Our first comparison with NIOSH
On September 9, 2026, we replayed a prepared sound sequence into one iPhone, first using NIOSH and then Lullasure. Eleven accepted fitting conditions supported a +23.0 dB correction. Applied to the saved readings, it brought three reserved test sounds within 1.0 dB of NIOSH.
That experiment covered one hardware identifier, iOS version and Check/Laboratory measurement mode. A same-day corrected-build run measured the three reserved sounds within 0.37 dB of the earlier NIOSH readings; its 4 kHz tones remained 1.6–1.9 dB lower. This follow-up used the earlier full reference sequence, so a fresh NIOSH pass is still needed. This comparison does not establish instrument accuracy, validate continuous Track or demonstrate performance across other phones.
In version 1.0 (build 2), Check uses a provisional conversion constant of 117 dB across device models. Track uses its separate, uncalibrated 94 dB baseline because the Check correction was not suitable for Track’s playback-compatible audio mode. Neither default has validated accuracy bounds or an uncertainty figure. The linked historical experiment results apply only to the measured Check/Laboratory setup.
Read the experiment report, setup photos, paired data and limitations. Future equipment-based reports will link back to this starting point.
What the engine computes
The audio-processing code includes unit tests for the digital A-weighting filter and numerical calculations. Check and continuous Track use different audio-session modes. Code tests do not establish microphone accuracy, and the current interface does not expose every metric or reliability state the engine computes.
Engine averages and the current live display
The engine computes rolling energy averages, a fixed initial 30-second average and a recent Fast-weighted maximum. The current Check screen uses a live estimate; it does not present a completed 30-second average with uncertainty. Watching that live number for 30 seconds does not turn it into an LAeq measurement.
The engine also computes reliability states, including settling, variability and clipping. The current gauge does not show all of them. A plausible-looking number can therefore still be unreliable, particularly in very quiet conditions or during loud transients.
The proposed reference comparison protocol
The following describes planned validation work, not completed experiments or approved infant exposure levels. There are no results from this protocol yet.
| Reference | A traceably calibrated Class 1 sound-level meter with a fresh acoustic calibrator check before and after each session. |
|---|---|
| Devices | Multiple physical units per model across at least eight iPhone model families, with and without common cases, in flat and upright orientations. |
| Levels | Nursery-relevant 35 to 70 dBA and event-relevant levels up to 100 dBA, stepped in 5 dB increments. |
| Sources | White, pink, and brown noise, a fan, music, crowd recordings, traffic, and impulsive event samples such as applause and fireworks. |
| Geometry | Source at 30 cm, 1 m, and 2 m from a mattress-height microphone position in a furnished room, plus a low-reflection control. |
| Statistics | Mean error, median absolute error, 95th-percentile absolute error, and worst underreading, reported by model, sound type, level band, case state, and orientation. |
| Publication | A readable report, the supported-device table, the raw dataset, the engine version it applies to, and the models that failed or were not tested. |
Planned device coverage
This is a proposed testing list. A model should be marked validated only with a linked report describing the units, conditions and measured uncertainty. Inclusion in this table is not evidence of accuracy or compatibility on every device.
| iPhone model | Role | Validation | Note |
|---|---|---|---|
| iPhone 16 Pro | Check | Pending | First lab batch |
| iPhone 15 | Check | Pending | First lab batch |
| iPhone 14 | Check | Pending | First lab batch |
| iPhone 13 | Check | Pending | Common spare phone |
| iPhone 12 | Check | Pending | Common spare phone |
| iPhone 11 | Check | Pending | Common spare phone |
| iPhone SE (2nd and 3rd gen) | Check | Pending | Second lab batch |
| iPhone XR / XS | Check | Needs units | Needs units |
Planned experiments for a future report
- Distance experiment. White, pink, and brown noise at 30 cm, 1 m, and 2 m from a mattress-height microphone, phone models and common nursery machines side by side with the reference.
- Output-route experiment. The same sound and app volume through the iPhone speaker, a Bluetooth speaker, and a HomePod, showing why a parent should run Check again when the playback route changes.
- Case and orientation experiment. How much common cases and flat versus upright placement shift readings on each model.
- Venue-position experiment. Dance floor, near-speaker table, distant table, lobby, outdoors: average, peak, and duration with stated uncertainty.
- Sound-catalog audit. Level matching, true-peak ceiling, and loop-seam results for all 15 sounds.
Known limitations
- Individual microphones, cases, orientation and room conditions can affect a reading. Their effects have not yet been quantified for Lullasure.
- Very quiet conditions and loud impulses can produce unreliable estimates. The calibration notice does not identify every unreliable reading.
- The engine’s Fast maximum is not a true acoustic peak measurement and cannot characterize every short impulse.
- Calibration profiles identify hardware model, engine version and input route. Those fields do not establish accuracy after an iOS change. Unverified profiles receive neutral presentation and the calibration limitation, while numerical estimates remain visible.
Sources
- American Academy of Pediatrics, Preventing Excessive Noise Exposure in Infants, Children, and Adolescents (2023)
- Hazardous sound outputs of white noise devices intended for infants (2021)
- Apple, AVAudioSession measurement mode
- NIOSH Sound Level Meter app, the right general-purpose recommendation when a parent needs a workplace-style meter rather than a nursery tool.