Source: https://jmrplens.github.io/phonometry/buildings/rooms/reporting-and-qualification/ # Reporting and source qualification (ISO 3382-1) Most of ISO 3382-1 is about how to measure. This page is about the four tables it prints and the rules that go with them: what a source has to be before it may be used, how many seats a survey has to reach, how the bands are averaged into the one number a hall gets quoted by, and what the report shall say. ## 1. Qualifying the source A source that is not omnidirectional measures a different hall depending on which way it faces. Table 1 says how far from omnidirectional it may be, band by band, and 4.2.1 says how to find out. *A source qualifies at 125 Hz and fails at 4 kHz, and Table A.1 does not average every quantity over the same bands.* The survey is made on a turntable, or from measurements every 5 degrees if there is none. Either way the readings are combined into **gliding 30 degree arcs**, and each arc is compared with a reference that is "a 360 degree energetic average in the measurement plane". Source and microphone are at least 1,5 m apart throughout. ```python import numpy as np from phonometry import room bearings = np.arange(72) * room.DIRECTIVITY_STEP_DEG pattern = 7.5 * np.cos(8.0 * np.deg2rad(bearings)) pattern += 2.4 * np.cos(16.0 * np.deg2rad(bearings)) deviation = room.gliding_directivity_deviation(94.0 + pattern) print(round(float(np.max(np.abs(deviation))), 2)) # 6.89 dB print(room.source_directivity_limit(4000.0)) # 6.0 dB ``` Table 1 prints six bands, 125 Hz to 4 kHz, and no more, so a survey in the 63 Hz or 8 kHz octave has no printed limit to be held to rather than the nearest one: ```python from phonometry import room print(room.MAX_SOURCE_DIRECTIVITY_DEVIATION_DB) # {125.0: 1.0, 250.0: 1.0, 500.0: 1.0, 1000.0: 3.0, 2000.0: 5.0, 4000.0: 6.0} ``` **Two things about that survey are not settled by what is printed.** The first is a contradiction: 4.2.1 and the caption of Table 1 both call its values the *maximum* acceptable deviation, and A.4 calls them "the minimum limits given in Table 1" when it asks for a marginal source to be measured again at three orientations. Read literally, A.4 asks for the extra work on the sources that need it least. The second is an omission: "gliding averages, each covering six neighbouring points" does not say whether the six lead, trail or straddle the arc they are reported against. Over a full turn that is a relabelling, so it moves the bearing each deviation is reported against by up to 15 degrees of the pattern and not the deviation itself, but the bearing is what A.4 asks a marginal source to be turned about. Both are in [the errata register](https://jmrplens.github.io/phonometry/reference/errata/), and `gliding_directivity_deviation` says in its docstring which readings it took. ## 2. How many positions, and where Table A.2 prints three rows: 500 seats want 6 microphone positions, 1 000 want 8 and 2 000 want 10. They lie exactly on a straight line in the logarithm of the seat count, two positions per doubling, which is what lets a hall between the rows be answered at all. ```python from phonometry import room print([round(float(room.minimum_receiver_positions(n)), 2) for n in (500, 1000, 1400, 2000)]) # [6.0, 8.0, 8.97, 10.0] print(round(float(room.minimum_receiver_positions(5000)), 2)) # 10.0 ``` The line stops where the table does. A.4 asks for "a minimum of between 6 and 10 representative microphone positions", so a 5 000-seat arena does not get thirteen positions on the strength of three rows, and a 200-seat studio does not get four. A.4 adds the geometry the table does not: at least three on-stage source positions in the normal case, a source height of 1,5 m, a microphone height of 1,2 m at audience seat locations, positions evenly distributed over all the seating, and more of them wherever a hall breaks into balconies and under-balcony areas. **How the measurement goes.** Qualify the source first: octave bands of pink noise in a free field, the microphone at least 1,5 m away, and the output averaged over gliding 30 degree arcs on a turntable or, without one, over six neighbouring readings taken every 5 degrees, each arc inside Table 1 against the 360 degree energetic average. In the hall, normally use at least three source positions on the stage with the acoustic centre 1,5 m up, and the minimum microphone positions of Table A.2 at 1,2 m at seats, spread evenly and added to where balconies split the seating. Hold the source at least 45 dB over the background without synchronous averaging, measure a marginal source again turned in at least three steps, and report the source and microphone positions with their heights, preferably on a plan, with the fifteen items of 9.2. ## 3. The single number, and the two exceptions in it Every quantity in Annex A gets quoted as one number, and A.5 asks for the index "m" on the symbol when it is. What the "m" averages is **not** the same for every quantity: Table A.1 gives each row its own band set, and A.5 prints two examples for exactly that reason, $G_m$ over the 500 Hz and 1 kHz octaves and $J_{\mathrm{LF}m}$ over four bands from 125 Hz. ```python import numpy as np from phonometry import room octaves = np.array([125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0]) strength = np.array([6.2, 5.4, 4.8, 4.4, 4.1, 3.6]) lateral = np.array([0.20, 0.26, 0.31, 0.28, 0.24, 0.19]) print(round(room.single_number_average("G", strength, octaves), 4)) # 4.6 print(round(room.single_number_average("J_LF", lateral, octaves), 4)) # 0.2625 print(room.TABLE_A1["G"].averaging_bands_hz) # (500.0, 1000.0) print(room.TABLE_A1["J_LF"].averaging_bands_hz) # (125.0, 