room.workroom_prediction

Predicting sound propagation in a workroom (ISO 11690-3:1998).

Part 1 of ISO 11690 says what a low-noise workplace is and part 2 says what to do about it. Part 3 is the part that answers “what will it be like before we build it”, and it is unusual among the standards this library implements: it prints almost no arithmetic. What it prints instead is a way of choosing, and the choice is between two families of method and four levels of detail of the data they are fed.

The two families. A diffuse field method sums a direct field and a reverberant field that is assumed to be the same everywhere, which is cheap, needs almost no data, and overestimates the level in a room whose field is not diffuse. A geometrical method traces the sound along straight lines, which costs a model of the room and pays for it in accuracy. Table 4 splits the second family into three by how finely the room has to be described, and Table E.1 says which level of detail of Tables 1 to 3 each category needs.

What it does compute. Annex C answers one practical question with one graph: by how much does the level at a machine’s own workstation rise when the machine is put in a room rather than measured in the open? The answer is the environmental correction of ISO 3744,

because the difference between the two printed emission quantities is the measurement surface itself, and the level in the room is the emission level plus that correction. Figure C.1 is that expression drawn as a flow chart, and Table C.2 works it for eight machines in a room of 195 m2.

Annex B then adds the contributions of several machines at one workstation on an energy basis, which is what turns a curve into a decision about which machine to buy.

The eighth machine of Table C.2. Figure C.1 stops at 10 dB, and M8 of the worked example needs more than that: its 29 dB between the two emission values gives 12,4 dB in a room of 195 m2, so the row that reports 10 dB is reporting the top edge of the diagram rather than a reading. The closed form has no such ceiling, and the errata registry records the row.

Read from BS EN ISO 11690-3:1999, which endorses EN ISO 11690-3:1998 without modification. The document is dated 1998 in its own header and 1999 on the British cover.

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detail_is_sufficient(
    category: str,
    *,
    room_detail: int,
    fitting_detail: int,
    source_detail: int,
) -> DetailVerdict

Does the data in hand match what Table E.1 asks of this category?

The table reads in both directions and both are useful: a reader with a room description of level 1 and fittings of level 1 is limited to the diffuse-field method, and a reader who wants ray tracing over an actual room shape has to go and gather a level-4 description of it.

Parameters

Returns: The verdict, as a DetailVerdict.

Raises

DetailVerdict(
    category: str,
    satisfied: bool,
    room_ok: bool,
    fittings_ok: bool,
    sources_ok: bool,
)

Whether the data in hand is what a category of method asks for.

Parameters

fitting_density(surface_area_m2: float, volume_m3: float) -> float

The density of the fittings, NOTE 3 of 6.2.2.

with $S$ the total surface area of the fittings and $V$ the volume of the room or of the zone they stand in. It is the quantity a geometrical method of category 2a or 2b takes instead of the fittings themselves.

Parameters

Returns: $q$, in reciprocal metres.

Raises

Constant (mapping).

FITTING_DETAIL_LEVELS = {1: 'fittings are not taken into account', 2: 'one mean density and one mean absorption for the whole room', 3: 'one mean density and one mean absorption per part of the room', 4: 'the actual shape and location, with shielding and reflection'}

prediction_method(category: str) -> PredictionMethod

One category of Table 4, with the detail levels of Table E.1.

Parameters

Returns: The row, as a PredictionMethod.

Raises

Constant (mapping).

