A yard crew works the lawn next door with a gas backpack blower, a string trimmer and a riding mower. Pick the crew (three workers, one rider who splits into three, or one worker switching tools), shape each machine's sound, move the neighbour closer or shut the window, and follow what the noise, the fuel and the exhaust add up to: for the people at home and for the crew.
Fair warning: the crew is already at work, and your first click turns its sound on, LOUD, the way it really goes. Turn your device volume down before you start. "Weed-whip past the window" sends the trimmer hunting the yard for overgrown patches: it revs, stalls, blares back on, wanders off and comes back. Then tweak the knobs until your world sounds better: battery, distance, the window, the sound lab, or the prairie.
Engine speeds stay within what real machines run at; the mixer only changes the voice of each firing. "Tune the crew to a chord" nudges the three engines to fire at B1, B2 and D♯3, all inside their normal range. For your ears only: the health numbers use the engine physics.
A two-stroke engine fires once per turn, so a blower at 7,500 rpm hums at 125 Hz with a ladder of harmonics above it. That low, buzzing tone carries far and passes through walls and windows better than high hiss, and the rise and fall of the throttle makes it hard to tune out. Battery machines run quieter and lack the low engine tone; their fan whine is higher pitched.
Going clockwise, each key is a fifth higher (7 semitones) and gains one sharp; anticlockwise, one more flat. Neighbours share six of their seven notes, so they sound related. The inner ring is each key's relative minor: the same notes, starting on the sixth.
Press the button, listen to a mystery engine, then click its note on the circle.
Perfect pitch (absolute pitch) is naming a note with no reference. It's rare, roughly 1 in 10,000 people, more common with early music training and among speakers of tonal languages. Relative pitch, hearing the distance between notes, is what most musicians use, and anyone can train it. Scales here are in equal temperament, except maqam Rast, which uses quarter tones (E and B "half-flat", marked with a reversed flat): engines, unlike pianos, can play between the keys.
Press "Listen to my voice", then sing or hum: a dot shows where your voice sits in the triangle and the pitch you're on.
How it works. A voice is a buzz from the vocal folds, shaped by the throat and mouth into resonances called formants. "Aah" has its first two formants high and spread (about 730 and 1,090 Hz in an adult man's voice); "ooo" has both low (about 300 and 870 Hz) with rounded lips; "mmm" closes the mouth and sends the sound through the nose, leaving a low, muffled murmur. Here each corner is its own filter shaping the same buzz, and the handle sets how much of each you hear, so the centre sounds all three at once. Your microphone is analysed in the browser by linear prediction, the method phone codecs use, to find your pitch and formants (Peterson & Barney 1952; Fant 1960).
Sounds that soothe. Some sounds are taken as pleasurable, even healing, and a few of the reasons have been measured. After a stressful task, people recover faster (skin conductance falls sooner) while listening to nature sounds than to traffic noise (Alvarsson et al. 2010). Reciting mantras or the rosary slows breathing to about six breaths a minute, where heart rate and blood pressure rhythms fall into step (Bernardi et al. 2001). Humming raises nitric oxide in the nose about fifteenfold, which helps the sinuses ventilate (Weitzberg & Lundberg 2002). The studies are small and the effects modest, but they point the same way as the rest of this page: the sounds around us reach the body.
Drag the divider on the street above to the left to switch into soundscape mode. The birds there sing songs assembled from parts, the way real songbirds build theirs: single notes, grouped into syllables (a chip, a slur, a whoop), repeated into phrases (a trill is one syllable repeated fast), and strung together by each bird's own rules. Pick a bird, then rebuild its song.
The science underneath. Songbirds learn their songs from adults, so songs have local dialects, and many species keep a repertoire of several song types. Songs are built hierarchically from notes, syllables and phrases, with species-specific rules for their order (Catchpole & Slater 2008). Neighbouring birds often avoid singing over one another, which is what "take turns" models. In noise, birds sing louder (the Lombard effect) and city birds sing higher, lifting their songs above the low rumble of engines (Brumm 2004; Slabbekoorn & Peet 2003). These six birds are fanciful, each loosely inspired by a real singer.
