emission.sound_power_in_situ

Sound power and sound energy levels of a noise source determined in situ by comparison with a reference sound source: ISO 3747:2010 (engineering grade 2 and survey grade 3).

The source stays where it works. A calibrated reference sound source (RSS) of known octave-band sound power LW(RSS) is set beside it and the same three or four microphone positions listen to each source in turn, in the part of the room where the field is reverberant, that is where the excess of sound pressure level over the free field, $\Delta L_f$, is at least 7 dB (clause 4.1, Annex A). Both sources then see the same room and the room drops out of the algebra: the sound power level of the source under test (ST) in each octave band is the calibrated power of the RSS carried across by the difference of the two mean corrected levels (clause 8.3.1),

where the mean corrected levels are the energy averages over the n microphone positions (Eq. 8, 9) of the levels corrected position by position for background noise (clause 8.1),

with three rules around it: a margin above 15 dB needs no correction, a margin between 6 dB and 15 dB takes Eq. (7), and a margin below 6 dB caps the correction at 1,3 dB and turns the band into an upper bound that the report must flag as not meeting the background requirement. A determination that carries no background reading at all cannot meet that requirement either, since 8.1 declares a measurement valid only where the margin is at least 6 dB and 7.5 has the background obtained once at each position. When the RSS is run at m locations around a large source the calibrated powers and the per-location means are each energy-averaged over the locations before the subtraction (clause 8.3.2, Eq. 12).

An impulsive source is described by its sound energy level instead. The single event levels measured at each position, either N events one at a time (Eq. 13, 15) or one measurement encompassing N events (Eq. 16, 17), are background-corrected with the same rule (Eq. 14), reduced to the level of one event and averaged over positions (Eq. 18); Eq. (19) and (20) are then Eq. (11) and (12) with $\overline{L_{E(\mathrm{ST})}}$ in place of $\overline{L_{p(\mathrm{ST})}}$ (clause 8.5). Eq. (14) subtracts the time-averaged background level from a time-integrated event level, exactly as ISO 3741:2010 (9.2.2) and ISO 3744:2010 (8.3.4) print it; the text only asks 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; the optional integration_time carries the background to the event’s interval ($+10{\log }_{10}(T/T_0)$, clause 3.4 NOTE 1) before the subtraction.

Annex C carries either level to the reference meteorological conditions of 101,325 kPa and 23,0 °C with the radiation-impedance correction $C_2=-10{\log }_{10}(p_{\mathrm{s}}/p_{\mathrm{s},0})+15{\log }_{10}((273.15+\theta )/296)$, the same C2 as ISO 3741:2010 clause 9.1.4, reused from that module; the whole ISO 3740 family prints ${\theta }_{\mathrm{ref}}$ = 296 K beside a 23,0 °C reference, so at the reference conditions C2 is +0,003 3 dB rather than zero. Eq. (C.2) estimates the static pressure from the altitude of the site. Annex D forms the A-weighted totals from the Table D.1 band corrections, which are the ISO 3744 Annex E octave values digit for digit.

Clause 9 estimates the uncertainty as ${\sigma }_{\mathrm{tot}}=\sqrt{{\sigma }_{R0}^2+{\sigma }_{\mathrm{omc}}^2}$ (Eq. 22) and $U=k{\sigma }_{\mathrm{tot}}$ (Eq. 23), with the typical upper bound of the reproducibility ${\sigma }_{R0}$ read from Table 2 by grade: 1,5 dB for grade 2, which needs $\Delta L_{f\mathrm{A}}\ge 7$ dB at every microphone position and a source directivity range within ±7 dB, and 4,0 dB for grade 3 otherwise. Table 1, the zoning of the test environment by lines of sight, is normative (7.4.2 divides the environment into zones with a shall, and 7.4.3 draws the microphone positions from them), but it constrains where the sources and microphones go, not what is computed from them: the positions arrive here already chosen, so the zoning is not evaluated.

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excess_sound_pressure_level(
    level: ArrayLike,
    lw_ref: ArrayLike,
    distance: ArrayLike,
) -> np.ndarray | float

Excess of sound pressure level over the free field at a distance from the reference sound source (ISO 3747:2010 Annex A, Eq. A.1).

