How the numbers are made
Measuring
The phone sits on the centre armrest and records the cabin's A-weighted level and its 1/3-octave spectrum every second, with GPS speed. Only steady driving counts, and every second is set to the centre of its 10 km/h speed band with the usual speed law (about 9 dB per doubling of speed).
Cleaning
Seconds with speech, music, blinkers, door slams or a handled phone are cut before anything is averaged. A drive with more than a quarter of its seconds cut isn't counted.
Phones and microphones
Each shared drive carries the exact calibration it was recorded with, so it can be corrected later when a better calibration for that phone arrives. Drives fall into tiers:
- Reference microphone: a measurement microphone (a UMIK-1, UMIK-2 or similar) with its calibration file.
- Measured phone: a phone measured against a reference microphone or meter.
- Verified default: a phone model whose sensitivity was measured.
- Assumed default: kept, but not counted until enough cars link it to measured phones.
Community calibration
Two things let drives from uncalibrated phones count:
- Calibration packs: drivers who measured their phone against a reference microphone can share that calibration. Once three independent packs for a phone model agree within 1.5 dB, their median becomes that phone's calibration, and its drives count as measured.
- Consensus phone offsets: when the same car models are measured with different phones, the difference between phones shows up. A phone model's offset is published once at least three cars overlap with calibrated phones and the offset is known to within 1 dB; its drives are then corrected by it.
Phone offsets
Positive means the phone reads louder than calibrated phones; drives are corrected by subtracting it. ± is the standard error.
| Phone model | Offset | Cars | Published |
|---|
No phone offsets yet.
Community packs
No community calibration packs yet.
Pooling
A car is one unit: its drives are pooled first, then cars are pooled into a model with a random-effects model, robust to odd drives. Intervals are 95%.
Thresholds
- A model page appears from one car, marked Early days below three cars (1–2 cars).
- Breakdowns by phone, microphone, tyre and wet roads need three cars each. Model years show from one car, marked Early days below three cars, like a model page. Under three cars, a speed band shows its level but not how many seconds or drives it came from.
- Rankings need three cars of a model; class ranges also need five cars in the class.
- Growing means 3–5 cars; Solid means 6 or more cars and a 95% interval of 1.5 dB or less.
"Sounds X% quieter" comes from loudness in sones, which follows how loud a sound seems; the difference in dB is shown alongside.
Privacy
Shared drives contain no location, no timestamps, no audio and no sound labels. Before sending, the phone keeps only steady driving, cuts it into 10–60 second pieces with a second or two missing between them, and shuffles them, which makes a route very hard to rebuild from speed. Speech, music and other cabin sounds are cut on the phone; only whether each second counts is sent. This site shows averages only: a model shared from one or two cars is marked Early days, and its numbers are those cars' averages, kept out of search engines. A model year shown from one or two cars is marked the same way. Any other split (by phone, tyre or wet roads) and every speed band in it needs at least three cars.
Just for fun
Buses, trams, trains, subways, planes, motorcycles, taxi back seats and walks can be shared too, by hand, for the Just for fun page. They're pooled the same way, one person at a time, but kept out of every car number: rankings, averages, classes and open data. A bus ride sends only that it was a bus, never its line or route; a flight or a walk is one level and sends no speeds.
Limits
Roads, tyres, phones and placement differ between drivers, so small differences (under about 1–2 dB) aren't meaningful. Wet roads are kept apart.
Open data
The pooled table is free to reuse under CC BY 4.0: open data.