The speed of sound in air at sea level is about 343 metres per second. That's roughly 1,235 km/h. It's fast by human standards but slow enough that you can watch a firework explode and count the seconds before the bang arrives. Light travels about 874,000 times faster, which is why lightning and thunder are separate events.
Now multiply sound's speed by ten. 3,430 metres per second. About 12,350 km/h. Sound now travels at roughly Mach 10, which is faster than any aircraft ever built except experimental hypersonic vehicles.
The physics of daily life changes in ways you wouldn't expect.
Thunder and lightning reunite
At the current speed of sound, thunder from a lightning strike one kilometre away takes about three seconds to reach you. At ten times the speed, it takes 0.3 seconds. From three kilometres away, under a second. From ten kilometres, about three seconds.
For any storm within a few kilometres, the flash and the crack arrive together. Lightning becomes what it looks like it should be: a simultaneous event. You see the bolt and hear the explosion in the same instant. The old trick of counting seconds between flash and bang to estimate distance stops working for anything nearby. You'd need a stopwatch to measure the fraction-of-a-second delays.
Distant storms would still have a slight delay, but the dramatic roll of thunder, that long rumble that builds and fades, changes character. Thunder rumbles because sound from different parts of the lightning bolt arrives at different times (the top of the bolt is further away than the bottom). At ten times the speed, those arrival-time differences compress. Thunder becomes shorter, sharper. More like a gunshot than a growl.
Echoes mostly disappear
Stand in a canyon and shout. You hear the echo because sound takes time to travel to the far wall and bounce back. If the wall is 170 metres away, the echo arrives about one second later at normal speed. Your brain registers it as a distinct repetition.
At ten times the speed, the same echo arrives in 0.1 seconds. The human auditory system can't distinguish an echo from the original sound if the delay is shorter than about 50 to 80 milliseconds (depending on the type of sound and the listener). At 0.1 seconds you're right on the boundary. For most practical distances, echoes merge with the original sound. They become reverb rather than repetition.
The Grand Canyon stops echoing. Cathedrals lose their acoustics. The specific resonance of a stone church, that lingering halo of sound after an organ note, compresses into something much drier and tighter. Buildings designed over centuries for their sound properties would need to be ten times larger to produce the same acoustic effect.
Music sounds the same everywhere in a room
At a concert, if you're sitting 30 metres from the stage, sound currently takes about 87 milliseconds to reach you. Someone in the front row at 3 metres hears it in about 9 milliseconds. That 78-millisecond difference is perceptible. It's why live music sounds slightly different from different seats, and why mixing engineers obsess over speaker placement and delay towers in large venues.
At ten times the speed, the same 30-metre distance produces an 8.7-millisecond delay. Front row to back row becomes less than 8 milliseconds of difference. That's below the threshold of human perception for timing differences. Everyone in the venue hears every note at what their brain perceives as the same instant.
This would actually be extraordinary for live performance. The reason recordings often sound more polished than live music isn't just studio engineering. It's that in a recording, every element arrives at your ears simultaneously. In a live room, arrival times vary by seat position. Remove that variation and live music gains the precision of recorded music, everywhere in the hall.
The flip side: acoustic design becomes less important. The careful shaping of concert halls, the angled walls, the diffusing panels, the calculated reverberation times, all of this is engineering around the limitations of a slow-moving medium. Speed sound up and you can hold a concert in a car park and it sounds nearly as good as the Royal Albert Hall. Acousticians would need new careers.
Sonic booms become gentle
A sonic boom occurs when an object moves faster than sound. The sound waves pile up into a shock front, a cone of compressed air that reaches the ground as a sharp pressure spike. Concorde produced booms that rattled windows across southern England, which was one of the reasons it was restricted to overwater supersonic flight.
If sound travels at Mach 10 equivalent, an aircraft would need to exceed 12,350 km/h to break the sound barrier. No commercial aircraft comes close. Even military fast jets top out around Mach 2 to 2.5 at current sound speeds, which translates to about 2,500 to 3,000 km/h. At the new sound speed, those jets are travelling at roughly Mach 0.2 to 0.25. Firmly subsonic. No boom.
Bullets, which currently travel at supersonic speeds (a 9mm round moves at about 370 m/s, just above Mach 1), would now be deeply subsonic. That characteristic crack of a bullet passing overhead disappears. Gunshots sound different too. The report is still loud, but the supersonic snap of the projectile is gone.
Formula 1 cars at top speed (around 370 km/h) are travelling at Mach 0.03 in this new world. They're not even fast by acoustic standards. The sound they produce would behave identically to how it does now, but with less Doppler shift as they pass (because the ratio of car speed to sound speed is much smaller). The characteristic rise-and-fall pitch change as a car zooms past would be far less dramatic.
Talking feels different
This is subtle but interesting. When you speak, you hear your own voice through two paths: bone conduction (vibrations through your skull) and air conduction (sound leaving your mouth, bouncing off surfaces, and entering your ears). The slight delay of the air path compared to the bone path contributes to how your voice sounds to you.
At ten times the speed, the air conduction path becomes nearly instant. In small rooms, the reflected sound arrives so quickly that it effectively merges with the bone-conducted sound. Your voice would sound slightly different to you. Possibly a bit more natural, closer to what other people hear, because the two paths are more synchronised.
Conversations across distances work better, too. Currently, if someone is 100 metres away and shouts, it takes about 0.3 seconds for their voice to arrive. You see their mouth move before you hear the words. At ten times the speed, the delay drops to 0.03 seconds. Lip-sync across a football pitch.
The unexpected casualties
Radar and sonar both rely on the speed of their respective waves. Sonar uses sound, usually underwater where it already travels faster (about 1,500 m/s in seawater). Multiply by ten and underwater sonar becomes incredibly fast but also far harder to calibrate for distance, because tiny timing differences correspond to large distances. Submarine warfare would need entirely new equipment.
Bats navigating by echolocation would lose resolution. Echolocation works by emitting a click and timing the return. A lesser horseshoe bat can detect objects a few millimetres in size by processing timing differences of microseconds. Speed sound up by a factor of ten and those timing differences shrink below what their neural circuitry can resolve. Bats go functionally blind. They'd need to evolve higher-frequency calls or more sensitive timing to compensate, and evolution doesn't work on human timescales.
Musical instruments designed for resonance at specific wavelengths would produce different harmonics. A guitar string's pitch depends on its length, tension, and mass, not on the speed of sound, so the fundamental pitch stays the same. But the way the sound resonates in the guitar body, which depends on the relationship between wavelength and cavity size, would shift. Instruments would need to be redesigned. A Stradivarius, worth millions precisely because of its acoustic properties, would sound like a plywood box.
That alone might be reason enough to leave the speed of sound where it is.