noise_control.screen_in_situ

What a screen on the shop floor is worth (ISO 11821:1997).

A removable screen is a panel or a flexible curtain put between a machine and the people near it, breaking the line of sight and nothing more. It is the cheapest thing in noise control and the hardest to quote a number for, because what it is worth depends on the room it stands in as much as on the screen.

ISO 11821 measures that number where the screen stands. The quantity is an insertion loss, the difference between the level at a position with the screen removed and the level at the same position with it in place:

Clause 5.8 prints that without an equation number, and the whole of the standard is arranging for those two levels to be comparable.

The Introduction draws three lines. A screen in an open-plan office is ISO 10053; an outdoor community-noise barrier is ISO 10847, which is phonometry.environment.propagation.barrier_in_situ; and this method is not a qualification of a screen as a product but a measurement of one installation. Indoors the room decides a large part of the answer, so two screens may only be compared where the test conditions were the same.

Within its own scope it wants a screen at least 1,5 m high and 1,5 m long, and outdoors it stops at 25 m from the screen.

Where the screen protects a defined operator position, 5.5.1 puts three microphones on a sphere of 0,3 m radius around the head and the answer is one number. Where it shields an area, 5.5.2 puts them along a line perpendicular to the screen at a quarter, a half, once and twice the screen height, never closer than 1 m, and the answer is a range: NOTE 2 says the smallest attenuation will be found at the most remote position and the largest at the nearest, which is why the Introduction asks for the maximum and the minimum rather than a mean.

Clause 5.7 corrects for the background with the ordinary energy subtraction, not with a table, and it draws two hard lines: under 6 dB “the environmental conditions are not acceptable”, and over 10 dB there is nothing to correct. background_corrected_level_db refuses the first and skips the second.

Clause 5.9 is the other: the A-weighted attenuation $D_{pA}$ shall not be determined when an artificial sound source is used, because an A-weighted number belongs to the spectrum that produced it and a loudspeaker’s spectrum is not the machine’s. screen_attenuation refuses it rather than compute a number the standard forbids.

Auto-generated from the source docstrings by scripts/generate_api_docs.py (make api-docs). Do not edit by hand.

background_corrected_level_db(
    levels_db: ArrayLike,
    background_levels_db: ArrayLike,
) -> NDArray[np.float64]

The level with the background taken off, clause 5.7.

The plain energy subtraction, applied band by band at each measurement position. Where ISO 11820 corrects from a stepped table, this standard prints the formula and boxes it.

Clause 5.7 draws the window itself. A margin over 10 dB needs no correction and the level is returned unchanged. A margin under 6 dB means “the environmental conditions are not acceptable”, which is a refusal and not a warning: the background it names includes wind-generated noise, so the remedy is to wait for a quieter day rather than to correct harder.

Parameters

Returns: The corrected level per band, in decibels.

Raises

Constant (tuple).

BACKGROUND_CORRECTION_WINDOW_DB = (6.0, 10.0)

Constant (float).

DIRECTIVITY_CIRCLE_RADIUS_M = 1.5

directivity_index_db(levels_db: ArrayLike) -> NDArray[np.float64]

The directivity index of a source, definition 3.10.

$D{I}_i=L_{360}-L_{30,i}$, where $L_{360}$ is the logarithmic mean of the levels at twelve positions evenly spaced on a horizontal circle of about 1,5 m radius around the source, and $L_{30,i}$ the level at one of them.

The sign is the way round to notice. Written as the mean less the position, the index is positive where the position is quieter than the mean, which is the opposite of the directivity index of the emission standards. Clause 5.2.2 then reads naturally: an artificial source qualifies while no position falls more than DIRECTIVITY_INDEX_LIMIT_DB below the mean, which is a bound on how much of a shadow the source casts on itself.

Parameters

Returns: $D{I}_i$ at each position, in decibels.

Raises

Constant (float).

DIRECTIVITY_INDEX_LIMIT_DB = 8.0

Constant (int).

DIRECTIVITY_POSITIONS = 12

Constant (float).

ENGINEERING_STANDARD_DEVIATION_DB = 2.0

Constant (float).

IMPULSE_INVALID_DEVIATION_DB = 5.0

impulse_mean_level_db(repeat_levels_db: ArrayLike) -> float

The level of an impulsive measurement, 5.6.2.1.

A single-impulse source is measured at least three times with the S time weighting, and the level is the arithmetic mean of the repeats, not the energy mean: the clause says “arithmetic mean values” and means it.

