# Frequency Range ( 5Hz vs. 15Hz)

Discussion in 'Sound Science' started by unpimpauto, Feb 27, 2013.

1. Quote:

Right, it doesn't matter. One does hardly hear anything below 20 Hz, but the harmonic distortion in the audible range. People are often confused between hearing a real 20 Hz sine wave, and hearing something when a 20 Hz sine wave is fed into the system. The "something" is often 40 Hz or any higher harmonic generated by mechanical imperfections.

If you want test signals to check these frequencies, have a look here : http://www.audiocheck.net/testtones_subwooferharmonicdistortion.php

2. Quote:

I digress. One can hear 20 Hz and below is they try hard enough and the volume is turned up on headphones with very low sub-bass extension like the Sennheiser HD 280 Pro.

I definitely can't count the vibrations in a 40 Hz signal, but I can do it with the 20 Hz's fundamental.

3. Quote:
Wait, what? You can count to 20 in a second?

The thing is, hearing threshold at 1 kHz is roughly 0 dB SPL. The noise floor in your room is probably 30 dB SPL, so you can imagine how faint 0 dB SPL is.
At 20 Hz this hearing threshold is about 80 dB SPL. So let's add 20 dB so you can hear (or feel) the tone properly. New we're at 100 dB SPL and the tone is still very faint. At this SPL the HD280 pro approaches 10% THD+N.

And if you hear anything but an extremely deep rumble the driver is probably clipping, producing all kinds of audible noises.

4. Quote:

Nicely wrapped up!

5. Why not? This guy can play Flight of the Bumblebee at 600 BPM. That's 10 beats per second, or 40 notes per second. It's not very clean at top tempo, but 20 notes a second would be a cakewalk to him.

I never said it was an accurate signal, but it's definitely 20 Hz.

6. Playing something at high BPM is a bit different than counting cycles of a sine wave. But lets say I grant you that, it's still not a clean 20 Hz sine wave but 20 Hz + 40 Hz + 60 Hz ... with the harmonics as high as -20 dB. How can you say you're hearing the 20 Hz tone when you're actually hearing a distorted tone?

7. I never claimed I was hearing a PURE 20 Hz tone, I just claimed I can hear the 20 Hz fundamental and then sit there and count the number of pulses per second.

So as an example, I play viola, I can definitely hear A on my instrument (440 Hz), even though with bowed string instruments the 2nd harmonic content and 3rd harmonic are often even larger than the fundamental.

Here's some FFTs (about the harmonic content) if you don't believe me:

http://www.maestronet.com/forum/index.php?/topic/319868-messing-with-fft-now-that-i-have-a-violin/

8. Quote:
But the hearing threshold for a 440 Hz tone is not considerably higher than that of its harmonics... it is for a 20 Hz tone however.

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Citation needed?

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http://en.wikipedia.org/wiki/Equal-loudness_contour

11. There are many studies.

The mean at 20 Hz is about 85 dB SPL and at 40 Hz it's about 60 dB (or lower). That means that the 20 Hz tone needs to be roughly 25 dB louder to reach the hearing threshold.
400 to 800 Hz it's less than 5 dB difference and the threshold is near 0 dB SPL...

12. Quote:

First of all, the Fletcher-Munson Wikipedia Page, suggests that the ISO standards were affected in the LF region due to several factors. Anyways, notwithstanding that, those tests were made using speakers and here's what the Equal-loudness contour page said:

Quote:

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Also we're not talking about near-threshold here, we're talking about SPLs that are loud enough that I can count the number of beats. I guarantee you it isn't a harmonic that I am hearing through the Sennheiser because it sounds the same and very pure across all my good cans, including the IEMs.

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I've got to say it's pretty funny that you quote part of the page that is marked with [citation needed].

Even given the differences in the low frequencies, it's still a lot quieter than the higher frequencies every time.

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Quote:
But using the data above the average threshold is even higher.

Listen to 1 kHz tone at 80 dB SPL, that's pretty loud. Now change the frequency to 20 Hz. You shouldn't hear anything. If you do hear something, the most likely explanation is that your headphones are distorting.