Chapter Questions
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?
Animals like dogs can hear sounds that have SPL less than 0 . Show how this is possible.
Dogs can hear sounds at pressures close to $2 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2$. What is this in decibels?
An air compressor emits pressure waves at $0.01 \mathrm{~N} / \mathrm{m}^2$. What is the SPL in decibels?
Why was $P_{\text {ref }}$ in Eq. (22.9) chosen at $0.00002 \mathrm{~N} / \mathrm{m}^2$ ? What if a mistake was made and $P_{\text {ref }}$ should really have been $0.00004 \mathrm{~N} / \mathrm{m}^2$ ? This is a $100 \%$ error. How could this affect the numbers in Table 22-1?
Given the following data, calculate the $L_{10}$ and the $L_{50}$.$$\begin{array}{lccc}\text { Time (s) } & \mathrm{dB}(\mathrm{~A}) & \text { Time }(\mathrm{s}) & \mathrm{dB}(\mathrm{~A}) \\\hline 10 & 70 & 60 & 65 \\20 & 50 & 70 & 60 \\30 & 65 & 80 & 55 \\40 & 60 & 90 & 70 \\50 & 55 & 100 & 50\end{array}$$
Suppose your dormitory is 200 yards from a highway. What truck traffic volume would be "allowable" in order to stay within the Federal Highway Administration guidelines?
If the SL were $80 \mathrm{~dB}(\mathrm{C})$ and $60 \mathrm{~dB}(\mathrm{~A})$, would you suspect that most of the noise was of high, medium, or low frequency? Why?
In addition to the data listed in Example 22.3 (Table 22-2), the following SL measurements were taken:$$\begin{array}{lccc}\text { Time }(\mathrm{s}) & \mathrm{dB}(\mathrm{~A}) & \text { Time }(\mathrm{s}) & \mathrm{dB}(\mathrm{~A}) \\\hline 110 & 80 & 160 & 95 \\120 & 82 & 170 & 98 \\130 & 78 & 180 & 82 \\140 & 87 & 190 & 88 \\150 & 92 & 200 & 75\end{array}$$Calculate the $L_{50}, L_{10}$, and NPL by using all 20 data points.
If the pressure wave was $0.3 \mathrm{~N} / \mathrm{m}^2$, what is the SPL in decibels? If this is all the information about the sound you have, what can you say about the SL in $\mathrm{dB}(\mathrm{A})$ ? What data would you need to make a more accurate estimate of the SL in $\mathrm{dB}(\mathrm{A})$ ?
If you sing at a level 10,000 times greater than the power of the faintest audible sound, at which decibel level are you singing?
How many times more powerful is a $120-\mathrm{dB}$ sound than a $0-\mathrm{dB}$ sound?
On a graph of decibels vs hertz ( 10 to 50,000 ), show a possible frequency analysis for: (a) a passing freight train, (b) a dog whistle, and (c) "white noise."
The OSHA standard for an 8 -h exposure to noise is $90 \mathrm{~dB}(\mathrm{~A})$. The Environmental Protection Agency (EPA) suggests that this should be $85 \mathrm{~dB}(\mathrm{~A})$. Show that the OSHA level is almost $400 \%$ louder in terms of sound level than the EPA suggestion.
A machine with an overall noise level of 90 dB is placed in a room with another machine putting out 95 dB .a. What will be the sound level in the room?b. Based on OSHA criteria, how long should workers be in the room during one working day?
What sound pressure level results from the combination of three sources: 68,78 , and 72 dB ?
If an occupational noise standard were set at 80 dB for an 8 -h day, 5 -dayper-week working exposure, what standard would be appropriate for a 4-h day, 5-dayper-week working exposure?
Carry a sound level meter with you for one entire day. Measure and record the sound levels as $\mathrm{dB}(\mathrm{A})$ in your classes, in your room, during sports events, in the dining hall, or wherever you go during the day.
Seek out and measure the three most obnoxious noises you can think of. Compare these with the noises in Table 22-5.
In your room measure and plot the sound level in $\mathrm{dB}(A)$ of an alarm clock vs distance. At what distance will it still wake you if it requires $70 \mathrm{~dB}(\mathrm{~A})$ to get you up? Draw the same curve outside. What is the effect of your room on the sound level?
Construct a sound level frequency curve for a basketball game. Calculate the noise pollution level.
A noise is found to give the following responses on a sound level meter: $82 \mathrm{~dB}(\mathrm{~A}), 83 \mathrm{~dB}(\mathrm{~B})$, and $84 \mathrm{~dB}(\mathrm{C})$. Is the noise of a high or low frequency?
A machine produces $80 \mathrm{~dB}(\mathrm{~A})$ at 100 Hz (almost pure sound).a. Would a person who has suffered a noise-induced threshold shift of 40 dB at that frequency be able to hear this sound? Explain.b. What would this noise measure on the $\mathrm{dB}(\mathrm{C})$ scale?
What reduction in sound intensity would have been necessary to reduce the takeoff noise of the American SST from 120 to 105 dB ?