Sanyo SGP-E120J2GU2, User Manual

Page: 69 / 175

Design
D - 25
(4)Additional sound from reflection
●
Operation sound from an outdoor unit has the characteristic that it will be reflected from the walls of the
building and ground surfaces. At the reception point these reflections will be received, adding to the sound
level of the system.
●
The sound received at the reception point is the sum [reception point
]
=
[
sound directly transmitted from the
source
]
+
[
reflected sound
]
.
The reflected sound is obtained by setting a virtual sound source A’, and estimating the sound level at B from
the sound source at A’(the distance attenuation from A’~B is subtracted).
See the section on combining sounds, for information on how to add the direct sound and the reflected sound.
(5) Combining sounds
By combining the sound from several outdoor units, it is possible
to know the sound level at a reception point.
The combination of sound from n units L
1
, L
2
, ...
L
n
is expressed
by the following formula.
If the combined sound is L, then
For example, adding 61 phons and 62 phons gives,
This formula is also used for combining the sounds from
multiple outdoor units.
This is the procedure for calculating the sound level,
however, it is easier to use graphs, so graphs have
been prepared for this purpose.
<Calculation example 1>
Combine L
1
= 62[dB] and L
2
= 61[dB]. L
1
- L
2
= 62-61 =
1[dB]. From Figure 5 the correction value is 2.5[dB].
62+2.5=64.5 [dB]. Therefore the combined sound level is
64.5[dB].
<Calculation example 2>
To combine 60[dB], 64[dB], 63[dB], and 65[dB], firstly the
values are arranged in order of magnitude.
65[dB]
.
64[dB]
.
63[dB]
.
60[dB]
Firstly combine 65[dB] and 64[dB],
difference is 65-64=1[dB], correction value is 2.5 dB, so
65+2.5= 67.5[dB]. Next, 67.5[dB] and 63[dB] are
combined, difference is 4.5[dB], so the correction value is
1.3[dB], so 67.5+1.3=68.8[dB].
In the same way, 68.8[dB] and 60[dB] have a level
difference of 8.8[dB], correction value is 0.5[dB].
Therefore 68.8+0.5=69.3[dB].
This is the result of adding the four sounds.
Figure 5 Combined sound correction values
L
1
-L
2
(dB or phon)
Correction value (dB or phon)
adding L
1
and L
2
(L
1
>L
2
)
L=L
1
+ correction value
(for a correction value corresponding
to (L
1
-L
2
) add to L
1
)
L=10 log
10
(10 +10 + +10 )
.......
10
L
1
10
L
2
10
L
3
L=10 log
10
(10 +10 )=64.5db
10
61
10
62
Fig.6 Addition of reflected sound (wall surface)
Fig. 7 Addition of reflected sound(ground surface)
6. Sound-proofing measures