PREDICTION_METHODS = {'1': PredictionMethod(category='1', family='diffuse field', rooms='rooms whose field may be treated as diffuse', room_detail=(1,), fitting_detail=(1,), source_detail=(1, 2, 3)), '2a': PredictionMethod(category='2a', family='geometrical', rooms='rooms that can be approximated by one mean absorption coefficient for each wall and one mean density for the fittings', room_detail=(1, 2), fitting_detail=(1, 2), source_detail=(1, 2, 3)), '2b': PredictionMethod(category='2b', family='geometrical', rooms='rooms that can be approximated by one mean absorption coefficient for each room surface and one mean density for the fittings in each zone', room_detail=(1, 2, 3), fitting_detail=(1, 2, 3), source_detail=(1, 2, 3)), '2c': PredictionMethod(category='2c', family='geometrical', rooms='rooms for which the individual distribution of absorption and fittings has to be considered', room_detail=(1, 2, 3, 4), fitting_detail=(1, 2, 3, 4), source_detail=(1, 2, 3))}

PredictionMethod(
    category: str,
    family: str,
    rooms: str,
    room_detail: tuple[int, ...],
    fitting_detail: tuple[int, ...],
    source_detail: tuple[int, ...],
)

One row of Table 4, with what Table E.1 asks it to be fed.

Parameters

Constant (mapping).

RECOMMENDED_DETAIL = {'1': ((1,), (1,), (1, 2, 3)), '2a': ((1, 2), (1, 2), (1, 2, 3)), '2b': ((1, 2, 3), (1, 2, 3), (1, 2, 3)), '2c': ((1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3))}

Constant (mapping).

ROOM_DETAIL_LEVELS = {1: 'the volume and the mean absorption coefficient of the surfaces', 2: 'a box-like shape, one absorption coefficient per surface', 3: 'a box-like shape, surfaces subdivided by absorption coefficient', 4: 'the actual shape, with absorption and reflection distributed over it'}

Constant (mapping).

SOURCE_DETAIL_LEVELS = {1: 'omnidirectional point sources', 2: 'point sources with a directivity pattern', 3: 'complex sources'}

total_workstation_level(
    contributions_db: ArrayLike,
    *,
    existing_level_db: float | None = None,
) -> float

What a workstation hears once the new machines are installed, Annex B.

The contributions are added on an energy basis, with whatever was already there added the same way. Annex B reads each contribution off the spatial sound distribution curve of the room at the distance between the machine and the workstation, except at a machine’s own workstation, where workstation_level gives it from the declared emission values.

Parameters

Returns: The total, in decibels.

Raises

typical_decay_range(region: str) -> _Range

What 4.3 says DL2 usually is in one region, in decibels.

Parameters

Returns: The lower bound and the upper one, which is None in the far region because the clause prints none.

Raises

Constant (mapping).

TYPICAL_DECAY_RANGE_DB = {'near': (5.0, 6.0), 'middle': (2.0, 5.0), 'far': (6.0, None)}

typical_excess_range(region: str) -> _Range

What 4.3 says DLf usually is in one region, in decibels.

The clause prints a range for the middle region alone, and adds that in the far region DLf may be negative; the near region it leaves open.

Parameters

Returns: The lower bound and the upper one, either of which may be None.

Raises

Constant (mapping).

TYPICAL_EXCESS_RANGE_DB = {'near': (None, None), 'middle': (2.0, 10.0), 'far': (None, None)}

workstation_level(
    *,
    sound_power_level_db: float,
    emission_level_db: float,
    absorption_area_m2: float,
) -> float

The level at the machine’s own workstation in the room, Annex C.

$L_{pA}^{\prime }=L_{pA}+\Delta L_A$, the emission value the machine was declared with plus what the room adds to it.

Parameters

Returns: $L_{pA}^{\prime }$, in decibels.

Raises

workstation_level_increase(
    *,
    sound_power_level_db: float,
    emission_level_db: float,
    absorption_area_m2: float,
) -> float

How much the room adds at the machine’s own workstation, Annex C.

The two emission quantities a machine is declared with differ by the measurement surface: the sound power level is the emission sound pressure level plus $10\lg (S/S_0)$. Put the machine in a room and the reverberant field adds the environmental correction of ISO 3744 on top, which is what Figure C.1 draws against the equivalent absorption area with $L_{WA}-L_{pA}$ as the parameter.

Parameters

Returns: $\Delta L_A$, in decibels.

Raises