The 11 dB is the spherical free-field relation $L_p=L_W-20{\log }_{10}(r/r_0)-11$ dB, so $\Delta L_f$ is zero in a free field and grows with the reverberant contribution; the microphone positions of the method must lie where it is at least 7 dB (4.1, 7.4.1). Measured with A-weighted levels the quantity is $\Delta L_{f\mathrm{A}}$, the indicator Table 2 grades the determination by. The three arguments broadcast against each other, so one calibrated power serves a whole traverse of levels and distances.

Parameters

Returns: The excess dLf(r), in decibels, as a float for scalar input or an array of the broadcast shape.

Raises

GradeConditions(
    excess_levels: ArrayLike | None = None,
    directivity_range: float | None = None,
)

The two conditions Table 2 puts on engineering grade 2.

They travel together because they answer one question between them, which row of Table 2 the determination may claim, and neither answers it alone: the grade is engineering only when the field is reverberant enough at every microphone position and the source is not too directional. Either one missing leaves the determination at survey grade 3, which is the grade the standard grants when the evidence is not there.

Parameters

InSituSoundPowerResult(
    frequencies: np.ndarray,
    sound_power_level: np.ndarray,
    sound_energy_level: np.ndarray,
    mean_source_level: np.ndarray,
    mean_reference_level: np.ndarray,
    reference_levels: np.ndarray,
    reference_power_level: np.ndarray,
    background_correction: np.ndarray,
    background_correction_ref: np.ndarray,
    background_requirement_met: np.ndarray,
    c2: float,
    grade: str,
    sigma_r0: float,
    sigma_omc: float,
    sigma_tot: float,
    expanded_uncertainty: float,
    coverage_factor: float,
    sound_power_level_a: float,
    sound_energy_level_a: float,
    quantity: str,
)

Result of an ISO 3747:2010 in situ determination by comparison.

quantity says which of the two determinations this is: 'power' carries the octave-band sound power level LW (Eq. 11 or 12) in sound_power_level with sound_energy_level all NaN, and 'energy' the sound energy level LJ (Eq. 19 or 20) in sound_energy_level with sound_power_level all NaN. Both are at the meteorological conditions of the test; the properties sound_power_level_ref and sound_energy_level_ref add the Annex C correction c2 (Eq. C.1, C.3).

mean_source_level is the mean corrected level of the source under test, $\overline{L_{p(\mathrm{ST})}}$ (Eq. 8) or $\overline{L_{E(\mathrm{ST})}}$ (Eq. 18); reference_levels the mean corrected level of the reference sound source at each of its m locations (Eq. 9, 10) and mean_reference_level their energy mean (the second term of Eq. 12, equal to Eq. 9 for one location); reference_power_level the calibrated power of the reference source, energy-averaged over its locations (the first term of Eq. 12).

background_correction is K1i at each microphone position and band for the source under test (Eq. 7; for N events measured one at a time it is the per-position shift the per-event corrections of Eq. 13 produce in the mean of Eq. 15), background_correction_ref the same for the reference source at each location (Eq. 9, 10), and background_requirement_met is True only where a background level reached every position (7.5) and every margin over it was at least 6 dB. Clause 8.1 writes that margin for the source under test alone ($\Delta L_{pi}=L_{pi}^{\prime }(\mathrm{ST})-L_{pi}(\mathrm{B})$); the flag extends the same test to the reference source, whose level enters Eq. 11 carrying a K1 of its own, rather than call a band sound on a correction the standard had to cap. It is False in a band where either margin fell below 6 dB, and False throughout when no background levels were supplied at all, since nothing was measured against; either way the level is an upper bound to be reported as such (8.1).

grade is the accuracy grade Table 2 grants ('engineering' or 'survey') and sigma_r0 its typical reproducibility; sigma_omc, sigma_tot and expanded_uncertainty are the operating-and-mounting deviation, Eq. (22) and Eq. (23) for coverage_factor, NaN when no sigma_omc was supplied. sound_power_level_a and sound_energy_level_a are the Annex D A-weighted totals of the level that was determined (NaN for the other).

