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I Why is it that the fundamental harmonic is louder than rest?

  1. Mar 28, 2017 #1
    Why is it that the fundamental harmonic is louder than rest? If energy is the same as frequency surely the greater the harmonic the louder it is.

    Also what does amplitude represent in waves?
     
  2. jcsd
  3. Mar 28, 2017 #2

    DrClaude

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    It's not.

    The maximum distance between peaks and troughs, measured parallel to the direction of oscillation.
     
  4. Mar 28, 2017 #3
    And the fundamental does not have to be the loudest. You can excite the system such that the higher harmonics have larger amplitudes. Even with zero amplitude for the fundamental.
    However the damping usually increases with frequency and after some time after the excitation, the higher harmonics die faster and the fundamental may dominate.
     
  5. Mar 28, 2017 #4
    Your question prompted me to do some reading and it turns out that it's not always the case e.g. for some musical instruments such as the trumpet the higher harmonics have a larger amplitude.
     
  6. Mar 28, 2017 #5
    I think that the fundamental is called that because it's the one you hear. If there are lower frequencies present and they are lower amplitude than the fundamental, they are called sub-harmonics. The amplitude is representative of the loudness, although loudness is a psychological phenomena in some cases.
     
  7. Mar 28, 2017 #6
    The term fundamental has nothing to do with loudness. It is the lowest frequency mode of the system. The sub harmonics have lower frequencies. Amplitudes are not relevant for these definition.
     
  8. Mar 28, 2017 #7

    sophiecentaur

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    It's not always. However, the overtones of any standing wave are usually the highest amplitude. The way the oscillations are matched to the air can bring out higher order overtones out more. I use the term Overtone because the higher orders may be far from harmonics. Brass instruments can be waaay out without the player pulling notes. But it's what we find pleasing.
     
  9. Mar 29, 2017 #8
    I was told by my physics lecturer energy is the same as frequency, if this is not the case what is energy represented by in a wave?
     
  10. Mar 29, 2017 #9

    sophiecentaur

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    What he was referring to was Quantum Mechanics. In particular, the formula
    E = hf tells you the energy of a photon.
     
  11. Mar 29, 2017 #10
    As sophiecentaur points out, the energy of a photon is proportional to the frequency of the light. The number of such photons determines the total energy at that frequency.
     
  12. Mar 29, 2017 #11
    what kind of system are you referring to?
     
  13. Mar 29, 2017 #12

    ZapperZ

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    You need context. While energy can be related to energy, it is NOT the ONLY factor when considering the energy of a classical wave. The amplitude of the wave also affects the energy. So your physics lecturer is correct. However, you understood it as it being the only factor affecting energy.

    Zz.
     
  14. Mar 29, 2017 #13
    He used it to explain how wavelength and wave speed change yet the frequency stays the same when light enters a medium. He stated frequency is energy and energy is conserved.
     
  15. Mar 29, 2017 #14

    ZapperZ

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    Actually, what is conserved is "power", the amount of energy going through a point in a unit time. It is why, for a light source with a fixed power, increasing the frequency will cause the intensity to drop, because there can only be a fixed amount of energy given off per second.

    So while this is true in the case of refraction, you need to be clear that this is the case where there is a fixed amount of energy being given to start with. It is not true in ALL general cases. This is easy to see if you have 2 different spring-mass systems. Use the same mass, but use different spring constant k. Now let them oscillate with the same amplitude. Which one do you think will have more "energy"? Next, change the amplitude of each one of them. Do you think each one will have the same energy as before if I oscillate them with a different amplitude? After all, the frequency of oscillation for each one of them remains the same as before.

    When you ask a question in this forum, it is imperative that you be very clear and concise. If it is related to something, or it is something you're thinking of in your head, don't assume that (i) we can read your mind and (ii) you have a general "rule" that will be true everywhere. When you are asking about something with a particular context in mind, you must reveal that context. Otherwise, we will be talking about chickens while you're thinking about cows.

    Zz.
     
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