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Beat Phenomena


PhysicsAddict9
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Beat Phenomena studies what happens when there are 2 waves, equal in amplitude, with 2 frequencies that are very close in value to each other mix in the same medium, as a result those waves will cancel each other at specific moments and add up at other moments.


So for example if there are 2 sound waves with frequencies 700Hz and 701 Hz that are running at the same time, then the sound will “Disappear” once every one second!, due to beat phenomena, although both sound sources are running. while if the frequencies where 700Hz and 702Hz, then there will be a silence twice every one second.



I was really amazed when I first saw it because it doesn't seem that it is going to happen as both sounds are running at the same time, to experiment this, following are 2 ways to do it:

using Hardware:


you can bring 2 tuning forks that produce each a sound (tone) of the same frequency, that is lets say each produce a tone of 700 Hz, then add to one of them a very light weight object, after the weight is added, if the tuning fork is hit, it will produce a sound of frequency slightly less than what it it was producing, lets say 698 Hz, now if the 2 tuning forks are struck together then the beats of silence will be heard.

using software:


if you don't want to buy a tuning fork, you can write your own code or also you can look for a software that has a simulator for beat phenomena, your code or the software should have 2 sound generators that can be running at the same time, if the frequencies are very close to each other when both are running at the same time, then the beat phenomena effect will take place.

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One hears beat frequencies frequently when tuning a guitar by using the relative tuning method in which adjacent strings are tuned to one another. It's quite a nice way to demonstrate a simple bit of physics.

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I use this bea phenomena when tuning a piano, it's actually more accurate than a digtal tuner.

 

here's an example of what you suggested, the left channel plays a slightly different frequency to the right channel, you can also hear the same thing with head phones, the beat phenomena sort of happens inside your brain as well as physically in the air.

 

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Interesting. I've just tried experimentingg with that comparing relative tuning of guitar strings using beats with tuning by electronic tuner.

 

I found the electronic tuner more accurate than the beat method. In fact even my ear is better than the beat method. I find beats are quite difficult to distinguish once they get down to 1 or 2 Hz. But my tuner and my ear can still tell the two strings are not in tune.

 

Beats are easier to hear with the lower strings than higher ones though.

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The beats heard in tuning a guitar are mostly from overtones, especially as the pitches get close. And most guitars are fretted in modern classical piano pitch intervals, just like most electric tuners have programmed into them starting at A=440, what its inventor JS Bach called "well-tempered" tuning (his A was a bit lower).

 

This does not quite match with one's ear, which hears in natural harmonics, so there's going to be some areas of compromise if your ear is good - it is impossible to precisely tune a modern fretted guitar to a natural singing voice getting its pitches from the harmonics of its key note; open tunings and slide notes are going to sound noticeably off the fret on the third and sixth of the scale; the pitches of the open strings are a shade off from the pitches at the frets; and so forth.

Edited by overtone
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Violonists would naturally follow a scale of no-beat, but must learn to play accordingly to Bach's tuning.

 

This makes very little difference on a perfect fourth, fifth... but a big one on both thirds. In some pieces, if the violonist follows his natural hearing, he accumulates the small differences and gets completely out of tune after one line.

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