InSituSoundPowerResult.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Plot the determined spectrum with the A-weighted total annotated.

One bar per octave band of LW (or LJ for an energy determination); a band whose background margin fell below 6 dB is hatched, because its level is an upper bound (8.1). Requires matplotlib (pip install phonometry[plot]); returns the Axes.

property

LJ under the reference meteorological conditions, LJ + C2 (ISO 3747:2010 Annex C, Eq. C.3); NaN for a power determination.

property

LW under the reference meteorological conditions, LW + C2 (ISO 3747:2010 Annex C, Eq. C.1); NaN for an energy determination.

sound_energy_in_situ(
    event_levels: ArrayLike,
    levels_ref: ArrayLike,
    lw_ref: ArrayLike,
    frequencies: ArrayLike,
    *,
    events: int | None = None,
    background_levels: ArrayLike | None = None,
    background_levels_ref: ArrayLike | None = None,
    integration_time: float | None = None,
    temperature: float = 23.0,
    static_pressure: float = 101.325,
    conditions: GradeConditions | None = None,
    sigma_omc: float | None = None,
    coverage_factor: float = 2.0,
) -> InSituSoundPowerResult

Sound energy level of an impulsive source in situ, by comparison with a reference sound source (ISO 3747:2010, clauses 8.4 and 8.5).

The single event levels are given in one of the two forms clause 8.4 admits. Measured one event at a time, event_levels is (n, N, bands): each event is corrected for background (Eq. 13, 14) and the N corrected levels are energy-averaged into the mean single event level of the position (Eq. 15). Measured once over N successive events, event_levels is (n, bands) with events=N: the level is corrected (Eq. 16) and reduced by $10{\log }_{10}N$ to one event (Eq. 17). Either way the per-position levels are energy-averaged (Eq. 18) and the sound energy level in each band is

or its m-location form (Eq. 20). The reference source is measured time-averaged, over 30 s (7.6), exactly as for a steady source.

Parameters

Returns: InSituSoundPowerResult with quantity='energy'.

Raises

sound_power_in_situ(
    levels: ArrayLike,
    levels_ref: ArrayLike,
    lw_ref: ArrayLike,
    frequencies: ArrayLike,
    *,
    background_levels: ArrayLike | None = None,
    background_levels_ref: ArrayLike | None = None,
    temperature: float = 23.0,
    static_pressure: float = 101.325,
    conditions: GradeConditions | None = None,
    sigma_omc: float | None = None,
    coverage_factor: float = 2.0,
) -> InSituSoundPowerResult

Sound power level of a steady or non-steady source in situ, by comparison with a reference sound source (ISO 3747:2010, clause 8.3).

The time-averaged octave-band levels of the source under test at the n microphone positions are corrected for background noise position by position (Eq. 7 with the rules of 8.1) and energy-averaged (Eq. 8); the reference source’s levels at the same positions are treated the same way (Eq. 9), or per location and then energy-averaged over the m locations together with its calibrated powers (Eq. 10, 12). The sound power level in each band is then

at the meteorological conditions of the test; the returned c2 and the sound_power_level_ref property carry it to the reference conditions of Annex C, and sound_power_level_a is the Annex D total.

Parameters

Returns: InSituSoundPowerResult with quantity='power'.

Raises

static_pressure_from_altitude(altitude: float) -> float

Static pressure at the altitude of the test site (ISO 3747:2010 Annex C, Eq. C.2).

Annex C prints $p_{\mathrm{s},0}$ = 1,013 25 x 10^5 Pa and states the quantity in pascals. The result here is in kilopascals so that it feeds static_pressure of sound_power_in_situ directly, matching ISO 3741, ISO 3744 and ISO 3745, which do print kilopascals. The pressure reaches C2 only as $p_{\mathrm{s}}/p_{\mathrm{s},0}$, so the two unit conventions give the same correction. A site below sea level is admissible (the base exceeds one); the formula stops meaning anything where the base reaches zero, some 44 km up, and that is refused.

Parameters

Returns: The static pressure ps, in kilopascals.

Raises