electroacoustics.microphone

Rated microphone characteristics (IEC 60268-4).

A microphone measurement/rating report gathers the rated characteristics IEC 60268-4:2014 defines around a measured free-field frequency response: the free-field sensitivity and its level re 1 V/Pa (clauses 11.1/11.2.1), the frequency response with the manufacturer’s tolerance (12.1) and the effective frequency range read against that tolerance (12.2), the directional pattern and the directivity index (13.1/13.2), the equivalent sound pressure level due to inherent noise (17), the overload sound pressure level at a stated total-harmonic-distortion limit (14.2/15.2), the rated impedance and the rated minimum permitted load impedance (10.2/10.3) and the rated power supply (9.1). This module bundles those into a single MicrophoneCharacteristics result whose report method renders the IEC 60268-4 rated-characteristics fiche, with the characteristic graphs laid out to the IEC 60263:1982 scale conventions.

Four of the characteristics are computed from the standard’s own definitions so the report never merely repeats a manufacturer number:

• Sensitivity level (11.1). The sensitivity M is the ratio of the output voltage to the sound pressure, in volts per pascal; its level is

  L_M = 20 lg(M / M_r),   M_r = 1 V/Pa,

  the rated sensitivity referring to the standard reference frequency of 1 000 Hz (11.3). This is the first clean-room oracle: 12,5 mV/Pa returns 20 lg 0,0125 = -38,06 dB re 1 V/Pa exactly.

• Effective frequency range (12.2). The range of frequencies over which the response does not deviate by more than a specified amount from the ideal (flat) response through the reference-frequency level. The band edges are the interpolated frequencies where the relative response crosses the +/- tolerance limits on either side of the reference frequency, which is the second oracle: a response crossing a limit at chosen frequencies returns exactly those frequencies.

• Directivity index (13.2.2). D = 20 lg(M_0 / M_diff) where the diffuse-field sensitivity of a rotationally symmetric pattern follows 11.2.2 a):

  M_diff^2 = (1/2) * integral over 0..pi of M^2(theta) sin(theta) dtheta.

  For the ideal cardioid M(theta) = M_0 (1 + cos theta) / 2 the integral is M_0^2 / 3, so D = 10 lg 3 = 4,77 dB, the third oracle.

• Equivalent sound pressure level due to inherent noise (17.2 d/e). The equivalent sound pressure is the ratio of the weighted inherent-noise output voltage to the rated free-field sensitivity, p_N = U_N / M, and its level is L_N = 20 lg(p_N / p_0) with p_0 = 20 uPa, the fourth oracle. The overload sound pressure level (15.2.2) is read from a measured distortion-against-level curve as the interpolated sound pressure level where the distortion reaches the specified limit.

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

microphone_characteristics

microphone_characteristics(
    frequencies: ArrayLike,
    response_db: ArrayLike,
    sensitivity_mv_per_pa: float,
    *,
    reference_frequency: float = 1000.0,
    tolerance_db: float = 2.0,
    rated_impedance: float | None = None,
    minimum_load_impedance: float | None = None,
    noise_voltage: float | None = None,
    equivalent_noise_level_db: float | None = None,
    noise_weighting: str = 'A',
    max_spl_db: float | None = None,
    max_spl_thd_percent: float = 1.0,
    distortion: tuple[ArrayLike, ArrayLike] | None = None,
    noise_spectrum: tuple[ArrayLike, ArrayLike] | None = None,
    polar: tuple[ArrayLike, ArrayLike] | None = None,
    polar_frequency: float | None = None,
    directivity_index_db: float | None = None,
    powering: str | None = None,
    supply_current_ma: float | None = None,
) -> MicrophoneCharacteristics

Assemble the rated microphone characteristics for an IEC 60268-4 report.

The sensitivity level (11.1), the effective frequency range (12.2), the directivity index (13.2.2, when a rear-reaching pattern is supplied) and the equivalent noise level (17.2, when the noise voltage is supplied) are computed from the standard’s definitions; the optional directional, noise and distortion data feed the corresponding report panels.

