Sound - Mitsubishi Electric Lossnay LGH-15RX3 Technical Manual

4. Sound

Sound is emitted when any object is excited causing it to vibrate. The object that vibrates is called the sound source, and the
energy that is generated at the source is transmitted through the air to the human ear. Humans can hear the sound only when
the ear drum vibrates.
4.1 Sound level and auditory perception
Sound level is the sound wave energy that passes through a unit
area in a unit time, and is expressed in dB (decibel) units.
The sound heard by the human ear differs according to the
strength of the sound and the frequency, and the relation to the
pure tone sound is as shown on the right. The vertical line shows
the strength of the sound and the horizontal line shows the
frequency. For frequencies between 20 Hz to 15,000 Hz which
can be felt by the human ear, the strength of sound that can be felt
that is equivalent to a 1,000 Hz sound is obtained for each
frequency. The point where these points cross is the sound level
curve, and a sound pressure level numerical value of 1,000 Hz is
expressed. These are called units of phons. For example, the
point on the 60 curve is perceived as 60 phons.
G
On average, the human senses a sound that is less than 1,000
Hz as rather weak, and a sound between 2,000 to 5,000 Hz as
strong.
4.2 How to measure sound levels
A sound level meter (JIS C1502) is used to measure sound levels.
This sound level meter has three characteristics (A, B and C
characteristics) as shown on the right. These represent various
sound wave characteristics.
Generally, the A characteristic, which is the most similar to the
human ear, is used.
CHAPTER 4 G Characteristics
ISO audio perception curve
120 dB
Frequency (Hz)
Frequency (Hz)
–200
100
–20
80
–2
60
–0.2
40
–0.02
20
–0.002
4.2
–0.0002
Sound Sound
presure strength
2
(Microbar) (W / cm
C characteristic
B characteristic
A characteristic
)
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