# Q & A: Sound Waves vs. Light Waves

Q:
i heard this from a friend, color has sound. from what i think i understand ,if matter is condensed vibration and pigments have different weights ,the intensity of vibration in each pigment would cause a certain tone . i need clarification thanks.
- matt (age 22)
hudson valley c.c., albany
A:

Matt -
The key background to this question is the nature of sound waves and light waves. You’re right in that sound waves are a vibration traveling through an object, including "condensed" things like solids and liquids. In solids, those waves can consist of either alternating compressed and stretched regions, or regions wiggling sideways, compared to the direction the wave is traveling. Light is a wave of oscillating electric and magnetic fields perpendicular to the direction it’s going. Light can travel fine through a vacuum, which can have fields in it, but there can’t be sound in a vacuum
because there’s no stuff there to oscillate.

Audible sound has frequencies that cover a very big range, from about 20 Hz to 20,000 Hz, meaning that the pressure at your ear oscillates back and forth 20 to 20,000 times per second. Each frequency gives a different audible pitch. Visible light has frequencies from around 4*10^14 Hz to around 8*10^14 Hz. Each frequency gives a slightly different visible color. Not only are the light frequencies much higher, but the highest one is only about twice the lowest one. The sound frequencies are much lower, and the highest one is a thousand times higher than the lowest one. So you can see that there’s no direct match between the sound and light oscillations.

If you are wondering what effect the pigments (light absorbers) in a material have on the type of sounds that come from it, the answer is usually: not much. There’s not much connection between the frequencies of light some pigment absorbs and the frequencies of audible sound it might absorb or emit. The color of a  pigment also is really unconnected with the density or rigidity of the molecules, which affect how sound travels. Lots of different common pigments are organic compounds with densities not too far from 1 gram/cm^3, yet these provide a whole array of different colors.

On a different note. Musicians often refer to sound as having color. This refers to a different concept than the color that pigments give. When you overlap various pure tones of sound, the overall effect sounds different but has the same fundamental tone. For example, a trumpet sounds vastly different than a flute even if both are playing the same note. The difference (or color) comes from higher frequencies (called harmonics) that the instrument adds to the fundamental tone.

(published on 10/22/2007)

## Follow-Up #1: sound and color

Q:
Hello! I respectfully disagree and propose the following hypothesis... If you measure the frequency of Middle-A, you will hear sound at 220 Hz. Hearing the A one octave up, will yield a frequency of double the previous octave, therefore 440 Hz. So we can safely say that you get the entire range of an octave between X and 2X where the X equals the frequency. Now let's look at the lowest frequency of light in the so-called visible spectrum (~400 THz), which is a deep, dark red. Compared to the highest frequency of light in the visible spectrum (~800 THz), which borders on Ultra-Violet, we see another X to 2X range! I propose that in this manner, any music can be represented in colour and I suspect that this is how musical cervants are able to "see music in colour". This includes people who claim to sing a particular note accurately on demand without hearing a note of reference beforehand. Regards, Heliac
- Anonymous
A:
You've taken one particular audible octave and showed that there's a simple mathematical map between it and the visible frequency range.  How do you represent the other 9 octaves or so that we can hear?

Here's another question: are there any studies of any kind showing that the mental sense associating sounds and color actually fits the particular map you've mentioned?

Mike W.

(published on 08/31/2009)

## Follow-Up #2: sound vs. light

Q:
It is true that sound and light are alike only to the extent that they are both waves. They are inherently different on the basis that light is electromagnetic radiation. It requires no medium and can therefore can propagate through both extremely sparse - space, upper atmosphere - and extremely dense - plastics, water - environments. Sound however, requires sufficient medium. It is required to have the interaction of molecules of the medium with other molecules of the medium. This is why, upon interrupting the medium with dense objects like foam, the interaction of molecules on one side of the interrupter can not transfer to those on the other side of the interrupter and can even be absorbed by the interrupter. One might say that light can be blocked as well, and they would be right. A leaf of an oak tree does absorb light and reflect light. Forests are darker than standing on a rooftop on a cloudless day. But the propagation of sound being in a medium of air, means that it relies on its own medium to transmit its propagation to somewhere else. Because light does not have a medium, it can transmit through objects in a way that sound cannot. SOUND REQUIRES MEDIUM.
- Wilson (age 19)
Charlotte, NC
A:
What you say is true.

Mike W.

(published on 01/24/2011)

## Follow-Up #3: hearing Tesla resonators

Q:
Okay, so we know sound requires a medium and light does not. Forget that for a moment and consider the following: Tesla resonators for example. It emits electromagnetic energy of its resonant frequency usually in the high RF spectrum. What if the resonant frequency was, say, 500Hz. Would you HEAR it when it resonates? What if the resonant frequency was 4*10^6Hz? Would it emit color since after all light is electromagnetic energy and the resonator is emitting that EM energy at a visible frequency?
- Harrison (age 22)
Bloomfield, MI, US
A:

If I understand right, a Tesla resonator is a type of electromagnetic waveguide. Although you would not directly hear the electromagnetic wave, you might hear some ordinary sound waves created by stresses and strains in the resonator as the EM wave traveled through it. If the EM wave was at 500 Hz, the lowest frequency sound would be at 1000 Hz, since the stress from the EM fields is the same if you flip their direction. To get 500 Hz sound out you'd need to drive some sort of element other than the Tesla resonator. Any sort of loudspeaker would do.

4*106 Hz is far below the visible frequency range. If you do make a waveguide for visible light, say with fiber optics, you can of course see the light that comes out. I don't see a good way to make that sort of waveguide with Tesla resonator, especially when there are such better alternatives.

Mike W.

(published on 06/08/2013)

## Follow-Up #4: synesthesia

Q:
In response to the comment that one can see colour when hearing a sound. this could be a neurological phenomenon known as synesthesia. I have this condition. It is when the senses get crossed, where stimulating one sense can involuntarily activate another sense.
- Laura (age 38)
Atlanta, GA USA
A:

Thanks!

Mike W.

(published on 02/08/2016)