Copyright Michael Karbo, Denmark, Europe.


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    Chapter 2. Frequency and sound waves

    Let me first very shortly describe the phenomenon sound understood as analog sound. Then we will look at sound reproduction.

    What is sound?

    Our ears are unbelievable arrangements. They never rest – they are active even while we sleep. And ears register sounds from all directions; even though there is only 15 cm between them, we are seldom in doubt about whether a sound comes from the right or from the left, from the front or from the back, over or under us. Our sense of hearing is incredible. But what is it our ears react to?

    Sound is blast waves that travel through the air. Waves vibrate with a frequency, which is measured in hertz (Hz), which means vibrations per second.

    Figure 6. Sound is waves, where the force vibrates as seen in the figure (only one vibration is shown).

    A very deep bass tone can, for example, vibrate with 40 Hz, which is 40 vibrations a second. Purely physically, deep tones consist of very long (8,5 meter) blasts that travel through the air from the source of the sound. The deepest tones contain so much energy, that you can feel it in the room and in your body.

    At the other end of the scale is the very high frequency treble sound. The highest tones that people can hear are about 20.000 Hz (dogs can hear up to 65.000 Hz). The human ear loses its sensitivity, as you grow older, so most adults can only hear up to 15.000 Hz. These high tones have very short wavelengths (see Figure 8), and they contain less physical energy.

    Figure 7. The higher the tone, the shorter the wave.

    The most important tone range is the middle tones (about 500-3000 Hz), which is the voice’s range, and where the human ear is most sensitive.

     

    Tone, Hz

    20

    80

    320

    1000

    5.000

    15.000

    Wave-length

    17 m

    4,25 m

    1,06 m

    0,34 m

    6,8 cm

    2,3 cm

    Figure 8. The higher the tone, the shorter the wavelength and the less energy contained in it.

    Pitches and octaves

    All music instruments, inclusive the human voice can range over a number of octaves, which corresponds to a certain frequency range.

    In the world of music there are 10 oc­taves, ranging from 16,35 Hz to 16.744 Hz. For every octave the frequency is doubled.

    A soprano singer can perhaps cover 4˝ octaves, for example from 5800 down to 260 Hz, while a bass singer can come right down to 80 Hz, but on the other hand cannot come as high up. A piano can maybe cover five or seven octaves, while a big church organ covers a full 9,5 oc­ta­ves (from 16 Hz to 12.000 Hz).

    The deeper the tones an instrument has to reproduce, the more energy is required. Which is why a double bass is physically much larger than a violin just as the lowest organ pipes are many meters long. And you never hear a dickybird roar, do you?


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