noise_control.enclosures

Insertion loss of a close or free-standing machine enclosure.

Wrapping a machine in a sealed enclosure reduces the radiated noise by the transmission loss of its panels, minus a penalty for the reverberant build-up inside the small, hard cavity. Bies, Hansen & Howard, Engineering Noise Control 5th ed., §7.4.2 (Eqs. (7.103), (7.111)) write the net reduction as

$$\mathrm{IL}=R-C,C=10{\log }_{10}\left[0.3+\frac{S_{\mathrm{E}}(1-{\alpha }_{\mathrm{i}})}{S_{\mathrm{i}}{\alpha }_{\mathrm{i}}}\right],$$

where R is the field-incidence transmission loss of the enclosure panels, S_E the external surface area, S_i the internal surface area (including the machine) and alpha_i the mean absorption of the enclosure interior. The reverberant term is exactly S_E over the interior room constant $R_{\mathrm{i}}=S_{\mathrm{i}}{\alpha }_{\mathrm{i}}/(1-{\alpha }_{\mathrm{i}})$ (phonometry.room.room_constant), so

$$C=10{\log }_{10}(0.3+S_{\mathrm{E}}/R_{\mathrm{i}}).$$

A hard interior (alpha_i small) makes C large and wastes much of the panel R; lining the enclosure drives C toward its floor $10{\log }_{10}0.3=-5.2$ dB (a fully absorbing interior, where $\mathrm{IL}=R+5.2$). Bies terms this net reduction the enclosure noise reduction; it is the insertion loss of the enclosure.

Norton & Karczub, Fundamentals of Noise and Vibration Analysis for Engineers 2nd ed., 4.10 (Equation (4.115)) derive the same design equation from the same power balance but without the 0.3:

$$\mathrm{IL}=R-10{\log }_{10}(S_{\mathrm{E}}/R_{\mathrm{i}}),$$

so a well-lined enclosure keeps rising instead of levelling off at $R+5.2$. The two agree to a few tenths of a decibel while $S_{\mathrm{E}}/R_{\mathrm{i}}$ stays above about unity (a hard or lightly lined interior) and diverge once the lining takes over, where Bies’ floor is the safer statement. model selects between them, and the difference is the reason a published worked answer has to be reproduced with the model its author used.

Turned around, the same equation answers the question a designer actually asks: given the noise reduction I need, what transmission loss must the panels have? That is enclosure_required_transmission_loss, which returns the required R per band in the same EnclosureResult.

The panel transmission loss R is supplied by the caller — measured, or predicted by a panel model — as a per-band array, a callable of frequency, or a panel prediction result (a phonometry.building.SoundReductionResult or phonometry.building.ApertureTransmissionResult, matched structurally so no dependency on building is introduced). This module never predicts R itself; it combines a given R with the interior absorption. The interior room constant reuses phonometry.room.room_constant.

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

enclosure_insertion_loss

enclosure_insertion_loss(
    panel_transmission_loss: ArrayLike | Callable[[NDArray[np.float64]], ArrayLike] | PanelTransmissionResult,
    external_area: float,
    internal_area: float,
    internal_absorption: ArrayLike,
    *,
    frequencies: ArrayLike | None = None,
    model: str = 'bies',
) -> EnclosureResult

Net insertion loss of a machine enclosure (Bies Eqs. (7.103), (7.111)).

$\mathrm{IL}=R-C$ with $C=10{\log }_{10}(0.3+S_{\mathrm{E}}/R_{\mathrm{i}})$ and the interior room constant $R_{\mathrm{i}}=S_{\mathrm{i}}{\alpha }_{\mathrm{i}}/(1-{\alpha }_{\mathrm{i}})$.

Parameters

Name	Description
panel_transmission_loss	Panel transmission loss R per band, dB. One of: a per-band array (measured); a callable mapping a frequency array to per-band R (then frequencies is required); or a panel prediction result carrying transmission_loss and frequencies, such as the SoundReductionResult of phonometry.single_panel_transmission_loss / phonometry.double_wall_transmission_loss or the ApertureTransmissionResult of phonometry.composite_transmission_loss (its frequencies are then used unless frequencies is given). This function does not predict R itself.
external_area	External enclosure surface area S_E, m2.
internal_area	Internal surface area S_i (including the machine), m2.
internal_absorption	Mean interior absorption alpha_i in (0, 1) (scalar or per-band).
frequencies	Band centre frequencies, Hz; required when panel_transmission_loss is a callable, optional otherwise (used to label the result and the plot).
model	Interior build-up model, one of ENCLOSURE_MODELS: "bies" (default) carries the 0.3 floor of Bies Equation (7.111), "norton" the bare $C=10{\log }_{10}(S_{\mathrm{E}}/R_{\mathrm{i}})$ of Norton & Karczub Equation (4.115).

