This week's forum asks you to guess the range of frequencies among certain sounds in your home and at work.
What is a range of frequencies? First, did you read the assigned audio reading in the Reader (pages 99 – 111)? Well, start there. Because it is important learning about how sound is represented by pitches which relate to a number of them vibrating in a second of time that we call frequency and the measurement of those frequencies are in Hertz. So, frequencies are pitches and are measured in Hertz.
The human ear hears from 20 Hertz – 20,000 Hertz (more commonly notated as 20Hz – 20kHz). Consider the following ranges of sound that you may have spoken about throughout your adult life in listening to music but didn’t really know exactly what it meant. Ever hear someone say that their car stereo has a lot of “low end” or “bass”? Well, that’s a range of 20Hz – 150Hz.
The midrange is known to be approximately 151Hz – 6kHz and the high end or treble is 6kHz – 20kHz. Most musical instruments sit squarely in the midrange of all of the tones they emit. That’s because we humans hear the midrange loudest and most clearly. Instruments have lots of overtones in the upper range (high end) too, but the main part of their tone is in the midrange.
A range of frequencies has to do with the fact that every sound contains a group of frequencies from its lowest to its highest frequency. Even a drip of water in a sink has a range of frequencies. It doesn’t have one pitch. Nothing in nature makes one pitch or one frequency. Only a sine wave (which is a very simple sound wave) has one pitch. All other sound is made up of more complex sound waves that contain a range of frequencies. Here is a great place to check out singular frequencies: http://www.phys.unsw.edu.au/jw/hearing.html
TAKE HEED to the instructions about just clicking on the top 1/3 of the chart as those are the loudest levels of each frequencies. Start around -30 at 45Hz and then move up the frequencies horizontally. Do NOT start at 0 which is the top of the chart. That would be the loudest level. (more on that next week).
Now that you’ve heard these frequencies, you can see how any sound you hear contains a range of frequencies, and not this single frequency that you hear. Perhaps aliens have voices that are one frequency. Yikes!
The sound of my voice is a range of about 200Hz – 6kHz. And the 6kHz only occurs when I say the letters “S, P, T, C, D “. The lower midrange of 200Hz occurs when I say words that contains the letters “M, N, K, F, A” etc. So, the letters with sibilance or the sound of an “es” or “ee” have a higher range of frequencies.
THE ASSIGNMENT
I would like for you to make a guess about the range of frequencies of FIVE sounds in your home or at work. They can be anything. It can be your refrigerator humming, your tea-kettle whistling, water running, footsteps, typing on a keyboard, etc. Make the list and then put the range of frequencies you think you hear. It's a guess, I know. Try it.
Here’s how I would like it to look, so here is my SAMPLE list:
1. Closing my kitchen window: 500Hz – 1.5kHz or 500 Hz to 1500 Hz
2. Chewing a carrot: 400Hz – 2kHz
3. The sound of my clock radio: 100Hz – 20kHz (It’s a Bose Wavestation, so it has good sound which is why the range is so wide.)
4. Eggs frying: 6kHz – 8kHz (the sound of “sizzle”)
5. Coughing: 300Hz – 900Hz
Post your list in this week's discussion forum so that we can all see what sounds and frequencies you’re guessing at. (5 points – due Sunday evening.)
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A Non-Guess
by Martha Raup - Sunday, 13 October 2013, 11:39 PM |
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I have no idea what the frequency of common household sounds might be. It's not a concept that resonates with me, so to speak. I did read many of the wonderful Australian articles, but the science is beyond me. The demonstration of timbre made the most sense - how flute, clarinet, bassoon, violin may all play the same note, but they sound different because they contain different harmonics. I understand that decibel is just a ratio, but it seems more real to me because I could visualize it - I downloaded an app for the iPhone called Decibel 10th, and used it to record different events. My HP computer registered 49 decibels, the printer 58, and the jazz at the restaurant hit 91. But what is the relation with frequency?  Anyway, I made a chart of everyone's response, which shows that most of the sounds we estimated were in the mid-range. I was surprised to find out how much of the low frequencies I couldn't hear, and surprised that different frequencies sounded louder or softer than others of the same intensity. SO - I hope I can still get credit for this contribution, even though I didn't exactly answer the question!  |
