These pages explain the terms and relationships you need for SPL Sense and SPL Cloud. They do not replace specialist literature. In Switzerland, the V-NISSG ordinance and the enforcement guide of the Federal Office of Public Health (BAG/FOPH) apply; in Germany, DIN 15905-5. Which templates SPL Sense provides for them is described under Templates for V-NISSG and DIN 15905-5.
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Basics
Regulations, terms, the right measuring point, the offset and how to deal with audience noise.
- 1: Templates for V-NISSG and DIN 15905-5
- 2: Glossary
- 3: Measuring point and offset
- 4: Audience noise
1 - Templates for V-NISSG and DIN 15905-5
Which value profiles and live screens SPL Sense provides for Switzerland and Germany.
SPL Sense provides value profiles and live screens for the V-NISSG (Switzerland) and DIN 15905-5 (Germany). Which requirements apply to your event is set out in the original documents (below).
Value profiles
| Template | Values and thresholds (Notification / Warning / Limit) |
|---|---|
| VNISSG 93dBA | LAeq 60′: 91 / 92 / 93 · LAeq 5′: – / 92 / 93 · LAFmax 1′: Limit 125 |
| VNISSG 96dBA | LAeq 60′: 94 / 95 / 96 · LAeq 5′: – / 95 / 96 · LAFmax 1′: Limit 125 |
| VNISSG 100dBA | LAeq 60′: 98 / 99 / 100 · LAeq 5′: – / 99 / 100 · LAFmax 1′: Limit 125 |
| DIN 15905-5 | LAeq 30′: – / 95 / 99 · LAeq 5′: – / 95 / 99 · LCFmax 1′: Limit 135 |
The values can be adjusted per measurement, see Value profiles. The matching live screens have the same names as the templates, each also in a variant with leveler display.
SPL Sense calculates averages such as LAeq 30′ or LAeq 60′ every minute as a moving average over the last 30 or 60 minutes. The value on the full and half hour equals the average over the past half hour, i.e. the 30-minute block of DIN 15905-5. If LAeq 30′ stays below the limit at all times, all blocks are met as well.
For the peak level, the DIN 15905-5 template uses LCFmax 1′: the highest C-weighted Fast value (125 ms) within one minute.
Original documents
- Swiss Federal Office of Public Health (BAG/FOPH): Vollzugshilfe zur V-NISSG, Schall (enforcement guide) and Messverfahren zur Ermittlung von Schallpegeln an Veranstaltungen (measurement procedure), on the FOPH website
- DIN 15905-5:2022-07, Event technology – Sound engineering – Part 5: Measures to prevent the risk of hearing loss of the audience by high sound exposure of electroacoustic sound systems
2 - Glossary
The most important terms and abbreviations in SPL Sense and SPL Cloud, in alphabetical order.
Measured values and notation
SPL Sense and SPL Cloud write measured values as is common in acoustics:
| Display | Meaning |
|---|---|
| LAeq 60′ | Equivalent continuous level (Leq), A-weighted, over 60 minutes. The “hourly level” of the V-NISSG. |
| LAeq 5′ | the same over 5 minutes |
| LCeq 1 s | Equivalent level, C-weighted, over 1 second (live value) |
| LAFmax 1′ | highest level, A-weighted with time weighting Fast, within one minute |
The letter after the L is the frequency weighting (A, C or Z), followed by the type (eq or Fmax) and then the time. A prime ′ stands for minutes. The unit is always dB.
CSV exports and PDF reports partly still use an older notation for the same values.
Terms A–Z
- A, C and Z weighting
- Filters that weight the frequency spectrum. A roughly corresponds to human hearing at low levels and strongly attenuates bass; the equivalent levels of the V-NISSG and of DIN 15905-5 are given in dB(A). C attenuates bass only slightly and shows how much low-frequency energy is involved; DIN 15905-5 uses it to limit the peak level. Z is unfiltered (zero). SPL Sense always measures all three.
- Assessment level (Lr)
- Term from DIN 15905-5: the LAeq over 30 minutes at the immission location, in blocks starting at every full and half hour. The permissible value is 99 dB.
- Audience noise, extraneous noise
- DIN 15905-5 calls everything that does not come from the sound system Störschall (extraneous noise), for example audience or pyrotechnics. See Audience noise.
- Calibration
- Adjustment of the sensor against a reference sound level. It has an expiry date. See Sensor and calibration.
- Correlation
- For the leveler, the ratio between measured and expected level. 1.000 means: only the sound system can be heard. Values above 1 indicate additional noise, for example from the audience.
- Day boundary
- Time at which a measurement day ends: between midnight and 06:00.
- Deviation, exceedance
- A value has exceeded a threshold of the value profile. The measurement details show them per day.