Noise reaches blood pressure by two routes. The fast one: the brain's alarm centres fire the sympathetic nerves, which speed the heart and squeeze the small arteries within seconds. The slow one: the same nerves tell the kidney to release renin, which sets off a hormone chain (angiotensin II, then aldosterone) that keeps squeezing after the noise stops and tells the kidney to hold on to salt and water. Cortisol runs alongside and makes the vessels more responsive to both. Boxes glow with the current minute.
A person at rest, breathing through the same hours, puts out about 25 g of CO₂ an hour: roughly 0.25 L of oxygen in and 0.2 L of CO₂ out each minute. That carbon came from food, so it cycles straight back; the engines' carbon is fossil.
What if the leaves just stayed where they fell? Let 'em rot, a detritivory simulator, is coming soon to the lab.
A fair scientific question: will the neighbour be done in sooner by the stress hormones the noise raises, or by the carbon dioxide-rich air the engines leave behind? First, a yardstick for CO₂, from one breath to the reefs. Then the race.
Your ideas stay in this browser, and the latest one goes along with your anonymous answers if you choose to share them under "Be counted". Hand-tool figures count only the extra breathing of the work; that carbon came from food, so it cycles back.
Low-cook, not raw. If one slice of toast for everyone on Earth is that much CO₂, the kitchen is worth a look too. Skipping the stove entirely isn't the answer: cooking makes some nutrients much easier to absorb (the lycopene in tomatoes, the beta-carotene in carrots, the starch in grains and roots), kills germs, and may be part of how our ancestors got the energy for big brains (Wrangham 2009). But most vegetables need only a little: steam them briefly, cook in one pot with the lid on, and eat plenty fresh, in as many colours as you can find.
Wild edibles close to home, in season and free of fuel: Diospyros virginiana, the American persimmon, sweet only when soft and fully ripe, often after frost; elm samaras (Ulmus), the papery spring seeds, mild and nutty, nibbled raw; dandelion (Taraxacum officinale), leaves for salad and flowers for fritters; purslane (Portulaca oleracea), lemony and rich in omega-3 fats; and, in Texas, pecans (Carya illinoinensis) and prickly-pear fruit (Opuntia). Be sure of what you pick, and never from a lawn or roadside that's been sprayed: one more reason to let the yard grow back.
Coming to the lab: the deep history of eating plants, from what people gathered thousands of years ago (palaeoethnobotany), to the pollen that tells us (palynology), to the animals that eat pollen itself (palynivory: bees, some butterflies and beetles, honey possums), to the pollen-filled coprolites, ancient human faeces, preserved in dry Texas rock shelters. And deeper still, the questions of the Cordaiteans: tiny coprolites in Pennsylvanian coal balls packed with cordaitalean pollen (Florinites), some of the oldest evidence of animals eating pollen, about 300 million years before the first bee.
The blower is only there because of the lawn. Across much of the middle of the continent, the lawn sits where tallgrass prairie or oak savanna grew for about 8,000 years since the ice left. Bison grazed it, fire renewed it, and the nations who lived there burned, hunted and named it.
| Then and now | Size |
|---|---|
| Lawn in the United States | ≈ 160,000 km² (40 million acres), more than any irrigated crop |
| Tallgrass prairie left | under 1–4% of its former area; in Illinois and Iowa about 0.1% |
| Bison before 1800 | tens of millions; estimates run from about 10 to 30 million or more |
| Bison in 1889 | about 1,100 counted |
| Bison today | ≈ 20,000 in conservation herds, plus tribal herds on more than 80 tribes' lands, and many more on ranches |
| Roots | turfgrass ≈ 15 cm; big bluestem 2 m and more; compass plant up to 4 m |
What bison do. They graze grass and leave the flowers, so more kinds of plants share the ground. They roll in wallows that hold rain and grow their own wetland plants. They move on, so the prairie rests. In long-running experiments, bison-grazed and burned prairie holds more plant species than ungrazed prairie.
