Why a music festival can be heard 15km away

"You could hear the festival 15km away."

I saw that in the news.

Hold on.

15km is a serious distance.

Fifteen kilometres from Tokyo Station in a straight line, and you are in a different town.

Could the "boom, boom" of a live venue really reach that far?

It turns out the answer is interesting.

You can't explain it with "the festival was just loud."

Frequency.

Air.

Distance.

Wind.

Temperature.

Terrain.

Put those together and sound moves in stranger ways than you would expect.

What you'll learn here

• What is actually travelling when sound travels
• How many seconds it takes to reach 15km
• How much distance alone weakens a sound
• Why only the bass reaches the far-away listener
• Why wind and temperature bend the path of sound

It started with a news story about bass reaching 15km

On 12 September 2026, Yomiuri Shimbun Online reported something interesting.

An outdoor music festival, Beriten Live 2026 Special, was held on 5 and 6 September at the Igashira Park sports ground in Moka City, Tochigi Prefecture. On the 6th, 60 noise complaints came in, many of them describing a "booming bass."

And the complaints were not only from around the venue.

They came from the Okamoto district of Utsunomiya and the area around JR Utsunomiya Station. The furthest was reported to be around 15km from the site.

On the previous day, the 5th, there was one complaint.

The organisers say they kept the show under 100dB.

So why did the sound travel so far on the 6th only?

Reports noted a strong wind blowing north-west from the venue that day, and experts suggested that weather conditions, including winds aloft, may have played a part.

This part matters.

Nobody has established that the wind was the cause.

There is no published analysis with frequency-by-frequency measurements at the distant locations, or detailed upper-air data.

So rather than analysing this particular festival as if the answer were settled, I want to ask a different question: what conditions have to line up for sound to reach 15km at all?

News: https://news.livedoor.com/article/detail/32306837/

Event details: https://humpback.jp/contents/1070135/

The same thing happened last year

This isn't the first time.

On 26 and 27 July 2025, Mrs. GREEN APPLE played an outdoor show at a special venue on Yamashita Pier in Yokohama, marking ten years since their debut.

100,000 people over two days.

A big event.

And over those two days, according to Kanagawa Shimbun, roughly 360 emergency calls came in about "loud bass."

Not only from Naka Ward in Yokohama, where the venue was.

Also from Kanagawa Ward and Tsurumi Ward in Yokohama. And from Kawasaki Ward and Saiwai Ward in Kawasaki City.

People more than 10km away reported hearing bass inside their homes.

The organisers later posted an apology on the official site, which also pointed to the wind direction on the day spreading the sound over a wider area than expected.

Moka and Yokohama.

Different places, different scales.

But three things are the same.

• Outdoors
• What travelled was the bass
• The weather that day became part of the story

Which suggests this is less a problem of one particular artist or promoter, and more something that can happen to anyone putting large amounts of sound into the open air.

Reference: https://www.kanaloco.jp/news/social/article-1341551.html

One footnote: a video that spread as "the sound leaking from the Mrs. GREEN APPLE show" turned out to have had its audio edited, according to a fact check. If you want to know how it actually sounded out there, the complaint records and the official statements are better evidence than a viral clip.

Fact check: https://www.factcheckcenter.jp/fact-check/lifestyle/false-mrs-green-apple-noise-video/

So what is actually flying through the air?

Start here.

Something does travel from the speaker to a point 15km away.

That much is true.

But the air that sat in front of the speaker does not fly 15km.

Sound is a change in air pressure.

The speaker cone moves forward.

It pushes the air.

That air pushes the air next to it.

And the air next to that.

And so on.

This "pushed, then back again" pressure change passes along.

Think of it as a game of telephone played by air.

Or the wave in a stadium.

No single spectator runs around the stadium. They stand up and sit down where they are, and yet the wave moves.

Sound is like that. The air particles don't travel 15km. The vibration, the information, is handed from neighbour to neighbour.

How many seconds to travel 15km?

Let's do the arithmetic.

In air at around 20℃, sound travels at roughly 343m/s.

About 343 metres per second.

For 15km: 15,000 ÷ 343 ≒ 43.7.

About 44 seconds.

In reality temperature, wind and the path taken change this a little.

But roughly speaking, the thud you hear 15km away was played at the venue about 44 seconds earlier.

Which is a nice thing to think about.

Normally, sound gets quieter with distance

Sound doesn't keep the same strength forever.

The further you go from the source, the wider the area the sound has spread across.

For an ideal point source, sound expands like a sphere. A bigger sphere has more surface area, so the same energy is spread thinner and thinner.

The shorthand: doubling the distance drops the level by about 6dB.

This basic distance attenuation is explained in Japanese government material too.

100m → 200m: about −6dB.

200m → 400m: about −6dB again.

Ministry of Health, Labour and Welfare: https://www.mhlw.go.jp/content/000893023.pdf

Ministry of the Environment: https://www.env.go.jp/content/900405768.pdf

So how weak is it at 15km?

Let's play with numbers.

Say the sound is 90dB at 100m.

A very simplified world: no ground, no buildings, no wind, no air absorption.

The formula is L(r) = 90 − 20 log10(r ÷ 100).

What surprised me is that the maths never takes the sound to zero at 15km.

Reality adds plenty of other losses, of course.

But on distance alone, sound keeps going, quietly.