- Excluded time range
- A period that does not count for maxima, rating and deviations, for example the system tuning. The data is kept and shown greyed out.
- Fast (F)
- Time weighting of 125 ms. Reacts quickly to peaks. Basis for LAFmax.
- Gain reduction (GR)
- How many dB the leveler is currently reducing the volume by. Always 0 or negative.
- Instance
- An installation of SPL Sense registered with SPL Cloud, for example a laptop or a Raspberry Pi.
- Interval
- A recorded section of one minute. It contains all values of that minute and is digitally signed.
- Job
- Groups several measurements in SPL Cloud, for example all measuring points of a festival.
- LAFmax, MaxF
- The highest level with time weighting Fast within the chosen time. The V-NISSG limits LAFmax to 125 dB(A).
- LCpeak
- C-weighted peak sound pressure level: the highest instantaneous value of the sound pressure, without time weighting. DIN 15905-5 limits it to 135 dB. Not the same as LCFmax: there, the level is first smoothed with the time weighting Fast (125 ms), and the highest of these values is taken. Short peaks therefore come out lower; LCpeak is always equal to or higher than LCFmax.
- Leq (equivalent continuous level)
- The energy average of the level over a given time. A short, very loud moment raises the Leq considerably; a quiet moment lowers it only slightly.
- Leveler
- Automatically controls the volume of the sound system so that the limit is met.
- Line offset
- For the leveler with audience compensation: the difference between the level at the sensor and the signal level at the output of the audio processor, measured without audience.
- Live screen
- Large display of the current values, for example for the DJ or the technicians. Layout freely configurable.
- Loudest place, immission location
- The loudest place in the audience area, at ear height. This is where the limit applies. The V-NISSG calls it Ermittlungsort. DIN 15905-5 calls it maßgeblicher Immissionsort (relevant immission location) and distinguishes one for LAeq (determined by mid and high frequencies) and one for the peak level (determined by the bass). See Measuring point and offset.
- Measurement
- A measuring point with its settings and all recorded data. Can run over many days.
- Measurement day
- A day of a measurement, delimited by the day boundary. The Pro billing also counts measurement days.
- Measuring position, substitute immission location
- Where the sensor actually stands, for example at the mixing desk. DIN 15905-5 calls it Ersatzimmissionsort (substitute immission location).
- Offset, correction value
- Value in dB added to each measured value to infer the level at the loudest place from the measuring position. One value each for A, C and Z. In DIN 15905-5 they are called correction values KA and KC.
- Operator PIN
- Protects SPL Sense against changes. The live screen remains accessible without PIN.
- Organization
- A company, a venue or a festival in SPL Cloud. It owns measurements, jobs and instances; several people work together in it.
- Pink noise
- Test signal with equal energy per octave. Used to determine the offset and line offset.
- Read access
- Allows another person to view a measurement or a job in SPL Cloud without changing anything.
- Recovery zone
- Area where the audience can recover from the noise (Ausgleichszone). The V-NISSG requires it for events with an hourly level above 96 dB(A) that last longer than three hours.
- Signature
- Every interval is digitally signed. This makes it possible to prove that the data has not been changed.
- Spectrum, third-octave band
- The level split by frequency, in third-octave bands. Visible in the interval details and on the live screen.
- Value profile
- Defines which values a measurement calculates (e.g. LAeq 60′, LAFmax 1′) and which thresholds apply. Each value has up to three levels: Notification, Warning and Limit. See Value profiles.
- Weather protection filter
- Compensates for the effect of a weather protection on the microphone. Must match the weather protection used.
3 - Measuring point and offset
Where the sensor belongs, how to determine the offset and what you should document.
Loudest place and measuring position
The limits apply at the loudest place in the audience area. The V-NISSG calls it Ermittlungsort (at ear height), DIN 15905-5 calls it maßgeblicher Immissionsort. The sensor can rarely stand there during an event: in the middle of the audience it would be at risk, and shouting and applause would distort the measurement.
That’s why you measure at another place, the measuring position (DIN: Ersatzimmissionsort). The offset (DIN: correction value) compensates for the difference between the two places. SPL Sense adds it to every measured value so that the displayed and stored values correspond to the level at the loudest place in the audience.
Choosing the measuring position
- The sensor should receive the direct sound of the sound system: clear line of sight to the loudspeakers, not behind pillars, tent poles or the roof of the mixing desk.
- As little audience and other noise sources nearby as possible.
- Not in room corners and not directly against walls.
- Outdoors with weather protection, and switch on the matching weather protection filter.
- Do not move it during the event. If you have to move it, determine the offset again.
Distance to the loudspeakers
The sensor needs a minimum distance to the sound system:
- Only at some distance do the high, mid and low frequency drivers combine into the sound the audience hears. Too close to a loudspeaker, the sensor mainly measures a single loudspeaker, and the offset no longer holds for music.
