound band hatched
plt.show()

# By hand: both sources per position above, Eq. 11 below.
corrected_st = st - res.background_correction
corrected_rss = rss - res.background_correction_ref[0]
x = np.arange(freqs.size)
fig, (axt, axb) = plt.subplots(2, 1, figsize=(10, 8.4), sharex=True)
for i, offset in enumerate(np.linspace(-0.27, 0.27, st.shape[0])):
    axt.plot(x + offset, corrected_st[i], "o", color="#1f77b4")
    axt.plot(x + offset, corrected_rss[i], "s", color="#2ca02c")
    axt.plot(x + offset, background[i], "x", color="#9e9e9e")
axt.plot(x, res.mean_source_level, "-", color="#1f77b4", label="mean, source under test")
axt.plot(x, res.mean_reference_level, "-", color="#2ca02c", label="mean, reference source")
axt.set_ylabel("Sound pressure level [dB]")
axt.legend()
bars = axb.bar(x, res.sound_power_level, width=0.62, color="#1f77b4")
for bar, met in zip(bars, res.background_requirement_met, strict=True):
    if not met:
        bar.set_hatch("//")
axb.plot(x, res.reference_power_level, "D--", color="#d62728", label="calibrated LW(RSS)")
axb.set_xticks(x, [f"{f:g}" for f in freqs])
axb.set_xlabel("Frequency [Hz]")
axb.set_ylabel("Sound power level LW [dB re 1 pW]")
axb.legend()
plt.show()

A machine that is long relative to the measurement distance gets the reference source at several locations along its sides (clause 7.3.3), and the levels arrive as one grid per location:

# The same compressor with the reference source run at two locations, one
# along each long side; the second sits nearer a wall and reads 1.2 dB lower,
# and was calibrated in a similar position 0.4 dB lower.
two = emission.sound_power_in_situ(
    st, np.stack([rss, rss - 1.2]), np.stack([lw_rss, lw_rss - 0.4]), freqs,
    background_levels=background,
)
print(two.reference_levels.shape)               # (2, 7): mean level per location (Eq. 10)
print(np.round(two.sound_power_level, 1))       # [89.1 92.  93.  92.2 89.3 85.1 78.9]
print(round(two.sound_power_level_a, 1))        # 96.5 dB(A)

`sound_power_in_situ()` parameters

Parameter	Type	Units	Range / default	Notes
`levels`	2D array	dB	`(n, bands)`	Measured $L_{p i (ST)}^{'}$ , one row per microphone position, three or four positions (7.4.1)
`levels_ref`	2D or 3D array	dB	`(n, bands)` or `(m, n, bands)`	The reference source at the same positions, one grid per location, corrected per its manufacturer for speed, temperature and pressure but not for background
`lw_ref`	1D or 2D array	dB	`(bands,)` or `(m, bands)`	Calibrated $L_{W (RSS)}$ , per location when each was calibrated in its own similar position (Eq. 12)
`frequencies`	1D array	Hz	63 Hz to 8 kHz octaves	Nominal octave mid-band frequencies of Table D.1; required. Clause 3.11 puts the general-purpose range at 125 Hz to 8 kHz; the 63 Hz row of Table D.1 carries footnote a, which allows it only where the test environment, the reference sound source and the instrumentation are satisfactory at that frequency
`background_levels`	1D or 2D array	dB	`(bands,)` or `(n, bands)`	$L_{p i (B)}$ ; one spectrum serves every position. `None` warns and leaves `background_requirement_met` `False` in every band, since 7.5 measures it at each position and 8.1 needs the margin
`background_levels_ref`	1D or 2D array	dB	same shapes	Background for the reference-source reading; `None` reuses `background_levels` (7.5)
`temperature`	float	°C	default `23.0`	Air temperature at the test, for $C_{2}$
`static_pressure`	float	kPa	default `101.325`	Static pressure at the test, for $C_{2}$ ; see `static_pressure_from_altitude`
`conditions`	`GradeConditions`			The two conditions Table 2 reads together: `excess_levels`, the $Δ L_{f A}$ at each position `(n,)` in decibels (Annex A), and `directivity_range`, the half-width of the A-weighted directivity survey in decibels (7.2). Either one left out leaves the determination at survey grade
`sigma_omc`	float	dB	$\geq 0$	Standard deviation of the operating and mounting conditions (9.2); `None` leaves the uncertainty `NaN`
`coverage_factor`	float		default `2.0`	$k$ of Eq. 23; 1,6 for a one-sided comparison with a limit

