...

1. Measuring sound
levels

2. People use decibels to indicate the sound intensity level.
0dB is the weakest voice heard.
30 ~ 40dB is an ideal quiet environment .
Sound louder than 50dB will affect sleep.
Sound above 70dB will affect efficiency.
Long-term with 90dB or more will affect the hearing.
If suddenly exposed to up to 150dB noise environment, hearing will
completely lost.!

3. There are a lot of normal things is related
to sound levels in daily life.

4. Assume that robson square features a noise monitoring
equipment.
A time display on the digital device displays 49.20,
this unit of this number is ________,
The velocity of oise propagation in air is approximately
__________m / s.

5. 1.The unit is dB(decibels)
2.The velocity is 340 m/s
explanation: using equation
v=(B/ρ)^(1/2)
Hint:The speed of sound in air is 340m/s

6. IThere are A, B and two sounding bodies, for the first time
by a separate body armor sounding voice, as measured by
the instrument is 62dB; the second by B vocal sounding
body alone, fixed in the same place the instrument
measured as 45dB. Here are a few to determine the correct
[]
A. A sound body some distance away Instruments
B. B vocal instrument must be far away from the body
C. A sound body away from the instrument may be near
D. None of the above three analysis

7. The answer is C.