Mitsubishi Electric Lossnay LGH-F1200RX5-E, Technical Manual

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U-42
CHAPTER 4
•
Characteristics
4. Sound
Sound is vibration transmitted through an object. The object that vibrates is called the sound source, and energy that is
generated at the source is transmitted through the air to the human ear at certain frequencies.
4.1 Sound Levels 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 is different according to the
strength of the sound and the frequency, and the relation to the
tone (see chart 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 detected
by the human ear, the strength of sound that can be detected that
is equivalent to a 1,000 Hz sound is obtained for each frequency.
The point where these 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.
•
On average, the human detects sounds that are less than 1,000
Hz as rather weak, and sounds between 2,000 to 5,000 Hz as
strong.
4.2 How to Measure Sound Levels
A sound level meter (JIS C 1502, IEC 651) is used to measure
sound levels and has three characteristics (A*
1
, C*
2
and Flat)
as shown on the right. These represent various sound wave
characteristics. Generally, Characteristic A, which is the most
similar to the human ear, is used. The value measured with the
Lossnay unit operating includes noise caused by the unit and
background noise*
3
.
*1. Characteristic A is a sound for which the low tones have
been adjusted to be similar to the auditory perception of the
human ear.
*2. Characteristic C is a sound for which the high and low tones
have been adjusted slightly.
*3. Background noise: any sound present in the target location
when no sound is being produced.
Sound le
vel (dB)
Frequency (Hz)
Minim
um audib
le valve
120 dB
100
–200
–20
–2
–0.2
–0.02
–0.002
–0.0002
80
60
40
20
4.2
R
esponse (dB)
Frequency (Hz)
Characteristic A
Characteristic C
Flat characteristic
Sound
pressure
(Pa)
Sound
strength
(W / cm 2 )
ISO Audio Perception Curve