The function returns an InSituSoundPowerResult: sound_power_level (Eq. 11 or 12, at the conditions of the test), mean_source_level and mean_reference_level (Eq. 8, 9), reference_levels per location (Eq. 10), reference_power_level, background_correction per position and band, background_correction_ref per location, position and band, background_requirement_met per band, c2, grade, sigma_r0, sigma_omc, sigma_tot, expanded_uncertainty, coverage_factor, sound_power_level_a and quantity. sound_power_level_ref adds c2 to the level (section 3).

2. Impulsive sources: the sound energy level (Eq. 13 to 20)

A press stroke or a door slam has no steady power to report. Clause 8.4 measures the single event level $L_{E}$ at each position instead, either one event at a time, at least five of them (clause 7.6), or once over a run of $N$ successive events, and clause 8.5 turns the mean into a sound energy level $L_{J}$ in dB re 1 pJ by the same comparison, with the reference source still read time-averaged over 30 s. Measured one at a time, each event is corrected for background with Eq. 14 (Eq. 7 with the event level in the margin) and the corrected levels are energy-averaged into the mean single event level of the position (Eq. 13, 15); measured once over $N$ events, the level is corrected and reduced by $10 lo g_{10} N$ to one event (Eq. 16, 17). The per-position levels are energy-averaged over the positions (Eq. 18), and

L_{J} = L_{W (RSS)} - \overline{L_{p (RSS)}} + \overline{L_{E (ST)}}

(Eq. 19), or its several-location form (Eq. 20), which is Eq. 12 with the event mean in the last term. sound_energy_in_situ takes the events as a 3D (n, N, bands) array for the one-at-a-time form or as a 2D (n, bands) measurement with events=N for the other, and returns the same result type with quantity='energy', the level in sound_energy_level and the Annex D total in sound_energy_level_a.

One line of Eq. 14 deserves a note. It subtracts the time-averaged background level $L_{p i (B)}$ from a time-integrated event level, and asks only that both be measured over the same integration time $T$ . As printed, the difference is a true signal-to-background margin for $T$ = 1 s; for a longer $T$ the background holds $10 lo g_{10} (T / T_{0})$ dB more energy over the event’s interval than its time-averaged level says (clause 3.4, NOTE 1), and the margin is overstated by that much. ISO 3741 and ISO 3744 print the same line for their single-event clauses, so it is the family’s convention and not a misprint of this part. The library applies Eq. 14 as printed by default and offers integration_time to carry the background to the event’s interval first; the two agree at $T$ = 1 s.

# The same room, a press beside the compressor: six strokes measured one at a
# time at the four positions, each integrated over 4 s, with the same
# reference source reading and the same floor.
strokes = np.array([
    [96.3, 98.1, 99.4, 98.8, 96.0, 92.1, 86.4],
    [95.1, 97.4, 98.7, 98.0, 95.3, 91.4, 85.6],
    [97.0, 98.9, 100.1, 99.5, 96.6, 92.8, 87.0],
    [95.8, 97.9, 99.0, 98.4, 95.8, 91.9, 86.0],
])
events = np.stack([strokes + d for d in (-0.3, 0.2, 0.0, 0.4, -0.2, 0.1)], axis=1)
energy = emission.sound_energy_in_situ(
    events, rss, lw_rss, freqs,                 # (4 positions, 6 events, 7 bands)
    background_levels=background, integration_time=4.0,
    conditions=emission.GradeConditions(excess_levels=[8.2, 7.6, 8.9, 8.0], directivity_range=4.0), sigma_omc=2.0,
)
print(energy.quantity)                            # energy
print(np.round(energy.sound_energy_level, 1))     # [103.7 105.3 106.1 105.3 102.4  98.6  93. ]
print(round(energy.sound_energy_level_a, 1))      # 109.7 dB(A) re 1 pJ
print(round(energy.expanded_uncertainty, 1))      # 5.0 dB: grade 2 with sigma_omc = 2 dB

The 125 Hz band is an upper bound here too, and for the reason the steady determination gave: the reference source’s own margin over the floor is below 6 dB there, and the flag follows both sources. The 5,0 dB is the standard’s own example in clause 9.5, reproduced because the inputs are the same: grade 2, $σ_{omc}$ = 2,0 dB, $k$ = 2.

