noise_control.hvac

HVAC duct acoustics: end reflection, bends, plenums and flow-generated noise.

A ventilation duct network attenuates fan noise through several mechanisms that add up along the path, and it regenerates noise wherever the airflow is disturbed. This module gathers the engineering methods of Bies, Hansen & Howard, Engineering Noise Control 5th ed., Chapter 8, for the passive attenuations — duct end reflection (§8.13, Table 8.14), bends/elbows (§8.11, Table 8.11) and plenum chambers (§8.17, Wells’ method) — and for the flow-generated (self) noise of straight ducts and bends (§8.15).

The end-reflection and elbow methods are empirical look-up tables (ASHRAE); they are interpolated over the duct size and, for the elbows, over the frequency-to-width ratio W / lambda. The plenum and flow-noise methods are closed forms evaluated directly.

Note

Bies 5th ed. gives the duct end reflection only as the ASHRAE Table 8.14 look-up (there is no closed form in this edition); this module reproduces that table and interpolates it. Rectangular ducts use the equivalent diameter D = sqrt(4 S / pi).

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

elbow_insertion_loss

elbow_insertion_loss(
    frequencies: ArrayLike,
    width: float,
    *,
    bend_type: str = 'square',
    vanes: bool = False,
    lined: bool = False,
    speed_of_sound: float = 343.0,
) -> HvacSpectrumResult

Duct bend/elbow insertion loss per bend (Bies Table 8.11, ASHRAE).

Indexed by the frequency-to-width ratio W / lambda (lambda = c / f). Lined bends assume the lining extends at least three duct diameters up- and downstream. Round bends are treated as unlined with no vanes.

Parameters

Name	Description
frequencies	Frequencies f, Hz (1-D array).
width	Duct width W in the plane of the bend, m.
bend_type	"square" or "round".
vanes	Turning vanes fitted (square bends only).
lined	Acoustically lined bend (square bends only).
speed_of_sound	Speed of sound c, m/s.

Returns: A HvacSpectrumResult of the insertion loss, dB per bend.

end_reflection_loss

end_reflection_loss(
    frequencies: ArrayLike,
    diameter: float,
    *,
    termination: str = 'flush',
    speed_of_sound: float = 343.0,
) -> HvacSpectrumResult

Duct end reflection loss (Bies Table 8.14, ASHRAE).

The low-frequency reflection of sound back up a duct at its open termination into a room. Interpolated over log diameter and log frequency from Table 8.14; it passes exactly through the tabulated (diameter, octave band) nodes.

Parameters

Name	Description
frequencies	Frequencies f, Hz (1-D array).
diameter	Duct internal diameter D, m (use D = sqrt(4 S / pi) for a rectangular duct of area S).
termination	"flush" (duct flush with a wall/ceiling) or "free" (free space / suspended in the room).
speed_of_sound	Speed of sound c, m/s (kept for signature symmetry; the table is indexed by frequency directly).

Returns: A HvacSpectrumResult of the reflection loss, dB.

flow_noise_bend

flow_noise_bend(
    frequencies: ArrayLike,
    flow_velocity: float,
    area: float,
    height: float,
    *,
    density: float = 1.206,
) -> HvacSpectrumResult

Flow-generated octave-band sound power of a mitred bend (Bies Eqs. (8.252), (8.254)).

L_WB = L_Ws - 10 log10(1 + 0.165 N_s^2) + 30 log10(U) - 103 with the stream power level L_Ws = 30 log10(U) + 10 log10(S) + 10 log10(rho) + 117 (Bies Eq. (8.252)) and the Strouhal number N_s = f H / U (H the duct height in the plane of the bend). The radiated sound power grows as the sixth power of the stream speed at low N_s (the inner-corner drag dipole) and the eighth power at high N_s (the outer-corner shear quadrupole); equivalently, the efficiency referenced to the stream power grows as U^3 and U^5 respectively.