250.0, 500.0, 1000.0) ``` One of the seven rows carries two symbols. The table prints the early lateral energy fraction as "$J_{\mathrm{LF}}$ or $J_{\mathrm{LFC}}$", one row for the two weightings of Equations (A.14) and (A.15), so `"J_LFC"` is taken wherever `"J_LF"` is and reads the same four bands, the same just-noticeable difference and the same range. ```python import numpy as np from phonometry import room octaves = np.array([125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0]) lateral = np.array([0.20, 0.26, 0.31, 0.28, 0.24, 0.19]) print(round(room.single_number_average("J_LFC", lateral, octaves), 4)) # 0.2625 print(room.perceptibly_different("J_LFC", 0.20, 0.26)) # True ``` Footnote a of the table makes one row an exception to the arithmetic: the late lateral sound level is **energy** averaged, through Equation (A.17). And two of its just-noticeable differences are not plain numbers either. The early decay time's is printed as "Rel. 5 %", a fraction of the value rather than a difference in seconds, so the same 60 ms means nothing in a two-second hall and is plain in a half-second one. The late lateral level's is printed as "Not known", and the library refuses to invent one. ```python from phonometry import room print(room.perceptibly_different("EDT", 2.0, 2.06)) # False print(room.perceptibly_different("EDT", 0.5, 0.56)) # True print(room.TABLE_A1["L_J"].just_noticeable_difference) # None ``` A.5 also offers a coarser presentation, the octave **pairs**: 125 Hz with 250 Hz for a low-frequency result, 500 Hz with 1 kHz for a mid one, and 2 kHz with 4 kHz for a high one, all arithmetic. That is a different product from the single number and the two must not share a code path: they are the same two bands for the five monaural quantities and different band sets for the lateral ones. ```python import numpy as np from phonometry import room octaves = np.array([125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0]) lateral = np.array([0.20, 0.26, 0.31, 0.28, 0.24, 0.19]) pairs = room.octave_pair_averages(lateral, octaves) print({k: round(v, 4) for k, v in pairs.items()}) # {'low': 0.23, 'mid': 0.295, 'high': 0.215} print(round(room.single_number_average("J_LF", lateral, octaves), 4)) # 0.2625 ``` A.5 notes that lateral energy fractions in the 4 kHz octave are not usually thought to be subjectively important, so the high pair means little for them. ## 4. Two routes to a mid-frequency reverberation time Clause 9.1 prints two ways to quote one number for the reverberation time and no third: the average of $T_{30}$ over the 500 Hz and 1 kHz **octave** bands, or "averages over the six one-third-octave bands from 400 Hz to 1 250 Hz". ```python from phonometry import room print(room.MID_FREQUENCY_OCTAVES_HZ) # (500.0, 1000.0) print(room.MID_FREQUENCY_THIRD_OCTAVES_HZ) # (400.0, 500.0, 630.0, 800.0, 1000.0, 1250.0) ``` What a one-third-octave analysis must not do is average the two one-third-octave bands that happen to be called 500 Hz and 1 kHz. That is two thirds of an octave against the two octaves either printed route covers, a third of the band, and it is neither of them. The [accredited fiche](https://jmrplens.github.io/phonometry/buildings/rooms/room-acoustics/) takes the six-band route when the analysis is in thirds and names it on the sheet. ## 5. What the report shall say Clause 9 is normative, unlike every annex on this page, and 9.2 is its only requirement about what is written down rather than what is measured. It lists fifteen items, a) to o), and `TEST_REPORT_ITEMS` carries them in order: the conformity statement, the room's name, place, plan and volume, its seating and upholstery, the shape and material of walls and ceiling, the occupancy, the state of any variable equipment, the curtains in a theatre, the stage furnishing, the temperature and humidity, the apparatus, the signal, the coverage with its positions and heights, and the date and the organization. ```python from phonometry import room print(len(room.TEST_REPORT_ITEMS)) # 15 print(room.TEST_REPORT_ITEMS[3]) # volume of the room, with an explanation of how it is defined if the room # is not completely enclosed ``` Most of that is metadata rather than measurement, and it reaches the accredited fiche through the `ReportMetadata` container the [room acoustic parameters page](https://jmrplens.github.io/phonometry/buildings/rooms/room-acoustics/) fills in. ## See also - [Room Acoustic Parameters](https://jmrplens.github.io/phonometry/buildings/rooms/room-acoustics/): the decay analysis these tables report the results of, and the accredited fiche. - [Sound strength G (ISO 3382-1)](https://jmrplens.github.io/phonometry/buildings/rooms/sound-strength/), [Spatial impression](https://jmrplens.github.io/phonometry/buildings/rooms/spatial-impression/) and [Stage support and uncertainty](https://jmrplens.github.io/phonometry/buildings/rooms/stage-and-uncertainty/): the quantities Table A.1 averages. - API reference: [`room.auditorium`](https://jmrplens.github.io/phonometry/reference/api/rooms/auditorium/). ## Standards ISO 3382-1:2009: Table 1 with the gliding arc survey of 4.2.1, Table A.1 with its per-quantity averaging bands, Table A.2 with A.4's geometry, the octave pairs of A.5, and the normative Clause 9 with its two single-number routes and its fifteen-item test report. Validated against the printed tables in the [conformance report](https://jmrplens.github.io/phonometry/reference/conformance/); the contradiction between Table 1 and A.4, and the gliding window the clause leaves unphased, are in the [errata register](https://jmrplens.github.io/phonometry/reference/errata/).