`sound_energy_in_situ()` parameters

Parameter	Type	Units	Range / default	Notes
`event_levels`	3D or 2D array	dB	`(n, N, bands)` or `(n, bands)`	$L_{E i, q (ST)}^{'}$ per event, or $L_{E i, N (ST)}^{'}$ of one measurement over $N$ events
`events`	int		$\geq 1$	$N$ for the 2D form (Eq. 17); must be `None` with the 3D form. Clause 7.6 asks for at least five events, so fewer than five warns and the determination is nonconforming, on either form
`integration_time`	float	s	$> 0$	$T$ of the event measurement; `None` applies Eq. 14 as printed
`levels_ref`, `lw_ref`, `frequencies`, `background_levels`, `background_levels_ref`, `temperature`, `static_pressure`, `excess_levels`, `directivity_range`, `sigma_omc`, `coverage_factor`				As in `sound_power_in_situ()`

3. Grade, uncertainty and reference conditions

Grade (Table 2). Engineering grade 2 needs the A-weighted excess $Δ L_{f A} \geq 7$ dB at every microphone position and a source directivity range within ±7 dB from the survey of clause 7.2, taken 1 m from the reference box at intervals of 2 m or less; either indicator failing, or not determined at all, gives survey grade 3. The table pairs each grade with a typical upper bound of the reproducibility of the method, 1,5 dB for grade 2 and 4,0 dB for grade 3, valid for a relatively flat spectrum in which the 250 Hz to 4 kHz octaves carry the A-weighted level; a source dominated by bands below 500 Hz reproduces worse than that. The excess itself is Annex A (Eq. A.1),

Δ L_{f} (r) = L_{p (RSS), r} - L_{W (RSS)} + 11 dB + 20 lo g_{10} \frac{r}{r _{0}}, r_{0} = 1 m,

measured along a line of sight from the reference source at varying $r$ , and it is zero in a free field: excess_sound_pressure_level evaluates it and broadcasts, so one calibrated power serves a whole traverse.

Uncertainty (clause 9). The standard deviation of reproducibility of the method and the deviation of the operating and mounting conditions of the source, $σ_{omc}$ , combine in quadrature (Eq. 22) and the expanded uncertainty follows with the coverage factor (Eq. 23):

σ_{tot} = σ_{R 0}^{2} + σ_{omc}^{2}, U = k σ_{tot},

with $k$ = 2 for the two-sided 95 % interval the standard assumes, or 1,6 for a one-sided comparison with a limit value. $σ_{omc}$ is the user’s number, from repeated determinations under the conditions of clause 9.2 and E.3; the NOTE of 9.2 puts it near 0,5 dB for a steady source, 2 dB for one with material flow and 4 dB for stone breaking, metal cutting or a press under load. The standard’s own example (clause 9.5), grade 2 with $σ_{omc}$ = 2,0 dB and $k$ = 2, gives $U = 2 1, 5^{2} + 2^{2}$ dB = 5 dB, which the energy example above reproduces. Without a sigma_omc the result carries sigma_r0 and leaves sigma_tot and expanded_uncertainty NaN rather than reporting a method uncertainty as if it were the whole.

Reference conditions (Annex C). Eq. 11 gives the level at the meteorological conditions of the test. Annex C carries it to 101,325 kPa and 23,0 °C with the radiation-impedance correction

C_{2} = - 10 lo g_{10} \frac{p _{s}}{p _{s, 0}} + 15 lo g_{10} \frac{273 , 15 + θ}{θ _{ref}}, θ_{ref} = 296 K,

the same $C_{2}$ as ISO 3741 clause 9.1.4 (the library evaluates it through that module), valid for a monopole and a mean value for other sources, and estimates the static pressure from the altitude of the site when no barometer was read (Eq. C.2): $p_{s} = p_{s, 0} (1 - a H_{a})^{b}$ with $a$ = 2,2560 × 10⁻⁵ m⁻¹ and $b$ = 5,2553. The result exposes c2 and the properties sound_power_level_ref and sound_energy_level_ref (Eq. C.1, C.3); the A-weighted total under reference conditions is sound_power_level_a + c2, since the shift is the same in every band. One detail of the annex is worth knowing: $θ_{ref}$ is printed as 296 K beside a reference temperature of 23,0 °C, which is 296,15 K, so at exactly the reference conditions $C_{2}$ is +0,003 3 dB and not zero. ISO 3741 and ISO 3744 print the same 296 K, so it is the family’s rounding and the library keeps it.

