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Mitsubishi Electric Lossnay series Technical Manual Page 52

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4.3 Sound Frequency Analysis
The human ear detects sound differently according to the frequency; however, the sound generated from vibrations is not
limited to one frequency, but instead, various frequencies are generated at different levels. NC curve will show how the various
frequencies are generated at different levels, which is determined according to the difficulty of detecting conversations.
Even if the sound is a very low level, it can be detected if it has a specific and loud frequency.
These sounds are low during product design stages, but sounds may become very disturbing if resonating on ceilings, walls,
etc.
Example: Continuous Frequency Analysis
Tolerable Sound Levels and NC Values According to Room Application
Room Application
Broadcasting studio
Music hall
Theater (approx. 500 seats)
Classroom
Conference room
Apartment
Hotel
House (living room)
Frequency (Hz)
dB
NC Value
25
15 - 20
30
20
35
20 - 25
40
25
40
25
40
25 - 30
40
25 - 30
40
25 - 30
CHAPTER 4
NC Curve
Min. audible limit
Frequency band (Hz)
Room Application
Cinema
Hospital
Library
Small office
Restaurant
Gymnasium
Large conference room
Factory
Characteristics
dB
NC Value
40
30
35
30
40
30
45
30 - 35
50
45
55
50
50
45
70
50 or more
U-43

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