ARCH 3433 Exam I + Acoustics Quiz

List 6 man-made noise sources: 2 off-site, 2 on-site, and 2 indoor

1. Airport (Off-site)

2. Traffic (Off-site)

3. Playgrounds (On-site)

4. Trash collection (On-site)

5. Fan rooms (Indoor)

6. Open stairs (Indoor)

T/F: Assuming a point-source of sound, sound energy spreads out in a form of a spherical wave front

True

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

True

T/F: Since the human ear is most sensitive to the 20,000 Hz frequency, it perceives sound at and near this frequency as louder than other frequencies

False

T/F: Our perception of sound intensity (sound pressure) follows a logarithmic scale. That is why sound intensity level is measured in Watt/cm2, while sound intensity is measured in dB (Decibel)

False

T/F: We perceive a sound level of 100 dB (10^-6 Watt cm/2) as ten times louder than the intensity of 10 dB (10^-15 Watt/cm2)

False

T/F: In theatre design, designers should determine the volume of the space (not only the floor area) in accordance to the recommended reverberation time

True

T/F: For effective sound masking, it is always recommended to maintain background noise (white noise) at least 30 to 40 dB below the wanted sound

False

T/F: In a large auditorium hall, the highest potential of echo is typically at the back seats

False

In terms of "equal loudness", which frequency is perceived louder than all other audible frequencies (assuming the same sound intensity in W/cm2)?

4,000 Hz

Approximately, what is the speech range of frequency?

125-4,000 Hz

Regardless of the volume of the space, which do you think is a desirable reverberation time for a small lecture hall?

0.40 seconds

Which type of finish typically absorbs more of the sound energy?

Soft surfaces

In a new opera hall, initial design showed that reverberation time is too small for the volume. What is your recommendation?

Reduce total sound absorption

What is the threshold of hearing for humans?

0 dB

Sound above which intensity level causes pain in the ear (even with very limited time of exposure)?

130 dB

The audible range for a healthy young person is:

20-20,000 Hz

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

All of the above: It is low intensity, continuously maintained, & not disturbing

Approximately, what is the difference in distance traveled by the same sound (and its reflections) in order to cause echo?

56 feet or more

In noise control, we try to avoid:

Sound leak & sound flanking

To minimize sound transmission between spaces, the wall assembly (between the spaces) must have the appropriate rating of

STC

Select the environmental control system from the list:

Fire protection, plumbing, lighting/daylighting, conveying (elevators)

Lighting/daylighting

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

HVAC, fire protection, lighting/daylight, acoustics/noise control

Fire protection

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

70 dB

List an example of possible on-site noise sources

Outdoor HVAC equipment such as an air-cooled chiller

T/F: 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 ____?

All of the above: a spherical wave front, a mechanical wave, & a rapid fluctuation of pressure

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

False

T/F: Low frequency sounds have short wavelengths, and high-frequency sounds have long wavelengths

False

Speed of sound = wavelength x frequency

Tone is sound of ____?

A single frequency of sound energy

Noise is defined as ____

Any unwanted sound

T/F: Short-term exposure to very loud sound may cause temporary loss of hearing, but long-term exposure may cause permanent hearing damage

True

T/F: We feel perfectly comfortable in silent spaces

False

We feel comfortable in quiet spaces and not in silent spaces

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

False

T/F: 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 3 strategies for noise control, we should apply them in the correct order, which is ____

1. Reduce noise at source

2. Reduce noise transmission

3. Masking noise

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 (Sound Transmission Class)

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

1. Fire Protection

2. Plumbing

3. Signal Systems

4. Conveying Systems

OSHA

Occupational Safety and Health Administration

dB (unit to measure sound intensity level)

Decibel

NRC (acoustic rating of finish materials)

Noise-reduction coefficient

NC (acoustic rating of supply air diffusers)

Noise criterion

STC (acoustic rating of interior partitions)

Sound Transmission Class

Assuming a point source of sound, sound energy spreads out in a form of a

Spherical wavefront

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

By definition, tone is the sound of a ____

Single frequency

Noise is defined as

Unwanted sound

Reverberation time is defined as

Time sound takes to decay below inaudibility

List the three strategies for sound control in buildings, MUST be written in correct order of application

1. Reduce noise at source

2. Minimize transmission

3. Masking

T/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/F: Silence is the virtual absence of sound in the space, i.e., no sound frequencies between 20 and 20,000 Hertz

True

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

True

Scale matches our perception

In large lecture halls where loudspeakers are needed to provide 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 reverberation time is much shorter than optimum. What is your recommendation?

Reduce sound absorption

(Reduce reverb to make it closer to the optimum)

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

90 dB

4

2 2

70 80 90

In noise control, we try to avoid

Sound leak & sound flanking

(The use of sound traps is OKAY)

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

Low intensity sound & continuously maintained sound