Mitsubishi Electric Lossnay LGH-F1200RX5-E, Technical Manual

Page: 54 / 105

U-45
CHAPTER 4
•
Characteristics
4.4 Indoor Sounds
(1) Indoor Sounds Principles
1) Power Levels
The Power level of the sound source (PWL) must be
understood when considering the effects of sound.
See formula below to obtain PWL from the measured sound
pressure data in an anechoic chamber.
PWL = SPLo + 20 log (
r
o) + 11 [dB] . . . . . . . . . . . . . . . . . . .(I)
PWL : Sound source power level (dB)
SPLo : Measured sound pressure in anechoic
chamber (dB)
ro : Distance from the unit to measuring point (ft,m)
2) Principal Model
Consider the room shown in Figs. 1 and 2.
•
Fig. 1 shows an example of an integrated unit (similar to a
cassette-type Lossnay unit) and supply air diffuser (with
return grille).
Fig. 2 shows an example of a separated unit (similar to a
ceiling-embedded type Lossnay unit) and supply air diffuser
(with return grille).
•
is the direct sound from the supply air diffuser (return
grille), and is the echo sound. ( to ) is the direct
sound emitted from the unit and duct that can be detected
through the finished ceiling. is the echo sound of .
3) Position of Sound Source and Sound Value
SPL [dB] = PWL + 10 log + .........................(II)
(i) (ii)
SPL : Sound pressure level at reception point [dB]
PWL : Power level of sound source [dB]
Q : Directivity factor (Refer to Fig. 3)
r : Distance from sound source [ft,m]
R : Room constant [R =
α
S/(1 –
α
)]
α
: Average sound absorption ratio in room
(Normally, 0.1 to 0.2)
S : Total surface area in room [ft 2 ,m 2 ]
Fig. 1.
Fig. 2.
Fig. 3. (Position of Sound Source and Directivity Factor Q)
3 1
Q
4
π
r
2
4
R
{ }
Unit
r
o
Supply air diffuser
(return grille)
Supply air diffuser
(return grille)
c
b
a
d
Unit
Position of Sound Source Q
a Center of room 1
b Center of ceiling 2
c Edge 4
d Corner 8