EXAM I

dB

decibel

When it is desired to contain noise in a noisy room (such as a mechanical room), we choose the enclosing walls, based on which rating (of the walls/partitions)?

STC (long question)

List four service systems in commercial buildings (NOT environmental systems)

1.plumbing 2.electrical 3.Fire protection 4.Conveying

OSHA

Occupational Safety & Heath Administration

NRC

Noise Reduction Coefficient

NC

Noise Criterion

STC

Sound Transmission Class

Select the environmental control system from the list.

Lighting/daylighting

From the list below, select a system that is NOT an environmental control system.

Fire Protection

Choose examples of possible on-site noise sources.

Outdoor HVAC equipment such as an air-cooled chiller

For good site planning, we should consider off-site sources of noise but not on-site sources of noise.

False

Assuming a point source of sound, sound energy travels in a form of .......... ?

A rapid fluctuation of air pressure, A mechanical wave, A spherical wave front

Speed of sound is constant. For example, speed of sound at sea level is the same as under water.

False

Low frequency sounds have short wavelengths, and high-frequency sounds have long wavelengths.

False

Tone is the sound of .......... ?

A single frequency of sound energy

Noise is defined as .........?

Any unwanted sound

Short-term exposure to very loud sound may cause temporary loss of hearing, but long-term exposure may cause permanent hearing damage.

True

We feel perfectly comfortable in silent spaces.

False

Inside the room, all hard and soft surfaces can equally absorb sound. All soft surfaces share the same coefficient of absorption (% sound energy absorbed).

False

When we design spaces for listening, acoustic quality becomes very essential. Longer reverberation times are recommended for smaller spaces (smaller in volume), and shorter reverberation times are recommended for larger spaces (larger in volume).

False

If we need to apply the three strategies for noise control, we should apply them in the correct order, which is ..........?

Reduce noise at source, reduce noise transmission, and masking noise

Noisy sites are sites at which sound intensity level exceeds .......... ?

70dB

Write the equation that describes the relationship between speed of sound, frequency, and wavelength

speed = frequency x wavelength

Human ear is most sensitive to the frequency at...

4000 Hz

Reverberation time is defined as

The time sound takes to become inaudible

List the 3 strategies for sound control in buildings. MUST be written in order of application

1.Reduce sound 2.Limit transmission 3.Masking sound

(T or F) Because sound is a mechanical phenomenon, it can only travel through physical matter. That is why it cannot travel through space (i.e. vacuum)

True

(T or F) Silence is the virtual absence of sound in the space (i.e. no sound frequencies between 20 and 20,000 Hz)

True

Since our perception of the intensity of sound (sound pressure) follows a logarithmic scale and not a linear arithmetic scale, the use of dB in acoustics matches our perception

True

In large lecture halls where loudspeakers are needed to provide a uniform distribution of sound intensity, one of the best locations of loudspeakers is to mount two groups of them on the two opposite side walls facing each other.

FALSE

What is the threshold of hearing for humans?

0 dB

Which type of finishing surfaces should absorb more of the sound energy?

SOFT surfaces

In a new auditorium that is built purposefully for jazz music, the reverb time is much shorter than the optimum. What is your recommendation?

Reduce sound absorption

Compared to a sound intensity level of 70 dB, which intensity will be perceived as four times louder?

90 dB

In noise control, we try to avoid:

Sound leak and Sound flanking

Which of the following is true about "White Noise"?

Low intensity sound, continuously maintained sound

Reverb time equation

Tr = 0.05 x volume (ft^3)/total absorption

Total absorption equation

Summation 1-n[(absorber area n) x (its NRC)]

What level of sound intensity is BACKGROUND noise?

20 dB

What level of sound intensity is WANTED noise?

60 dB

What is the desirable minimum distance from transportation noises?

highway = 1000ft; railroad = 3000ft; aircraft = 1mile - 3.5mile from side of runway

What are some natural and manmade site sound barriers?

trees, hills and walls, non-critical buildings

What are some things to consider when site SELECTION?

1.Avoid outdoor sources of noise 2.future plans for site 3.site shielded by sound barriers 4.prefer upwind locations to downwind 5.prefer low dense to high dense areas

What are some things to consider when site PLANNING?

1.Building perpendicular to road 2.building as barrier 3.sound sensitive spaces away from noise source 4.NO PARALLEL building surfaces facing noise 5.locate on site noisy activities away from sound sensitive areas

What is the threshold of pain for intensity?

10^-3

What is the 4 hour exposure intensity?

10^-7

What is hearing loss intensity?

10^-8

When does echo occur? (in feet)

When the distance of sound is greater than 56.5ft

When does echo occur? (in seconds)

When the time of sound is greater than 0.05 seconds`

What are the steps for finding the Tr and percentage of acoustic curtain?

1.Find Tr on chart 2.solve for T.Abs 3.Find T.Abs formula through summation 4. divide A by sf of side walls to get percentage 5. repeat for 2nd category 6. solution: reduce noise 7. percentage less than 100% = acceptable

What are the steps for finding Intensity of speakers?

1. find intensity of each speaker using given formula (cm) 2. Sum intensity of speakers 3. Find IL 4. use IL to find hrs on chart 5. use delta distance to find echo

What is the speed of sound in air at sea level?

770 mph or 1130 fps

What is sound power?

Acoustic power generated by a sound source

Audible range of frequency?

20-20,000 Hz