Measuring Sound Speed/Frequency

[mimipham02]

Hi,
I'm working on a science fair project and I'm thinking about measuring how a sound wave's frequency is different in the three states of matter.
Yet, I don't know how to measure the sound wave frequency.
I know that the unit of measurement for frequency is the Hertz, but the only device I found for measuring frequency was the multimeter, but that measures ELECTRICAL wave frequency.

Does anyone know what I can use to measure the wave frequency?
I have a last result of using a decibel meter, which measures the sound intensity/amplitude, but I prefer to measure the sound speed.

Please send any suggestions. Anything will help!
Michelle Pham

[norman40]

Hello mimipham02,

Sound wave frequencies can be measured with a frequency counter or with a spectrum analyzer. These devices work by using a microphone to convert the sound wave into an electrical signal. The peaks and valleys of wave are counted to find the frequency.

There are inexpensive smartphone apps designed for measuring sound frequencies. A quick search online search showed several available frequency counters and spectrum analyzers. One of these apps will probably work fine for your project.

You might want to use a tone generator to produce the sound waves that you measure. There are smartphone apps available that generate a selected audio frequency tone.

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman

[mimipham02]

Thank you so much, A. Norman!

I actually found a free Audio Frequency Counter in the Google Play store.
I was also looking around and found a few experiments similar to mine, so I found a free computer application for MacBook, called Audacity, which allows you to analyze sound waves.
I will probably be using both to ensure accuracy in my experiment.

Additionally, I may invest in a tuning fork, since they are quite inexpensive, or borrow one from my band teacher. They are usually labeled with the amount of Hertz they create. This way, I can test how accurate Audacity and the phone app are compared to the tuning fork.

Once again, thanks.
I will definitely come back if I need anymore help!

[mimipham02]

Dear A. Norman,

I actually have come up with another problem in my researching so far.
It would be extremely difficult to perform this experiment (how does a substance in its three states of matter affect sound frequency) or set it up.
Do you have any ideas on how I could set up and perform this experiment?

Additionally, I am not sure of what pure substance to use that is easily attainable in solid, liquid, and gas form.
It would be possible to use water, but in my researching, I noticed that unlike most substances, water's liquid form is denser than water's solid form. This may negatively affect my results.
Are there any easily attainable pure substances that I could use for this? Otherwise, I could stick with water.

One of my set-up ideas if I were to use water would be to put about 300 mL of water in three Ziploc bags, and put one in the freezer to make it solid, and one in the sun so it evaporates and becomes water vapor.
Yet, I'm worried that some of the plastic may melt in the sun and mix with the water vapor and become a hazard or an unknown variable with unknown outcomes on the experiment.

I'm sorry that I've had so many questions on this experiment. You've been a big help!
Thanks again, Michelle

[norman40]

Hello mimipham02,

I think that assuring that you are measuring the frequency of waves that have traveled through your media might be an issue. Because sound travels from its source in all directions, if you place a container of water between the sound source and measuring device, you would not know whether the measured frequency was from a wave that went through the water or around the water.

You might try enclosing your sound generator in a box with some sound insulation inside. The box would need a window cut out on one side. Tape a plastic bag filled with water over the window. Put the sound generator inside the box. Measure the frequency outside the box and near the water-filled plastic bag. This set-up might increase the level of sound passing through the water. By the way, you might want to measure sound level in addition to frequency. I’m sure the sound level will change but I’m not so sure that the frequency will.

My suggestion is to use water for your substance. You are correct that liquid water is more dense than ice. But the elasticity of a material also influences sound propagation, and ice is less elastic than water.

You idea of using the same volume of water to make the solid, liquid and gas samples does standardize on the amount of water. I think it would be OK to use 300 ml of water and 300 ml of ice. But the volume of vapor from 300 ml of liquid water would be huge! One easy way to make a water vapor sample would be to breathe into a plastic bag – exhaled air has a relative humidity of 100%.

I hope this helps. Please post again if you have more questions.

A. Norman

[mimipham02]

Hello,
Thank you so much for all of your help and suggestions. I will make sure to keep all of your ideas in consideration. If I happen to encounter any other problems, I will definitely hit you up!

Thanks again,
Michelle

[mimipham02]

Hello again,
As a re-cap, I came up with a project idea of testing how the media of the sound wave affects the frequency/speed of the sound.
I was planning on using a sound frequency counter to measure the hertz of a sound wave after it traveled through water as a solid, liquid, and gas.
Yet, I planned a test trial and had my phone emit a 440 Hz sound. The frequency meter only measured the sound as about 10 Hz. Therefore, it was not accurate and I had to move to another option.

Then, I downloaded the audio spectrum analyzer application "Audacity" to my Macbook. Yet, I using my phone, I emmited several sounds with different frequencies. I looked at the spectrum graphs of the sound waves and compared them, but I couldn't notice any big consistent differences.

Do you know any other way I can perform my experiment? I cannot find any other frequency meters that are easy to access... Are there any other devices that measure the speed/frequency of sound?
Thanks, M. Pham

[norman40]

Hi Michelle,

Your measurement of 10 Hz for your 440 Hz input tone is so far off that it may suggest some other problem. And you may be able to use the frequency counter if that issue is resolved.

What kind of sound frequency counter did you use to measure your 440 Hz tone? What kind of microphone is connected to the frequency counter? Can you hear the 440 Hz tone from your phone?

I’m not familiar with “Audacity” but I did read a little about the spectrum analyzer capability in the online manual for the software. There’s a sample sound spectrum and other information about this function here:

http://manual.audacityteam.org/o/man/plot_spectrum.html

I think you should be able to record tones of various frequencies using your computer’s built-in microphone and use the “Anaylze>Plot Spectrum” commands to make charts like the one shown at the above link.

You mentioned that you tried testing sounds of different frequencies. Did you try a 440 Hz tone? If so you should see a peak in the spectrum centered at about 440 Hz. The same experiment with a 500 Hz tone should give a spectrum that looks the same as the one for 440 Hz, but with the peak centered at about 500 Hz. If you’re not able to see the frequency change with different tones from your phone, you might want to try another tone generator. The Audacity manual mentions a tone generator so you might be able to use it.

I hope this helps. Please post again if you have more questions.

A. Norman

[mimipham02]

Thank you, your previous response has greatly helped.
I finished my experimentation, and have come to my analysis and conclusion.
Now that I realize it, do you know any way that my experiment is impactful toward the real world?
Most of the connections I made were indirect and vague...
(As a recap, my experiment was the effects of a medium's state of matter on sound's velocity)
Please help ASAP!

[norman40]

Hi Michelle,

You’re welcome and I’m glad to hear that your experiment went well.

I’m drawing a blank on a technological application of sound speed differentials due to the medium. Some applications of sound wave interactions with different materials that might be somewhat related to your experiments include SONAR, ultrasound imaging and acoustic attenuation.

I hope this helps. Please post again if you have more questions.

A. Norman