Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Hannah LS on 22/11/2018 12:26:37
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Eric asks:
Recently I used an online frequency tone generator and I tested my hearing range. I was surprised to find out that I can hear as low as 4Hz and over 20,154Hz. Is this normal?
What do you think?
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When I was young I could hear 20kHZ now at near 90 I have a job to hear 3kHZ.
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Recently I used an online frequency tone generator and I tested my hearing range. I was surprised to find out that I can hear as low as 4Hz and over 20,154Hz. Is this normal?
Online you could be getting a distorted sound which includes harmonics (https://en.wikipedia.org/wiki/Harmonic) & sub-harmonics (https://en.wikipedia.org/wiki/Undertone_series),
e.g. you could actually be hearing some multiple of "4Hz", like 40Hz , and half of "20,154Hz" , (10,077Hz).
Intermodulation (https://en.wikipedia.org/wiki/Intermodulation) is another possible explanation: some computer sound-cards produce artifact-tones which are audible, one of those tones mixed with an inaudible sound could generate a new audible sounds.
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I would be shocked if you had a loudspeaker that can produce 4Hz in any meaningful way.
20.2 KHz is possible if you are young and haven't spent much time listening to loud stuff.
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I would be shocked if you had a loudspeaker that can produce 4Hz in any meaningful way.
The 1974 film Earthquake had an enhanced soundtrack that extended down to 17Hz, and was played during the earthquake scenes.
To reproduce this frequency range, the cinema installed large loudspeaker boxes containing 18 inch loudspeakers. In many cinemas, they needed to remove a row of seats to fit in the loudspeaker boxes.
These low frequencies are felt, rather than heard.
To add to the drama, in some old cinemas, the sound effects reportedly loosened plaster from the ceiling, adding some early "3D" effects.
See: https://en.wikipedia.org/wiki/Sensurround
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Getting air to move at 4 Hz is no problem, but it is unlikely that anyone senses this as "sound" rather than aural discomfort at very high pressures. Perception changes around 15 Hz, below which we feel movement and above which we interpret as sound. The ability to discriminate between tones diminishes with decreasing frequency (which is why I can get away with some very amateur playing on the double bass, accompanying a very professional flautist).
Upper frequency limit is usually stated as 20 kHz but 22 kHz is not unusual in young people.
An online tone generator can be very accurate but what comes out of your loudspeaker or headphone, outside of the range 50 - 8000 Hz, depends more on the transducer and its coupling to your ears than on the input frequency.
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Getting air to move at 4 Hz is no problem,
Really?
Why do so few loudspeakers reproduce sound below about 50 Hz properly then?
Can you show me a loudspeaker that's got a flat frequency response (say +/- 5dB ) down to 20Hz and costs less than a new car?
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Flat? No. But if you pulse a bass cabinet very slowly, you can see the cone move at the fundamental frequency. Problem is that the coupling to ambient is inefficient below 20 Hz and you will get lots of cabinet and cone resonances even with a pure sine wave drive, so the amount of power delivered at 4 Hz will be a lot less than the input.
If you imagine a rigid piston moving in a cylinder you can obviously generate very low frequency pressure waves with negligible loss, but rigid means heavy and you will get a lot of hysteresis loss at high frequencies, so it isn't a practical audio source.
By breathing in and out, I can get air to move at 0.2Hz. I have done so since birth.
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Why do so few loudspeakers reproduce sound below about 50 Hz properly then?
In an audio magazine, I regularly saw oscilloscope traces of the performance of loudspeakers at 50Hz - and many of them were visibly distorted.
There was one unit whose trace looked like a perfect sinewave - but the Total Harmonic Distortion was shown as something like 98%! It was almost totally 3rd harmonic...
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Flat? No. But if you pulse a bass cabinet very slowly, you can see the cone move at the fundamental frequency. Problem is that the coupling to ambient is inefficient below 20 Hz and you will get lots of cabinet and cone resonances even with a pure sine wave drive, so the amount of power delivered at 4 Hz will be a lot less than the input.
If you imagine a rigid piston moving in a cylinder you can obviously generate very low frequency pressure waves with negligible loss, but rigid means heavy and you will get a lot of hysteresis loss at high frequencies, so it isn't a practical audio source.
By breathing in and out, I can get air to move at 0.2Hz. I have done so since birth.
All those words, and still there are no loudspeakers that will actually deliver 4Hz well enough for the OP to be sure of hs measurement.
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Agreed, which is why I said
......it is unlikely that anyone senses this as "sound"......
...........what comes out of your loudspeaker or headphone, outside of the range 50 - 8000 Hz, depends more on the transducer and its coupling to your ears than on the input frequency..........
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I strongly suspect that what the OP heard was the speaker diaphragm rattling when it hit the ends of its travel, together with other distortions + harmonics.
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The normal range which humans and hear is 20Hz to 20Khz.