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Da "Fisica, onde Musica": un sito web su fisica delle onde e del suono, acustica degli strumenti musicali, scale musicali, armonia e musica.

  1. Generalities on waves and sound
    1. What is the difference between sound and noise?
    2. Why do we talk about the principle of wave superposition and not the law of wave superposition?
    3. I have read that the superposition of two sine sound waves in phase opposition generates silence (the two waves "cancel each other out"). Well, then where does the energy of each wave go?
    4. If sound is a wave, is it possible to build acoustic "lenses" or "mirrors"?
    5. Does sound always propagate in a straight line?
    6. Do sound "mirages", like optical mirages, exist?
    7. Why does lightning create the sound of thunder?
    8. Why is it that when lightning strikes nearby we hear a sharp sound but when it strikes far away, the sound is not just weaker but also longer and blurred?
  2. Perception of sound
    1. Why can we hear a sound with one ear (e.g. the left) when it is actually coming from the direction of the other (e.g. the right)?
    2. What is the purpose of having two ears?
  3. Unit of measurement
    1. What unit of measurement is the decibel?
    2. Why should we complicate our lives with a logarithmic scale?
    3. Why are decibels more commonly used than Bels?
    4. Why do scales in dB all have a factor of 10 in their definition?
    5. Are there different types of decibel scales?
    6. Why does the sound pressure level (SPL) scale have a factor of 20 instead of 10 in its definition?
    7. Why are there sometimes scales with negative dB on apparatuses?
    8. Why is the level ± 3 dB highlighted on some apparatuses?
    9. Does a 20 dB sound have double the intensity of a 10 dB sound?
    10. Why do we measure the angles in radians?
  4. Characteristics of sound
    1. Does an environment with absolutely no sound exist?
    2. What is the loudest possible sound that can be produced?
    3. What is the relationship between the frequency and the pitch of a sound?
    4. If a sound is composed of many harmonic sounds of different frequencies, which harmonic determines the sound pitch that is perceived?
    5. Is it true that sound intensity is proportional to the square of pressure? Why?
  5. Architectural and environmental acoustics
    1. Why is it that when we put our heads underwater in the bathtub, we hear the noises in our home better?
    2. Why is it that we seem to sing better in the shower?
    3. Is it true that if we place our ear on a train track, we will hear the approaching train sooner than if we were to hear it in the air?
    4. I’ve seen perforated panels hanging in some concert halls. What purpose do they serve?
  6. Resonance
    1. How does the body of a string instrument make the sound produced by its strings louder?
    2. Is it true that a bridge can collapse after relatively mild stresses due to the phenomenon of resonance?
    3. What are the possible practical applications of the phenomenon of resonance? Are there any devices that exploit this phenomenon?
    4. Is it possible to shatter a glass with only the force of the human voice?
    5. The resonance wavelength of an open tube is equal to twice its length. Is it possible to build a smaller resonator with the same frequency?
  7. Stationary waves
    1. Seeing that a stationary wave does not propagate, how is it a wave?
  8. Beats
    1. How can we listen to the phenomenon of beats in a real instrument?
    2. Why have I never heard the phenomenon of beats between two different instruments?
  9. Technology
    1. I know that two pure sounds with opposite phases cancel each other out; but is it really possible to cancel a sound by adding one with the opposite phase to it?
    2. What are the parameters that determine "good quality" in Hi-Fi system speakers?
    3. What are a "tweeter" and a "woofer" and what are they used for?
    4. Why do home-theatre systems have many small "speakers" instead of one large one in the centre?
    5. What is "Dolby" used for?
    6. Why is it that when I hear my recorded voice it sounds so different than my real voice?
    7. I’ve heard that old Hi-Fi systems with valves are still the best. Is this true?
  10. Musical instruments
    1. The voice
      1. Why do our voices sound so silly after we have inhaled helium from a balloon?
      2. Is it possible to sing two notes simultaneously?
      3. Why is it that when a soprano sings in a high register, it is very difficult to distinguish the vowel sounds being sung?
      4. Why are we able to distinguish vowel sounds if we pronounce them all with the same intonation?
    2. Wind instruments
      1. Is it true that sound also reflects at the open end of a tube and not just at the closed end?
      2. Why do the flute, clarinet and oboe play in completely different registers even though they are almost the exact same length (about 60 cm)?
      3. How important is the material with which a wind instrument is made?
      4. Is it possible to play two notes simultaneously with one wind instrument?
    3. String instruments
      1. Why do all string instruments have a concave body?
      2. How important is the material with which a string instrument is made?
      3. Why is it that when we rub, pluck or strike the same string, we get different sounds even if it is the same note?
      4. If we use harmonics to tune an instrument, will we always get good tuning?
      5. We can create natural and artificial harmonic sounds on a violin and a guitar. How are they different?
      6. Why are the expressions "trumpet in B flat" and "tenor saxophone in E flat" used but not the expression "violin in B flat"?
      7. What is "Tartini's third sound" and how is it obtained?
      8. Why are some guitar strings made from nylon while others are covered with metal?
    4. Percussion instruments
      1. Why don't all percussion instruments produce a precise note the way string instruments do?
      2. Why are some percussion instruments, such as the timpani, tuned while others, such as the cymbals, are not?
  11. Musical scales
    1. What are the rules for generating the Pythagorean scale? How is the circle of fifths made?
    2. Why is it not possible to close the circle of fifths using only natural fifths?
    3. Why is a unclosed circle of fifths a problem?
    4. Why does the temperate scale contain 12 notes?
"Fisica, onde Musica": un sito web su fisica delle onde, acustica degli strumenti musicali, scale musicali, armonia e musica.

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