The spread decides whether the set counts. Past IMPULSE_REPEAT_DEVIATION_DB the clause asks for three more repeats, which is reported here; past IMPULSE_INVALID_DEVIATION_DB the measurement is invalid, which is refused.

Parameters

Returns: The arithmetic mean, in decibels.

Raises

Constant (float).

IMPULSE_REPEAT_DEVIATION_DB = 3.0

Constant (int).

IMPULSE_REPEATS = 3

Constant (mapping).

ISO11821_BAND_RANGE_HZ = {3: (100.0, 5000.0), 1: (125.0, 4000.0)}

Constant (float).

ISO11821_MINIMUM_BACKGROUND_MARGIN_DB = 6.0

Constant (float).

ISO11821_PREFERRED_BACKGROUND_MARGIN_DB = 10.0

microphone_distances_m(screen_height_m: float) -> NDArray[np.float64]

Where the microphones stand in front of a screen, 5.5.2.

A quarter, a half, once and twice the screen height, along a line perpendicular to the screen, and never closer than MINIMUM_MICROPHONE_DISTANCE_M. Under 4 m the quarter-height position falls inside that floor and is pushed out to it; at 2 m and under the half-height one is pushed out too, and then the two nearest positions coincide. The clause keeps the floor rather than the factor, so the returned distances may repeat, and that is the printed rule rather than an oversight here.

NOTE 2 of 5.5.2 says what the spread of the answers means: the smallest attenuation will be found at the most remote position and the largest at the nearest, which is why the Introduction asks for both rather than for an average.

Parameters

Returns: The four distances from the screen, in metres.

Raises

Constant (float).

MINIMUM_MICROPHONE_DISTANCE_M = 1.0

Constant (float).

MINIMUM_SCREEN_DIMENSION_M = 1.5

Constant (float).

OPERATOR_HEIGHT_M = 1.55

Constant (float).

OPERATOR_HEIGHT_TOLERANCE_M = 0.075

Constant (float).

OUTDOOR_RANGE_M = 25.0

screen_attenuation(
    unscreened_levels_db: ArrayLike,
    screened_levels_db: ArrayLike,
    *,
    frequencies: ArrayLike | None = None,
    source_kind: SourceKind = 'actual',
    a_weighted_unscreened_level_db: float | None = None,
    a_weighted_screened_level_db: float | None = None,
    distance_m: float | None = None,
) -> ScreenInSituResult

The in-situ attenuation of a screen, clauses 5.8 and 5.9.

$D_p=L_{p1}-L_{p2}$, the unscreened level less the screened one at the same position, band by band. Clause 5.8 adds the condition that makes the subtraction mean anything: either both levels are time-averaged, or both are arithmetic means of several $L_{S\text{max}}$ values. The two kinds are not mixed, and impulse_mean_level_db is the second of them.

$D_{pA}=L_{pA1}-L_{pA2}$ is clause 5.9, and it carries the standard’s one flat prohibition: it shall not be determined when an artificial sound source is used. An A-weighted number belongs to the spectrum that produced it, and a loudspeaker’s spectrum is not the machine’s, so the pair is refused rather than computed under source_kind="artificial".

Parameters

Returns: The attenuation, as a ScreenInSituResult.

Raises

Constant (tuple).

SCREEN_DISTANCE_FACTORS = (0.25, 0.5, 1.0, 2.0)

ScreenInSituResult(
    frequencies: NDArray[np.float64] | None,
    unscreened_levels_db: NDArray[np.float64],
    screened_levels_db: NDArray[np.float64],
    attenuation_db: NDArray[np.float64],
    a_weighted_attenuation_db: float | None,
    source_kind: str,
    distance_m: float | None,
)

The in-situ attenuation of a removable screen, ISO 11821 clause 5.8.

Attributes

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

Draw the two levels and the attenuation between them.

Requires matplotlib (pip install phonometry[plot]).

Parameters

Returns: The Axes.

ScreenInSituResult.rounded() -> NDArray[np.int_]

The band values as 7.4 c) reports them, to the nearest integer.

attenuation_db keeps the unrounded difference. A tie goes to the even decibel, Rule A of ISO 80000-1:2009 Annex B, as in the other in-situ standards of this library.

ScreenInSituResult.rounded_a_weighted() -> int | None

$D_{pA}$ as 7.4 c) reports it, to the nearest integer.

The clause gives the A-weighted attenuation the same rounding as the band values. None where no A-weighted pair was given.

The measurement is outside a condition ISO 11821 states.