444 ENVIRONMENTAL, ENGINEEFUNG
’kble 22-5. Some Domestic Noisemakers
Item (distance from noise source) Sound level, &(A)Vacuum cleaner (10 ft) 75
Quiet car at 50 mph (inside) 65
Sports car at 50 mph (inside) 80
Hushing toilet (5 ft) 85
Garbage disposal (3 ft) 80
Window air conditioner (10 ft) 55
Ringing alarm clock (2 ft) 80
Powered lawn mower (operator’s position) 105
Snowmobile (driver’s position) 120
Rock band (10 ft) 115health hazard and should be numbered among our more serious pollutants. It is possible,
using available technology, to lessen this form of pollution. However, the solution costs
money, and private enterprise cannot afford to give noise a great deal of consideration
until forced to by either the government or the public.
PROBLEMS22.1 If an office has a noise level of 70 dB and a new machine emitting 68 dB is
added to the din, what is the combined sound level?
22.2 Animals like dogs can hear sounds that have SPL less than 0. Show how this
is possible.
22.3 Dogs can hear sounds at pressures close to 2 x N/m2. What is this
in decibels?
22.4 An air compressor emits pressure waves at 0.01 N/m2. What is the SPL in
decibels?
22.5 Why was Pref in Eq. (22.9) chosen at 0.00002 N/m2? What if a mistake was
macle and Pref should really have been 0.00004N/m2? This is a 100% error. How
could this affect the numbers in Table 22-l?
22.6 Given the following data, calculate the Llo and the Lso.Time (s) WA) Time (s) CWA)
10
20
30
40
5070 60 65
50 70 60
65 80 55
60 90 70
55 100 5022.7 Suppose your dormitory is 200 yards from a highway. What truck Mc vol-
ume would be “allowable” in order to stay within the Federal Highway Administration
guidelines?