metrology.reference_values

Preferred reference values for acoustical and vibratory levels (ISO 1683:2015).

A level in decibels is a ratio to a reference value, so the number means nothing until the reference is known: the same pressure reads 26 dB higher against the 1 µPa of water than against the 20 µPa of air, and the same vibration 34 dB higher against 1 nm/s than against 50 nm/s. ISO 1683:2015 fixes one reference per quantity in three tables, and the level functions of this library count their decibels from them unless the standard they implement names another:

Table 1, sounds in air and other gases: sound pressure 20 µPa, sound exposure (20 µPa)² s, sound power 1 pW, sound energy 1 pJ and sound intensity 1 pW/m².
Table 2, sounds in water and other liquids: sound pressure 1 µPa, sound exposure 1 µPa² s, sound power 1 pW, sound energy 1 pJ, sound intensity 1 pW/m², sound particle displacement 1 pm, velocity 1 nm/s and acceleration 1 µm/s², and a distance of 1 m for the compound quantities of its note c (a source level re 1 µPa m, for one).
Table 3, vibratory quantities: displacement 1 pm, velocity 1 nm/s, acceleration 1 µm/s² and force 1 µN. Its note b adds the 50 nm/s that is also used for structure-borne sound, against which the velocity level comes out close to the associated sound pressure and intensity levels.

ISO1683_REFERENCE_VALUES holds all of them, keyed by medium and then by quantity, and every value is in the coherent SI unit its row names, so the 20 µPa of air is 2e-05 Pa:

from phonometry import metrology

p0 = metrology.ISO1683_REFERENCE_VALUES["gas"]["sound_pressure"]
p0.value, p0.unit, p0.printed  # (2e-05, 'Pa', '20 µPa')

Note b of Table 2 gives the offset between the two pressure references, a level re 1 µPa being $10 l g (2 0^{2} / 1^{2}) \approx 26.0$ dB above the same pressure re 20 µPa; phonometry.underwater.in_air_to_underwater_spl applies it.

The values were transcribed from the Spanish text UNE-EN ISO 1683:2016, which adopts ISO 1683:2015 unchanged, PDF pages 8 and 9 (printed folios 8 and 9), and the quantity names are given here in English. A module that counts its decibels from a different reference keeps it, and names the document it comes from beside it: DIN 45672-2 defines its own 5·10⁻⁸ m/s for railway vibration (Formula (2)), and ISO/TS 7849 and ISO 9611 refer the surface velocity to the same 5·10⁻⁸ m/s, which is the 50 nm/s of note b of Table 3. scripts/check_reference_values.py holds the tree to that: a reference value declared in the package either points at this table or says where it was read.

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

ISO1683_REFERENCE_VALUES

Constant (mapping).

ReferenceValue

ReferenceValue(
    quantity: str,
    medium: str,
    value: float,
    unit: str,
    printed: str,
    table: str,
)

One reference value of ISO 1683:2015, with what it is a reference of.

Attributes

Name	Description
`quantity`	The quantity the value is the reference of, in English (`"sound pressure"`, `"vibratory velocity"`).
`medium`	`"gas"` (Table 1), `"liquid"` (Table 2) or `"solid"` (Table 3, structure-borne sound and vibration).
`value`	The reference value, in the coherent SI unit `unit` names: 20 µPa is `2e-05` with `unit` `"Pa"`.
`unit`	The SI unit of `value`.
`printed`	The value as the table prints it, prefix and all.
`table`	Where the value is printed: `"Table 1"` to `"Table 3"`, or `"Table 3, note b"` for the 50 nm/s alternative.

Created and maintained by José Manuel Requena Plens ORCID All projects