| Prairie plant | Name in the language of this land |
|---|---|
| Big bluestem, Andropogon gerardii | waiting: ask a tribal language program |
| Little bluestem, Schizachyrium scoparium | waiting |
| Purple coneflower, Echinacea spp. | waiting |
| Compass plant, Silphium laciniatum | waiting |
| Butterfly milkweed, Asclepias tuberosa | waiting |
| Wild bergamot, Monarda fistulosa | waiting |
| Leadplant, Amorpha canescens | waiting |
Why the names are blank. These plants had names long before they had Latin ones, in Lakota, Dakota, Ojibwe, Potawatomi, Ho-Chunk, Myaamia, Pawnee and many more languages, depending on where you stand. Those words belong to the nations that speak them, and many language programs have rules for how they're shared. This column fills in only with a program's permission, and with credit to them.
Starting points. Plant a few native seeds in a strip of lawn. Support tribal bison restoration, such as the InterTribal Buffalo Council, and the language programs of the nations whose land you live on.
Pick who it's to and what you're asking for. The letter fills in from the visit you've set up above; edit anything before you copy it. Nothing is sent from this page.
Opens a short form with no name or email field. It carries over only your stance, this page's settings (distance, window, sensitivity, start time, crew) and which knobs you reached for once the noise came on, in order, so we can see what people tend to try first; you add your region (state, or the first three digits of your ZIP) if you like. "Mow on" counts just as much as "phase out gas". Only totals are ever published, such as "18% said mow on".
A separate mailing list for news when the model, the data or the letters improve, with an opt-in for a free packet of seeds for a native perennial border suited to your region: something to plant along the lawn that never needs a blower. Your email is used only for these updates, and is never linked to your answers in the form on the left. Unsubscribe any time.
More from the lab: Neighborhood Barbecue. One block, two eras: a 1957 cookout and a greener someday where sheep, goats and bison keep the grass. It ends at a Tejano barbecue festival where, today, you can't hear the band for the leaf blowers.
Our promise. The form collects no names, emails or exact locations, and only totals are shared. The mailing list keeps only what it needs to send updates (and, if you ask for seeds, a postal address, deleted once the packet ships). The two are kept apart and never matched.
Sound. Each machine's level is set at 15 m (50 ft), the distance used in ANSI B175.2 blower ratings, and falls 6 dB per doubling of distance. An open window cuts about 10 dB; a closed one about 25 dB at high pitches but only about 15 dB at the engine's low tone. Tonal and pulsing sound gets a penalty of up to 6 dB, as in ISO 1996-1 for tonal and impulsive noise. Levels add by energy, never by simple sum.
Body. Above about 50 dB(A), noise drives the stress response: heart rate rises about 3 beats per minute and systolic pressure about 3 mmHg per 10 dB, scaled by noise sensitivity; a stress index builds over about 15 minutes and fades over about 30. These are round values for illustration, consistent in direction and size with laboratory studies (Basner et al. 2014; Münzel et al. 2014). Long-term rows use the WHO 2018 exposure–response relations for road traffic noise, the best-studied source; leaf blowers, being tonal and intermittent, are probably more annoying than traffic at the same level, so treat these as lower bounds.
