Can sound kill you?
We all know that some sounds can be annoying.
And sometimes sound can be painfully loud.
But could sound ever be so dangerous that it could
kill you instantly, on the spot.
Well, we are about to see just how powerful sound
can be, so powerful that it can levitate objects.
And yes, we are going to uncover the most dangerous
sound on Earth ever.
But first, what do we actually mean by dangerous
sound, and how loud is too loud?
We can measure the level of a sound in units called
decibels. And basically the bigger this decibel
reading, the more dangerous the sound is likely to be.
And so I have here a decibel meter.
And as you can see, it's measuring the decibels as
I speak. Now at home, you can do the same and you
can just use a free decibel meter on your phone.
And when it comes to decibels, any noise above 70
decibels for a prolonged period may start to damage
your hearing.
And any noise above 120 can instantly damage your ears.
And with that known, let the hunt begin for
the most dangerous noise in our homes.
What could it be?
Are you fan of Worcester sauce?
Okay, so the most dangerous noise in your home is
most probably you followed by a hair dryer.
But these sounds are only dangerous over a prolonged
period. So unless you're sat there with someone
screaming in one ear and a hair dryer in the other
all day long, your home is going to be relatively safe.
To find the real dangerous sounds, we have to
head outside.
We start our journey at 120 decibels where you're
likely to start feeling the pain and ringing in
your ears.
Swiftly moving on to 140 decibels.
Even short exposure at this level begins to cause
permanent ear damage.
Increasing the level even further,
it becomes hard to swallow and you
experience sensations of being underwater.
And then we reach a whopping 170 decibels where
permanent hearing loss is likely.
So you get the picture. Sounds can be dangerous.
And obviously the longer you spend around those
sounds, the more damage they can cause.
But the question that we all want to know the
answer to is, How many decibels does it take to kill
you? And is that even possible?
Well, the general consensus is that anything above
185 decibels could be enough to kill us.
A sound at that level could be so powerful that the
pressure from the sound wave alone could fatally
damage our organs.
Pretty grim!
But hang on.
How can sound, so something that you can't even
touch be so powerful that it can cause that type of
damage? I think we need to understand sound a
little bit better. Now, you might think that sound
is just something that you hear or something that
makes a noise.
But at its heart, sound is a series of vibrations.
Think of an annoying morning alarm.
That alarm has a bell,
the bell is vibrating. As it vibrates,
it causes the particles of air around it to
vibrate, too.
Then those particles run into the air particles
next to them, and so on and so on.
As a result, the air molecules end up moving
backwards and forwards as the sound travels along
until it reaches your eardrum.
Now, all sounds, even the quietest of whispers,
have these vibrations.
They have power, and you can use this power to do
unexpected things.
Which brings me here to the Multi-Sensory Devices
Group in the Computer Science Department at UCL,
where I have Professor Sriram, who has worked on
acoustic levitation for the past 12 years.
And here we have...What is it?
A phased array transducer.
Otherwise known as an acoustic levitator.
So, Professor Sriram, talk me through it.
What have we got here?
So what we have here is 256 speakers at the bottom,
another 256 speakers on the top.
And when we turn them all on, we can create a
pattern of sound on which we can levitate an object.
Can we give it a go?
Absolutely. So I'm going to just put this
polystyrene bead over here.
So it's a little tiny bead. When we put it there and
we can turn the system on.
We can float this particle.
That's incredible.
And there's nothing around it that is just being
held there by sound.
Yeah, yes. So you can move your hand around.
You can see there's nothing there.
But I suppose...I don't know, can we see the
sound at all?
We can try. So when we put dry ice here, you can
see the pattern of how the sounds are coming
together to create that focal point there.
We have 512 different waves that are coming
together and then they are making a pattern over
there.
They're colliding in lots of different ways, and
then that makes a whole different pattern.
And then you use that pattern of sound to levitate
the ball.
Yes, but you make it sound very slow.
The thing is, we can do that 40,000 times a second.
And as you can see now, what's going to happen is
as soon as we go at that speed, you don't see the
particle, you just see the whole pattern.
So that's the persistence of vision and that's a 3D
display.
I'm excited to ask this, but can we do anything
else?
We can do some fun things here.
Yeah. So what we've shown you is just simple, basic
things. So I think actions speak louder than words.
Let's see.
That is awesome!
That is the power of sound
holding that in the air.
So not only was that absolutely incredible, it did
show us just how powerful sound can be.
So I was wondering how powerful could sound get.
You know, what if we just kept on increasing the
decibel level?
Well, here's the thing.
When you reach 194 decibels, something absolutely
awesome happens.
Sound starts to become so powerful that it stops
being a sound wave and instead becomes a shock wave.
It travels faster than the speed of sound itself.
It bunches up.
It's like loads of noise hitting you all in one go.
And that is powerful.
But has it ever happened here on Earth?
Well, yes, because in 1883, on the Indonesian
island of Krakatoa, a volcanic eruption is
estimated to have reached the highest ever level of
decibel reading.
Now, this eruption was absolutely devastating.
It destroyed two-thirds of the island, causing
tsunami waves 46 metres high.
100 miles away the sound level was still 172 decibels.
Now, that is loud.
It's enough to permanently damage your hearing and
even cause death.
It could even be heard in Australia, which is 3100
miles away. And even there it sounded like a
cannonball going off.
So can sound kill you?
Well, unfortunately, yes, but that's not the whole
of the story. We've seen how scientists are using
their knowledge of sound to come up with
applications that we never thought possible.
The fact that you can use sound and acoustic
levitation as invisible tweezers.
And when it comes to other applications such as
levitation.
Yes. At the moment they can levitate small balls.
But in theory, human levitation is also one day
possible. So you never know.
It might happen soon.
And if it did, Would you give it a go?