- The sensor has a maximum level. Too close to a loudspeaker, peaks can overload it. SPL Sense shows this as Clip in the measurement data.
Within these limits: the farther the measuring position is from the audience and the better it lies in the direct sound of the sound system, the less audience and other sources interfere. If the measuring position is closer to the sound system than the loudest place in the audience, the offset becomes negative. DIN 15905-5 recommends such a measuring position.
Determining the offset
The offset is determined before the event with pink noise, as loud as during operation and through exactly the sound system that will play during the event. In SPL Sense this is done with Tune Offsets, described step by step in the Quick start. In short:
- Play pink noise at operating volume.
- Walk through the audience area with the sensor. SPL Sense remembers the highest level, this is your loudest place.
- Place the sensor at the measuring position and set the offset so that the level at the measuring position plus the offset equals the highest level.
Alternatively, measure the level at the loudest place with a handheld meter and enter the difference directly under Edit Measurement. DIN 15905-5 requires a measuring duration of at least 15 seconds for this.
The offset applies per weighting: there is a separate value for A, C and Z.
- A (for LAeq and LAFmax): the loudest place is determined by the mid and high frequency drivers.
- C (for LCFmax and the peak level): the loudest place is determined by the bass and may be somewhere else. DIN 15905-5 allows the C offset to be determined from the LCeq; this is more reliable than using peak values.
Tips
- Check the offset afterwards with typical music. If it deviates strongly, measure again.
- Don’t calculate the offset with rules of thumb, measure it.
- The offset only applies to this loudspeaker setup and this measuring position. If either changes, measure again.
- During the event, briefly check whether the values are plausible (the V-NISSG enforcement guide mentions this as an option).
Function test and calibration
For mobile measuring systems, DIN 15905-5 requires a function test with a calibrator before and after each event. The industry recommendation on the measurement procedure for the V-NISSG also recommends calibration before and after each measurement for mobile systems; the enforcement guide itself does not require organizers to calibrate. SPL Sense shows the calibration status of the sensor and warns before the start if it has expired. See Sensor and calibration.
Documentation
Record in writing how you measured.
- V-NISSG: at least the loudest place, the offset and the method you used to determine the offset.
- DIN 15905-5: a measurement report including organizer, date and place, start and end of the measurement, assessment levels and peak levels, measuring and calibration devices, result of the function test, location of the immission locations and the measuring position with justification, and the correction values and how they were determined. The complete list is in the standard, section “Messprotokoll”.
The measured values are provided, for example, by the PDF day report.
SPL Sense helps: every change of the offset automatically appears in the events, and with comments you record special circumstances directly in the measurement. In SPL Cloud you can also attach pictures of the measuring position to the measurement (SPL Cloud Pro).
Original documents: see Templates for V-NISSG and DIN 15905-5.
4 - Audience noise
How the audience and other noise sources affect the measurement and how SPL Sense deals with it.
What counts towards the level?
The regulations differ here:
- V-NISSG (Switzerland): everything that can be heard at the loudest place counts: sound system, stage, instruments and also the audience (industry recommendation on the measurement procedure).
- DIN 15905-5 (Germany): only the sound of the sound system is assessed. Audience and other sources are Störschall (extraneous noise) and should not distort the result. That’s why the standard recommends a measuring position where the audience hardly matters.
In both cases, the SPL Sense recording contains the total level at the sensor. No setting removes the audience from the stored measured values. How much it counts is therefore determined by your choice of measuring position.
The audience has little influence on the hourly level at most events (V-NISSG enforcement guide). For short periods, however, it can contribute significantly to the level: applause, chanting, singing along, loud stage monitors or rain on a tent roof.
What you can do
- Choose the measuring position well: if the sensor is above head height, away from the crowd and in the direct sound of the sound system, the audience has less effect. Keep enough distance to the loudspeakers. See Measuring point and offset.
- Keep the stage level low: loud monitors and backline increase the level without the technicians at the mixing desk being able to do much about it.
- Add comments: record special moments in the measurement, for example “Encore, audience singing along”. Comments appear in the day chart and help explain peaks later.
Leveler with audience compensation
The leveler automatically turns the sound system down when it gets too loud. Without further information, it would also do so when the audience is loud, making the music unnecessarily quieter even though the sound system is not to blame.
In the mode Leveler with panic and audience compensation, SPL Sense compares the measured level with the signal the audio processor is currently outputting. If it is louder than the sound system alone can explain (correlation above 1), the leveler only takes the share of the sound system into account. The measurement itself still records the full level.
For this to work, the leveler needs an accurately calibrated line offset. How to do this is described under Leveler.