# Frequency?

Discussion in 'General Science & Technology' started by TheFrogger, Jan 23, 2019.

1. ### TheFroggerBannedValued Senior Member

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Frequency: how frequent something is; how often it happens.

On a stringed instrument this should be how often a string passes the mid-point: a more tightly wound string passing more frequently; but eventually coming to an end.

My question is this: what is the highest frequency; if there is one??

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3. ### mathmanValued Senior Member

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Are you asking abstractly (no limit) or about string instrument (physical limit)?

5. ### Q-reeusBannedValued Senior Member

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The correct answer (echoed with slight modifications in next post) is of course that given by Lubos Motl. Unless you really are only interested in 'highest guitar note'.

Last edited: Jan 24, 2019

7. ### billvonValued Senior Member

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There isn't really one. You won't be able to measure a frequency faster than 1/Planck time, but at those frequencies photons are really measured by energy, not frequency (although they can be described by frequency.) And you can always add energy to a photon.

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8. ### exchemistValued Senior Member

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This is incorrect, actually.

The frequency is the number of cycles per unit time. In a stringed instrument, the string passes the mid-point twice per cycle, once passing from left to right and once passing from right to left, before getting back to where it started. So the frequency is half the number of times it crosses the mid-point.

9. ### TheFroggerBannedValued Senior Member

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The answer is as I suspected: there isn't a limit.

10. ### Write4UValued Senior Member

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The frequency depends on the length of the vibrating object. You cannot generate a wavelength longer than the emitting object.
This is one of the reasons we know that the universe began smaller than it is today. The longest wavelengths are missing from the BB background noise, which suggests a small beginning.

p.s. all illustrations which show a wavelength longer than the emitting object are incorrect..

Watch the naturally evolving patterns emerging from an equal dynamic stimulation of different string lengths.
It is really remarkable to see how the wave pattern of DNA can form itself.

Last edited: Jan 24, 2019
11. ### billvonValued Senior Member

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So you think a short antenna cannot emit a wavelength longer than its own length?

12. ### Write4UValued Senior Member

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An antenna does not vibrate. It is a transmitter of pulses which can be timed.

I am looking at this in simple terms. If an object is not long enough to generate one full wave length then it cannot produce that wavelength. You cannot possibly generate a low E on a short string , it's physically impossible.
This is why we have violin, viola, cello, basso, basso profundo, string instruments in music. The strings of each instrument are tuned to specific sets of frequencies,

Of course today, we have little electronic gadgets which can create and manipulate simulated wavelengths in just about every frequency imaginable, but that is artificial, not natural.

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13. ### billvonValued Senior Member

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No, EM transmitter (i.e. antennas) transmit waves, not 'pulses.' In some ways they are quite similar to guitar strings - they have resonances, preferred modes etc.
Of course it's not impossible. I could design a driver that touched the string and drove it at a low E frequency. (That's similar to how speakers work.)
And we have speakers that drive a diaphragm at a wide range of frequencies. The above examples are just examples of cases where it's _easy_ to make a given frequency, because the mechanical resonance tends to turn any energy (like a bow vibrating a string at random frequencies) into a specific frequency.

But if you had a bow that produced energy through friction at only ONE frequency, then that's the frequency you would hear - no matter what the string was tuned for.

14. ### Write4UValued Senior Member

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And do they transmit waves lengths larger than they are capable of producing?

I gave you an example: a violin string is not capable of generating a low E on a musical scale.
It requires the full length of a bass string to produce a single completed wave length of low E. On a bass the low E is a fully "open" string tuned precisely to produce a low E wave length.

15. ### billvonValued Senior Member

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They definitely can. For example, a 1/4 wavelength whip antenna is a common design for handheld radios.

However, since most handheld radios use different frequencies, a given antenna will not be exactly 1/4 wavelength for the frequency you are using - but will still work. In fact, you can go arbitrarily low on the frequency and the antenna will still work. In engineering terms that is an "electrically small antenna" but they still work albeit at lower efficiencies.

And I am saying it can. For example, let's say you drive the violin string with a driver (a voice coil.) Violin strings want to produce frequencies at their resonances - specifically 659, 440, 293 and 196Hz. These are the most efficient frequencies for them to generate, and if you hit those strings with white noise stimulus (i.e. a bow) then that is the frequency they will generate most easily (with nothing else touching the strings, of course.) So if you use your driver to drive them at those frequencies, you will hear those frequencies very clearly.

But let's say you want to drive the G string at low E (41Hz) and so you use your driver to do that. The string will then vibrate at that frequency; it can do nothing else. You will then hear a low E. It will be nowhere near as loud as the G note you would usually hear, because the string does not "want" to vibrate there - it does not mechanically resonate at those frequencies. In engineering terms the driver is poorly matched to the string.

But let's say you want more efficiency, and so you add some weight to the driver. Now the spring constant of the string combined with the weight of the driver generates new resonances, and you can choose the weight so that it resonates at 41Hz. In engineering terms the driver is now well matched to the string. You now have a system that produces low E very easily and efficiently - yet when you take away the driver you are back to a standard violin.

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16. ### Write4UValued Senior Member

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Maybe we are not talking about the same thing. I am speaking of physical wave-length such as sound waves or the universal "Pilot Wave" of space itself.
There seems to be a universal wave-length with a cyclic duration of two billion years. Which means the universe's own wave-length has completed 6 cycles (complete oscillations) since the BB and we're halfway through the seventh cycle.

https://www.iflscience.com/space/universe-ringing-bell/
https://history.amazingspace.org/resources/explorations/light/star-light-science.html

Last edited: Jan 24, 2019
17. ### billvonValued Senior Member

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Yes. You can get the G string of a violin to create sound waves at low E. It's just not efficient at doing that.

18. ### Write4UValued Senior Member

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I am thoroughly confused now. Can you point to where I am missing something.

19. ### billvonValued Senior Member

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?? You are not.

A G string generates a G tone very easily. You can also get it to produce low E - it's just not efficient.

A 300Hz signal results in a wavelength of 1000 kilometers (about 600 miles.) You could do a fairly efficient 1/4 wavelength antenna - but it would be 150 miles long. However, you could do an _inefficient_ antenna any length you wanted.

For proof of this, look at the 60Hz hum you can sometimes pick up in wireless receivers. Does that mean that your receiving antenna is 750 miles long? Nope. It just means that the short antenna you DO have can pick up the energy at 60Hz because there is a lot of it, and even the inefficient wires in your house/building (that are also far shorter than 750 miles) are good enough to transmit that hum.

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20. ### Write4UValued Senior Member

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I have read that fractal antennas are the most efficient over a wide spectrum.

p.s. An after-thought. Does a string have to have tension for it to be able to produce a wave function?

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22. ### parmaleeperipatetic artisanValued Senior Member

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Violins are typically tuned to perfect fifths, from the A string (440), rather than standard--so 660, rather than 659.

Edit: Unless you're Tony Conrad or you're doing some crazy Gamelan shit or somesuch...

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What NOW?