Parameters

Name	Description
frequencies	Free-field response frequency axis, in Hz (1-D, > 0).
response_db	Free-field frequency response, in dB, relative to the output at a stated frequency (12.1.1); it is re-normalized to 0 dB at reference_frequency.
sensitivity_mv_per_pa	Rated free-field sensitivity M at the reference frequency, in mV/Pa (11.2.1/11.3).
reference_frequency	Stated reference frequency, in Hz; the 11.3 standard reference frequency of 1 000 Hz by default.
tolerance_db	Half-width of the response tolerance, in dB (default 2), defining the effective frequency range (12.2).
rated_impedance	Rated impedance, in ohm (10.2).
minimum_load_impedance	Rated minimum permitted load impedance, in ohm (10.3).
noise_voltage	Weighted r.m.s. output voltage due to inherent noise, in V (17.2 b); the equivalent noise level is computed from it.
equivalent_noise_level_db	Stated equivalent sound pressure level due to inherent noise, in dB SPL (17.1), when not computed from noise_voltage.
noise_weighting	Weighting of the inherent-noise measurement (default "A", the IEC 60268-1 6.2.1 recommendation).
max_spl_db	Stated overload sound pressure level, in dB SPL (15.2); when omitted it is read from distortion at max_spl_thd_percent.
max_spl_thd_percent	Distortion limit defining the overload level, in % (default 1, a common 15.2.1 note value).
distortion	Total harmonic distortion against level as (spl_db, thd_percent) (14.2).
noise_spectrum	Inherent-noise spectrum as (frequencies, band_levels_db) in (Hz, dB SPL) (17.2 b).
polar	Directional pattern as (angles_deg, relative_db) at polar_frequency (13.1.2).
polar_frequency	Stated frequency of the directional pattern, Hz.
directivity_index_db	Stated directivity index, in dB (13.2); when omitted it is computed from polar if the pattern reaches the rear.
powering	Rated power supply description (9.1), e.g. "Phantom P48, 48 V (IEC 61938)".
supply_current_ma	Current drawn from the power supply, in mA (9.1).

Returns: A MicrophoneCharacteristics.

Raises

Exception	When
ValueError	If the inputs are invalid.

MicrophoneCharacteristics

MicrophoneCharacteristics(
    frequencies: NDArray[np.float64],
    response_db: NDArray[np.float64],
    reference_frequency: float,
    sensitivity_mv_per_pa: float,
    sensitivity_level_db: float,
    tolerance_db: float,
    effective_range: tuple[float, float],
    rated_impedance: float | None,
    minimum_load_impedance: float | None,
    equivalent_noise_level_db: float | None,
    noise_weighting: str,
    max_spl_db: float | None,
    max_spl_thd_percent: float,
    distortion_spl_db: NDArray[np.float64] | None,
    distortion_thd_percent: NDArray[np.float64] | None,
    noise_frequencies: NDArray[np.float64] | None,
    noise_band_levels_db: NDArray[np.float64] | None,
    polar_angles_deg: NDArray[np.float64] | None,
    polar_db: NDArray[np.float64] | None,
    polar_frequency: float | None,
    directivity_index_db: float | None,
    powering: str | None,
    supply_current_ma: float | None,
)

Rated microphone characteristics for an IEC 60268-4 report.

The free-field frequency response and the rated free-field sensitivity are the required inputs; the directional pattern, the inherent-noise spectrum and the distortion-against-level curve are optional panels rendered when supplied. The sensitivity level, the effective frequency range, the directivity index and the equivalent noise level are computed from the standard’s definitions (see the module docstring).