Parameters

Name	Description
frequencies	Octave-band centre frequencies f, Hz (1-D array).
flow_velocity	Mean flow speed U, m/s.
area	Duct cross-sectional area S, m2.
height	Duct height H in the plane of the bend, m.
density	Air density rho, kg/m3.

Returns: A HvacSpectrumResult of the band sound power level, dB re 1e-12 W.

flow_noise_straight_duct

flow_noise_straight_duct(
    frequencies: ArrayLike,
    flow_velocity: float,
    area: float,
) -> HvacSpectrumResult

Flow-generated octave-band sound power of a straight duct (Bies Eq. (8.251)).

L_WB = 7 + 50 log10(U) + 10 log10(S) - 2 - 26 log10(1.14 + 0.02 f / U) in dB re 1e-12 W (VDI 2081-1), for airflow speed U in a duct of area S.

Parameters

Name	Description
frequencies	Octave-band centre frequencies f, Hz (1-D array).
flow_velocity	Mean flow speed U, m/s.
area	Duct cross-sectional area S, m2.

Returns: A HvacSpectrumResult of the band sound power level, dB re 1e-12 W.

HvacSpectrumResult

HvacSpectrumResult(
    frequencies: np.ndarray,
    values: np.ndarray,
    quantity: str,
    label: str,
)

A per-frequency HVAC quantity (attenuation or regenerated power level).

Attributes

Name	Description
frequencies	Frequencies f, Hz.
values	The quantity per frequency (dB, or dB re 1e-12 W for a sound power level).
quantity	What values holds ("attenuation" or "sound_power_level").
label	A short human label of the element.

HvacSpectrumResult.plot()

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

Plot the quantity against a continuous log-frequency axis.

Requires matplotlib (pip install phonometry[plot]).

HvacSpectrumResult.report()

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

Render an HVAC duct-noise-spectrum fiche to path.

Writes a one-page HVAC-noise sheet: the method-basis line naming the reported quantity and the Bies, Hansen & Howard chapter (Engineering Noise Control 5th ed., Chapter 8), an optional metadata header (client, duct element, test environment, instrumentation, climate, date), a per-band table (nominal frequency and the reported quantity) beside the spectrum, the boxed single-number result (for a regenerated-noise spectrum the A-weighted sound power level L_WA re 1 pW with the overall unweighted total; for an attenuation spectrum the mean attenuation with its band range), an optional verdict row against a declared limit, and a method-basis strip stating the reported quantity’s relation.

Parameters

Name	Description
path	Destination path of the PDF file.
metadata	Optional ReportMetadata supplying the header (client, specimen the duct element, 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 maximum A-weighted sound power level for a regenerated-noise spectrum (lower is better) or a declared minimum mean attenuation for an attenuation spectrum (more is better).
engine	Rendering back end; only "reportlab" is supported.
verbose	When True a regenerated-noise table adds the A-weighting correction and the A-weighted band level columns.
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]).

plenum_attenuation

plenum_attenuation(
    exit_area: float,
    line_of_sight: float,
    wall_area: float,
    mean_absorption: ArrayLike,
    *,
    angle: float = 0.0,
) -> np.ndarray | float

Plenum-chamber transmission loss by Wells’ method (Bies Eq. (8.275)).

TL = -10 log10[ S_out ( cos(theta) / (pi r^2) + (1 - alpha) / (S_w alpha) ) ], where the reverberant term uses the plenum room constant R = S_w alpha / (1 - alpha) (phonometry.room.room_constant). The method holds above the inlet cut-on and when the plenum is large compared with the wavelength; it underpredicts the low-frequency loss by 5-10 dB.

Parameters

Name	Description
exit_area	Outlet-opening area S_out, m2.
line_of_sight	Straight-line inlet-to-outlet distance r, m.
wall_area	Total internal wall area S_w, m2.
mean_absorption	Mean Sabine wall absorption alpha in (0, 1) (scalar or per-band).
angle	Angle theta between the inlet axis and the line to the outlet, rad (default 0).

Returns: The transmission loss, dB (float for scalar absorption, else a per-band array).