# A plant 640 m above sea level, at 27 degC, with no barometer on site.
ps = emission.static_pressure_from_altitude(640.0)
print(round(ps, 2))                                 # 93.87 kPa (Eq. C.2)
high = emission.sound_power_in_situ(
    st, rss, lw_rss, freqs, background_levels=background,
    temperature=27.0, static_pressure=ps,
)
print(round(high.c2, 3))                            # 0.423 dB
print(round(float(high.sound_power_level[3]), 2), round(float(high.sound_power_level_ref[3]), 2))
# 91.76 at the test conditions, 92.18 under the reference conditions (1 kHz)

# Annex A along a line of sight from the reference source, A-weighted.
print(np.round(emission.excess_sound_pressure_level([81.0, 76.5, 73.8], 92.5, [1.5, 3.0, 6.0]), 2))
# [3.02 4.54 7.86]: reverberant enough for grade 2 only from about 6 m out

A-weighted totals (Annex D). $L_{W A}$ and $L_{J A}$ are the energy sums of the band levels plus the Table D.1 corrections $C_{k}$ , which are −26,2, −16,1, −8,6, −3,2, 0,0, 1,2, 1,0 and −1,1 dB from 63 Hz to 8 kHz, the ISO 3744 Annex E octave values digit for digit; the library reads them from the shared table and requires every entry of frequencies to be one of those eight nominal centres, distinct and in ascending order; the 63 Hz row is for use only where the environment and the instrumentation are satisfactory there (Table D.1, footnote a).

What this guide covers

Covered
The ISO 3747 comparison in situ (sound_power_in_situ): the per-position background correction of clause 8.1 with its 6 dB and 15 dB rules and the 1,3 dB cap, the mean corrected levels of clause 8.2, the sound power level for one (Eq. 11) or several (Eq. 12) reference-source locations, the single-event levels of clause 8.4 in both forms and the sound energy level of clause 8.5 (sound_energy_in_situ), the Table 2 grade with its $σ_{R 0}$ , the clause 9 uncertainty (Eq. 22, 23), the Annex A excess of sound pressure level (excess_sound_pressure_level), the Annex C reference conditions with Eq. C.2 (static_pressure_from_altitude) and the Annex D A-weighted totals.
Not covered
The Annex E uncertainty budget (Table E.2 and its sensitivity coefficients) is documented but not modelled: $σ_{R 0}$ is the typical upper bound of Table 2 by grade, not a machine-specific value from a round robin (9.3.2) or from the model of 9.3.3. The zoning of Table 1, the directivity survey of clause 7.2 and the placement rules of clause 7.3 are the operator’s decisions, made before the levels exist; the library takes the levels and the two indicators the grade needs. The reference source’s own corrections for speed, temperature and static pressure are its manufacturer’s, applied before the levels arrive. The other in situ routes are their own guides: Sound Power by Pressure Methods for the enveloping surface, Sound Power by Intensity Scanning for the probe.

References

International Organization for Standardization. (2010). Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound pressure — Engineering/survey methods for use in situ in a reverberant environment (ISO 3747:2010). The comparison method of this guide: the background correction of clause 8.1, the mean levels and the sound power and sound energy levels of clauses 8.2 to 8.5, the Table 2 grades, the clause 9 uncertainty and Annexes A, C and D.
International Organization for Standardization. (2010). Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound pressure — Precision methods for reverberation test rooms (ISO 3741:2010). The precision comparison method of a qualified room, whose Eq. 21 is Eq. 11 of this guide plus the same radiation-impedance correction C2 (clause 9.1.4), reused here for Annex C.

Created and maintained by José Manuel Requena Plens ORCID All projects