Cortisol. Salivary cortisol follows a daily rhythm: about 13 nmol/L on waking, a rise of about 50% over the next 30–45 minutes (the cortisol awakening response), then a slow fall to 2–3 by evening. Noise adds to it through the hypothalamic–pituitary–adrenal (HPA) axis. Release lags the stress index by about 15 minutes, and cortisol clears with a half-life of about an hour, so the peak comes after the noise stops and lingers; the minute-by-minute chart runs 90 minutes past the visit to show it. The size of the rise is illustrative: noise-only studies find small, variable effects (a few nmol/L, larger in noise-sensitive people and with noise at night), far less than a laboratory social-stress test. The concern is repetition: brief daily rises in an otherwise normal rhythm, week after week, and a flattened daily curve, which is linked to poorer health (Selander et al. 2009; Adam et al. 2017).
The riding mower and the crew modes. The riding mower is a four-stroke V-twin: two cylinders each firing every other turn, so at 3,600 rpm it fires 60 times a second, with a half-order rumble, a blade-passing tone near 100 Hz and a deck whoosh. It is set at 71 dB(A) at 15 m (about 95 dB(A) at the rider's ear), burns about 1.8 L of petrol an hour, and makes far less smog per litre than a two-stroke: about 300 car-miles per hour, against 1,100 for the blower (CARB). The crew modes do the same work on different schedules: three workers overlapping; one rider who, for the middle half hour, divides into three so that every machine runs at once (ballet mode); or one worker using one tool at a time (mower-blower mode), which lowers the peaks and stretches the noise out. The sound lab changes only what you hear: every engine speed it offers is within the normal range for that machine.
Fuel and exhaust. Commercial two-stroke backpack blower ≈ 0.7 L of fuel per hour, string trimmer ≈ 0.35 L/h (typical; varies with model and throttle). Petrol releases ≈ 2.35 kg CO₂ per litre. Two-strokes pass roughly a quarter of their fuel through unburned while scavenging, which is why their smog-forming emissions are so high: one hour of the best-selling commercial blower ≈ 1,100 miles of driving a 2017 Camry (CARB). The trimmer figure is scaled from the blower by fuel use and is an estimate. Battery equipment: about 1 kWh per hour of blowing, at ≈ 0.37 kg CO₂ per kWh (US grid average).
Blood pressure system. A small version of the classic whole-body regulation picture (Guyton, Coleman & Granger 1972). Sympathetic drive follows the noise within about a minute and fades over about 4; plasma noradrenaline rises about 25% per unit of drive from about 250 pg/mL. Renin follows the nerves over about 10 minutes and falls with a half-life of about 17. Angiotensin II tracks renin within 2 minutes (it is converted by ACE, mostly in the lungs, and lasts only 1–2 minutes in blood). Aldosterone follows angiotensin II with a 20-minute time constant, plus a little from ACTH. Systolic pressure adds 3 mmHg per unit of nerve drive and 10 mmHg per doubling-equivalent of angiotensin II; cortisol scales both up slightly (its permissive effect). Aldosterone's salt and water retention takes hours to days and is not added. The sizes are illustrative; the order and time scales are textbook. Over years, repeated rises, especially at night, damage the lining of the arteries through oxidative stress, which is the leading explanation for noise-related hypertension (Münzel et al. 2018).
The CO₂ yardstick. One resting breath is about 0.5 L at 4% CO₂, ≈ 0.04 g; a modern adult exhales about 1 kg CO₂ a day. Other species scale by body mass to the ¾ power (Kleiber's law). Foragers spend about as much energy a day as office workers (Pontzer et al. 2012), so there is no bonus for a hard life. Body masses (Proconsul ≈ 25 kg, A. afarensis ≈ 38 kg, H. erectus ≈ 57 kg) and the 30–35-year fossil lifespans are rough, for scale only. The lawn's weekly uptake uses about 120 g C per m² over a 30-week season, inside the 73–173 g measured over an irrigated Denver lawn by eddy covariance. The breath is exhaled carbon from food that plants fixed weeks earlier, so it is carbon-neutral; the blower's is fossil. Local air: one blower-hour of CO₂ mixed into the air over the yard to 10 m. The world's air: about 425 ppm, rising about 2.5 ppm a year (NOAA).