Here's the interesting part: pitch changes what survives

The striking word in the complaints is "bass."

Not "I can hear music." Bass.

That is about frequency.

Pitch is measured in hertz (Hz).

63Hz is very low. 125Hz is low. 1,000Hz is considerably higher.

With sound at 343m/s, wavelength is speed ÷ frequency.

63Hz: 343 ÷ 63 ≒ 5.4m.

1,000Hz: about 34cm.

Same "sound," wildly different wave sizes.

Bass fades with distance too, but loses less on the way

This part is easy to get wrong.

People say "bass doesn't attenuate, that's why it travels."

Not quite.

Bass gets weaker with distance like everything else. Japan's Ministry of the Environment states that for a point source, low-frequency sound also drops around 6dB per doubling of distance.

The important bit comes next.

The same ministry explains that for low-frequency sound, the additional losses from ground absorption and air absorption are very small compared with ordinary noise.

So: bass fades with distance.

But over a long journey, the higher frequencies lose more on top of that.

The cymbals, the guitars, the vocals thin out, and what's left standing is boom… boom… boom.

That is why, far away, it isn't "I can hear the songs" but "there's bass coming from somewhere."

Ministry of the Environment on low-frequency sound: https://www.env.go.jp/air/teishuha/yokuwakaru/index.html

Don't buildings stop it?

Also interesting.

Sound diffracts: waves bend around the back of an obstacle.

And long-wavelength bass bends around large obstacles easily.

So "there are houses in the way" or "there is a forest in the way" does not mean a full stop.

Buildings and terrain do weaken sound.

But you cannot block bass the way you block treble.

Which is exactly why low-frequency noise is the hard case in soundproofing.

FHWA on outdoor acoustics: https://www.fhwa.dot.gov/Environment/noise/noise_barriers/design_construction/design/design03.cfm

And then there's the wind

So far: bass survives long distances relatively well.

That alone doesn't explain one complaint on Saturday and sixty on Sunday.

Enter the weather. Wind in particular.

But "the tailwind carried the sound" undersells it.

Something more interesting happens.

Sound bends in mid-air

We imagine sound travelling in straight lines.

It bends.

The same refraction that bends light entering water happens to sound.

The key is that conditions change with height.

Near the ground there is friction from trees, buildings, the ground itself. So wind is often stronger above the ground than at it.

Now imagine sound heading downwind.

Strong tailwind up high. Weaker tailwind near the ground.

That difference tilts how the sound advances relative to the ground.

The result is that the direction of travel is bent. On the downwind side, conditions can arise that bend sound back toward the ground.

The US FHWA explains that wind shear (wind speed changing with height) causes refraction, and that levels downwind can be higher than in still air, while levels upwind are lower.

And the effect tends to grow with distance from the source.

FHWA: https://www.fhwa.dot.gov/ENVIRonment/noise/measurement/handbook.cfm

So it's less "the wind carried it"

Rather than the wind loading sound onto a truck and driving it 15km.

Think of sound that should have escaped upward being bent back down by the state of the air.

That is the better picture.

Which is how you get a spot far away where people ask, "why on earth can we hear this?"

Temperature bends sound too

It gets better.

It isn't only wind. A vertical temperature difference bends sound as well.

At night, the air near the ground cools while the air above stays warmer. That's a temperature inversion.

Under those conditions sound can refract back toward the ground and be heard strongly far away.

During the day, when the ground warms the air below and it is cooler above, sound tends to bend upward instead.

Same place. Same speakers. Same volume.

And still: nothing yesterday, clearly audible today.

I built something you can play with

Somewhere in the research I thought: this would be so much clearer if you could see it.

So I built it.

How far does festival sound travel? (simulator)

Two things to try.

First, distance and frequency.

Switch between 63Hz, 125Hz, 250Hz and 1kHz, then stretch the distance from 100m to 15km and watch how differently each one survives. You can toggle air absorption on and off.

Second, wind and temperature.

Move the upper wind from −10m/s to +10m/s, and the temperature gradient from −2℃/100m to +2℃/100m, and the rays go from travelling straight to being bent back toward the ground.

Hit the inversion preset and you can see sound that escaped upward returning to the ground far away.

It is not a scientific reconstruction of this festival. I don't have the speaker layout, the output per frequency band, the upper-air data from the day, the terrain, or measurements at the distant locations.

It is a model for understanding the mechanism, and nothing more.

"It was under 100dB" doesn't settle it

One last thing, the part that stuck with me.

The organisers said they stayed within their volume limit.

They probably did.

But as we've seen, what a house 15km away experiences is not decided by the level at the venue alone.

The wind that day.

The temperature difference between ground and sky.

The pitch of the sound.

The terrain.

The same volume reaches a different area on a different day.

And the difference is hard to predict in advance.

So "did they respect the volume limit" and "did it reach the neighbours" are two separate questions.

In Moka, and in Yokohama.

It doesn't look like anyone set out to blast the neighbourhood.

But people 10 or 15km away still heard bass inside their homes.

Stop at "it was the weather, nothing to be done" and it happens again next year.

Stop at "the organisers are to blame" and you have only looked at half the cause.

What's needed is probably in between.

Watching the weather on the day and adjusting low-frequency output and speaker aim.

Measuring at a distance, not only at the venue.

Having somewhere for complaints to go, set up in advance.

Unglamorous operational work, in other words.