Attributes

Name	Description
frequencies	Free-field response frequency axis, in Hz.
response_db	Free-field frequency response relative to the level at reference_frequency (0 dB there), in dB (12.1.1).
reference_frequency	Stated reference frequency of the rated sensitivity and the response normalization, in Hz (11.3).
sensitivity_mv_per_pa	Rated free-field sensitivity M at the reference frequency, in mV/Pa (11.2.1/11.3).
sensitivity_level_db	Sensitivity level 20 lg(M / 1 V/Pa), in dB re 1 V/Pa (11.1).
tolerance_db	Half-width of the response tolerance, in dB (12.1.1).
effective_range	Computed effective frequency range (lo, hi) against the tolerance limits, in Hz (12.2).
rated_impedance	Rated (internal) impedance, in ohm (10.2), or None.
minimum_load_impedance	Rated minimum permitted load impedance, in ohm (10.3), or None.
equivalent_noise_level_db	Equivalent sound pressure level due to inherent noise, in dB SPL with noise_weighting weighting (17), or None.
noise_weighting	Weighting of the inherent-noise measurement (IEC 60268-1), "A" by default.
max_spl_db	Overload sound pressure level at max_spl_thd_percent total harmonic distortion, in dB SPL (15.2), or None.
max_spl_thd_percent	Distortion limit defining max_spl_db, in % (15.2.1).
distortion_spl_db	Distortion-curve sound-pressure-level axis, in dB SPL (14.2), or None.
distortion_thd_percent	Total harmonic distortion against level, in % (14.2), or None.
noise_frequencies	Inherent-noise spectrum frequency axis, in Hz (17.2 b), or None.
noise_band_levels_db	Inherent-noise equivalent band levels, in dB SPL (17.2 b), or None.
polar_angles_deg	Directional-pattern angles, in degrees (13.1), or None.
polar_db	Directional pattern G(theta) relative to the reference-axis response, in dB (13.1.2), or None.
polar_frequency	Stated frequency of the directional pattern, in Hz, or None.
directivity_index_db	Directivity index at polar_frequency, in dB (13.2), or None.
powering	Rated power supply description, e.g. the IEC 61938 phantom-powering designation and voltage (9.1), or None.
supply_current_ma	Current drawn from the power supply, in mA (9.1), or None.

MicrophoneCharacteristics.diffuse_field_sensitivity_level_db

property

Diffuse-field sensitivity level, in dB re 1 V/Pa, or None.

Per 11.2.2.1 the diffuse-field sensitivity level equals the free-field plane-wave sensitivity level minus the directivity index (13.2).

MicrophoneCharacteristics.plot()

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

Plot one IEC 60268-4 microphone rated characteristic on one axes.

One concept per figure, drawn by the same shared renderer the .report() fiche composes: "response" (the free-field response with its tolerance band, reference-frequency and effective-range markers, the default), "directivity" (the polar directional pattern on the 25 dB reference circle), "noise" (the inherent-noise band-level spectrum) and "distortion" (total harmonic distortion against sound pressure level).

Parameters

Name	Description
quantity	Which characteristic to plot (see above).
ax	Existing axes to draw on, or None for a fresh figure (a polar axes is created for "directivity").
language	Label language, "en" (default) or "es".

Returns: The axes the characteristic was drawn on.

Raises

Exception	When
ValueError	If quantity or language is unknown, or the result carries no data for quantity.
ImportError	If matplotlib is not installed (pip install phonometry[plot]).

MicrophoneCharacteristics.report()

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

Render the IEC 60268-4 microphone-characteristics fiche to a PDF.

Writes a one-page rated-characteristics data sheet: the standard-basis line (IEC 60268-4:2014, graphs to IEC 60263:1982), an optional metadata header, the rated-characteristics table beside the free-field response with its tolerance band and effective-range markers, the directional, inherent-noise and distortion panels for the data supplied, a boxed sensitivity/range result, an optional equivalent-noise verdict when a requirement is given, and the footer.

Parameters

Name	Description
path	Destination path of the PDF file.
metadata	Optional ReportMetadata supplying the header identity and, through requirement, a maximum permitted equivalent noise level (dB SPL) the verdict row compares against.
engine	Rendering back end; only "reportlab" is supported.
verbose	Accepted for a uniform .report() signature; the fiche has one layout, so it has no effect.
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 is not installed (pip install phonometry[report]).

MicrophoneCharacteristics.sensitivity_v_per_pa

property

Rated free-field sensitivity M, in V/Pa (11.1).

MicrophoneCharacteristics.signal_to_noise_ratio_db

property

Signal-to-noise ratio re 1 Pa (94 dB SPL), in dB, or None.

The datasheet companion of the equivalent noise level: the level of 1 Pa (20 lg(1 Pa / 20 uPa) = 93,98 dB SPL) minus the equivalent sound pressure level due to inherent noise (17), carrying the same weighting.