Returns: An EnclosureResult.

ENCLOSURE_MODELS

Constant (dict).

ENCLOSURE_MODELS = {'bies': 0.3, 'norton': 0.0}

enclosure_required_transmission_loss

enclosure_required_transmission_loss(
    insertion_loss: ArrayLike | Callable[[NDArray[np.float64]], ArrayLike],
    external_area: float,
    internal_area: float,
    internal_absorption: ArrayLike,
    *,
    frequencies: ArrayLike | None = None,
    model: str = 'bies',
) -> EnclosureResult

Panel R an enclosure needs to deliver a given insertion loss.

The design equation of enclosure_insertion_loss solved the other way, $R=\mathrm{IL}+C$: the enclosure geometry and its interior lining fix the build-up correction C, and the panels have to make up the rest. This is the number an enclosure is specified from, and the form Norton & Karczub use in 4.10 when the target IL is the gap between the level a machine produces in the room and a noise-criterion curve.

Parameters

Name	Description
insertion_loss	Required insertion loss IL per band, dB (a per-band array, or a callable of the frequency array, in which case frequencies is required).
external_area	External enclosure surface area S_E, m2.
internal_area	Internal surface area S_i, m2, including the surface of the enclosed machine.
internal_absorption	Mean interior absorption alpha_i in (0, 1) (scalar or per-band); e.g. from phonometry.room.mean_absorption over the lined enclosure walls and the machine surface.
frequencies	Band centre frequencies, Hz; required for a callable insertion_loss, optional otherwise.
model	Interior build-up model, one of ENCLOSURE_MODELS (see enclosure_insertion_loss).

Returns: An EnclosureResult whose panel_transmission_loss is the required R and whose insertion_loss is the requested target, so it plots and reports like a forward calculation.

EnclosureResult

EnclosureResult(
    frequencies: np.ndarray | None,
    panel_transmission_loss: np.ndarray,
    correction: np.ndarray,
    insertion_loss: np.ndarray,
    external_area: float,
    internal_area: float,
    room_constant: np.ndarray,
)

Insertion loss of a machine enclosure over frequency (Bies §7.4.2).

Attributes

Name	Description
frequencies	Frequencies f, Hz, or None if the panel R was given as a bare per-band array with no frequency labels.
panel_transmission_loss	The supplied panel transmission loss R per band, dB.
correction	The interior-build-up correction C per band, dB.
insertion_loss	The net enclosure insertion loss $\mathrm{IL}=R-C$, dB.
external_area	External enclosure surface area S_E, m2.
internal_area	Internal surface area S_i, m2.
room_constant	Interior room constant R_i per band, m2.

EnclosureResult.plot()

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

Plot the panel R, correction C and net insertion loss.

Requires matplotlib (pip install phonometry[plot]); returns the Axes.

EnclosureResult.report()

EnclosureResult.report(
    path: str,
    *,
    metadata: ReportMetadata | None = None,
    engine: str = 'reportlab',
    verbose: bool = False,
    language: str = 'en',
) -> str

Render a machine-enclosure insertion-loss fiche to path.

Writes a one-page enclosure-performance sheet: the method-basis line naming the Bies, Hansen & Howard insertion-loss model (Engineering Noise Control 5th ed., section 7.4.2), an optional metadata header (client, enclosed machine, test environment, instrumentation, climate, date), a per-band table (nominal frequency, the supplied panel transmission loss R, the interior build-up correction C and the net insertion loss $\mathrm{IL}=R-C$) beside the R, C and IL curves, the boxed mean insertion loss over the analysis bands with the external and internal surface areas, an optional verdict row against a declared minimum, and a method-basis strip stating $\mathrm{IL}=R-C$ with $C=10{\log }_{10}(0.3+S_{\mathrm{E}}/R_{\mathrm{i}})$.

Parameters

Name	Description
path	Destination path of the PDF file.
metadata	Optional ReportMetadata supplying the header (client, specimen the enclosed machine, test_room the test environment, instrumentation, temperature, relative_humidity, pressure, test_date), the footer identity (laboratory, operator, report_id, notes) and, via requirement, a declared minimum mean insertion loss (more insertion loss is better). The surface areas come from the result itself.
engine	Rendering back end; only "reportlab" is supported.
verbose	When True the per-band table adds the interior room constant R_i column.
language	Fiche language: "en" (default) or "es".

Returns: The written path as a str.

Raises

Exception	When
ValueError	If engine is not "reportlab" or language is unknown.
ImportError	If reportlab (or, for the figure, matplotlib) is not installed (pip install phonometry[report]).