# Why can't we see sound waves?

## Main Question or Discussion Point

Why can't we see sound waves?

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phinds
Gold Member
2019 Award
why would you EXPECT to be able to see sound waves ???

jbriggs444
Homework Helper
2019 Award
Why can't we see sound waves?
We can, to the extent that dense air refracts light. This is visible in the shock waves resulting from exploding bombs.

Low volume sound waves in air move fast, don't refract much and have even less effect when viewed from the direction of either source or receiver, so you cannot expect to see the sound of your own voice with your own naked eyes.

We can, to the extent that dense air refracts light. This is visible in the shock waves resulting from exploding bombs.

Low volume sound waves in air move fast, don't refract much and have even less effect when viewed from the direction of either source or receiver, so you cannot expect to see the sound of your own voice with your own naked eyes.
The short answer is you can, but the sound has to be very loud.

Gold Member
Google "schlieren" and you can see even some minute sound waves. If the waves are powerful enough to cause large density gradients we can see them through the light they refract. Slightly weaken and we can use schlieren or shadowgraph techniques to see them.

In a sense we can see sound, we just call it "hearing".

Or do you also wonder why we can't hear light?

phinds had it right though. There is no reason to assume we can.

phinds had it right though. There is no reason to assume we can.
Yes there is. Sound waves are density waves, and the index of refraction of air changes with density, so you should be able to see the wavefront as an interface between two regions of different density, which you can, if the amplitude is high enough, or if you use the methods boneh3ad posted.

phinds
Gold Member
2019 Award
Yes there is. Sound waves are density waves, and the index of refraction of air changes with density, so you should be able to see the wavefront as an interface between two regions of different density, which you can, if the amplitude is high enough, or if you use the methods boneh3ad posted.
Yeah, I was just assuming he meant voice-level sound waves. I knew really strong density waves would be visible, as you say.

I don't think anything that would not break your eardrums if you were anywhere near it would be strong enough to see.

Have you ever seen a jet break the barrier for the speed of sound?

But we see that second hand, I assumed the OP meant directly.

OmCheeto
Gold Member
Why can't we see sound waves?
I think it is because air is fairly transparent.

If you could see air, then you would probably be able to see sound waves, of certain magnitudes and frequencies. Kind of like sitting and staring at your audio speakers. You can see the woofers moving, but the tweeters just sit there, and make your ears hurt.

remember that a wave is only "how energy travels" sound waves are more of a slight amount of energy exerted from initial contact, or an after effect of disruption in the air traveling outward.

you disrupt the water by dropping a stone, you see waves.

you disrupt the air by clapping your hands, you hear a wave.

your only going to see sound waves that are large relatively in comparison to yourself

Drakkith
Staff Emeritus
Why can't we see sound waves?
While the above replies make it clear that we can see sound waves in specific circumstances, I feel they don't really answer the question. I would say that we can't see sound waves because our eyes aren't designed to be able to do so. The eye uses a lens that focuses light onto the retina where special cells that are sensitive to light reside. These cells detect the light and send signals to your brain. The end result is sight.

Sound waves do not activate any part of the visual system and so we cannot see sound waves directly, only when light interacts with a sound wave in a certain way. Instead our ears are designed to detect sound waves.

phinds
Gold Member
2019 Award
Have you ever seen a jet break the barrier for the speed of sound?
No, have you? I have HEARD it several times but there has never been anything to see.

ZapperZ
Staff Emeritus